REESE LIBRARY 
 
 UNIVERSITY OF CALIFORNIA. 
 Class 
 
 
 flB 
 
 -J 
 
Si 
 
 V 
 
 * 
 
SPECTRUM ANALYSIS. 
 

 
 
 
SPECTRUM ANALYSIS. 
 
 SIX LECTURES, 
 
 DELIVERED IN 1868, BEFORE THE SOCIETY OF 
 APOTHECARIES OF LONDON. 
 
 HENRY E. ROSCOE, B.A. PH.D. F.R.S. 
 
 PROFESSOR OF CHEMISTRY IN THE OWENS COT.I.EOE, MANCHESTER. 
 
 WITH APPENDICES, COLOURED PLATE*, AND ILLUSTRATIONS. 
 
 OF THE 
 
 UNIVERSITY 
 
 THIRD EDITION. 
 
 MAC MIL LAN AND CO. 
 
 1873. 
 
 [ T/te Right of Translation and Reproduction is reserved. 
 
1*73 
 
 LONDON : 
 
 B. CLAY, SONS, AND TAYLOR, PRINTEKS, 
 BBEAD STREET HILL. 
 
 \\ 
 
PREFACE TO THE THIRD EDITION. 
 
 IN this edition of my Lectures on Spectrum Analysis 
 I have endeavoured to introduce all the more important 
 facts and conclusions resulting from investigations which 
 have been carried on during the last two years. 
 
 As regards the general subject, the interesting question 
 as to whether an elementary body possesses more than 
 one spectrum has received much attention ; and from 
 experiments on the spectrum of nitrogen, referred to in 
 Lecture IV., it seems that we must, with Angstrom, pro- 
 bably answer this question in the negative. Another 
 important inquiry, though one as yet far from being in a 
 satisfactory position, refers to the question as to whether 
 the wave-lengths of the various bright lines in the 
 spectrum of an element stand in any simple or harmonic 
 ratio to one another : the results of observations on this 
 point are found on page 317. The secret of the singular 
 spectrum of the Bessemer flame has at length been 
 unravelled ; it proves to be identical with that of oxide 
 
vi PREFACE TO THE THIRD EDITION. 
 
 of manganese : a drawing of the two spectra is found on 
 page 175. 
 
 In solar and stellar chemistry the additions to our 
 knowledge have been numerous and important. The 
 phenomena of two total solar eclipses have been care- 
 fully observed by spectroscopists and astronomers of 
 all nations ; and, thanks to their efforts, whilst much 
 still remains to be settled concerning the solar corona 
 and the zodiacal- and auroral-lights, it is certain that our 
 knowledge of the chemistry and physics of our lumi- 
 nary has progressed immensely. Indeed, the discussion of 
 the details of the observations, and of the different views 
 of the several observers, has already quite passed beyond 
 the limits of a work of this kind, so that I have felt 
 obliged to confine myself to a brief Summary, at the 
 end of Lecture V., of the chief and generally recognized 
 results of later inquiry. In order, however, to render 
 more evident the basis upon which our knowledge 
 of solar chemistry rests, I have (with the Author's 
 kind permission) introduced at page 308 an extract 
 from Professor Balfour Stewart's admirable chapter on 
 Eadiation and Absorption. 
 
 With respect to the metals whose presence has been 
 detected in th^sun, I have to notice an error which 
 
PREFACE TO TUE THIRD EDITION. vii 
 
 appears in the text on page 244, but which has been 
 corrected in an Appendix on page 308. The new line 
 seen in the chromosphere is identical in position with a 
 Ruthenium and not with a Kubidium line. 
 
 The results of Dr. Huggins' recent work, with his 
 newly acquired magnificent instrument, on the proper 
 motion of the so-called fixed stars and the nebulae, 
 as well as on the absorption spectrum of the planet 
 Uranus, are found in the last Lecture, and more fully 
 and satisfactorily, as being given in his own words, 
 in an Appendix on page 413. 
 
 Finally, I have only been able to refer in Appendix 
 F to Lecture VI. (page 436) to an important and 
 interesting observation just made by Mr. Lockyer, re- 
 specting the cause of the variation in intensity and in 
 length observed in the bright lines in the spectra of 
 certain metals, which goes to explain why in the solar 
 spectrum some only of the lines of a given metal are 
 found to be reversed whilst the others do not make 
 their appearance. 
 
 H. E. ROSCOE. 
 
 February 1873. 
 
PREFACE TO THE SECOND EDITION, 
 
 IN the year which has elapsed since the first publication 
 of these Lectures on Spectrum Analysis, much has been 
 done by the active workers in this branch of science to 
 extend our knowledge, especially concerning the physics 
 of the sun. I have, therefore, found it necessary to 
 rewrite almost the whole of the portion of the book 
 relating to celestial chemistry, introducing into the text 
 the latest discoveries of Huggins, Lockyer, Janssen, and 
 Zollner, which in the former edition were but imperfectly 
 given. It has also been found expedient to re-arrange 
 the subject-matter of Lectures III. and IV., and to add 
 thereto a short description of investigations in several 
 collateral branches of science. The Appendices have been 
 enriched by abstracts of the original communications 
 made to learned Societies by the investigators them- 
 selves. Many new illustrations have been introduced 
 into the text, and no pains have been spared to render 
 the work as complete a record as possible of the present 
 state of the subject. 
 
 v H. E. ROSCOE. 
 
 April 1870, ^ 
 
PREFACE TO THE FIRST EDITION. 
 
 IN publishing the following Lectures I have endeavoured 
 to preserve the elementary character which they naturally 
 assumed in delivery, thinking it best to give further 
 detail in a series of Appendices. If the book thus 
 assumes less of the character of a complete treatise 
 than might be desirable, it gains in value for the 
 general reader, inasmuch as the science of Spectrum 
 Analysis is at present in such a rapid state of growth 
 that much of the subject is incomplete, and, therefore, 
 necessarily unsuited to the public at large. I hope, 
 however, that the addition of many extracts from the 
 most important Memoirs on the subject may prove 
 interesting to all, as it will certainly be useful to those 
 specially engaged in scientific inquiry, as indicating 
 the habits of exact research and accurate observation, 
 by which alone such striking results have been attained. 
 For the permission to reproduce exact copies of Kirch- 
 hoff's, Angstrom's, and Huggins' maps, together with 
 the Tables of the positions of the dark solar and bright 
 metallic lines, I have to thank the above-named gentle- 
 
x PREFACE TO THE HRST EDITION. 
 
 men. These maps will render the work valuable to the 
 student for a reference, whilst the chromolithographic 
 plates of the spectra of the metals of the alkalies 
 and alkaline earths, and of the spectra of the stars, 
 nebulae, and non-metallic elements, serve to give some 
 idea of the peculiar beauty of the real phenomena thus 
 represented. 
 
 Since last summer, when these Lectures were delivered, 
 our knowledge of the constitution of the sun especially 
 has made giant strides ; and although I have been 
 unable to introduce these newest facts into the text 
 of the Lectures, I have still brought forward the most 
 important of these discoveries in the Appendices to 
 Lecture V. 
 
 As the latest news on this subject, I may mention the 
 arrangement contrived by Mr. Huggins, by which the 
 wonderful changes of the red solar prominences can 
 all be viewed at once ; changes so enormously rapid 
 that Mr. Lockyer has observed one of these red solar 
 flames, 27,000 miles in length, disappear altogether 
 in less than ten minutes. Mr. Lockyer has also 
 succeeded in seeing in the flames the red (c) line of 
 hydrogen, as well as the line in the violet, which 
 he finds corresponds Ho the line marked 2796 on 
 
PREFACE TO THE FIRST EDITION. xi 
 
 KirchhofPs map, and riot, as was supposed, identical 
 with Fraunhofer's line G. 
 
 At the end of the volume will be found a tolerably 
 complete List of Memoirs forming the literature on 
 the subject. 
 
 My thanks are due to Mr. J. D. Cooper and Mr. 
 Collings for the very great care which they have be- 
 stowed upon the illustrations, and especially upon the 
 difficult task of reproducing Kirchhoffs maps in four 
 tints. 
 
 H. E. E. 
 
 MANCHESTER, April 1869. 
 
CONTENTS. 
 
 LECTURE I. 
 
 Introduction. Newton's Discovery of the Composition of White Light, 
 1675. Properties of Sun Light. Heating Rays. Luminous Rays. 
 Chemically Active Rays. The Solar Spectrum. Position of 
 Maxima. Illustrations of these Radiations. Means of obtaining a 
 pure Spectrum. Fraunhofer's Lines. Planet and Moon Light. 
 Star Light 1 
 
 APPENDIX A. Extracts from " Newton's Opticks " 31 
 
 APPENDIX B. Burning Magnesium Wire a Source of Light for photo- 
 graphic purposes 41 
 
 APPENDIX C. On the Chemical Action of the constituent parts of Solar 
 
 Light 43 
 
 LECTURE II. 
 
 Continuous Spectrum of Incandescent Solids. Effect of Increase of 
 Heat. Broken Spectrum of glowing Gas. Application to Chemical 
 Analysis. Spectra of the Elementary Bodies. Construction of 
 Spectroscopes. Means of obtaining Substances in the state of 
 glowing Gas. Examination of the Spectra of Coloured Flames. 
 Spectra of the Metals of the Alkalies and Alkaline Earths. Map- 
 ping Spectra, according to Bunsen ; according to Wave-lengths. 
 Delicacy of the Spectrum Analytical Method and its Application to 
 Physiological Research 49 
 
 APPENDIX A. Description of the Spectrum Reactions of the Salts of 
 the Alkalies and Alkaline Earths 77 
 
 APPENDIX B. Bunsen and Kirchhoff on the Mode of using a Spec- 
 troscope 94 
 
 APPENDIX C. Bunsen on a Method of mapping Spectra 97 
 
x iv CONTENTS. 
 
 LECTURE III. 
 
 PAGE 
 
 Historical Sketch. Talbot. Herschel, Bimsen, and KirchhofF. Dis- 
 covery of New Elements by means of Spectrum Analysis. Caesium, 
 Rubidium, Thallium, Indium : their History and Properties. 
 Spectra of the Heavy Metals. Examination of the Light of the 
 Electric Discharge. Wheatstone. Volatilization of Metals in the 
 Electric Arc. KirchhofF, Angstrom, Thalen, and Huggins. Maps 
 of the Metallic Lines 100 
 
 APPENDIX A. Spectrum Reactions of the Rubidium and Caesium 
 
 Compounds 128 
 
 APPENDIX B. Contributions towards the History of Spectrum Ana- 
 lysis. By G KirchhofF .132 
 
 APPENDIX C. On the Spectra of some of the Chemical Elements. By 
 
 Wm. Huggins. With Maps and Tables 140 
 
 LECTURE IV. 
 
 Mode of obtaining the Spectra of Gases and other Non-metallic Bodies. 
 
 Piiicker and Hittorf. Huggins. Influence of Change of Density -4 
 ;md of Temperature. KirchhofF. Frankland and Lockyer. Vari- 
 ation of the Spectra of certain Metals with Temperature. Spectra 
 of Compounds. Double Spectra, Angstrom's Conclusions.- Spec- 
 trum of the Bessemer Flame. Selective Absorption. Blood 
 Bands. Detection of Colouring Matters. Phosphorescence. 
 Fluorescence : 15(5 
 
 APPENDIX A. Description of the Spectra of the Gases and Non- 
 metallic Elements. Can an Element possess more than one Spec- 
 trum ? On the Spectrum of Nitrogen .191 
 
 APPENDIX B.-^On the Effect of increased Temperature apon the Nature 
 of the Light emitted by the Vapour of certain Metals or Metallic 
 Compounds . 7()4 
 
 APPENDIX C. Kirchhoff on the Variation of the Spectra of certain 
 
 Elements 9( p, 
 
 APPENDIX D. Ignited Gases under certain circumstances give continuous 
 
 Spectra. Combustion of Hydrogen in Oxygen under great pressure 208 
 
 APPENDIX E On the Spectrum of the Bessemer Flame 210 
 
 APPENDIX F.-On the Spectra of Erbium and Didymium Compounds . 217 
 
 APPENDIX G Description of the Micro-Spectroscope . .219 
 
CONTENTS. xv 
 
 LECTURE V. 
 
 PA(iK 
 
 Foundation of Solar and Stellar Chemistry. Examination of the Solar 
 Spectrum. Fraunhofer, 1814. Kirchhoff, 1861. Coincidence of 
 Dark Solar Lines with Bright Metallic Lines. Reversion of the 
 Bright Sodium Lines. KirchhofFs Explanation. Constituents of 
 the Solar Atmosphere. Lockyer and Janssen's Researches. Pheno- 
 mena observed during Total Eclipses. Constitution of the Red 
 Solar Prominences ; their gaseous Nature and rapid Motion. 
 The Chromosphere. Physical Constitution of the Sun. The . 
 Corona. Sun-spots and Faculse '.*.... 222 
 
 APPENDIX A." Recherches stir le Spectre normal du Soleil," by A. J. 
 
 Angstrom 272 
 
 APPENDIX B. The Total Solar Eclipses of August 18, 1868, of 
 December 22, 1870, and of December 11, 1871. Extracts from 
 Reports of the Council of the Royal Astronomical Society . . . 276 
 
 APPENDIX C. Spectroscopic Observations of the Sun, being abstracts 
 of the various Papers on this subject by Lockyer, Janssen, Huggins, 
 and Zollner 293 
 
 APPENDIX D. Preliminary Catalogue of Bright Lines in the Spectrum 
 
 of the Chromosphere, by Professor C. A. Young 304 
 
 APPENDIX E. Professor Balfour Stewart on the Equality of Radiation 
 
 and Absorption 308 
 
 APPENDIX F. On the Harmonic Ratios observed in the Wave-lengths 
 
 of the Lines of certain Spectra 316 
 
 LECTURE VI. 
 
 Planet and Moon Light. Stellar Chemistry. Huggins and Miller. 
 Spectra of the Fixed Stars. Difficulties of Observation. Methods 
 employed. Variable Stars. Double Stars. Temporary Bright 
 Stars. Nebulae. Comets. Motion of the Stars (Huggins). 
 Determinations of Velocity of Solar Storms (Lockyer) 320 
 
 APPENDIX A. Extract from a Memoir " On the Spectra of some of 
 
 the Fixed Stars" 359 
 
 APPENDIX B. On the Spectrum of Mars, with some Remarks on the 
 
 Colour of that Planet 368 
 
 APPENDIX C. On the Occurrence of Bright Lines in Stellar Spectra, 
 
 and on the Spectra of Variable Stars 373 
 
 APPENDIX D. Further Observations on the Spectra of some of the 
 Stars and Nebulae, with an Attempt to determine herefrom 
 whether these Bodies are moving towards or from the Earth, also 
 Observations on the Spectra of the Sun and of Comet II. 1808 . 374 
 
xvi CONTENTS. 
 
 PACK 
 
 APPENDIX E. On the Spectrum of the Great Nebula in Orion, and on 
 
 the Motions of some Stars towards or from the Earth 413 
 
 APPENDIX F. Researches on Gaseous Spectra in relation to the 
 
 Physical Constitution of Sun, Stars, and Nebulae ...... 432 
 
 APPENDIX G. Tables of the Dark Lines from Kirchhoff's Drawings. 
 Explanation of Angstrom and ThaleVs Tables. Notice of Browning's 
 new Automatic Spectroscope 438 
 
 LIST OF THE PRINCIPAL MEMOIRS, ETC. ON SPECTRUM 
 ANALYSIS. 
 
 I. Relating to the Subject generally 459 
 
 II. Relating to Terrestrial Chemistry 462 
 
 III. Relating to Celestial Chemistry 472 
 
 INDEX . . . .481 
 
LIST OF ILLUSTRATIONS. 
 
 FIO. 
 
 1. Fac-simile of Diagram in " Newton's Opticks " 4 
 
 2. Ditto 5 
 
 3. Ditto 6 
 
 4. Coloured Rotating Disc 7 
 
 5. Curves of Intensities of Heating, Luminous and chemically 
 
 Active Rays in Solar Spectrum 12 
 
 6. Tyndall's Experiments on Calorescence 14 
 
 7. Explosion of Chlorine and Hydrogen by Magnesium Light ... 16 
 
 8. Chemical Action of Blue Rays shown 17 
 
 9. Curve of chemically Active Light in Solar Spectrum 19 
 
 ] 0. Experiment of Photography in the Blue Rays -. . 21 
 
 11. Ditto 22 
 
 12. Curves of Chemical Intensity of Total Daylight for Kew, 1866 . 24 
 
 13 & 14. Ditto, ditto, for Para, April 1866 25 
 
 15. Fac-simile of Fraunhofer's Map (1814) of the Dark Lines in the 
 
 Solar Spectrum 28 
 
 16. Repetition of Newton's Diagrams 36 
 
 17. Ditto 38 
 
 18. Ditto 40 
 
 19. Arrangement of Electric Lamp, Prism, and Screen . . . . . . 52 
 
 20. Arrangement of Lamp, Lens, and Prisms 53 
 
 21. Bunsen's Flame coloured by Alkaline Salt 55 
 
 22. Bunsen's Old Form of Spectroscope 59 
 
 23. Steinheil's Improved Form of Spectroscope 59 
 
 24. Arrangement of Slit of Spectroscope 60 
 
 24a. Ditto for two flames 60 
 
 25. Kirchhoff's delicate Spectroscope 62 
 
 26. Bunsen's Maps of the Spectra of the Alkalies and Alkaline 
 
 Earths . 67 
 
 27. Repetition of Steinheil's Form of Spectroscope and Slit .... 94 
 
 28. Arrangement of Slit of Spectroscope 95 
 
 29. Repetition of Bunsen's Maps of the Spectra 98 
 
 30. Arrangement for obtaining Spectra of the heavy Metals . . . .113 
 
 b 
 
xv iii LIST OF ILLUSTRATIONS. 
 
 . 
 
 31 .Wheats tone's Metallic Lines ............. 1 
 
 32. Large Spectroscope with Nine Prisms .......... 117 
 
 33. Repetition of Steinheil's Spectroscope ....... ... 129 
 
 34 Huggins' form of Spectroscope ............. I 42 
 
 35. Electric Spark in different Gases ............ 157 
 
 36. Geissler's Tubes, experimental form ........... 158 
 
 37. Ditto, showing Stratification ....... ' ...... 159 
 
 38. Ditto, ditto ................... 16 
 
 39._Spectra of Lithium and Strontium seen with intense Spark . . .163 
 40. _ Spectrum of Calcium Compounds compared with that of the Metal 165 
 41. Arrangement for Bessemer Steel-making ......... 170 
 
 42. Maps of the Bessemer Spectrum ............ 174 
 
 42 a. Comparison of Bessemer Spectrum with that of Manganese Oxide 175 
 
 43. Selective Absorption by Iodine Vapour and by Nitrous Fumes . . 177 
 
 44. Chromium Absorption Spectrum ............ 179 
 
 45. Potassium Permanganate Absorption Spectrum ....... 179 
 
 46. Absorption Spectra of Chlorophyll and Chloride of Uranium . .180 
 47. Absorption Spectra of Alizarine and Purpurine . . ..... 180 
 
 48. Dark Band in Magenta Spectrum and in Blood Spectrum . . .181 
 
 49. -Stokes' Blood Bands ...... .......... 182 
 
 50. Browning's Micro- Spectroscope ............ 183 
 
 51. Section of the Micro-Spectroscope ........... 184 
 
 52. Becquerel's Phosphoroscope ............. 187 
 
 53. Spectra of Phosphorescent Bodies ........... 189 
 
 54. Repetition of Maps of Bessemer Spectrum ........ 213 
 
 55. Browning's Micro-Spectroscope .... 219 
 56. Fraunhofer's Map ......... 224 
 
 57. Large Spectroscope . . ...... 225 
 
 58. Section of Large Spectroscope . ............ 226 
 
 59. Repetition of Kirchhoff's Spectroscope .......... 227 
 
 60. Ultra-Violet Rays, from Photograph ........... 229 
 
 61. Comparison of Kirchhoff's Map with Rutherfurd's Photograph of 
 
 the Lines near F ............. ... 230 
 
 62. Spectrum of Burning Sodium compared with that of the Soda 
 
 Flame ............... .... 233 
 
 63. Experiment showing Production of the Black Sodium Absorption 
 
 Flame ................... 234 
 
 64. Bunsen's Apparatus for obtaining a Constant Black Sodium Flame 236 
 
 65. Spectrum showing Absorption Bands from Earth's Atmosphere . 250 
 
 66. Janssen's Maps of the Telluric Lines .......... 251 
 
 67. Appearance of Red Solar Prominences in the Total Eclipse of 1860 253 
 68. Ditto ..................... 253 
 
 69. Eclipse of 1869 observed in America .......... 255 
 
 70. Lockyer'ss Drawings of Bright Lines in Solar Chromosphere . . . 258 
 
LIST OF ILLUSTRATIONS. xix 
 
 FIG. PAGE 
 
 71. Forms of the Red Solar Prominences (Zollrier) 261 
 
 72. Ditto 262 
 
 73. Ditto 262 
 
 74 Ditto 262 
 
 75. Ditto 262 
 
 76. Broadening of the F Line (Lockyer) 266 
 
 77. Appearance of the Corona, 1869 266 
 
 78. Comparison of Photographs and Sketches of the Corona . . . 268 
 
 79. Absorption Spectrum of Uranus 323 
 
 80. Huggins' Star-Spectroscope 324 
 
 80 a. Browning's New Spark Condenser 326 
 
 81. Maps of the Lines in Aldebaran and a Orionis 328 
 
 81 a. Comparison of a Nebular Spectrum with the Spark Spectrum . 336 
 
 82. Nebula in Aquarius . 337 
 
 83. Nebula 18 H IV 337 
 
 84. Nebula in Andromeda 338 
 
 85. Comparison of Nebular Spectrum with the Bright Lines of known 
 
 Substances 339 
 
 86. Nebula in the Sword-handle of Orion 341 
 
 87. Comparison of Cometary and Nebular Spectra with those of 
 
 Carbon and other known Substances 344 
 
 88. Comet II. 1868 346 
 
 89. Apparatus for ascertaining the presence of Carbon in the Comet . 347 
 90. Spectrum (F Line) of Sirius compared with the Spectra of Hydrogen 
 
 and the Sun 350 
 
 91. Deviation of the F Line in a Spot-Spectrum (Lockyer) .... 354 
 
 92.- Shifting of the F Line in the Chromosphere 355 
 
 93. Powerful Star Spectroscope of Mr. Huggins 379 
 
 94. Repetition of arrangement used for comparing the Spectrum of a 
 
 Comet with that of Carbon 405 
 
LIST OF ILLUSTRATIONS: 
 
 PLATES. 
 
 Chromo-lithograph of the Spectra of the Metals of the Alkalies and 
 
 Alkaline Earths, from the Drawings of Kirchhoffand Bunsen. Front. 
 
 Huggins' Map of the Metallic Spectra facing Lect. IV. 156 
 
 Kirchhoff's and Angstrom's Maps facing Lect. V. 222 
 
 Forms of Eruptions and cloud-like Prominences as observed and drawn 
 
 by Professor Zollner facing 262 
 
 The Total Eclipse of Dec. 22, 1870. Photographed by A. Brothers at 
 
 Syracuse facing 268 
 
 Total Eclipse of Dec. 12, 1871, as photographed at Baikul, India, by 
 
 Mr. Davies, photographer to Lord Lindsay's Expedition . facing 270 
 Chromo-lithograph of the Spectra of the Stars, Nebulae, and Comets, 
 
 together with those of some of the Non-Metallic Elements. 
 
 facing Lect. VI. 320 
 
at u jflj^ 
 
 UNIVERSITY 
 ox 
 
 SPECTRUM ANALYSIS. 
 
 LECTURE I. 
 
 Introduction. Newton's Discovery of the Composition of White 
 Light, 1675. Properties of Sun Light. Heating Rays. Lumi- 
 nous Rays. Chemically Active Rays. The Solar Spectrum. 
 Position of Maxima. Illustrations of these Radiations. Means 
 of obtaining a Pure Spectrum. Fraunhofer's Lines. Planet and 
 Moon Light. Star Light. 
 
 APPENDIX A. Extracts from "Newton's Opticks." 
 
 APPENDIX B. Burning Magnesium Wire a Source of Light for photo- 
 graphic purposes. 
 
 APPENDIX C. On the Chemical Action of the constituent parts of 
 Solar Light. 
 
 AMONGST all the discoveries of modern science none has 
 deservedly attracted more attention, or called forth more 
 general admiration, than the results of the application 
 of Spectrum Analysis to chemistry. Nor is this to be 
 wondered at when we remember that a new power has 
 thus been placed in the hands of the chemist, enabling 
 him to detect the presence of chemical substances with 
 a degree of delicacy and accuracy hitherto unheard of, 
 and thus to obtain a far more intimate knowledge of 
 the composition of terrestrial matter than he formerly 
 
 B 
 
2 SPECTRUM ANALYSTS. [LECT. i. 
 
 enjoyed. So valuable a means of research has this new 
 process of analysis proved itself to be that since its 
 first" establishment, some seven short years ago, no less 
 than four new chemical elements have by its help been 
 discovered. 
 
 Not only, however, have we to consider the importance 
 and interest which attaches to the subject as evidenced 
 by the discovery of these new elementary bodies, but 
 we are forced to admit that by the application of the 
 simple principles of spectrum analysis the chemist is 
 able to overstep the narrow bounds of our planet, and, 
 extending his intellectual powers into almost unlimited 
 space, to determine, with as great a degree of certainty 
 as appertains to any conclusion in physical science, the 
 chemical composition of the atmosphere of the sun and 
 far distant fixed stars. Nay, he has even succeeded in 
 penetrating into the nature of those mysteries of astro- 
 nomy, the nebulae ; and has ascertained not only the 
 chemical composition, but likewise the physical condition, 
 of these most distant bodies. 
 
 It does, indeed, appear marvellous that we are now 
 able to state with certainty, as the logical sequence of 
 exact observations, that bodies common enough on this 
 earth are present in the atmosphere of the sun, at a 
 distance of ninety-one millions of miles, and still more 
 extraordinary that in the stars the existence of such 
 metals as iron and, sodium should be ascertained beyond 
 a shadow of doubt. We thus see that the range of 
 
 <D 
 
 inquiry which the subject opens out is indeed vast, and 
 it is well to bear in mind that as the discoveries in this 
 branch of science are so recent, they are necessarily 
 incomplete, so that we must expect to meet with many 
 facts and observations which still stand alone, and require 
 
LECT. i.] INTRODUCTION. 3 
 
 further investigation to bring them into harmony with 
 the rest. The advance in these new fields of research 
 is, however, so rapid that, as time rolls on, and our 
 range of knowledge widens, new facts quickly come 
 to support the hitherto unexplained phenomena, and 
 thus our theory becomes more and more complete. It 
 will be my duty in the Lectures which I have the 
 honour of delivering in this Hall to endeavour to explain 
 to you that these results, apparently as marvellous as 
 the discovery of the elixir vitse or the philosopher's stone, 
 are the plain and necessary deductions- from exact and 
 laborious experiment, and to show how two German 
 philosophers, quietly working in their laboratories in 
 Heidelberg, obtained this startling insight into the 
 processes of creation. 
 
 The only means of communication which we possess 
 with the sun, planets, or far distant stars, or by which 
 we can ascertain anything respecting their chemical 
 constitution, is by means of the life-supporting radiation 
 which they pour down upon the earth, producing the 
 effects which we call light and heat. It will, therefore, 
 be our business, in the first place, to investigate the 
 composition of the radiations which these bodies give 
 off, and next gradually to notice, as our field of obser- 
 vation enlarges, the applications to which the properties 
 of the light thus emitted lead us. One cannot help 
 regretting that when, as at present, the sunlight is 
 shining so brightly, we are unable to utilize it, and 
 illustrate by experiments made with the sunlight itself 
 the points which we wish to explain. In this climate 
 however, even if we could conveniently do it, the sun 
 shines so intermittently, and it is so doubtful if we can 
 have it just when it is required, that we have to make 
 
 B 2 
 
SPECTRUM ANALYSIS. 
 
 [LECT. i. 
 
 use of other means, especially of this bright light of the 
 electric arc, which, if less perfect than sunlight, is more 
 under our control. 
 
 In the year 1675, Sir Isaac Newton presented to the 
 Koyal Society his memorable treatise on Optics. 1 In this 
 treatise, which contains a large number of experimental 
 and theoretical investigations, one point especially attracts 
 our attention : it is the discovery of the decomposition 
 of white light. We have here (Fig. 1) a fac-simile of 
 the drawing illustrating Newton's experiment on this 
 subject. He heads the first paragraph in his memoir, 
 
 \ 
 
 FIG. 1. 
 
 .written in the year 1675, with the words, "lights which 
 differ in colour differ also in refrangibility." Newton 
 allowed the sun to shine through a round hole (Fig. 1, r) 
 in a shutter, and he then examined the character of this 
 light by means of a triangular piece of glass (A B c) called 
 a prism. He found that the white light, after passing 
 through the prisnij was bent or refracted out of its 
 course, and split up into a coloured band (p T) which, 
 when received on the white screen (M N), exhibited all 
 the colours of the rainbow in regular succession, passing 
 from red through all the shades of orange, yellow, green, 
 
 1 For extracts from " Xewton's Opticks," see Appendix A. 
 
LECT. 1.] 
 
 NEWTON 'S /; I SCO VER Y. 
 
 indigo blue, to violet. Newtou termed this coloured 
 band the Solar Spectrum, and came to the conclusion 
 that the light of the sun consists of rays of different 
 degrees of refrangibility. He also showed that all the 
 various portions of this coloured band, when again 
 brought together, produce upon the eye the effect of 
 white light. This experiment (represented in Fig. 2) 
 Newton performed by simply allowing the light passing 
 through the round hole (F) in the shutter to fall on a 
 prism (A B c), producing the solar spectrum, and then 
 
 FIG. 2. 
 
 on looking at this coloured band through another prism 
 (a b c) placed in the same direction, instead of seeing 
 a coloured band he observed a spot of white light, thus 
 showing that the whole of these differently coloured rays, 
 when brought together by means of the second prism, 
 produce on the eye the effect of white light. Here 
 we have the intensely white electric light, and by 
 means of these two prisms you observe that I can split 
 the light up into its various constituent parts, and we 
 obtain this splendid coloured band, the spectrum of the 
 electric arc. Now I shall endeavour to show you the 
 
SPECTR UM ANAL YS1S. 
 
 [LECT. 
 
 second effect which Newton observed. For this purpose 
 I have only to reverse the position of one of the prisms ; 
 for if I allow this band of coloured light emitted from 
 the first prism to pass through the second prism, placed 
 in the opposite direction to the first, I shall again bring 
 these coloured rays together, the second prism neutralizing 
 altogether the effects of the first, and we obtain the 
 bright white image of the slit. 
 
 I should like next to show you a third part of the 
 experiment made by Newton. If I cut off, by means of 
 this screen, a portion of the spectrum which has passed 
 through the first prism, say the yellow or the green or 
 
 the red, you will see that another refraction through the 
 second prism does not alter this coloured light. Here, 
 for instance, I take the green, and bring my prism into a 
 proper position : we shall find that I only get the same 
 green light on the screen behind, proving that the green 
 ray cannot again be split up by further refraction. The 
 mode in which Newton performed this experiment is 
 seen in Fig. 3. The green rays (g) in the spectrum 
 (d e), when refracted through a second prism (a b c), 
 appear as a green band (N M) on the second screen. 
 
 Now the reason why all these different coloured lights, 
 when they reach the eye, produce the effect of white 
 
LECT. 1.] 
 
 COMPOSITION OF WHITE LIGHT. 
 
 light, is a physiological question which we cannot 
 explain. We find that not only do all the colours of 
 the spectrum, when they are brought upon the eye, pro- 
 duce the effect of white light, but that several mixtures 
 of only a few out of all these different colours have the 
 same power of producing upon the eye the effect of 
 white light. 
 
 Thus Helmholtz and Maxwell have shown that the 
 
 FIG. 4. 
 
 following mixtures of two complementary colours when 
 brought together into the eye produce the effect of 
 whiteness : Violet and greenish yellow ; indigo and 
 yellow ; blue and orange ; greenish blue and red. 
 This I may readily illustrate to you by taking a re- 
 volving disc (Fig. 4), upon which segments of various 
 colours have been painted. When I turn this disc 
 which you observe contains, to begin with, all the colours 
 of the spectrum in due proportion and then, when it is 
 
8 SPECTRUM ANALYSIS. [LECT. i. 
 
 revolving, exhibit it to you by the light of burning 
 magnesium, you will notice that the effect produced 
 upon the eye is that of a uniformly white disc. Let 
 me now substitute for this painted disc another one, 
 which only contains the three colours red, yellow, and 
 blue. You will still perceive that when quickly revolved 
 the disc appears white ; and so I might substitute any 
 of the above mixtures of colours, all of which produce 
 on the eye the sensation of white light by the rapid 
 succession of the images of the different colours, the 
 effect of the one colour not having time to disappear 
 from the retina before that of the other comes into play. 
 If I illuminate the rotating disc by means of an instan- 
 taneous electric spark, you will see that all the colours of 
 the disc become noticeable at once. This is because the 
 period of illumination is so exceedingly short that the 
 disc appears as if stationary. It was indeed at one time 
 supposed that the various shades of colour in the solar 
 spectrum were produced by an overlapping, as it were, 
 of three distinct coloured spectra, one red, the second 
 yellow, and the third a blue spectrum, the maxima of 
 which are situated at different points, that of the red and 
 blue at the extremes, and that of the yellow in the middle 
 of the visible spectrum. This theory of Brewster's has, 
 however, been proved to be fallacious, for Helmholtz has 
 shown that the green ray, for example, is not made up 
 of blue and yellow light superposed, and we cannot 
 separate anything else but green out of it. Hence we 
 conclude that each particular ray has its own peculiar 
 colour, and that light of each degree of refrangibility 
 is monochromatic. But, on the other hand, although 
 physically, and in the actual spectrum, there is no such 
 thing as a superposition, or overlapping of different 
 
LECT. i.] THEORY OF FISION. 9 
 
 spectra, yet it is very likely, nay, more than likely, that 
 the retina is mainly sensitive to three impressions, viz. 
 red, yellow, blue ; in fact it appears that there are some 
 nerves especially sensitive to red, others to yellow, and 
 others again to blue light, whilst the impressions of the 
 other tints are obtained by the joint impressions pro- 
 duced on these three classes of nerves. This theory, 
 indeed, was proposed so long ago as the beginning 
 of the century by our celebrated countryman, Thomas 
 Young, and quite recently it has been proved by Max 
 Schulze, that in the eyes, not indeed as yet of man, but of 
 certain animals, there exist differences which are observ- 
 able in the nerve ends situated at the back of the retina : 
 some of these end in little red drops, some of them in 
 yellow drops, and some of them in colourless ones. The 
 nerves whose ends contain the little red drops are more 
 sensitive to red colour than the others ; and so those con- 
 taining yellow drops are more sensitive to the yellow 
 colour ; and in this way we believe that the peculiar 
 effects which we observe in the mixtures of colour may 
 be explained. 
 
 In noticing the physical properties of the variously 
 coloured light obtained when the sunlight or white light 
 is decomposed into its constituent parts, we must remem- 
 ber, in the first place, that light is due to the undulations 
 of the elastic medium pervading all space, to which 
 physicists have given the name of luminiferous ether. 
 As the undulations of the particles of water, causing the 
 waves of the sea, differ in length (as from crest to crest), 
 and in amplitude (as measured by the extent of the vibra^- 
 tion of each particle), sometimes being minute and shallow 
 like the ripples on the surface of a pond, sometimes rising 
 and falling into the gigantic crests and valleys of the 
 
10 SPECTRUM ANALYSIS. [LECT. i. 
 
 storm-ridden ocean, so also the undulations of the ether- 
 producing light differ in wave-length and amplitude, 
 giving rise to the different effects of colour to which we 
 have referred. 
 
 Let us now compare the power of the ear and the eye, 
 the one to receive the vibrations of the air called sound, 
 and the other the vibrations of the ether termed light. 
 
 The human ear has the power of distinguishing 
 variations in sounds differing widely in wave-length and 
 in rapidity of vibration. Thus, for instance, the musical 
 note, the deepest in the bass of all those that can be 
 heard by the human ear, is produced by the regular suc- 
 cession of impulses occurring about 16 times in each 
 second, whereas the highest continuous sound which is 
 perceptible to the ear is caused by about 38,000 vibra- 
 tions per second. Hence the range of audible notes 
 extends over about 11 octaves. Let us next examine 
 what is the range to which the eye is sensitive. It is 
 found that we can observe, ordinarily, in the solar spec- 
 trum from the position indicated by a fixed dark line in 
 the red portion termed A (see frontispiece of the Solar 
 Spectrum) to a line H in the violet or most refrangible 
 portion of the visible spectrum. Now the difference in 
 the number of the vibrations from A to H is but slight ; 
 it is indeed not one octave. The length of the undula- 
 tion of each of these waves is excessively small, Avhilst 
 the number of the vibrations of the ether which take 
 place every second is enormously large. By certain 
 methods of exact measurement, physicists have been 
 enabled to determine with accuracy the length and the 
 duration of these various waves of light ; and they have 
 come to the conclusion that the wave causing this red ray 
 which is only just visible to the eye has a length of the 
 
LECT. i.J HEATING RAYS. \ \ 
 
 n^oYoVooth part of an inch, and that in one second of time 
 no less than 458 millions of millions of these vibrations 
 occur whereas at the line H in the violet the length of 
 the wave is 100 oo 5 oo-oth part of an inch, and the* number of 
 vibrations is 727 millions of millions per second. Hence 
 the difference is only from 458 to 727, and you see that 
 the rapidity of the vibration at the one point is not twice 
 as great as it is at the other, and we are correct in stating 
 that we can hear about 11 octaves, but that we cannot 
 see a single octave. 
 
 Nevertheless, although they do not produce on the 
 retina the impression which we call light, there are rays 
 extending both beyond the visible red and beyond the 
 visible blue. By certain devices we can make ourselves 
 aware of the existence of these invisible rays, which play 
 a most important part in the nature of the solar light. 
 
 If we observe the effects which 'are produced by the 
 different rays constituting the visible portion of the solar 
 spectrum, we find, to begin with, that those rays which 
 mainly produce heating effects are situated at the red 
 end of the solar spectrum. We learn that the maximum 
 heating effect is produced at a point beyond that at 
 which we can see any red light. The maximum of the 
 luminous rays as affecting the eye exists in the yellow. 
 Passing on from the red towards the violet portion, we 
 find, by means of a thermo-pile and a delicate galvano- 
 meter, that the quantity of heating effect produced in 
 the yellow and green portions of the spectrum gradually 
 diminishes, and sinks down to a very insignificant 
 amount in the violet part of the band. In the blue and 
 violet portion of the spectrum, so slightly endowed with 
 heating power, we have, however, to notice the existence 
 of a new and striking peculiarity, that of producing 
 
12 SPECTRUM 4XJLY81S. [LECT. i. 
 
 chemical action ; that is, of causing the combination and 
 decomposition of certain chemical substances, as for 
 instance the decomposition and blackening of silver salts, 
 upon which the art of photography is based. 
 
 It is to Sir W. Herschel that we are indebted for the 
 first notice, in the year 1800, of the fact of the heating 
 rays existing especially in the red portion of the spectrum, 
 whilst Bitter and Scheele at the early part of this century 
 observed the peculiar power possessed by the blue, violet, 
 and ultra-violet rays to blacken silver salts. 
 
 In Fig. 5 we have a graphical representation of the 
 varying intensity of the heating, luminous, and chemi- 
 
 FIG. 5. 
 
 cally active rays in the various parts of the solar spectrum. 
 The figure exhibits three curves, A, B, and c, showing the 
 distribution of these three actions produced by the rays 
 of the solar spectrum, whose position is given in the 
 upper part of the diagram, the differently coloured por- 
 tions being indicated by certain fixed lines to which 
 letters are attached, beginning with A in the red, and 
 ending with o in the ultra-violet portion of the spectrum. 
 This curve (A, Fig. 5) represents the intensity of the 
 heating power of the spectrum. You observe how far it 
 
LECT. i.J CALORESCEXCE. 13 
 
 extends, a long way beyond the visible red, which ends 
 a little to the left of the line A. In fact it has been 
 noticed by those who have made careful measurements, 
 that half the rays of heat reaching the earth from the 
 sun are invisible, and I shall hope to show you directly 
 the effect of these invisible heating rays. 
 
 In the part shaded with vertical lines only, there is no 
 perceptible luminous or chemical activity ; in that shaded 
 only with horizontal lines we find that chemical action is 
 the chief characteristic. From the beginning to the end 
 of the luminous spectrum shaded with oblique lines, two, 
 at least, of these three forms of action exist simul- 
 taneously. The intensity of each at any point of the 
 spectrum is measured by the vertical line drawn from the 
 point on the base line to meet its proper curve. It must, 
 however, be remembered that whenever 'the luminous or 
 the chemical rays are absorbed, heat is evolved, so that, 
 strictly speaking, the curve of the heating action should 
 extend, although very feebly, along the whole length of 
 the spectrum. 
 
 "Whilst noticing these peculiar properties of the dif- 
 ferent rays we must carefully remember that there 
 really is no difference in kind between those rays which 
 are called heating rays, those which are called light 
 rays, and those which are called chemically active rays. 
 These differ one from the other in exactly the same way 
 that the visible yellow rays differ from the green rays, 
 or as the green rays differ from the blue ; only in wave- 
 length and intensity of vibration. In any particular 
 portion of the spectrum we cannot separate the rays of 
 light and leave the rays of heat behind; we cannot, 
 for instance, separate out the yellow rays of light from 
 the yellow portion of the spectrum, and leave behind 
 
14 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. i. 
 
 any rays of heat of the same degree of refrangibility. 
 But, as I shall show you, we can separate from the 
 whole radiation the luminous rays, and with them the 
 heating effect of those luminous rays, and still leave 
 the dark or invisible rays of heat of lower refrangibility. 
 
 I will endeavour to prove to you, hi the first place, 
 the existence of these dark heating rays of really in- 
 visible light. We see that the maximum of these rays 
 
LKCT. i.J CALORESCENCE. 15 
 
 is placed beyond the visible red. This may be clearly 
 exhibited with the electric light in the beautiful experi- 
 ment by which Dr. Tyndall first accomplished the sepa- 
 ration of which I have just spoken. I have for this 
 purpose placed in the dark box (D, Fig. 6) an electric 
 lamp (L), which gives us a very bright light, and by 
 means of this mirror (M) I can bring the rays to a focus at 
 any desired point. Here is a cell (c) which Dr. Tyndall 
 very expressively calls a ray-filter, by which I can filter 
 out the whole of the luminous rays, by passing them 
 through this opaque solution of iodine in disulphide 
 of carbon, whilst the invisible heating rays are trans- 
 mitted, and will soon render themselves evident to you. 
 A current of cold water circulates through a double 
 jacket on the outside of the eel], to keep the volatile 
 disulphide cool. Now I think you will observe that no 
 rays of light come through, but if I take a piece of black 
 paper, and place it in the focus of our mirror, you see 
 the paper is ignited, owing to the presence of these dark 
 heating rays. I may now do the same with a piece of 
 blackened platinum (p, Fig. 6) ; you see that this also 
 is heated to redness. I can show you this again in a 
 variety of forms. Here is some gunpowder strewed on 
 this paper ; you observe that it at once explodes when 
 brought into the focus of the dark rays. Here I have 
 some blackened gun-cotton, which instantly catches fire. 
 I may vary the experiment by lighting a cigar ; and 
 here you see the brilliant scintillations of charcoal burn- 
 ing in oxygen, having been heated up to the tempera- 
 ture of ignition in the focus of the dark rays. Dr. 
 Tyndall has measured the proportional amount of the 
 entire heating rays which, pouring forth from this incan- 
 descent carbon, has passed through this dark filter, and 
 
16 
 
 SCEPTRUM ANALYSIS. 
 
 [LECT. i. 
 
 he has found that this consists of |- of the whole amount ; 
 so that only \ of the radiation is really visible. 
 
 Understanding then the existence in this ultra-red of 
 a large amount of heating rays, let us pass on now to 
 consider the properties of the light which is given off at 
 the opposite or blue end of the spectrum, which I have 
 called the chemically active rays. Allow me to show 
 you an experiment to prove that it is in the blue 
 portion of the spectrum that we have essentially these 
 
 FIG. 7. 
 
 chemically active rays. In order to render the illustra- 
 tion more perfect, I will first make an experiment with 
 reference simply to white light, to show you that 
 the brilliant light which is emitted by this burning 
 magnesium, and is almost too dazzling for the eye to 
 bear, contains a very large proportion of the rays which 
 we are about to investigate. 1 
 
 O 
 
 1 See Appendix B for the measurement o f the chemical intensity 
 
 of magnesium light. 
 
LSCT. I. 
 
 CHEMICALLY ACTIVE RAYS. 
 
 I have here a thin glass bulb containing a mixture of 
 equal volumes of two gases, chlorine and hydrogen. 
 These gases when exposed to a bright light combine 
 together, and form hydrochloric acid gas. If I were to 
 throvv r this bulb out into the sunlight, so rapid would be 
 the combination, and so great the consequent evolution 
 of heat and sudden expansion, that this little bulb would 
 instantly be shattered into a thousand fragments. Al- 
 most as sudden an effect will be produced if I simply burn 
 
 FIG. 8. 
 
 a bit of magnesium wire in the neighbourhood of the 
 bulb (Fig. 7) ; it explodes with a pretty loud report, the 
 bulb is shattered, and the gases have been combined 
 by virtue of the blue rays contained in this kind of 
 light. In order to convince you that the red rays 
 cannot produce the action which the blue ones are able 
 to effect, I here burn a piece of phosphorus, first in 
 a red globe full of oxygen gas, when, as you see, an 
 
 e 
 
18 SPECTRUM ANALYSTS. [LECT. i. 
 
 intense light is emitted wholly without action on our 
 little bulb of sensitive gas. Next I burn a similar piece 
 of phosphorus in oxygen contained in this blue globe, and 
 as soon as the intensity of the light attains its maximum, 
 the bulb explodes with a loud report. I will next show 
 you in another way that it is the blue rays which 
 thus act chemically. This lantern (Fig. 8) contains 
 panes of different coloured glass, here a white one, 
 there a yellow one ; here a red one, there a blue one. 
 I am going to put another of these little bulbs filled with 
 chlorine and hydrogen in the inside of this lantern, 
 and then I will produce, not by magnesium wire, but 
 by another means, a very bright blue light, a light 
 which contains these chemically active rays in great 
 quantity. I will first allow this blue light to shine 
 upon the bulb through the red pane of glass. Here I 
 produce a very bright flame, by throwing some carbon 
 disulphide into a tall cylinder full of nitric oxide gas, 
 and igniting the mixture. There you have the bright 
 flash, but you have noticed no explosion of the bulb, for 
 all the chemical rays have been held back : filtered off 
 by this red glass, they cannot pass through ; and the 
 consequence is, there has been no action on my bulb. I 
 will now allow another of these flashes of light to pass 
 through the blue glass, which being of course transparent 
 to the blue rays my little bulb will be shattered into a 
 fine powder, as you observe. Here then we have ascer- 
 tained by experiment that the blue rays act chemically, 
 whilst the red rays produce heating effects. 
 
 This sensitive mixture of chlorine and hydrogen, 
 which, as you have seen, explodes when the chemical 
 activity of the light is great, may be used as a most 
 delicate means of measuring the amount of light of a 
 
LECT. 1.] 
 
 CHEMICAL ACTION. 
 
 1.9 
 
 less intensity. The combination of the gases then occurs 
 slowly, and may be rendered evident by allowing the 
 hydrochloric acid thus formed to be absorbed by water, 
 when the consequent diminution in bulk of the gas 
 accurately represents the chemical action effected. 
 
 The varying intensity of the chemically active rays in 
 different parts of the solar spectrum has been carefully 
 measured by means of this sensitive mixture of chlorine 
 
 FIG. 9. 
 
 arid hydrogen gases. 1 The accompanying figure (Fig. 
 9) exhibits the chemical action effected by the various 
 portions of the spectrum on the sensitive mixture for one 
 particular zenith distance of the sun. The lines marked 
 with the letters of the alphabet from A to w, at the 
 bottom of the figure, represent the fixed dark lines 
 which exist in the solar spectrum, of which I shall have 
 much to say in the subsequent lectures. They serve as 
 landmarks by which to ascertain the position of any given 
 
 1 See Apperiix C for description of method. 
 c 2 
 
20 SPECTRUM ANALYSIS. [LECT. i. 
 
 point in the spectrum. The greatest amount of chemical 
 action is noticed between the line in the indigo marked G, 
 and that in the violet marked H. In the direction of the 
 red end of the spectrum, the action becomes imperceptible 
 about D, in the orange (the maximum of visible illumi- 
 nation) ; whilst towards the other end of the spectrum 
 the action was found to extend as far as the line 
 marked u, or to a greater distance beyond the line H in 
 the violet than the total length of the ordinary visible 
 spectrum. For other chemical substances, such as the 
 salts of silver, which are capable of undergoing decom- 
 position when exposed to the light, different curves of 
 sensitiveness are obtained. All these bodies are acted 
 upon by the blue rays, but some have their maximum 
 action at one part, some at another part of the spectrum. 
 This fact of the greater chemical activity of the more 
 refrangible rays may again be illustrated by showing 
 that I can photograph with these blue rays, whereas I 
 fail to produce the same effect with the red rays. I will 
 coat a plate with collodion, and then darken the room, 
 with the exception of this yellow monochromatic flame, 
 produced by the volatilization of soda salts, which is 
 incapable of acting chemically, and with which we may 
 work without at all affecting our photographic plate. Now 
 I have coated a plate with collodion, and sensitized it in 
 the silver bath. I shall next expose this to the action of 
 the light of the spectrum of the electric lamp. Let me 
 first show you that I have here (Fig. 10) a negative 
 photograph, of which T am about to take a print by 
 means of the blue rays of the electric lamp. You will 
 observe that there are two figures upon the negative, one 
 marked V and the other marked E : these letters being 
 intended to signify Violet and Red. The one figure 
 
LECT. I.J 
 
 PHOTOGRAPHY IN BLUE RATS. 
 
 21 
 
 marked V, I propose to place in front of my sensitized 
 plate in the blue or violet ray, and the one marked E 
 I shall open in the red ray, and I hope to be able to 
 produce a chemical effect on that portion of my sen- 
 sitized plate which has been exposed to the blue, whilst 
 we shall get no corresponding effect on the portion 
 exposed to the red ray. I next place my plate with its 
 face downwards on the negative ; we now start our 
 electric lamp, using a small spectrum in order to have 
 
 FIG. 1.0. 
 
 the action rather more distinct. I then expose half my 
 plate in the red rays for about twenty seconds, and 
 afterwards expose the other half, with the V upon it, for 
 about the same length of time, to the violet light. I 
 will now develop and wash the photograph, and throw 
 the image produced on the screen, when you will observe 
 (Fig. 11) a very marked difference between the two 
 halves, the one showing that no action has been produced 
 
22 SPECTRUM ANALYSIS. LECT. i. 
 
 on the sensitive plate exposed to the red rays, and the 
 other giving us the perfect picture with the V upon it. 
 
 Another very interesting example of the chemical 
 changes effected by these refrangible rays, recently studied 
 by Professor Tyndall, 1 is the decomposition which the 
 vapours of certain organic bodies undergo when exposed 
 to the concentrated solar rays, or to the concentrated 
 beam of the electric light. To investigate these remark- 
 able changes Tyndall passes a very small quantity of the 
 
 FIG. 11. 
 
 colourless and invisible vapours of such liquids as nitrite 
 of amyl, together with air, into a long glass tube closed 
 at each end by glass plates; on allowing a beam of 
 parallel rays to fall through the length of the tube, 
 the space at first appears to be empty and dark, but 
 after a few seconds singularly beautiful coloured cloud - 
 
 1 " On the Action of Bays of high Refrangibility upon Gaseous 
 Matter," by J. Tyndall, F.R.S., Phil. Trans. 187CH p. 333. 
 

 LECT. i.] CHEMICAL ACTION OF DAYLIGHT. 23 
 
 forms make their appearance, and as these are not seen 
 when the tube contains only air, we thus learn that 
 a chemical change has taken place in the vapour itself. 
 Of the exact nature of the changes here produced we 
 are as yet ignorant, but in many cases it is probable 
 that an oxidizing action is going on. The delicacy of 
 these reactions is remarkable, < even by the side of the 
 phenomena of spectrum analysis, for the quantity of 
 matter capable of producing these actinic clouds is found 
 to be extremely small. 
 
 The chemically active rays which the sun constantly 
 pours down upon our earth, doubtless exert a most im- 
 portant influence on the fauna and flora of a country, 
 and it becomes a matter of some importance to measure 
 accurately their varying intensity with the changing 
 seasons, and at different parts of the globe. It may not 
 be uninteresting if I point out some of the results which 
 have already been obtained by measurements of this 
 kind, made by a method proposed by Professor Bunsen 
 and myself, and depending on the darkening of a sensi- 
 tive paper prepared with chloride of silver. The prin- 
 ciples upon which the method is based are : (1) that a 
 photographic paper can be prepared which always shall 
 possess a constant degree of sensitiveness ; and (2) that 
 the darkening effect produced by the light on this paper 
 is constant when the product of the intensity of the light 
 into the time of exposure is also constant. Measurements 
 according to this method have been carried out at Kew 
 Observatory, and an interesting series of curves obtained, 
 showino 1 the variation of the chemical action of the day- 
 
 o / 
 
 light with the seasons. The curves (Fig. 12) show the 
 rise and Ml of monthly chemical intensity with the hour 
 of the day, from 6 A.M. to 6 P.M., for the year 18GG. 
 
24 SPECTRUM ANALYSTS. [LECT. i. 
 
 We see from these curves that the maximum amount of 
 chemical action occurs at 12 o'clock, and that this action 
 is equal at hours equidistant from noon ; we learn also 
 that if the chemical intensity in July 186G be repre- 
 sented by the number 100, that in January is represented 
 by 14 ; or in mid-summer the chemical intensity of the 
 sun is more than seven times as creat as in mid-winter. 1 
 
 o 
 
 Still more interesting is it to ascertain the distribution 
 of the chemically active rays on the earth's surface, about 
 which we as yet know but little. According to the 
 vague observations of photographers, it would appear 
 
 Kew 1866. 
 
 FIG. 12. 
 
 that in advancing from England towards the equator 
 the difficulty of obtaining good pictures is increased, and 
 more time is said to be needed to produce the same 
 effect on the photographic plate under the full blaze of a 
 tropical sun than in the gloomier atmosphere of London. 
 It has likewise been stated that in Mexico, where the 
 light is very intense, from twenty minutes to half an 
 hour was required to produce photographic effects which 
 in England occupy only a minute ; and it is said that 
 
 B.kerian Lecture, Phil. Trans, part ii. 1865, p. 005 ; 
 and also (liosnoe) Phil. Trans. 18G7, p. 555. 
 
LUCT. i.] CHEMICAL ACTION IN THE TROPICS. 25 
 
 travellers engaged in copying the antiquities of Yucatan 
 have on several occasions been obliged to abandon the 
 use of the photographic camera, and have had to take 
 to their sketch-books ! In order to test the validity of 
 these statements, it becomes a matter of great importance 
 to determine directly the intensity of the chemically 
 active rays in the tropics ; and, thanks to the zeal and 
 ability of my friend Professor Thorpe, I am able to 
 show you the results of such measurements, made at 
 Para, situated nearly under the equator, in the northern 
 province of the Brazils, and lying on a branch of the 
 
 April PJrf 1 1866. April 25*1* 1866. 
 
 FIG. 13. FIG. 14. 
 
 Amazons. Owing to the rainy season having commenced 
 when the experiments were made, the changes in the 
 chemical intensity as observed from hour to hour, and 
 even from minute to minute, are very sudden and re- 
 markable, and are well seen on the curves (Figs. 13 and 
 14) ; and these, compared with the dotted lines below 
 indicating the corresponding action on the same day at 
 Kevv, show the enormous variation in chemical intensity 
 
26 SPECTRUM ANALYSIS. [LECT. i. 
 
 which occurs under a tropical sun in the rainy season. 
 Kegularly every afternoon, and frequently at other hours 
 of the day, enormous thunder-clouds obscure the sky, 
 and, discharging their contents in the form of deluging 
 rain, reduce the chemical action nearly to zero. The 
 storm quickly passes over, and the chemical intensity 
 rapidly rises to its normal value. By comparing the 
 curves for Para and Kew on the same days, we obtain 
 some idea of the energy of chemical action at the tropics, 
 and it is at once evident that the alleged failure of the 
 photographer cannot at any rate be ascribed to a diminu- 
 tion in the sun's chemical intensity, which in the month 
 of April 1866 was nearly seven times as great at Pard, 
 as at Kew. 
 
 I have in conclusion to point out to you that the 
 solar spectrum differs in certain respects from that 
 beautiful spectrum of the electric arc with which we 
 have been working ; and it differs in this way, that the 
 solar spectrum consists, not of a continuous band, passing 
 without break or interruption from red to violet, through 
 all the shades of colour which we know as the rainbow 
 tints, but that in the solar spectrum we find, interspersed 
 between these colours, certain dark lines which we may 
 regard as shadows in the sunlight, spaces where certain 
 rays : are absent. The first person who observed these 
 dark lines was Dr. Wollaston. 1 Newton did not observe 
 them, and for the good reason that he allowed the light 
 to fall on the prism from a round hole in the shutter. 
 In this way he did not obtain what is termed a pure 
 spectrum, but a series of spectra, one overlapping the 
 other, owing to the light coming through different parts 
 of the round hole. If he had allowed the light to 
 ] Phil. Trans. 1802, p. 378. 
 
LECT. i.] FRAUXHOFER'S LINES. 27 
 
 pass through a fine vertical slit, arid if this slit of 
 light, if we may use such a term, had then fallen upon 
 the prisms, placed so that the edge of the refracting 
 angle is parallel to the slit, he would have observed that 
 the solar spectrum was not continuous, but broken up 
 by permanent dark lines. Dr. Wollaston, making use 
 of a fine slit of light, discovered these fixed dark lines 
 in the solar spectrum. 
 
 I invite your attention to the drawings of these lines 
 in this very imperfect sketch of the solar spectrum 
 (see coloured diagram on Frontispiece). These dark 
 lines are always found in the same position in the sun- 
 light, whether you take direct, diffused, or reflected sun- 
 light. The exact mapping and observation of these lines 
 in the solar spectrum is a matter of as great import- 
 ance to astronomy and to physical science generally 
 as the mapping of the stars in the heavens, because 
 by knowing exactly the position of these dark lines in 
 the solar spectrum we can ascertain that iron, sodium, 
 and other well-known substances exist in the solar 
 atmosphere. 
 
 I will now show you a diagram illustrative of this 
 fact, and remind you that we are indebted for the first 
 careful examination of these lines to a German optician, 
 Fraunhofer, whose name has been attached to these lines. 
 Fraunhofer mapped no less than 576 of these lines in 
 the year 18 [4. 1 This is an exact reduced copy of his 
 map (Fig. 15). On the left is the red and on the right is 
 the violet portion of the visible spectrum. You observe 
 how this spectrum is shaded. Notice, if you please, 
 the immense number of lines which intersect and almost 
 appear to make the solar spectrum dark. Fraunhofer 
 1 Denkschriften der Miinchener Akademie, 1814. 
 
28 SPECTRUM ANALYSIS. [LECT. i. 
 
 employed the letters of the alphabet to designate some 
 
 Vt& 
 
 of the principal lines, beginning with A in the red and 
 
LECT. i.J FRAUNHOFE&S LINES. 29 
 
 passing on to H in the violet. Many of these lines 
 are as line as the finest spider's web, so that they 
 occupy but a small portion of the whole area of the 
 spectrum that is, the portion which is filled with light 
 is far greater than the portion filled with these shadows, 
 although the number of these shadows is so exceedingly 
 large. The curve in the upper part of the figure gives 
 Fraunhofef's estimate of the intensity of the visible rays 
 at different parts of the spectrum, and this corresponds 
 closely to the curve B in Fig. 5. 
 
 Fraunhofer first ascertained that these lines are present 
 in every kind of sunlight, and that moonlight, as well as 
 the light of the planet Venus, exhibits the same dark lines. 
 He like wise measured the refractive indices and the wave- 
 lengths of these lines, that is, determined their relative 
 positions in the solar light ; and he found that the 
 relative distances between any given lines remained 
 constant, whether he took direct sunlight, or sunlight 
 reflected from the moon or planets. 
 
 Since Fraunhofer's time more accurate determinations 
 of the wave-lengths of the various dark solar lines have 
 been made. Of these the most recent and exact are 
 those observed by Professor Angstrom, 1 of Upsala ; and 
 the numbers obtained by him for the wave-lengths of 
 the most important solar lines may be taken as the 
 standard measurements in this branch of science. In one 
 column of the table on the next page you will find these 
 standard wave-lengths in Angstrom's numbers expressed in 
 tenth-metres (or in ten-millionths of a millimetre) ; in the 
 other column are seen the numbers obtained by Fraunhofer 
 in 1814 for the wave-lengths of the same dark lines. 
 
 1 Angstrom, " lieclierches sur le Spectre Solaire, Spectre Normal du 
 Soleil," p. 25. Upsala, 1868. 
 
30 SPECTRUM ANALYSTS. [LECT. 
 
 v f T Angstrom's Wave-lengths. FraunhotVr's Wave-lengths. 
 
 (In ten-millionths of a millimetre.) 
 
 A. 7604-00 
 
 B. 6867-00 6879-f> 
 
 C. 6562-10 6562-3 
 
 D. 5892-12 5892-0 
 
 E. 526913 5265-3 
 
 F. 4860-72 4849 5 
 
 G. 430725 4293-3 
 H r 3968-19 3945-0 
 H 2 . 3933-00 
 
 Another important observation was made by Fraun- 
 hofer, namely, that the light from the fixed stars, which, 
 as you know, are self-luminous, also contains dark lines, 
 but different lines from those which characterize the 
 sunlight, the light of the planets, and that of the moon ; 
 and hence in 1814 Fraunhofer came to this remarkable 
 conclusion : that whatever produced these dark lines 
 and he had no idea of the cause was something which 
 was acting beyond and outside our atmosphere, and 
 not anything produced by the sunlight passing through 
 the air. 
 
 This conclusion of Fraunhofer has been borne out 
 by subsequent investigation, and the observations upon 
 which it was based may truly be said to have laid the 
 foundation-stone of solar and stellar chemistry. 
 
APPEND. A.] EXTRACTS FROM NEWTON. 31 
 
 LECTURE I. APPENDIX A. 
 
 EXTRACTS FROM "NEWTON'S OPTICKS," 1673. 
 BOOK I. PART 1. 
 
 PROP. I. THEOR. Lights which differ in colour, differ also in 
 degrees of refrangibility. 
 
 THE PROOF BY EXPERIMENTS. 
 
 Exper. 1. I took a black oblong stiff paper terminated by 
 parallel sides, and, with a perpendicular right line drawn across 
 from one side to the other, distinguished it into two equal parts. 
 One of these parts I painted with a red colour and the other with 
 a blue. The paper was very black, and the colours intense and 
 thickly laid on, that the phenomenon might be more conspicuous. 
 This paper I viewed through a prism of solid glass, whose two 
 sides through which the light passed to the eye were plane and 
 well polished, and contained an angle of about 60 : which angle 
 I call the refracting angle of the prism. And whilst I viewed 
 it, I held it and the prism before a window in such manner that 
 the sides of the paper were parallel to the prism, and both those 
 sides and the prism were parallel to the horizon, and the cross 
 line was also parallel to it ; and that the light which fell from 
 the window upon the paper made an angle with the paper, equal 
 to that angle which was made with the same paper by the light 
 reflected from it to the eye. Beyond the prism was the wall of 
 the chamber under the window covered over with black cloth, 
 and the cloth was involved in darkness that no light might be 
 
32 SPECTRUM ANALYMS. OSCT. i. 
 
 reflected from thence, which in passing by the edges of the paper 
 to the eye might mingle itself with the light of the paper, and 
 obscure the phenomenon thereof. These things being thus 
 ordered, I found that if the refracting angle of the prism be 
 turned upwards, so that the paper may seem to be lifted upwards 
 by the refraction, its blue half will be lifted higher by the refrac- 
 tion than its red half. But if the refracting angle of the prism 
 be turned downward, so that the paper may seem to be carried 
 lower by the refraction, its blue half will be carried something 
 lower thereby than its red half. Wherefore in both cases the 
 light which conies from the bine half of the paper through the 
 prism to the eye, does in like circumstances suffer a greater 
 refraction than the light which comes from the red half, and by 
 consequence is more refrangible. 
 
 Exper. 2. About the aforesaid paper, whose two halves were 
 painted over with red anJ blue, and which was stiff like thin 
 pasteboard, I lapped several times a slender thread of very black 
 silk, in such manner that the several parts of the thread might 
 appear upon the colours like so many black lines drawn over 
 them, or like long and slender dark shadows cast upon them. I 
 might have drawn black lines with a pen, but the threads were 
 smaller and better defined. This paper thus coloured and lined 
 I set against a wall perpendicularly to the horizon, so that one 
 of the colours might stand to the right hand, and the other to 
 the left. Close before the paper at the confine of the colours 
 below, I placed a candle to illuminate the paper strongly : for 
 the experiment was tried in the night. The flame of the candle 
 reached up to the lower edge of the paper, or a very little higher. 
 Then at the distance of six feet and one or two inches from the 
 paper upon the floor I erected a glass lens four inches and a 
 quarter broad, which might collect the rays corning from the 
 several points of the paper, and make them converge towards so 
 many other points at the same distance of six feet and one or 
 two inches on the other side of the lens, and so form the image 
 of the coloured paper upon a white paper placed there, after the 
 same manner that a lens at a hole in a window casts the images 
 of objects abroad upon a sheet of white paper in a dark room. 
 
APPEND. A.] EXTRACTS FROM NEWTON. 33 
 
 The aforesaid white paper, erected perpendicular to the horizon 
 and to the rays which fell upon it from the lens, I moved some- 
 times towards the lens, sometimes from it, to find the places 
 where the images of the blue and red parts of the coloured paper 
 appeared most distinct. Those places I easily knew by the 
 images of the black lines which I had made by winding the 
 silk about the paper. For the images of those fine and slender 
 lines (which by reason of their blackness were like shadows 
 on the colours) were confused and scarce visible, unless when 
 the colours on either side of each line were terminated most 
 distinctly. Noting therefore, as diligently as I could, the places 
 where the images of the red and blue halves of the coloured 
 paper appeared most distinct, I found that where the red half 
 of the paper appeared distinct, the blue half appeared confused, 
 so that the black lines drawn upon it could scarce be seen ; and 
 on the contrary, where the blue half appeared most distinct, the 
 red half appeared confused, so that the black lines upon it were 
 scarce visible. And between the two places where these images 
 appeared distinct there was the distance of an inch and a half: 
 the distance of the white paper from the lens, when the image 
 of the red half of the coloured paper appeared most distinct, 
 being greater by an inch and a half than the distance of the 
 same white paper from the lens, when the image of the blue 
 half appeared most distinct. In like incidences therefore of the 
 blue and red upon the lens, the blue was refracted more by the 
 lens than the red, so as to converge sooner by an inch and a half, 
 
 and therefore is more refrangible 
 
 Scholium. The same things succeed notwithstanding that 
 some of the circumstances be varied ; as in the first experiment 
 when the prism and paper are any ways inclined to the horizon, 
 and in both when coloured lines are drawn upon very black 
 paper. But in the description of these experiments, I have set 
 down such circumstances by which either the phenomenon might 
 be rendered more conspicuous, or a novice might more easily try 
 them, or by which I did try them only. The same thing I have 
 often done in the following experiments ; concerning all which 
 this one admonition may suffice. Now from these experiments 
 
34 SPECTRUM ANALYSIS. [LECT. i. 
 
 it follows not that all the light of the blue is more refrangible 
 than all the light of the red ; for both lights are mixed of rays 
 differently refrangible, so that in the red there are some rays not 
 less refrangible than those of the blue, and in the blue there are 
 some rays not more refrangible than those of the red ; but these 
 rays in proportion to the whole light are but few, and serve to 
 diminish the event of the experiment, but are not able to destroy 
 it. For if the red and blue colours were more dilute and weak, 
 the distance of the images would be less than an inch and a 
 half; and if they were more intense and full, that distance would 
 be greater, as will appear hereafter. These- experiments may 
 suffice for the colours of natural bodies. For in the colours 
 made by the refraction of prisms this proposition will appear 
 by the experiments which are now to follow in the next 
 proposition. 
 
 PROP. IT. TIIEOR. 2. The light of the sun consists of rays 
 differently refrangible. 
 
 THE PROOF BY EXPERIMENTS. 
 
 Exper. 3. In a very dark chamber at a round hole about one 
 third part of an inch broad made in the shut of a window I 
 placed a glass prism, whereby the beam of the sun's light which 
 came in at that hole might be refracted upwards towards the 
 opposite wall of the chamber, and there form a coloured image 
 of the sun. The axis of the prism (that is, the line passing 
 through the middle of the prism from one end of it to the other 
 end parallel to the edge of the refracting angle) was in this and 
 the following experiments perpendicular to the incident rays. 
 About this axis I turned the prism slowly, and saw the refracted 
 light on the wall or coloured image of the sun first to descend, 
 and then to ascend. Between the descent and ascent when the 
 image seemed stationary, I stopped the prism and fixed it in 
 that posture, that it should be moved no more. For in that 
 posture the refractions of the light at the two sides of the re- 
 
APPEND. A.] EXTRACTS FROM NEWTON. 35 
 
 fracting angle, that is at the entrance of the rays into the prism 
 and at their going out of it, were equal to one another. So also 
 in other experiments, as often as I would have the refractions on 
 both sides the prism to "be equal to one another, I noted the 
 place where the image of the sun formed by the refracted light 
 stood still between its two contrary motions, in the common 
 period of its progress and regress ; and when the image fell upon 
 that place, I made fast the prism. And in this posture, as the 
 most convenient, it is to be understood that all the prisms are 
 placed in the following experiments, unless where some other 
 posture is described. The prism therefore being placed in this 
 posture, I let the refracted light fall perpendicularly upon a sheet 
 of white paper at the opposite wall of the chamber, and observed 
 the figure and dimensions of the solar image formed on the paper 
 by that light. This image was oblong and not oval, but termi- 
 nated with two rectilinear and parallel sides, and two semicircular 
 ends. On its sides it was bounded pretty distinctly, but on its 
 ends very confusedly and indistinctly, the light there decaying 
 and vanishing by degrees. The breadth of this image answered 
 to the sun's diameter, and was about two inches and the eighth 
 part of an inch, including the penumbra. For the image was 
 eighteen feet and a half distant from the prism ; and at this 
 distance that breadth, if diminished by the diameter of the hole 
 in the window- shut, that is by a quarter of an inch, subtended 
 an angle at the prism of about half a degree, which is the sun's 
 apparent diameter. But the length of the image was about ten 
 inches and a quarter, and the length of the rectilinear sides about 
 eight inches, and the refracting angle of the prism whereby so 
 great a length was made was 64. With a less angle the 
 length of the image was less, the breadth remaining the same. 
 If the prism was turned about its axis that way which made the 
 rays emerge more obliquely out of the second refracting surface 
 of the prism, the image soon became an inch or two longer, 
 or more ; and if the prism was turned about the contrary way, 
 so as to make the rays fall more obliquely on the first refracting 
 surface, the image soon became an inch or two shorter. And 
 therefore, in trying this experiment, I was as curious as I could 
 
 D 2 
 
SPECTRUM ANALYSIS. 
 
 [LECT. r. 
 
 be, in placing the prism by the above-mentioned rule exactly in 
 such a posture that the refractions of the rays at their emergence 
 out of the prism might be equal to that at their incidence on it. 
 This prism had some veins running along within the glass from 
 one end to the other, which scattered some of the sun's light 
 irregularly, but had no sensible effect in increasing the length of 
 the coloured spectrum. For I tried the same experiment with 
 other prisms with the same success ; and particularly with a 
 prism which seemed free from such veins, and whose refracting 
 angle was 62 J. I found the length of the image 9f or 10 
 inches at the distance of 18| feet from the prism, the breadth of 
 the hole in the window-shut being of an inch, as before. And 
 because it is easy to commit a mistake in placing the prism in 
 its due posture, T repeated the experiment four or five times, and 
 always found the length of the image that which is set down 
 
 Fro. 16. 
 
 above. With another prism of clearer glass and better polish, 
 which seemed free from veins, and whose refracting angle 
 was 63J, the length of this image at the same distance of 
 18J feet was also * about 10 inches, or 10 J. Beyond these 
 measures for about J or J of an inch at either end of the spec- 
 trum the light of the clouds seemed to be a little tinged with 
 red and violet, but so very faintly, that T suspected that tincture 
 might either wholly or in great measure arise from some rays of 
 the spectrum scattered irregularly by some inequalities in the 
 substance and polish of the glass, and therefore I did not include 
 
APPEND. A.] EXTRACTS FROM NEWTON. 37 
 
 it in these measures. Now the different magnitude of the hole 
 in the window-shut, and different thickness of the prism where 
 the rays passed through it, and different inclinations of the prism, 
 to the horizon, made no sensible changes in the length of the 
 image. Neither did the different matter of the prisms make 
 any : for in a vessel made of polished plates of glass cemented 
 together in the shape of a prism and filled with water, there is 
 the like success of the experiment according to the quantity of 
 the refraction. [After giving a rigorous proof that the rays in 
 different parts of the spectrum are differently refracted, Newton 
 proceeds.] 
 
 This image or spectrum P T was coloured, being red at its least 
 refracted end T, and violet at its most refracted end P, and yellow, 
 green, and blue in the intermediate spaces, which agrees with the 
 first proposition, that lights which differ in colour do also differ 
 in refrangibility. The length of the image in the foregoing ex- 
 periments I measured from the faintest and outmost red at one 
 end, to the faintest and outmost blue at the other end, excepting 
 only a little penumbra, whose breadth scarce exceeded a quarter 
 of an inch, as was said above. 
 
 PKOP. III. THEOR. 3. The sun's light consists of rays differing 
 in reflexibility , and those rays are more inflexible than others 
 which are more refrangible* 
 
 This is manifest by the ninth and tenth experiments, for in the 
 ninth experiment, by turning the prism about its axis until the 
 rays within it, which in going out into the air were refracted by 
 its base, became so oblique to that base as to begin to be totally 
 reflected thereby ; those rays became first of all totally reflected 
 whicli before at equal incidences with the rest had suffered the 
 greatest refraction. And the same thing happens in the reflexion 
 made by the common base of the two prisms in the tenth 
 experiment. 
 
38 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. i. 
 
 BOOK I. PART 2. 
 
 PKOP. V. THEOR. 4. Whiteness and all grey colours between 
 ivliite and Hack may be compounded of colours, and the 
 whiteness of the sun's light is compounded of all the 
 primary colours mixed in a due 'proportion. 
 
 Exper. 11. Let the sun's coloured image P T (Fig. 17) fall upon 
 the wall of a dark chamber, as in the third experiment of the 
 first book, and let the same be viewed through a prism a I c, 
 held parallel to the prism A B c, by whose refraction that image 
 was made, and let it now appear lower than before, suppose in 
 the place s over against the red colour T. And if you go near 
 to the image P T, the spectrum s will appear oblong and coloured 
 
 FIG. 17. 
 
 like the image P T ; but if you recede from it, the colours of the 
 spectrum s will be contracted more and more, and at length 
 vanish, that spectrum s becoming perfectly round and white : 
 and if you recede yet farther, the colours will emerge again, but 
 in a contrary order. , Now that spectrum s appears white in that 
 case when the rays of several sorts which converge from the 
 several parts of the image P T, to the prism a I c, are so refracted 
 unequally by it, that in their passage from the prism to the eye 
 they may diverge from one and the same point of the spectrum 
 s, and so fall afterwards upon one and the same point in the 
 bottom of the eye, and there be mingled. 
 
APPEND. A.] EXTRACTS FROM NEWTON. 39 
 
 And farther, if the comb be here made use of, by whose "teeth 
 the colours at the image P T may be successively intercepted, the 
 spectrum s when the comb is moved slowly will be perpetually 
 tinged with successive colours ; but when, by accelerating the 
 motion of the comb, the succession of the colours is so quick that 
 they cannot be severally seen, that spectrum s, by a confused 
 and mixed sensation of them all, will appear white. 
 
 PKOP. II. THEOK. 2. All homogeneal light lias its proper colour, 
 answering to its degree of ref Tangibility, and that colour 
 cannot be changed ~by reflexions or refractions. 
 
 In the experiments of the fourth proposition of the first book, 
 when I had separated the heterogeneous rays from one another, 
 the spectrum p t formed by the separated rays did, in the 
 progress from its end p, on which the most refrangible rays fell, 
 unto its other end t, on which the least refrangible rays fell, 
 appear tinged with this series of colours, violet, indigo, blue, 
 green, yellow, orange, red, together with all their intermediate 
 degrees in a continual succession, perpetually varying. So that 
 there appeared as many degrees of colours as there were sorts of 
 rays differing in refrangibility. 
 
 Exper. 5. Now, that these colours could not be changed by 
 refraction, I knew by refracting with a prism sometimes one very 
 little part of this light, sometimes another very little part, as is 
 described in the twelfth experiment of the first book (see Fig. 18). 
 For by this refraction the colour of the light was never changed in 
 the least. If any part of the red light was refracted, it remained 
 totally of the same red colour as before. No orange, no yellow, no 
 green or blue, no other new colour was produced by that refraction. 
 Neither did the colour any way change by repeated refractions, 
 but continued always the same red entirely as at first. The like 
 constancy and immutability I found also in the blue, green, and 
 other colours. So also if I looked through a prism upon any 
 body illuminated with any part of this homogeneal light, as in 
 the fourteenth experiment of the first book is described, I could 
 not perceive any new colour generated this way. All bodies 
 illuminated with compound light appear through prisms con- 
 
40 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. i. 
 
 fused (as was said above), and tinged with various new colours, 
 but those illuminated with homogeneal light appeared through 
 prisms neither less distinct, nor otherwise coloured, than when 
 viewed with the naked eyes. Their colours were not in the 
 least changed by the refraction of the interposed prism. I speak 
 here of a sensible change of colour : for the light which I here 
 call homogeneal, being not absolutely homogeneal, there ought to 
 arise some little change of colour from its heterogeneity. But if 
 that heterogeneity was so little as it might be made by the said 
 experiments of the fourth proposition, that change was not 
 sensible, and therefore in experiments, where sense is judge, 
 ought to be accounted none at all. 
 
 Exper. 6. And as these colours were not changeable by 
 refractions, so neither were they by reflexions. For all white, 
 
 FIG. 18. 
 
 grey, red, yellow, green, blue, violet bodies, as paper, ashes, 
 red-lead, orpiment, indigo, bise, gold, silver, copper, grass, blue 
 flowers, violets, bubbles of water tinged with various colours, 
 peacock's feathers, the tincture of Lignum nepliriticum, and such 
 like, in red homogeneal light appeared totally red, in blue light 
 totally blue, in green light totally green, and so of other colours. 
 In the homogeneaL light of any colour they all appeared 
 totally of that same colour, with this only difference, that some 
 of them reflected that light more strongly, others more faintly. 
 I never yet found any body which by reflecting homogeneal light 
 could sensibly change its colour. 
 
 From all which it is manifest, that if the sun's light consisted 
 of but one sort of rays, there would be but one colour in the 
 
APPEND. B.] MAGNESIUM LIGHT. 41 
 
 whole world, nor would it be possible to produce any new 
 colour by reflexions and refractions, and by consequence that 
 the variety of colours depends upon the composition of light. 
 
 DEFINITION. 
 
 The homogeneal light and rays which appear red, or rather make 
 objects appear so, I call rubrific or red-making; those which 
 make objects appear yellow, green, blue, and violet, I call yellow- 
 making, green-making, blue-making, violet-making, and so of the 
 rest. And if at any time I speak of light and rays as coloured 
 or endued with colours, I would be understood to speak not 
 philosophically and properly, but grossly, and accordingly to 
 such conceptions as vulgar people in seeing all these experiments 
 would be apt to frame. For the rays, to speak properly, are not 
 coloured. In them there is nothing else than a certain power 
 and disposition to stir up a sensation of this or that colour. For 
 in a bell or musical string, or other sounding body, is 
 nothing but ^trembling motion, and in the air nothing but that 
 motion propagated from the object, and in the sensorium 'tis a 
 sense of that motion under the form of a sound ; so colours in 
 the object are nothing but a disposition to reflect this or that 
 sort of rays more copiously than the rest, in the rays they are 
 nothing but their dispositions to propagate this or that motion 
 into the sensoriuin, and in the sensorium they are sensations of 
 those motions under the forms of colours. 
 
 APPENDIX B. 
 
 BURNING MAGNESIUM WIRE, A SOURCE OF LIGHT FOR 
 PHOTOGRAPHIC PURPOSES. 1 
 
 Another interesting practical application of our knowledge 
 concerning the properties of the kind of light which certain 
 bodies emit when heated, is the employment of the light evolved 
 by burning magnesium wire for photographic purposes. The 
 
 1 Professor Roscoe on Spectrum Analysis, Royal Institution of Great Britain 
 Proceedings, May 6, 1864. 
 
42 SPECTRUM ANALYSIS. [LECT. i. 
 
 spectrum of this light is exceedingly rich in violet and ultra- 
 violet rays, due partly to the incandescent vapour of magnesium 
 and partly to the intensely-heated magnesia formed by the com- 
 bustion. Professor Bunsen and the speaker in 1859 determined 
 the chemically active power possessed by this light, and com- 
 pared it with that of the sun ; and they suggested the application 
 of this light for the purpose of photography. They showed 1 that 
 a burning surface of magnesium wire, which, seen from a point 
 at the sea's level, has an apparent magnitude equal to that of 
 the sun, effects on that point the same chemical action as the 
 sun would do if shining from a cloudless sky at a height of 
 9 53' above the horizon. On comparing the visible brightness 
 of these two sources of light it was found that the brightness of 
 the sun's disc, as measured by the eye, is 524'7 times as great 
 as that of burning magnesium wire, when the sun's zenith dis- 
 tance is 67 22' ; whilst at the same zenith distance the sun's 
 chemical brightness is only 3G'6 times as great. Hence the 
 value of this light as a source of the chemically active rays for 
 photographic purposes becomes at once apparent. 
 
 Professor Bunsen and the speaker state, in the memoir above 
 referred to, that " the steady and equable light evolved by mag- 
 nesium wire burning in the air, and the immense chemical 
 action thus produced, render this source of light valuable as a 
 simple means of obtaining a given amount of chemical illumina- 
 tion ; and that the combustion of this metal constitutes so definite 
 and simple a source of light for the purpose of photochemical 
 measurement, that the wide distribution of magnesium becomes 
 desirable. The application of this metal as a source of light 
 may even become of technical importance. A burning magnesium 
 wire of the thickness of 0*297 millimetre evolves, according to 
 the measurement we have made, as much light as 74 stearine 
 candles of which five go to the pound. If this light lasted one 
 minute, 987 metre of wire, weighing O120 gramme, would be 
 burnt. In order to produce a light equal to 74 candles burning 
 for ten hours, whereby about 20 Ibs. of stearine are consumed, 
 72-2 grammes (2 J ounces) of magnesium would be required. The 
 
 1 Phil. Trans. 1859, p. 920. 
 
APPEND, c.] CHEMICALLY ACTIVE RAYS. 43 
 
 magnesium wire can be easily prepared by forcing out the metal 
 from a heated steel press having a tine opening at bottom : 
 this wire might be rolled up in coils on a spindle, which could 
 be made to revolve by clockwork, and thus the end of the wire, 
 guided by passing through a groove or between rollers, could be 
 continually pushed forward into a gas or spirit-lamp flame in 
 which it would burn." 
 
 It afforded the speaker great pleasure to state that the foregoing 
 suggestion had now been actually carried out. Mr. Edward 
 Sonstadt has succeeded in preparing magnesium on the large 
 scale, and great credit is due to this gentleman for the able 
 manner in which he has brought the difficult subject of the 
 metallurgy of magnesium to its present very satisfactory position. 
 
 Some fine specimens of crude and distilled magnesium weigh- 
 ing 3 Ibs. were exhibited as manufactured by Mr. Sonstadt's 
 process, by Messrs. Mellor and Co. of Manchester. 
 
 The wire is now to be had at the comparatively low rate of 3d. 
 per foot ; and half an inch of the wire evolves on burning light 
 enough to transfer a positive image to a dry collodion plate; 
 whilst by the combustion of 10 grains a perfect photographic 
 portrait may be taken; so that the speaker believed that for 
 photographic purposes alone the magnesium light will prove 
 most important. The photochemical power of the light was 
 illustrated by taking a portrait 1 during the discourse. In doing 
 this the speaker was aided by Mr. Brothers, photographer, of 
 Manchester, who was the first to use the light for portraiture. 
 
 APPENDIX C. 
 
 ON THE CHEMICAL ACTION OF THE CONSTITUENT PARTS OF 
 SOLAR LIGHT. 2 
 
 The chemical action effected by the several portions of the 
 solar spectrum depends not only upon the nature of the refract- 
 ing body, but also upon the thickness of the column of air 
 through which the light has to pass before decomposition. In 
 
 1 Of Professor Faraday. - Bunsen and Roscoe, Phil. Trans. 1859. 
 
44 SPECTRUM ANALYSIS. [LECT. i. 
 
 the following experiments we have employed prisms and lenses 
 of quartz, cut by Mr. Darker of Lambeth, instead of glass 
 prisms, which, as is well known, absorb a large portion of the 
 chemically active rays. In order to render our experiments as 
 free as possible from the irregularities arising from variation in 
 the atmospheric absorption, the observations were made quickly 
 one after the other, so that the zenith distance of the sun altered 
 but very slightly. 
 
 A perfectly cloudless day was chosen for these observations, 
 and the direct sunlight reflected from the speculum mirror of 
 a Silbermann's heliostat through a narrow slit into our dark 
 room. The spectrum produced by the rays passing through 
 two quartz prisms and a quartz lens fell upon a white screen, 
 which was covered with a solution of sulphate of quinine to 
 render the ultra-violet rays and the accompanying dark lines 
 visible. In this screen a narrow slit was made, through which 
 the rays from any wished-for portion of the spectrum could be 
 allowed to pass, so as to fall directly upon the insolation vessel, 1 
 situated at the distance of from four to five feet. A finely- 
 divided millimetre scale was also placed on the screen, by means 
 of which the distance between the Fraunhofer lines could be 
 accurately measured, and the portion of light employed thus 
 exactly determined. 
 
 In order to recognize with accuracy the various portions of 
 the spectrum, we employed a map of the dark lines prepared 
 by Mr. Stokes, which he most kindly placed at our disposal. 
 The figure (Fig. 9) contains a copy of Mr. Stokes's map, with 
 the distance measured by him, and letters given according to his 
 notation. We have divided the space between the letter A in 
 the red to the last ray Stokes observed, w in the lavender rays, 
 into 160 equal parts, and we represent the position and breadth 
 of the bundle of rays which effected a given action upon the 
 insolation vessel as follows : If a bundle of rays lying between 
 
 1 This vessel was filled with the sensitive mixture of chlorine and hydrogen 
 gases together with water. The chemically active rays effected a union of the 
 gases, and the resulting hydrochloric acid gas being absorbed by the water, gave 
 a diminution of volume, directly proportional to the intensity of the acting 
 chemical rays. 
 
APPEND. C.] 
 
 CHEMICALLY ACTIVE RAYS. 
 
 45 
 
 the abscissa} 20*5 and 34 in Fig. 9, page 19, had to be 
 represented, we should call the edge of the bundle towards 
 A, \ DE, and that towards w, J FG, whilst the middle of the 
 portion of the spectrum, which produces the action, we call 
 "i DE to J FG." The breadth of this bundle of rays in which 
 the insolation vessel was completely bathed was __fa of the 
 total length of the spectrum. 
 
 The following table gives the direct results of a series of 
 observations made by perfectly cloudless sky at Heidelberg, 
 on the 14th of August, 1857, under a barometric pressure of 
 07494 m. The first column gives the numbers of the obser- 
 vations in the order in which they were made ; Column II. the 
 times of observation in true solar time ; Column III. the portion 
 of spectrum under examination; and Column IV. the action 
 corresponding to this portion. 
 
 I. 
 
 II. 
 
 III. 
 
 IV. 
 
 
 H. M. 
 
 
 
 1 
 
 10 54A.M. 
 
 From | GH to I . 
 
 48-80 
 
 2 
 
 10 58 A.M. 
 
 From | DE to E , 
 
 1-27 
 
 3 
 
 11 4 A.M. 
 
 From C to 4 DE . 
 
 0-47 
 
 4 
 
 5 
 
 11 8 A.M. 
 11 13 A.M. 
 
 From Nj to f QR . 
 From J ES to | ST 
 
 18-28 
 2-03 
 
 6 
 
 11 41 A.M. 
 
 From f ST to UV 
 
 1-27 
 
 7 
 8 
 
 11 47 A.M. 
 11 50 A.M. 
 
 From i K 4 Q to RS 
 From | ST to | UV 
 
 1173 
 1-02 
 
 9 
 
 11 54A.M. 
 
 From f IMj to N 4 . 
 
 37-87 
 
 10 
 
 11 57 A.M. 
 
 From H! to f 1M X . 
 
 57-42 
 
 11 
 
 1 P.M. 
 
 From Hj to | IMj . 
 
 52-30 
 
 12 
 
 4 P.M. 
 
 From i GH to H. . 
 
 61-38 
 
 13 
 
 7 P.M. 
 
 From FG to G . 
 
 27-64 
 
 14 
 
 16 P.M. 
 
 From $ FG to G . 
 
 2874 
 
 15 
 
 20 P. M. 
 
 From | DE to F . 
 
 1-39 
 
 16 
 
 25 P.M. 
 
 From 4 N 4 Q to RS 
 
 13-19 
 
 17 
 
 32 P.M. 
 
 From i N 4 Q to A RS 
 
 12-41 
 
 18 
 
 40 P.M. 
 
 From G to | GH . 
 
 53-78 
 
 19 
 
 42 P.M. 
 
 From I GH to H . 
 
 58-74 
 
 20 
 
 45 P.M. 
 
 From f GH to I . 
 
 53-9 
 
 If the refraction of the unit amount of incident light which 
 is reflected from the mirror of the heliostat at the commence- 
 ment and at the end of the series of the experiments be cal- 
 
SPECTRUM ANALYSIS. 
 
 [LECT. i. 
 
 culated, we get the numbers 0'644 and 0'642, which differ so 
 slightly that the variations brought about by the reflection may 
 be neglected without overstepping the observational errors. At 
 the times of observation on the 14th of August, 1857, the sun's 
 zenith distance was as follows : 
 
 At lOh. 54m. A.M. 
 At A.M. 
 At 45 P.M. 
 
 37 35' 
 
 35 13 
 
 36 16 
 
 The chemical intensity of the sun's rays at these various periods 
 may be calculated by formula (14). They are in the proportion 
 of the numbers 1-002, 1-000, and 1-016. Although the differ- 
 ences between these numbers are but small, we have reduced 
 all the observations to that chemical action which would have 
 been observed if they had all been made at 12h. Om. A.M. 
 upon the day in question. The following table contains the 
 numbers thus reduced, the mean value having been taken of 
 those observations which occur more than once : 
 
 No. 
 
 True solar time. 
 
 Position in the Spectrum. 
 
 Relative 
 chemical 
 action. 
 
 
 H. M. 
 
 
 
 1 
 
 10 54 A.M. 
 
 From | GH to I . 
 
 52-7 
 
 2 
 
 10 58 A.M. 
 
 From i DE to E . 
 
 1-8 
 
 3 
 
 11 4A.M. 
 
 From C to 1 DE . 
 
 0-5 
 
 4 
 5 
 
 11 8 A.M. 
 11 13 A.M. 
 
 From N! to f QR . 
 From i RS to 1 ST 
 
 18-9 
 21 
 
 6 
 
 11 41 A.M. 
 
 From | ST to 1 UV 
 
 1-2 
 
 7 
 
 11 47 A.M. 
 
 From i N 4 Q to ^ RS 
 
 12-5 
 
 8 
 
 11 54A.M. 
 
 Fromf lA^toN, 
 
 38:6 
 
 9 
 
 1 P.M. 
 
 From Hj to f IMj 
 
 551 
 
 10 
 
 4 P.M. 
 
 From i GH to H 
 
 60-5 
 
 11 
 
 16 P.M. 
 
 From i FG to G 
 
 28-4 
 
 12 
 
 20 P.M. 
 
 From | DE to F 
 
 1-4 
 
 13 
 
 40 P.M. 
 
 From G to | GH 
 
 54-5 
 
 The lines a a a a (Fig. 9, page 19) give a representation 
 of the relative chemical action which the various parts of the 
 spectrum, the rays of which have only passed through air 
 and quartz, effect on the sensitive mixture of chlorine and 
 
APPEND, c.j CHEMICALLY ACTIVE RAYS. 4 7 
 
 hydrogen. It is seen that this action attains many maxima, 
 of which the largest lies by ^ G H to H, and the next at I, and 
 also that the action diminishes much more regularly and rapidly 
 towards the red than towards the violet end of the spectrum. 
 
 The sun, when it was employed for these experiments, was 
 35 13' removed from the zenith. If the atmosphere were 
 throughout of the density corresponding to 076 m. and C., the 
 perpendicular height which, during our experiment, it would 
 have possessed, is 
 
 = 7)88 i met re S . 
 
 The depth of atmosphere through which the rays had to pass in 
 this experiment was, however, 
 
 7881 
 
 cos 35 13' 
 
 9,647 metres. 
 
 We have stated in one of our previous communications, 1 
 that the solar rays which at different hours of the day pass 
 through the same column of chlorine are altered in a very 
 different manner. This shows that rays of different chemical 
 activity are absorbed in very different ways by the air. The 
 above results are therefore only applicable for sunlight which 
 has passed through a column of air, measured at 076 m. and C. 
 of 9,647 metres in thickness. For rays which have to pass 
 through a column of air of a different length from this, the 
 chemical action of the various constituents of the spectrum 
 must be different. The order and degree in which the chemical 
 rays are absorbed, may be obtained by repeating the observa- 
 tions according to the above method from hour to hour during 
 a whole day. Such a series of experiments we have unfortu- 
 nately as yet been unable to execute, owing to the variability 
 of the weather in our latitudes. One very imperfect series of 
 observations we can, however, quote, and they suffice to show 
 that the relation between the chemical action of the spectral 
 colours is perceptibly altered when the thickness of air through 
 which the rays pass changes from 9,647 to 10,735 metres. 
 
 1 Phil. Trans. 1857, p. 617, &c. 
 
48 
 
 SPECTRUM ANALYSIS. 
 
 [LRCT. 
 
 These experiments were likewise made on August 14th, 
 1857, in the short space of time from 9h.44m. to lOh. 19m. A.M., 
 and gave the following numbers reduced to the zenith distance 
 (42 46'), corresponding to lOh. Om. A.M. They were, however, 
 made with a bundle of rays of a different thickness from the 
 former experiments, and therefore cannot be compared with 
 those. 
 
 
 
 
 
 
 
 
 Relative 
 
 No. 
 
 Time. 
 
 Portion of Spectrum. 
 
 chemical 
 
 
 
 
 action. 
 
 
 H. M. 
 
 
 
 1 
 
 9 44 A.M. 
 
 From f GH to I 
 
 14-5 
 
 2 
 
 9 48 A.M. 
 
 From N 3 to E 2 . 
 
 10-1 
 
 3 
 
 9 54 A.M. 
 
 From T V R, 2 S to i ST 
 
 2-4 
 
 4 
 
 9 59 A.M. 
 
 From 4 ST to U 
 
 o-o 
 
 5 
 
 10 4 A.M. 
 
 From G to | GH 
 
 13-0 
 
 6 
 
 10 8 A.M. 
 
 From F to | FG 
 
 7-1 
 
 7 
 8 
 
 10 11 A.M. 
 10 15 A.M. 
 
 From b to 4 FG 
 From 4 DE to f EF 
 
 32 
 
 0-4 
 
 From this it is seen that the relation of the chemical action of 
 the spectrum from the line E to the line H undergoes a consider- 
 able alteration when the rays have to pass through a column of 
 air 10,735 metres in height instead of 9,647 metres. 
 
 An extended series of measurements of the chemical action 
 of the several portions of the solar spectrum under various con- 
 ditions of atmospheric extinction may prove of great interest, 
 if, as we can now scarcely doubt, the solar spots appear at 
 regular intervals, and our sun belongs to the class of fixed stars 
 of variable illuminating power. It is possible that such obser- 
 vations, made during the presence and during the absence of the 
 solar spots, may give rise to some unlooked-for relations con- 
 cerning the singular phenomena occurring on the sun's surface. 
 Whether, however, the atmospheric extinction can ever be 
 determined with sufficient accuracy to render visible the alter- 
 ation in the light which probably occurs with the spots, is a 
 question which can only be decided by a series of experimental 
 investigations which must extend far beyond the scope of any 
 single observer. 
 
LECTURE II. 
 
 Continuous Spectrum of Incandescent Solids. Effect of Increase of 
 Heat. Broken Spectrum of glowing Gas. Application to 
 Chemical Analysis. Spectra of the Elementary Bodies. Con- 
 struction of Spectroscopes. Means of obtaining Substances in the 
 state of glowing Gas. Examination of the Spectra of Coloured 
 Flames. Spectra of the Metals of the Alkalies and Alkaline 
 Earths. Mapping Spectra, according to Bunsen ; according to 
 Wave-lengths. Delicacy of the Spectrum Analytical Method and 
 its application to Physiological Eesearch. 
 
 APPENDIX A. Description of the Spectrum Reactions of the Salts of 
 the Alkalies and Alkaline Earths. 
 
 APPENDIX B. Bunsen and Kirchhoff on the Mode of using a Spec- 
 troscope. 
 
 APPENDIX C. Bunsen on a Method of mapping Spectra. 
 
 r -v^ 
 
 IN the last lecture I pointed out to you some of the chief 
 properties of the light with which we are now, I am glad 
 to say, illumined the light of the sun. I explained 
 that the white sunlight can be divided up into a large 
 number of different ^ coloured rays by means of the 
 prism ; that these differently refrangible rays possess 
 different properties ; that we find the heating rays chiefly 
 situated at the red end, or in the least refrangible part. 
 I showed that we could separate wtt by certain means 
 the light rays from the less refrangible ultra-red rays, 
 and obtain at the dark focus of these rays the phenomena 
 of incandescence and of combustion, showing that these 
 rays, which do not affect the eye, are capable when 
 
50 SPECTRUM ANALYSIS. [LECT. n. 
 
 brought together of producing ignition. We also saw 
 that at and beyond the other end, the blue end, of the 
 spectrum we have the rays termed the chemically active 
 rays, and that these rays are capable of effecting 
 chemical change. 
 
 We proceed to-day in the examination of the action of 
 heat upon terrestrial matter in so far as it evolves light. 
 The question may very properly be asked, " What has all 
 this to do with chemical analysis ? " It might be said, 
 " It is true you have pointed out the difference between 
 the various parts of the solar spectrum ; but how is this 
 connected with the analysis which we expect to be told 
 about with the method by means of which chemical 
 substances may be detected or examined with a degree 
 of accuracy beyond anything that has hitherto been 
 attained ? " In order to enable you to answer this 
 question, let us begin by examining the action of heat 
 upon terrestrial matter, and, in the first place, upon solid 
 bodies. I have here the means of heating a long piece 
 of platinum wire, first of all to redness, and by diminish- 
 ing its length I shall be able to increase the temperature 
 of the wire gradually until I raise it to the melting-point 
 of platinum. The first thing we observe when a solid 
 body, such as this wire, is heated, is that it becomes red- 
 hot ; and that as we increase the temperature, the light 
 which it gives off increases in refrangibility, so that it 
 ends by em it ting, light of every degree of refrangibility. 
 I cannot show you on the screen the spectrum which this 
 heated wire yields, simply because the intensity of light 
 which it emits is insufficient for the purpose ; but if I 
 were to allow the light to fall into my eye through a 
 prism, I should see that. the red rays become first visible, 
 and that then a gradual increase in the refrangibility of 
 
LEGT. ii.] INCANDESCENT SOLIDS. 51 
 
 the light occurs, and that successively yellow, green, blue, 
 and violet rays will be emitted as the temperature is 
 increased up to a white heat, when all the rays of light 
 are given off. 
 
 I will endeavour to render this fact visible to you in a 
 rougher way by heating the wire gradually up to white- 
 ness, and allowing the light to pass through these coloured 
 glasses placed between you and the wire. At first, when 
 it is red-hot, the glowing wire will be visible only through 
 the red glass, none of the rays being able to pass through 
 the blue glass ; or, in other words, there is no blue light 
 given off : when the temperature is increased, blue rays 
 begin to be given off, and these can pass through the 
 blue glass, as you now plainly see when I raise the 
 temperature of the wire. Here I can increase the tem- 
 perature of the wire until we get a,t a point at which 
 I have no doubt you will be able to see that the blue 
 rays are emitted ; and if I continue this and go on 
 until the wire becomes intensely white-hot, you will see 
 it through this blue glass perfectly well. 
 
 Such then is the action of increased temperature upon 
 solid bodies. If I had taken any other substance which 
 I could have heated in the same way, I should have 
 produced the same effect : for it has been found that all 
 solid and liquid substances act in this same way with 
 regard to increase of heat ; they all begin to be visibly 
 hot at the same temperature, and the spectrum thus 
 produced is in every case a continuous one. 1 I may 
 remind you that this is the case by again throwing on 
 the screen the spectrum of the white-hot carbon points 
 
 1 This law was discovered by Draper (Phil. Mag. 1847). The only 
 known exception to this law is glowing solid Erbia, whose spectrum 
 exhibits bright lines ; see Appendix F to Lecture IV. 
 
 E 2 
 
52 SPECTRUM ANALYSIS. [LKCT. n. 
 
 heated in the electric arc. Here we have this grand 
 continuous band of light. The arrangements for pro- 
 ducing this are simple enough. We require to connect 
 the terminal wires from about sixty pairs of Grove's or 
 Bunsen's cells with the carbon electrodes of a Duboscq's 
 lamp (B, Fig. 1 9) contained inside this lantern. The light 
 passes through a narrow vertical slit (s), and by means 
 of the moveable lens (c) a distinct image of the slit is 
 thrown upon the screen (w w). A hollow prism filled 
 with bisulphide of carbon ( p,) is now introduced at the 
 distance of about two feet from the lens ; next the lamp, 
 
 FIG. 19. 
 
 with the arm carrying lens and prism, is turned round 
 until the coloured band falls upon the screen, and the 
 prism then adjusted to the angle of minimum deviation 
 for the yellow rays. A second prism ( p 2 ) is then inter- 
 posed, and the lamp and arm again turned so as to 
 allow the lengthened spectrum to fall on the screen. 
 A drawing of lamp, lens, and prisms, thus placed, is shown 
 in Fig. 20. 
 
 How does the case stand with respect to that impor- 
 tant form of matter termed the'gaseous ? Do gases when 
 
LECT. II.] 
 
 INCANDESCENT GASES. 
 
 they become incandescent all emit the same kind of light, 
 like solids, or does each chemically different gas emit a 
 characteristic and peculiar kind of light 1 I purpose now 
 to show you that every different chemical element in the 
 
 state of gas, when heated until it becomes luminous, gives 
 off a peculiar light, so that the spectrum of every element 
 in the state of glowing gas is totally different from 
 that of any solid body, inasmuch as, instead of giving a 
 continuous spectrum, it presents a broken or discontinuous 
 
54 SPECTRUM. ANALYSIS. [LECT. n. 
 
 one containing bright bands or lines, indicative of the 
 presence of the particular elementary gas in question. 1 I 
 will illustrate this fundamental difference to you by means 
 of the following experiment. It has long been knoxvn 
 to chemists that certain substances have the power when 
 brought into a colourless flame of producing peculiar 
 tints. Thus, for instance, if we bring various bodies into 
 the flame, such as the alkalies soda and potash, we 
 observe that the flame becomes coloured in the first case 
 of a bright yellow, and in the second of a pale violet 
 tint ; whilst the salts of strontium colour the flame 
 crimson, and those of barium produce a green tint, and 
 calcium compounds impart a red colour to the flame. Here 
 we have the beautiful non-luminous gas flame produced 
 by the combustion of coal gas mixed with air, in what 
 we know as the Bunsen burner. The air and gas mix in 
 the chimney, the gas issuing from a jet at the centre of 
 the foot, and the air entering by the holes at the side ; 
 the mixture burns with a light blue flame, which we can 
 tinge with the peculiar colours of the alkalies by bringing 
 a small fused bead of salt into the outer mantle of the 
 flame on the loop of thin platinum wire (Fig. 21). Here 
 is another substance called lithium ; if we bring the 
 slightest trace of this lithium salt into the flame, you 
 perceive the magnificent crimson tint which it at once 
 imparts to the flame : whilst in these other burners we 
 see the colours due to the salts of potassium, calcium, 
 strontium, and barium. 
 
 A most important observation has now to be made, 
 namely, that all the salts of sodium give off this yellow 
 light when brought into the flame ; so, too, all the lithium 
 
 1 Under peculiar circumstances certain dense incandescent gases give 
 continuous spectra ; see Appendix C to Lecture I V. 
 
LECT. ii.] COLOURED FLAMES. 55 
 
 compounds tint the flame crimson ; and this property of 
 emitting a peculiar kind of light is one of the means by 
 which the presence of these various chemical substances 
 can be detected. Here I will produce a peculiar blue 
 flame by a substance which differs entirely from the 
 foregoing in properties, viz. the non-metallic element 
 selenium : it is a very volatile substance, and the blue 
 flame lasts only for a short time. In these other flames 
 
 FIG. 21. 
 
 we see the characteristic green colours communicated to 
 flame by salts of copper and boracic acid. 
 
 I will next show you the same thing in other ways ; 
 for instance, I can here produce a much larger flame, 
 and show you the colour of the same salts. I have a 
 large gas burner which, when urged by this blowpipe, 
 gives us a colourless flame three feet long. If I hold in 
 this flame pieces of pumice-stone moistened with solutions 
 of the chlorides of sodium, potassium, lithium, barium, 
 
5f> SPECTRUM ANALYSIS. L LKCT - 
 
 strontium, and calcium, the colours imparted by these 
 substances will be rendered evident. Again, I have 
 another illustration in these gun-papers, which have 
 been soaked in solutions of the chlorates of these metals 
 and then dried. The combustion is rather quick, but by 
 reflection on the white screen their peculiar colours come 
 out well. Here you have the violet potash tint ; here 
 the bright green colour characteristic of the barium 
 compounds. The common fireworks of the stage are 
 further illustrations of the peculiar colours produced by 
 certain chemical substances. I may imitate the red fire 
 by igniting some chlorate of strontium in coal gas ; we 
 must melt the salt and then plunge it into the jar of 
 burning coal gas, when we get this splendid combustion 
 of oxygen in coal gas, coloured crimson by the ignited 
 vapour of strontium salt. 
 
 We have already seen that the quality of the light 
 emitted by solid bodies varies with difference of tem- 
 perature. The quality of the light emitted by gaseous 
 bodies, however, with certain exceptions about which 
 I shall have to speak subsequently does not vary 
 under change of temperature. Here I have the means 
 of igniting some sodium salt at various temperatures. 
 There, in the first place, is the bluish flame of burning 
 sulphur, one of the coldest flames we can obtain, the 
 temperature being about 1*820 Centigrade ; then I next 
 ignite the flame of burning carbon disulphide, having a 
 temperature of 2*229 C. Here we see the flame of coal 
 gas burning mixed with air : if I cut off the air, we get 
 the common luminous flame of coal gas ; but if I allow 
 the' air to mix with it before it burns, then we have this 
 beautiful non-luminous flame. The temperature of this 
 flame has been calculated to be 2 0> 350 C. Here I have 
 
LKCT. ii.] COLOURED FLAMES. 57 
 
 another jet, from which the blue flame of carbonic oxide 
 gas (the body which produces the blue lambent flame 
 frequently seen in coal fires) is seen burning in oxygen : 
 the temperature of this flame is somewhat higher, and 
 has been found to be over 3'000. If I bring a little 
 common salt (sodium chloride) into these flames, you 
 observe that in all cases we get them coloured yellow. I 
 have here the beautiful purple flame of cyanogen gas, 
 which possesses a temperature of 3*300 0., and you see, 
 when we bring the sodium salt into it, we have the same 
 yellow colour produced : in other words, we cannot get 
 sodium vapour either red-hot or blue-hot, it always 
 remains yellow-hot ; that is to say, the first moment that 
 the sodium vapour becomes luminous, it gives off this 
 particular and peculiar yellow light, and if we heat it 
 more, the effect is not to alter the refrangibility of the 
 rays, but merely to increase their intensity. 
 
 Thus we see that when a body becomes gaseous, the 
 light which it gives off is of a particular kind, and does not 
 alter when we increase the temperature. One other experi- 
 ment will indicate this to you still more fully, and this I 
 can make by means of the electric spark, which I have here 
 the means of producing. The temperature of this electric 
 spark is so high that it has never been measured, but it 
 is certainly infinitely higher even than the temperature 
 of any of the flames which we have just now used. Still, 
 if I bring this .piece of sodium salt into the electric spark, 
 I find that the same thing occurs I get the same yellow- 
 coloured light ; and if I take some other substance, such 
 as lithium, and bring a small trace of this substance first 
 into the different flames and then into the electric spark, 
 the permanent red colour which lithium vapour gives off 
 will in each case be clearly seen. 
 
58 SPECTRUM ANALYSIS. [LECT. n. 
 
 Now the methods by means of which we can obtain 
 bodies in the state of luminous gas vary with the nature 
 of the substance ; but I would beg you to understand 
 that the property which we have noticed with regard to 
 sodium and the other alkalies is not confined to those 
 bodies which have the power of being volatilized in such 
 a flame as I have burning before me. This property 
 belongs to matter in general; it belongs to every chemical 
 element; and if we can by any method get the vapour of 
 a chemical element so hot as to become luminous, we 
 find that the light emitted by it is peculiar to itself, and 
 is distinctive of that special body, whether under the 
 ordinary circumstances the element be gaseous, solid, or 
 liquid. Hence you see that we have at last reached the 
 principles upon which the science of spectrum analysis 
 is based, by means of which we can detect the presence 
 of any of the elementary bodies when they can be 
 obtained in this state of glowing gas. 
 
 We must now pass on to the consideration of the 
 various methods by which the elements can be obtained 
 as luminous gases. 
 
 I purpose to confine our attention in this lecture to 
 the method by which we can detect the presence of the 
 metals of the alkalies and alkaline earths. Let me, how- 
 ever, first point out to you the kind of spectrum which 
 we obtain when we look at any one of these variously- 
 coloured flames through a prism or spectroscope, the 
 construction of which we will now briefly consider. 
 
 The simplest form of spectroscope which Bunsen 
 adopted in his first experiments is represented in Fig. 22. 
 It consists of a common hollow prism (F) placed in a 
 box ; a telescope (c) is fixed at one side of the box, and 
 a slit is placed at one end of a tube having a lens at the 
 
LECT. IT.] 
 
 SPECTROSCOPES. 
 
 59 
 
 other end, in order to obtain a pure spectrum, and to render 
 the rays parallel ; this is called a collimator. This colli- 
 mator (B), the employment of which was first proposed by 
 
 Professor Swan of St. Andrews so long ago as 1856, is fixed 
 at the other side of the box. The substance to be ezamiued 
 is placed in the non-luminous Bunsen's flame, and the light 
 passing through the slit falls upon the prism, and having 
 
 
 FIG. 23. 
 
 been split up into its constituent parts, the differently co- 
 loured rays pass through this telescope, are magnified, and 
 then fall upon the retina. 
 
 In Fig. 23 we have the more 
 
60 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. n. 
 
 FIG. 24. 
 
 perfect form of the instrument represented, as made by 
 Steinheil of Munich. 1 With this we are enabled to use two 
 flames, and the apparatus is so arranged that we can see the 
 two spectra placed one above the other. The rays from one 
 A of the flames pass -direct through the 
 upper part of the slit, whilst those 
 (A) from the other flame, placed on 
 one side, are reflected (by total 
 internal reflexion) from the surface 
 of the prism through the lower part 
 of the slit in the direction indicated by Fig. 24. The 
 object of this superposition of the spectra is evident : it 
 is to enable us to see whether the substance under exa- 
 mination really is the body which it is supposed to be. 
 For instance, putting a small quantity of the substance 
 we know to contain sodium in this flame, we place a sub- 
 stance supposed to contain sodium in the other flame, and 
 then by means of a small reflecting prism placed on the 
 end of the slit, we have the spectra of 
 these two flames sent into the telescope 
 one above the other, so that we see at 
 FIG. 2 ia. the same time the spectrum of the pure 
 
 1 This instrument consists of a prism (a) fixed upon a firm iron 
 stand, and a tube (5) carrying the slit (d), seen on an enlarged scale in 
 Fig. 24a, through which the rays from the coloured flames (e and e) 
 fall upon the prism, being rendered parallel by passing through a lens. 
 The light having been refracted, is received by the telescope (/), and 
 the image magnified before reaching the eye. The rays from each flame 
 are made to pass into the telescope (/); one set through the upper un- 
 covered half of the slit, the other by reflection from the sides of the small 
 prism (c), Figs. 24, 24a, through the lower half ; thus bringing the 
 two spectra into the field of view at once, so as to be able to make any 
 wished-for comparison of the lines. The small luminous gas flame (h), 
 Fig. 23, is placed so as to illuminate a fixed scale contained inside the 
 tube (g) : this is reflected from the surface of the prism (a) into the 
 telescope, and serves as a means of measuring the position of the lints. 
 
LECT. ii.] SPECTROSCOPES. 61 
 
 sodium and the spectrum supposed to be that of sodium ; 
 and we can readily observe whether the lines coincide. 
 If they coincide, and the two spectra have these lines 
 exactly continuous one below the other, then we are quite 
 certain that sodium, or any other substance which we 
 may have been investigating, is present. Another 
 arrangement for facilitating the comparison of spectra 
 consists in the illuminated millimetre scale contained in 
 the tube cj (Fig. 23), a magnified reflection of which is 
 thrown into the telescope from the surface of the prism. 
 The illuminated scale is thus seen between the two 
 superimposed spectra, and the position of any line or 
 lines can be accurately determined. The further arrange- 
 ments mechanical and optical of these instruments I 
 need hardly trouble you with in detail. I have here a 
 variety of spectroscopes kindly lent to me by the maker, 
 Mr. Browning ; one with one, one with two, one with 
 three, and one with four prisms. The more prisms we 
 employ, of course the greater dispersion we get, the more 
 is the light drawn out into its special varieties, and the 
 greater also is the intensity of the light which it is 
 necessary to employ in order to get the rays to pass 
 through this greater number of prisms. 
 
 I will next show you a drawing of the actual arrange- 
 ment used by Kirchhoff (Fig. 25). There you see the 
 prisms employed, four in number, placed one behind 
 another on a horizontal table of cast iron. The light 
 passes through the slit at the end of this tube. Here (top 
 of Fig. 25) is an enlarged representation of the slit, the 
 breadth of which can be altered at pleasure by means of 
 the screw ; on this slit is placed a small reflecting prism 
 to enable us to get two superposed spectra. The light 
 passes through the fine vertical slit, the rays are rendered 
 
62 
 
 SPECTRUM ANALYSIS. 
 
 [LKCT. n. 
 
 parallel by the lens fixed at the end of the tube (A) ; it 
 then passes through these four prisms, and the rays thus 
 split up into constituent parts fall on to the telescope (B), 
 at the end of which the eye is placed. This, then, gives 
 you the simplest, and at the same time the most delicate 
 and complete, form of spectroscope. 
 
 We have here representations as truly painted as 
 possible (see Frontispiece) of what is seen when we allow 
 a light from such coloured flames as those which have 
 been burning to fall on to the retina through a spectro- 
 scope properly arranged. 
 
 At the top of the diagram (No. 1) is a drawing 
 showing a solar spectrum, and underneath we have the 
 
 FIG. 25. 
 
 spectra of the alkalies and alkaline earths, potassium 
 (No. 2), sodium (No. 7), and lithium (No. 8), calcium 
 (No. 9), strontium (No. 10), and barium (No. 11), 
 together with the two new metals rubidium and caesium 
 
"' 
 
 7 
 
 LECT. ii.] SPECTRA OF ALKALIES. 
 
 ^^o 
 
 (Nos. 3 and 4) discovered by Bunsen, about which I 
 si) all speak in my next lecture ; also the spectra of 
 thallium and indium (Nos. 5 and 6), two other new 
 metals, the first of which was lately discovered by our 
 countryman Mr. Crookes, and the second by two German 
 chemists, Messrs. Reich and Richter. You will perceive 
 in the first place that each of these spectra is different 
 from the others, although they all possess the common cha- 
 racteristic of containing bright lines or bands, which occur 
 in various portions of the spectrum and indicate the 
 peculiar kind of light which these various bodies, when 
 brought into a state of glowing gas, emit. The sodium 
 flame when observed by means of the spectroscope ex- 
 hibits only one bright double yellow line together with 
 a faint continuous spectrum ; in other words, this light is 
 monochromatic, or nearly so : almost all the light which 
 glowing sodium vapour gives off is light of one degree of 
 refrangibility, and the spectrum is confined to one very 
 narrow yellow band. The red light, which we saw was 
 due to the presence of lithium, when seen through a prism 
 gives this beautiful red line, together with this paler 
 orange line. I need not describe the more complicated 
 spectra of strontium, calcium, and barium : suffice it to 
 say that they each yield peculiar bright bands, perfectly 
 characteristic of the metal in question, as is seen at once 
 by reference to the drawings. 1 
 
 For the purpose of enabling any observer unacquainted 
 with the spectra to identify with certainty the presence 
 of any of the foregoing metals by means of their bright 
 lines, and to lay down their positions in his own instru- 
 ment, the following method of mapping the spectra has 
 been devised by Bunsen. The millimetre scales (Fig. 
 
 1 For the special description of these spectra see Appendix A, p. 79. 
 
64 SPECTRUM ANALYSIS. [LECT. ir. 
 
 26) represent the illuminated divisions seen with the 
 scale of the spectroscope (</, Fig. 23) : the exact position 
 of the bright lines in any spectrum is shown by the 
 black marks below the divisions ; whilst their breadth, 
 intensity, and gradation are indicated by the breadth, 
 depth, and contour of these blackened surfaces. When 
 the spectrum contains a continuous portion of light, this 
 is shown by a continuous black band above the divisions. 
 The positions of the fixed solar lines are given on the 
 first horizontal scale, and those of the most prominent 
 bands in several of the elements are placed as fiducial 
 points at the bottom of the map. 1 
 
 If the prisms employed in two spectroscopes are made 
 of different kinds of glass, the relative positions of the 
 dark or of the bright lines will be found to vary on 
 account of the varying dispersive powers of the different 
 sorts of glass. We can however procure a spectrum by 
 diffraction, as it is termed ; that is, by the interference of 
 the waves of light when the rays pass through a fine grating. 
 This you can easily see for yourselves by looking at the 
 flame of a candle through a feather or through your own 
 eyelashes, when the white candle-light will be split up 
 into its many coloured constituents. Now the great 
 difference between the spectra obtained by means of the 
 prism (or by dispersion) and those obtained by means of 
 the grating (or by diffraction), is that by the former 
 method the relative positions of the various portions of 
 the spectrum will vary with the kind of glass of which the 
 prism is made, whereas in the latter method the various 
 portions of the spectrum will always occupy the same 
 relative positions, whatever be the kind or size of the 
 gratings used, because in this case the position of each 
 1 For further information see Appendix C, p. 97. 
 
LECT. ii. J SPECTRA OF ALKALIES. 65 
 
 part of the spectrum is influenced only by the refrangibility 
 of the ray or by its wave-length. There are, however, 
 certain practical reasons why spectroscopes with prisms 
 are more useful than those in which gratings are employed. 
 Hence the only absolute method of measuring the positions 
 of the bright lines in dispersion-spectra obtained by using 
 a prism is to ascertain their several wave-lengths, and to 
 map all spectra according to this unalterable property of 
 the distinct rays. A mode of thus mapping the spectra 
 of all the elements according to their wave-lengths has 
 lately been carried out for certain substances by Professor 
 Angstrom, and for others by Dr. Wolcott Gibbs, 1 and by 
 Dr. Marshall Watts. 2 From Dr. Watts's Index of 
 Spectra I extract the following table, showing the relative 
 positions of the Fraunhofer lines B, D, E, F, and G (the 
 whole length from B to G being divided into 1,000 equal 
 parts), in dispersion-spectra where different substances 
 are employed, compared with the positions of the same 
 lines obtained by diffraction. Thus it is seen that the 
 blue end of the spectrum is much more compressed in 
 the diffraction-spectrum than in any of the dispersion- 
 spectra, whilst the red end is correspondingly lengthened 
 out. 
 
 DISPERSION. 
 
 Fraunhofer's 
 Lines. 
 
 B. 
 
 Crown Glass. 
 
 
 
 Flint Glass. 
 
 
 \ 
 
 Carbon 
 Bisulphide. 
 
 
 
 DlFFftACTION. 
 
 
 
 D. 
 
 236 
 
 220 
 
 194 
 
 381 
 
 E. 
 
 451 
 
 434 
 
 400 
 
 624 
 
 F. 
 
 644 
 
 626 
 
 590 
 
 784 
 
 G. 
 
 1,000 
 
 1,000 
 
 1,000 
 
 1,000 
 
 1 On the Measurement of Wave-lengths by means of Indices of 
 Refraction (Phil. Mag. [4] xi. p. 177, 1870). 
 
 2 Index of Spectra, by W. Marshall. Watts, D.Sc. London : Henry 
 Gillman, Boy Court, Ludgate Hill, 1872. 
 
 F 
 
60 SPECTRUM ANALYSIS. [LECT. n. 
 
 It would lead me too far were I to attempt to explain 
 to you how the observations made with a prism can best 
 be reduced to wave-lengths ; suffice it to say that this 
 is done by a system of interpolation, which is detailed 
 in the book to which I have referred, where a method 
 for accomplishing this end is clearly set forth. 
 
 Having thus made ourselves acquainted with this 
 new mode of chemical analysis, we may ask ourselves, 
 " What improvement is this upon our ordinary chemical 
 methods ? What benefit is it to us that barium gives 
 us these peculiar bands, that strontium yields certain 
 different bands, that calcium produces others again ? 
 We know already that the chemical reactions of these 
 bodies are very different, and we can detect these sub- 
 stances by ordinary chemical analysis/' The answer to 
 this is, that the new method is far more delicate than any- 
 thing which we have hitherto employed, so delicate indeed 
 as almost to pass belief, so that we have hereby obtained 
 a means of examining the composition of terrestrial 
 matter with a degree of exactitude hitherto unknown. 
 
 I will try to give you some idea of the delicacy of 
 these spectrum reactions. I can show that the reaction 
 for sodium is so sensitive that we can detect the presence 
 of this element everywhere. There is not a speck of dust 
 or a mote seen dancing in the sunbeam which does not 
 contain chloride of sodium. Sodium is a prevailing 
 element in the atmosphere ; we are constantly breathing 
 in portions of the compound of this elementary substance 
 together with the air which we inhale. Two-thirds of 
 the earth's surface is covered with salt water, and the 
 fine spray which is continually being carried up into the 
 air by the dashing of the waves evaporates, leaving the 
 minute specks of salt which we see dancing as motes in the 
 
LECT. II.] 
 
 MAPPING SPECTRA. 
 
 G7 
 
 -= 
 
 
 
 o 
 
 l 
 
 "4 -= 
 
 s- 
 I- 
 
 0_ 
 
 s-= 
 
 ^ 
 
 8-= 
 
 L. 
 
 F 2 f 
 
68 SPECTRUM ANALYSIS. [LECT. n. 
 
 sunbeam. If I clap my hands, or if I shake my coat, or if I 
 knock this dusty book, I think you will observe that this 
 flame becomes yellow, and this not because it is the hand 
 or coat of a chemist, but simply because the dust which 
 everybody carries about with him is mixed with sodium 
 compounds. When I place in the colourless flame this 
 piece of platinum wire, which has been lying on the table 
 for a few minutes since I heated it red-hot, you see there 
 is sodium in it ; there, we have for one moment a glimpse 
 of a yellow flame. If I heat the wire in the flame, the 
 sodium salts will all volatilize, and the yellow tinge will 
 quite disappear ; but if I now draw the wire once through 
 my fingers, you observe the sodium flame will on heating 
 the wire again appear. If I draw it through my mouth 
 and heat it again, it will be evident that the saliva con- 
 tains a very considerable quantity of sodium salts. Let 
 me leave the wire exposed here, tied round this rod, so 
 that the end does not touch anything, for ten minutes 
 or a quarter of an hour ; I shall then obtain the sodium 
 reaction again, even if the wire be now perfectly clean. 
 This is because sodium salts pervade the atmosphere, 
 and some particles of sodium dust flying about in 
 the air of the room settle on the wire, and show their 
 presence in the flame. 
 
 I hope in the next lecture to consider the history of 
 the subject, and to point out to you that this constant 
 reaction of sodium puzzled the old observers very much. 
 They thought this , reaction must be due to the presence 
 of water, for there was no other substance which was 
 so "commonly diffused ; and it is only recently that this 
 yellow reaction has been recognized as being due to this 
 metal, sodium. 
 
 To refer for a moment to the distribution of lithium 
 
LKCT. ii.] DELICACY OF SPECTRUM ANALYSIS. 61) 
 
 compounds : we must remember that this substance, 
 giving the beautiful red flame which you saw just now 
 arid the spectrum exhibiting the one bright . red line, 
 was until lately only known to exist in three' or in four 
 comparatively rare minerals. The moment, however, 
 we come to examine substances by the method of spec- 
 trum analysis, we find that the brilliant red line, which 
 is characteristic of the presence of lithium, occurs very 
 frequently. And why, then, was not the red flame 
 noticed before ? Because when the light was examined 
 by means of the eye alone, the red-coloured flame was 
 masked by the presence of soda salts, and other sub- 
 stances affecting the flame, so that the red tint produced 
 by the small quantity of lithium was unseen. But when 
 we examine the flame with the prism, then all these 
 lines range themselves into due order, no one interfering 
 with the other. The presence of lithium may be thus 
 easily detected, though it may be mixed with ten thou- 
 sand times its bulk of sodium compounds, because, as 
 you see by reference to this chart, the sodium line occurs 
 in a different position to the lithium line, according to the 
 differences in their refrangibilities. We now learn that 
 this supposed rare substance is found to be most widely 
 distributed, not, it is true, in very large quantities, 
 but still that it is one of the most widely diffused of 
 the elementary bodies. Lithium not only occurs in very 
 many minerals, but also in the juice of plants, in the 
 ashes of the grape, in tea, coffee, and even in milk ; in 
 human blood, and in muscular tissue. It has also been 
 found by Dr. Bence Jones in many varieties of fruit 
 and vegetables, in all the different kinds of wine, in ale 
 and porter, and in bread. So who can tell what part 
 this hitherto rare substance may not play even in the 
 
70 SPECTRUM ANALYSIS. [LECT. n. 
 
 animal economy ? It has been also found in meteoric 
 stones, in the water of the Atlantic Ocean, as well as 
 in that of most mineral springs and many rivers. It 
 is present in the ashes of tobacco, and, if we hold the 
 end of a cigar in the colourless flame, we may always 
 notice the red lithium line when the light is examined 
 with a spectroscope. Dr. W. Allen Miller has lately 
 found lithium in very large quantities in the water of 
 a spring in the Wheal Clifford Mine in Cornwall. 1 This 
 water contains 26 grains of lithium chloride in one 
 gallon, and the spring flows at such a rate as to pour 
 forth 800 Ibs. of this salt every twenty-four hours ! 
 
 Here we have a table showing the great delicacy of 
 the methods of spectrum analysis : 
 
 1. Sodium. 3000000 part of a milligramme, or i800000U o 
 part of a grain, of soda can easily be detected. Soda 
 is always present in the air. All bodies exposed to the 
 air show, when heated, the yellow soda line. If a book 
 be dusted near the flame, the soda reaction will be seen. 
 
 2. Lithium, f^o part of a milligramme, or 
 
 600 oooo 
 
 part of a grain, can be easily detected. Lithium was 
 formerly only known to exist in four minerals : it is now 
 found by spectrum analysis to be one of the most widely 
 distributed elements. It exists in almost all rocks, in 
 sea and river (Thames) water, in the ashes of most plants, 
 in milk, human blood, and muscular tissue. 
 
 3. Strontium. 1QOOOO of a milligramme, or 1000 ooo of a 
 grain, of strontia is easily detected. Strontia has been 
 shown to exist in very many limestones of different 
 geological ages. 
 
 4i Calcium. HfoToo of a milligramme, or Too^oFo f a 
 grain, of lime can be easily detected. 
 1 Chem. News, x. 181. 
 
LSCT. ii.] DELICACY OF THE METHOD. 71 
 
 5. Caesium and Rubidium. These new alkaline metals 
 were discovered by Bunsen in the mineral waters of 
 Baden and Diirkheim. Forty tons of mineral water 
 yielded 200 grains of the salts of the new metals. 
 
 6. Thallium. A new metal discovered by Mr. Crookes 
 in 1861, distinguished by the splendid green line which 
 its spectrum exhibits. It is found in iron pyrites, and 
 resembles lead in its properties. 
 
 7. Indium. Discovered in zinc blende by Professors 
 Reich and Richter : found in very minute quantities, 
 it is distinguished by one blue and one indigo coloured 
 band seen in its spectrum. 
 
 I will now endeavour to illustrate, by means of the 
 electric lamp, the fact that all these bodies give off 
 coloured lights, and that each of these coloured lights is 
 of a peculiar kind ; and I would wish first to show you 
 that when we bring a small fraction of a grain of 
 common salt, chloride of sodium, on to the lower carbon 
 of the lamp, we obtain a distinct yellow band which 
 was not seen before, for previously, you will remember, 
 we had a perfectly continuous speccrum. This yellow 
 band is due to the presence of sodium. You will 
 probably see thnt there are other bands present as well 
 as the sodium band, because it is impossible, owing to 
 the delicacy of these reactions, to obtain any carbon 
 which is perfectly free from other chemical salts, and the 
 small impurities which exist in the carbon come out as 
 evidence against us on the screen ; yet I think you will 
 see that we have the sodium line more distinctly visible 
 than anything else. 
 
 No other metal but sodium gives this yellow band ; 
 still I must beg you to understand that this rough repre- 
 sentation is not exactly that which you would see if you 
 
72 SPECTRUM ANALYSIS. [LECT. n. 
 
 were to look at the yellow soda flame through a prism, 
 by means of an accurate spectroscope. I would wish 
 you to remember that this yellow line is in reality double 
 when examined with a perfect optical arrangement, and 
 that these lines are very fine, placed close together, and 
 as thin as the finest spider's web. It is only because 
 the arrangements I have to employ here for the purpose 
 of exhibiting these lines on the screen are, optically 
 considered, very crude and rough, that we get any 
 appreciable breadth of this line. 
 
 Now allow me to show you the light which the sub- 
 stance lithium gives off. For this purpose I will bring 
 a little lithium salt on the same carbon, for by taking 
 a new one we should not gain much, as -ell these poles 
 are more or less impure. Here you observe the red line, 
 which was not noticeable before. This splendid red band 
 is due to the presence of lithium ; and when we see it 
 through an accurate instrument, it appears as fine as the 
 finest slit of light which we can take. This bright red 
 line is always found exactly in the same position ; 
 and the fixity of these lines is in fact the most im- 
 portant principle involved in our inquiry : they are 
 unalterable in refrangibility. 
 
 I have next to direct your attention to the blue line 
 which is now visible on my right. This is also caused 
 by lithium, for when we heat up lithium vapour beyond 
 a certain point, as high as I am now doing with the elec- 
 tric lamp, this blue band also becomes visible ; but it is 
 not visible when the temperature of the incandescent 
 lithium vapour is lower. The blue ray may perhaps 
 always be given off, even at lower temperatures ; for if 
 light requires to be of a certain intensity before it can 
 affect the retina and become visible, and if, in order that 
 
. ii.] SPECTRUM OF LITHIUM. 73 
 
 the intensity of the light may thus increase, we must heat 
 the vapour to a higher point, we have a complete expla- 
 nation of the appearance of the blue line. It is important 
 to notice that the positions of the red and of the orange 
 lines seen at the lower temperature never shift or change 
 the least when the temperature is changed. Hence the 
 appearance of the red line is proof positive of the pre- 
 sence of lithium. In this lithium spectrum you will also 
 notice the sodium line. We can never get rid of our friend 
 sodium, he always remains stedfast to us ; in fact, we 
 should be sometimes glad to dispense with his presence, 
 but it is not an easy matter to induce him to leave us. 
 
 As an interesting application of spectrum analysis, we 
 must not forget the examination of the rate of circula- 
 tion in the animal and vegetable body lately made by 
 Dr. Bence Jones, by means of observations with the 
 red lithium line. Experiments made upon men and 
 animals showed that when any lithium salt is taken in 
 with the food, the lithium can be detected very shortly 
 afterwards in the most distant parts of the body, even 
 where no circulation exists, as for instance in the lens 
 of the eye, proving the extraordinary rapidity with 
 which the chemical circulation in the body goes on. 
 Thus twenty-four minutes after injecting 3 grains of 
 lithium salt under the skin of a guinea-pig, the lithium 
 was found to be present in the lens and in every texture, 
 it only being necessary to burn a portion of the animal 
 tissue in a colourless flame in order to see the bright red 
 line of lithium ; ten minutes after the injection lithium 
 was found slightly in the lens but plentifully everywhere 
 else ; whilst four minutes after the injection the lithium 
 was not found in the lens but plentifully in the aqueous 
 humour of the eye, and in the bile. 
 
74 SPECTRUM ANALYSIS. [LECT. n. 
 
 The same quickly penetrating power of lithium salts 
 was shown to exist in the human body, and for this 
 purpose the lenses of several persons who had been 
 operated upon for cataract were examined, the patients 
 having previously partaken of lithia water. It was 
 thus seen that in the human body 20 grains of carbonate 
 of lithium will in three and a half hours penetrate 
 through every part of the body, and be capable of de- 
 tection in each particle of the lens. The rate of passage 
 of salts out of the body can likewise be satisfactorily 
 examined by the spectroscope, and thus spectrum 
 analysis may be made materially to aid the physiologist 
 in his researches into the chemistry and physics of the 
 body. 
 
 I would next show you the spectra of metals of the 
 alkaline earths. I will first bring a small quantity of 
 strontium salt on to the pole, and we find that the 
 strontium spectrum is characterized by a series of red 
 lines, and also by a beautiful blue band almost identical, 
 but not exactly so, with the blue line of lithium which I 
 had the pleasure of showing you an instant ago. What 
 a large number of bands we have here, especially in the 
 red ! Those red and blue bands are the ones to which I 
 beg to draw your attention. These red lines now come 
 out very distinctly; and we have here also the bright 
 blue line flashing out brightly. This then is the stron- 
 tium spectrum. In like manner I may show you the 
 beautiful and characteristic spectrum of barium, with its 
 five green bands; and that of calcium, exhibiting special 
 orange and green lines together with a purple band in 
 the more refrangible part of the spectrum. 
 
 Now let us suppose that we have a mixture of com- 
 pounds of all these substances which are capable of being 
 
LECT. ii.] SPECTRA ON THE SCREEN. 75 
 
 volatilized, namely potassium, sodium, lithium, barium, 
 strontium, and calcium, and let us expose this mixture 
 to such a temperature that all the salts become vola- 
 tilized, one after another ; we shall see, in the first place, 
 that the bands of those substances which are the most 
 volatile appear first ; that then, when these have burnt 
 out, those next in order of volatility make their ap- 
 pearance ; and that those which are the least volatile 
 come out last. Thus we have the beautiful appearance 
 of what may be called a natural dissolving view. 
 
 I place on the carbon poles a mixture containing a few 
 grains of salts of all the above-mentioned metals. You 
 see in the first place that the sodium line comes out 
 at once, and afterwards the lines of the other metals 
 gradually make their appearance. We have thus simply 
 to place the smallest fraction of a grain of such a mixture 
 as this before the slit of our spectroscope, and with the 
 merest trace of substance we can in a moment obtain 
 absolute and decisive evidence of the presence of all 
 these substances, the lines coming out, as I said, like 
 a dissolving view, one after another ; and the minute 
 quantity which we can thus detect is something almost 
 marvellous. Here we have this splendid series of varie- 
 gated bands, exhibiting the superposed spectra of all the 
 substances 1 have mentioned. There you see the lithium 
 red line ; here the less refrangible red line of potassium ; 
 there the orange band of calcium and the red strontium 
 bands : observe, if you please, the two blue bands, one 
 due to strontium and the other to lithium. I shall 
 have occasion to show you that there are some other 
 very beautiful purple bands, characteristic of caesium and 
 rubidium, the new metals discovered by Bun sen, about 
 the history of which I purpose speaking to you in the 
 
76 SPECTRUM ANALYSIS. [LBCT. n. 
 
 next lecture. Now the sodium is very nearly burnt out, 
 and the lithium will soon disappear, whereas the green 
 bands produced by the less volatile barium compounds 
 will remain for a greater length of time. 
 
 In conclusion, gentlemen, I have to remind you that 
 it is simply a question of temperature ; it is only a 
 matter of experimentation how, and in what way, we 
 can best obtain the elementary bodies in the condition of 
 glowing gas. Having done that, we can readily detect 
 their presence by this very interesting and important 
 property they possess, of each body emitting light of 
 a peculiar and characteristic kind, and of various 
 degrees of refrangibility ; each giving what we term a 
 discontinuous spectrum. 
 
APPEND. A.] EXTRACTS FROM KIRCHHOFF AND BUNSEN. 
 
 LECTURE II. APPENDIX A. 
 
 DESCRIPTION OF THE SPECTRUM REACTION OF THE SALTS OF 
 THE ALKALIES AND ALKALINE EARTHS.i 
 
 WE now proceed to describe the peculiarities of the several 
 spectra, the exact acquaintance with which is of practical 
 importance, and to point out the advantages which this new 
 method of chemical analysis possesses over the older processes. 
 
 SODIUM. 
 
 The spectrum reaction of sodium is the most delicate of all. 
 
 The yellow line ISTa a (see Chromolith. Table, No. 7), the only 
 one which appears in the sodium spectrum, is coincident with 
 Fraunhofer's dark line D, and is remarkable for its exactly 
 defined form and for its extraordinary degree of brightness. 
 If the temperature of the flame be very high, and the quantity 
 of the substance employed very large, traces of a continuous 
 spectrum are seen in the immediate neighbourhood of the line. 
 In this case, too, the weaker lines produced by other bodies 
 when near the sodium line are discerned with difficulty, and are 
 often first seen when the sodium reaction has almost subsided. 
 
 The reaction is most visible in the sodium salts of oxygen, 
 chlorine, iodine, bromine, sulphuric acid, and carbonic acid. 
 But even in the silicates, borates, phosphates, and other non- 
 volatile salts, the reaction is always evident. Swan 2 has 
 already remarked upon the small quantity of sodium neces- 
 sary to produce the yellow line. 
 
 The following experiment shows that the chemist possesses 
 no reaction which in the slightest degree will bear comparison 
 
 1 From Kirchhoff and Bunsen's first Memoir on Analysis by Spectrum Obser- 
 vations (Phil. Mag. vol. xx. 1860). 
 
 2 Trans. Roy. Soc. JEdin. vol. xxi. part iii. p. 411. 
 
78 SPECTRUM ANALYSIS. [LECT. n 
 
 as regards delicacy with this spectrum-analytical determination of 
 sodium. In a far corner of our experiment room, the capacity of 
 which was about sixty cubic metres, we burnt a mixture of three 
 milligrammes of chlorate of sodium with milk-sugar, whilst the 
 non-luminous colourless flame of the lamp was observed through 
 the slit of the telescope. Within a few minutes the flame, which 
 gradually became pale yellow, gave a distinct sodium line, which, 
 after lasting for ten minutes, entirely disappeared. From the 
 weight of sodium salt burned and the capacity of the room, it 
 is easy to calculate that in one part by weight of air there is 
 suspended less than 2 -ooFoolTo of a P art of soda smoke - As 
 the reaction can be observed with all possible comfort in 
 one second, and as in this time the quantity of air which is 
 heated to ignition by the flame is found, from the rate of issue 
 and from the composition of the gases of the flame, to be only 
 about 50 cub. cent, or O0647 grin, of air, containing less than 
 f sodium salt, it follows that the eye is able to 
 
 detect with the greatest ease quantities of sodium salt less than 
 30U u UUO of a milligramme in weight. With a reaction so deli- 
 cate, it is easy to understand why a sodium reaction is almost 
 always noticed in ignited atmospheric air. More than two- 
 thirds of the earth's surface is covered with a solution of chloride 
 of sodium, fine particles of which are continually being carried 
 into the air by the action of the waves. These particles of sea 
 \yater cast thus into the atmosphere evaporate, leaving almost 
 inconceivably small residues, which, floating about, are almost 
 always present in the air, and are rendered evident to our 
 eyesight in the sunbeam. These minute particles perhaps serve 
 to supply the smaller organized bodies with the salts which 
 larger animals and plants obtain from the ground. In another 
 point of view, however, the presence of this chloride of sodium 
 in the air is of interest. If, as is scarcely doubtful at the 
 present time, the explanation of the spread of contagious disease 
 is to be sought for in some peculiar contact-action, it is possible 
 that the presence of so antiseptic a substance as chloride of 
 sodium, even in almost infinitely small quantities, may not be 
 without influence upon such occurrences in the atmosphere. 
 
APPEND. A.] EXTRACTS FROM KIRCHHOFF AND BUNSEN. 79 
 
 By means of daily and long-continued spectrum observations, 
 it would be easy to discover whether the alterations of intensity 
 in the line Na a produced by the sodium in the air have any 
 connection with the appearance and direction of march of an 
 endemic disease. 
 
 The unexampled delicacy of the sodium reaction explains 
 also the well-observed fact, that all bodies after a lengthened 
 exposure to air show the sodium line when brought into a flame, 
 and that it is only possible in a few salts to get rid of the line 
 even after repeated crystallization from water which had only 
 been in contact with platinum. A thin platinum wire, freed 
 from every trace of sodium salt by ignition, shows the reaction 
 most visibly on allowing it to stand for a few hours in the air : 
 in the same way the dust which settles from the air in a room 
 shows thoJfcright line Na a. To render this evident it is only 
 necessary to knock a dusty book, for instance, at a distance of 
 some feet from the flame, when a wonderfully bright flash of 
 yellow band is seen. 
 
 LITHIUM. 
 
 The luminous ignited vapour of the lithium compounds gives 
 two sharply defined lines ; the one a very weak yellow line, Li /3, 
 and the other a bright red line, Li a. This reaction exceeds in 
 certainty and delicacy all methods hitherto known in analytical 
 chemistry. It is, however, not quite so sensitive as the sodium 
 reaction, only, perhaps, because the eye is more adapted to 
 distinguish yellow than red rays. When nine milligrammes 
 of carbonate of lithium mixed with excess of milk-sugar were 
 burnt, the reaction was visible in a room of sixty cubic metres' 
 capacity. Hence, according to the method already explained, 
 we find that the eye is capable of distinguishing with absolute 
 certainty a quantity of carbonate of lithium less than 100000UU 
 of a milligramme in weight : 0'05 grm. of carbonate of lithium, 
 burnt in the same room, was sufficient to enable the ignited air 
 to show the red line Li a for an hour after the combustion had 
 taken place. 
 
80 SPECTRUM ANALYSIS. [LECT. n. 
 
 The compounds of lithium with oxygen, iodine, bromine, and 
 chlorine are the most suitable for the peculiar reaction; still 
 the carbonate, sulphate, and even the phosphate, give almost 
 as distinct a reaction. Minerals containing lithium, such as 
 triphylline, triphane, petalite, lepidolite, require only to be held 
 in the flame in order to obtain the bright line in the most 
 satisfactory manner. In this way the presence of lithium in 
 many felspars can be directly detected ; as, for instance, in the 
 orthoclase from Baveno. The line is only seen for a few 
 moments, directly after the mineral is brought into the flame. 
 In the same way the mica from Altenburg and Penig was found 
 to contain lithium, whereas micas from Miask, Aschaffenburg, 
 Modum, Bengal, Pennsylvania, &c., were found to be free from 
 this metal. In natural silicates which contain only small traces 
 of lithium this metal is not observed so readily. The examina- 
 tion is then best conducted as follows : A small portion of the 
 substance is digested and evaporated with hydrofluoric acid or 
 fluoride of ammonium, the residue moistened with sulphuric 
 acid and heated, the dry mass being dissolved in absolute alcohol. 
 The alcoholic extract is then evaporated, the dry mass again 
 dissolved in alcohol, and the extract allowed to evaporate on a 
 shallow glass dish. The solid pellicle which remains is scraped 
 off with a fine knife, and brought into the flame upon the thin 
 platinum wire. For one experiment ^ of a milligramme is in 
 general quite a sufficient quantity. Other compounds besides 
 the silicates, in which small traces of lithium require to be 
 detected, are transformed into sulphates by evaporation with 
 sulphuric acid or otherwise, and then treated in the manner 
 described. 
 
 In this way we arrive at the unexpected conclusion that 
 lithium is most widely distributed throughout nature, occurring 
 in almost all bodies. Lithium was easily detected in forty cubic 
 centimetres of the water of the Atlantic Ocean, collected in 
 41 41' N. latitude and 39 14' W. longitude. Ashes of marine 
 plants (kelp), driven by the Gulf Stream on the Scotch coasts, 
 contain evident traces of this metal. All the orthoclase and 
 quartz from the granite of the Odenwald which we have 
 
APPEND. A] EXTRACTS FROM KIRCHHGFF AND BUNSEN. 81 
 
 examined contained lithium. A very pure spring water from 
 the granite in Schleierbach, on the west side of the valley of the 
 Neckar, was found to contain lithium, whereas the water from 
 the red sandstone which supplies the Heidelberg laboratory 
 was shown to contain none of this metal. Mineral waters, 
 in a litre of which lithium could hardly be detected according 
 to the ordinary methods of analysis, gave plainly the line Li a 
 even if only a drop of the water on a platinum wire was brought 
 into the flame. 1 All the ashes of plants growing in the 
 Odenwald on a granite soil, as well as Russian and other 
 potashes, contain lithium. 
 
 Even in the ashes of tobacco, in vine leaves, in the wood of 
 the vine, and in grapes, 2 as well as in the ashes of the crops 
 grown in the Rhine plain near Waghausel, Deidesheim, and 
 Heidelberg, on a non-granite soil, was lithium found. The milk 
 of the animals fed upon these crops also contains this widely 
 diffused metal. 3 
 
 It is necessary to say that a mixture of volatile sodium arid 
 lithium salts gives the reaction of lithium alongside that of 
 sodium with a precision and distinctness which are hardly 
 perceptibly diminished. The red lines of the former substance 
 are still plainly seen when the bead contains J^ part of 
 lithium salt, and when to the naked eye the yellow soda flame 
 appears untinged by the slightest trace of red. In consequence 
 of the somewhat greater volatility of the lithium salt, the 
 sodium reaction lasts longer than that of the other metal. I 
 those cases, therefore, in which small quantities of lithium 
 have to be detected in presence of large quantities of sodium 
 salt, the bead must be brought into the flame whilst the observer 
 is looking through the telescope. The lithium lines are often 
 
 1 When liquids have to be brought into the flame, it is best to bend the end of 
 the platinum wire, of the thickness of a horsehair, to a small ring, and to beat 
 this ring flat. If a small drop of liquid be brought into this ring, enough adheres 
 to the wire for one experiment. 
 
 2 In the manufactories of tartaric the mother liquors contain so much lithium 
 salts, that considerable quantities can thus be prepared. 
 
 3 Dr. Falwarczny has been able to detect lithium in the ash of human blood 
 and muscular tissue by the help of the line Li o. 
 
82 SPECTRUM ANALYSIS. [LKCT. n. 
 
 only seen during a few moments amongst the first products 
 of the volatilization. 
 
 In the production of lithium salts on the large scale, in 
 the proper choice of a raw material, and in the arrangement 
 of suitable methods of separation, this spectrum analysis affords 
 most valuable aid. Thus it is only necessary to place a drop 
 of mother liquor from any mineral spring in the flame and 
 to observe the spectrum produced, in order to show that in 
 many of these waste products a rich and hitherto unheeded 
 source of lithium salts exists. In the same way, during the 
 course of the preparation any loss of lithium in the collateral 
 products and residues can be easily traced, and thus more con- 
 venient and economical methods of preparation may be found 
 to replace those at present employed. 1 
 
 * 
 
 POTASSIUM. 
 
 The volatile potassium compounds give, when placed in the 
 flame, a widely-extended continuous spectrum, which contains 
 only two characteristic lines, namely, one line, Kaa, in the 
 outermost red, approaching the ultra-red rays, exactly coinciding 
 with the dark line A of the solar spectrum ; and a second line, 
 Ka ft situated far in the violet rays towards the other end of 
 the spectrum, and also identical with a particular dark line 
 observed by Fraunhofer. 
 
 A very indistinct line, coinciding with Fraunhofer's line B, 
 which, however, is only seen when the light is very intense, 
 is not by any means so characteristic. The violet line is 
 somewhat pale, but can be used almost as well as the red line 
 for the detection of potassium. Owing to the position of these 
 two lines, both situated near the limit at which our eyes cease 
 to be sensitive to the rays, this reaction for potassium is not 
 
 1 AVe obtain by such an improved method from two jars (about four litres) of a 
 mother liquor from a mineral spring, which by evaporation with sulphuric acid 
 gave 1 '2 kil. of residue, half an ounce of carbonate of lithium of the piirity of the 
 commercial, the cost of which is about 140 florins the pound. A great number 
 of other mineral-spring mother liquors which we examined showed a similar 
 richness in compounds of lithium. 
 
APPEND. A.] EXTRACTS FROM KIRCHHOFF AND BUNSEN. 83 
 
 so delicate as the reaction for the two metals already mentioned. 
 The reaction became visible in the air of our room when 
 one gramme of chlorate of potassium mixed with milk-sugar 
 was burnt. In this way, therefore, the eye requires the presence 
 of jj~ of a milligramme of chlorate of potassium in order to 
 detect the presence of potassium. 
 
 Caustic potash, and all compounds of potassium with volatile 
 acids, give the reaction without exception. Potash silicates, 
 and other non-volatile salts, on the other hand, only produce 
 the reaction when the metal is present in very large quantities. 
 It is only necessary, however, to melt the substance with a 
 bead of carbonate of sodium in order to detect potassium even 
 when present in a very small quantity. The presence of the 
 sodium does not in the least interfere with the reaction, and 
 scarcely diminishes its delicacy. Orthoclase, sanidine, and 
 adularia may in this way be easily distinguished from albite, 
 oligoclase, labradorite, and anorthite. In order to detect the 
 smallest traces of potassium salt, the silicate requires only to 
 be slightly ignited with a large excess of fluoride of ammonium 
 on a platinum capsule, after which the residue is brought into 
 the flame on a platinum wire. In this way it is found that 
 almost every silicate contains potash. Salts of lithium diminish 
 or influence the reaction as little as soda salts. Thus we need 
 only to hold the end of a burnt cigar in the flame before the 
 slit in order at once to see the yellow line of sodium and the 
 two red lines of potassium and lithium, this latter metal being 
 scarcely ever absent in tobacco ash. 
 
 STRONTIUM. 
 
 The spectra produced by the alkaline earths are by no means 
 so simple as those produced by the alkalies. That of strontium 
 is especially characterized by the absence of green bands. Eight 
 lines in the strontium spectrum are remarkable, namely, six red, 
 one orange, and one blue line. The orange line Sr a, which 
 appears close by the sodium line towards the red end of the 
 spectrum, the two red lines, Sr /3 and Sr X, and, lastly, the blue 
 
 G 2 
 
84 SPECTRUM ANALYSIS. [LECT. n. 
 
 line, Sr 8, are the most important strontium bands, both as 
 regards their position and their intensity. For the purpose of 
 examining the intensity of the reaction we quickly heated an 
 aqueous solution of chloride of strontium, of a known degree 
 of concentration, in a platinum dish over a large flame, until the 
 water was evaporated and the basin became red-hot. The salt 
 then began to decrepitate, and was thrown in microscopic 
 particles out of the dish in the form of a white cloud carried up 
 into the air. On weighing the residual quantity of salt, it was 
 found that in this way 0*077 grin, of chloride of strontium had 
 been mixed in the form of a fine dust with the air of the room, 
 weighing 77,000 grms. As soon as the air in the room was 
 perfectly mixed, by rapidly moving an umbrella, the character- 
 istic lines of the strontium spectrum were beautifully seen. 
 According to this experiment, a quantity of strontium may be 
 thus detected equal to the 1( y^j5 part of a milligramme in 
 weight. The chloride and the other haloid salts of strontium 
 give the action less vividly, the sulphate less distinctly, whilst 
 the compounds of strontium with the non-volatile acids give 
 either a very slight reaction or else none at all. Hence it is 
 well first to bring the bead of substance alone into the flame, 
 and then again after moistening with hydrochloric acid. If it 
 be supposed that sulphuric acid is present in the bead, it must 
 be held in the reducing part of the flame before it is moistened 
 with hydrochloric acid, for the purpose of changing the sulphate 
 into the sulphide, which is decomposed by hydrochloric acid. 
 In order to detect strontium when combined with silicic, 
 phosphoric, boracic, and other non-volatile acids, the following 
 course -of procedure gives the best results. Instead of fusing 
 with carbonate of sodium in a platinum crucible, a conical 
 spiral of platinum wire is employed: this spiral is heated to 
 whiteness in the flame, and dipped whilst hot into finely 
 powdered dried carbonate of sodium, which properly should 
 contain so much water that a sufficient quantity adheres to the 
 wire when it is once dipped into the salt. The fusion takes 
 place 'in this spiral much more quickly than in a platinum 
 crucible, as the mass of platinum requiring heating is small, and 
 
APPEND. A.] EXTRACTS FROM KIRCHHOFF AND BUNSEN. 85 
 
 the flame comes into direct contact with the salt. As soon as 
 the finely powdered mineral has been brought into the fused 
 soda by means of a small platinum spatula, and the mass 
 retained above the fusion point for a few minutes, the cooled 
 mass has only to be turned upside down and knocked on the 
 porcelain plate of the lamp in order to obtain the salt in one 
 coherent bead. The fused mass is covered by a piece of 
 writing-paper, and then broken by pressing it with the blade 
 of a steel spatula until the whole is in the state of a fine 
 powder. The powder is collected to one spot on the edge of the 
 plate, and carefully covered with hot water, which is allowed to 
 flow backwards and forwards over it, so that, after decanting and 
 rewashing the powder several times, all the soluble salts are 
 extracted without losing any of the residue. If a solution of 
 chloride of sodium be employed instead of water, the operation 
 may be conducted still more rapidly. The insoluble salt contains 
 the strontium as carbonate, and one or two tenths of a milli- 
 gramme of the substance brought on to the wire, and moistened 
 with hydrochloric acid, is sufficient to produce the most intense 
 reaction. It is thus possible, without help of platinum crucible, 
 mortar, evaporating basin, or funnel and filter, to fuse, powder, 
 digest, and wash out the substance in the space of a few minutes. 
 The reactions of potassium and sodium are not influenced by 
 the presence of strontium. Lithium also can be easily detected 
 in presence of strontium, where the proportion of the former 
 metal is not very small. The lithium line Sr a appears as an 
 intensely red, sharply-defined band upon a less distinct red 
 ground of the broad strontium band Sr ft. 
 
 CALCIUM. 
 
 The spectrum produced by calcium is immediately dis- 
 tinguished from the four spectra already considered by the very 
 characteristic bright green line Ca /3. A second no less charac- 
 teristic feature in the calcium spectrum is the intensely bright 
 orange line, Ca a, lying considerably nearer to the red end of the 
 spectrum than either the sodium line, Na a, or the orange band 
 
86 SPECTRUM ANALYSTS. [LBCT. u. 
 
 of strontium, Sr a. By burning a mixture consisting of chloride 
 of calcium, chlorate of potassium, and milk-sugar, a white cloud 
 is obtained which gives the reaction with as great a degree of 
 delicacy as strontium salts do under similar circumstances. In 
 this way we found that 1UU0 6 0000 of a milligramme in weight of 
 chloride of calcium can be detected with certainty. Only the 
 volatile compounds of calcium give this reaction; the more 
 /olatile the salt, the more distinct and delicate does the reaction 
 become. The chloride, bromide, and iodide of calcium are in this 
 respect the best compounds. Sulphate of calcium produces the 
 spectrum after it has become basic, very brightly and con- 
 tinuously. In the same way the reaction of the carbonate 
 becomes more distinctly visible after the acid has been expelled. 
 Compounds of calcium with the non-volatile acid remain in- 
 active in the flame ; but if they are attacked by hydrochloric 
 acid, the reaction may be easily attained as follows: A few 
 milligrammes of finely powdered substance are brought on to 
 the moistened flat platinum ring in the moderately hot part of 
 the flame, so that the powder is fritted but not melted on to the 
 wire : if a drop of hydrochloric acid be now allowed to fall into 
 the ring, so that the greater part of the acid remains hanging on 
 to the wire, and if then the wire be brought into the hottest part 
 of the flame, the drop evaporates in the spheroidal state without 
 ebullition. The spectrum of the flame must be observed during 
 this operation ; and it will be noticed that at the moment when 
 the last particles of liquid evaporate a bright calcium spectrum 
 appears. If the quantities of the metal present are very small, 
 the characteristic lines are only seen for a moment; if larger 
 quantities are contained, the phenomenon lasts for a longer time. 
 Only in the silicates which are decomposed by hydrochloric 
 acid can the calcium ^be thus found. In those minerals which 
 are not attacked by that acid the following method may be 
 best employed for the detection of calcium. A few milligrammes 
 of the substance under examination, in a state of fine division, 
 are brought upon a flat platinum lid, together with about 
 a gramme of fluoride of ammonium, and the mixture is gently 
 ignited until all the fluoride is volatilized. The slight crust 
 
APPEND. A.] EXTRACTS FROM KIRCHHOFF AND BUN SEN. 87 
 
 of salt remaining is moistened with a few drops of sulphuric 
 acid, and the excess of acid removed by heat. If about a 
 milligramme of the residual sulphates be scraped together with 
 a knife, and brought into the flame, the characteristic spectra 
 of potassium, sodium, and lithium, supposing these three metals 
 to be present, are first obtained, either simultaneously or con- 
 secutively. If calcium and strontium be also present, the 
 corresponding spectra generally appear somewhat later, after 
 the potassium, sodium, and lithium have been volatilized. When 
 only traces of strontium and calcium are present, the reaction 
 is not always seen : it becomes, however, immediately apparent 
 on holding the bead for a few moments in the reducing flame, 
 and, after moistening it with hydrochloric acid again, bringing it 
 into the flame. 
 
 These easy experiments, such as either heating the specimen 
 alone, or after moistening with hydrochloric acid, or after 
 treating the powder with fluoride of ammonium either alone 
 or in presence of sulphuric or by hydrochloric acid, provide the 
 mineralogist and geologist with a series of most simple methods 
 of recognizing the components of the smallest fragment of many 
 substances (such, for instance, as the double silicates containing 
 lime) with a certainty which is attained in an ordinary analysis 
 only by a large expenditure of time and material. The follow- 
 ing examples will illustrate this statement : 
 
 1. A drop of sea- water heated on the platinum wire shows at 
 first a strong sodium reaction; and after volatilization of the 
 chloride of sodium, a weak calcium spectrum is observed, which 
 on moistening the wire with hydrochloric acid becomes at once 
 very distinct. If a few decigrammes of the residual salts 
 obtained by the evaporation of sea-water be treated in the 
 manner described under lithium with sulphuric acid and alcohol, 
 the potassium and lithium reactions are obtained. The presence 
 of strontium in sea- water can be best detected in the boiler-crust 
 from sea-going steamers. The filtered hydrochloric acid solution of 
 such a crust leaves on evaporation and subsequent treatment with 
 a small quantity of alcohol a residue slightly yellow-coloured 
 from basic iron salt, which is deposited after some days, and 
 
88 SPECTRUM ANALYSIS. [LECT. n. 
 
 can then be collected on a small filter and washed with alcohol. 
 The filter burnt on a fine platinum wire and held in the flame 
 gives besides the calcium lines an intensely bright strontium 
 spectrum. 
 
 2. Mineral waters often exhibit the reactions of potassium, 
 sodium, lithium, calcium, and strontium by mere heating. If, 
 fur example, a drop of the Diirkheim or Kreuznach waters be 
 brought into the flame, the lines Na a, Li a, Caa, and Ca/3 are 
 at once seen. If instead of using the water itself a drop of the 
 mother liquor is taken, these bands appear most vividly. As 
 soon as the chlorides of sodium and lithium have been to a 
 certain extent volatilized, and the chloride of calcium has 
 become more basic, the characteristic lines of the strontium 
 spectrum begin to show themselves, and continue to increase 
 in distinctness until at last they come out in all their true 
 brightness. In this case, therefore, by the mere observation 
 of a single drop undergoing vaporation, the complete analysis 
 of a mixture containing five constituents is performed in a few 
 seconds. 
 
 3. The ash of a cigar moistened with hydrochloric acid and 
 held in the flame shows at once the bands Na a, Ka a, Li a, Ca a, 
 Ca/3. 
 
 4. A piece of hard potash-glass combustion tubing gave, both 
 with and without hydrochloric acid, the lines Na a and Ka a : 
 treated with fluoride of ammonium and sulphuric acid, the bands 
 Ca a, Ca /3, and traces of Li a were rendered visible. 
 
 5. Orthoclase from Baverio gives, either alone or when 
 treated with hydrochloric acid only, the lines Na a and Ka a, 
 with traces of Li a : with fluoride of ammonium and sulphuric 
 acid, the bright lines Na a and Ka a, and a somewhat less distinct 
 Li a, are seen. After volatilization of the bodies thus detected, 
 the bead moistened with hydrochloric acid gives a scarcely 
 distinguishable fl ash of the lines Ca a and Ca /3. The residue 
 on the platinum wire, when moistened with cobalt solution 
 and heated, gives the blue colour so characteristic of alumina. 
 If the well-known reaction of silicic acid be otherwise employed, 
 we may conclude from this examination made in the course 
 
APPEND. A.] EXTRACTS FROM KIRCHHOFF AND BUNSEN. 89 
 
 of a very few minutes that the orthoclase from Baveno contains 
 silicic acid, alumina, potash, with traces of soda, lime, andlithia- 
 and also that no trace of baryta or strontia is present. 
 
 6. Adularia from St. Gothard comported itself in a similar 
 manner, with the exception that the calcium reaction was 
 indistinctly seen, whilst that of lithium was altogether wanting. 
 
 7. Labradorite from St. Paul gives the sodium line Na a, but 
 no calcium spectrum. On moistening the fragment with hydro- 
 chloric acid, the lines Ca a and Ca /5 appear very distinctly : with 
 the fluoride of ammonium test a weak potassium reaction is 
 obtained, and also faint indications of lithium. 
 
 8. Labradorite from the Corsican diorite gave similar reac- 
 tions, except that no lithium was found. 
 
 9. Mosanderite from Brevig and Tscheffkinite from the 
 Ilmengebirge showed when treated alone the sodium reaction : 
 on the addition of hydrochloric acid the lines Ca a and Ca ft 
 appeared. 
 
 10. Melinophane from Lamoe gave the line Na a when placed 
 in the flame ; with hydrochloric acid the lines Ca a and Li a 
 became visible. 
 
 11. Scheelite and sphene give, on treatment with hydro- 
 chloric acid, a very intense calcium reaction. 
 
 12. When small quantities of strontium are present together 
 with calcium, the line Sr 8 may be most conveniently employed 
 for the detection of this metal. In this way the presence of 
 small quantities of strontium can be easily detected in very 
 many sedimentary limestones. The lines Na a, Li a, Ka a, and 
 especially Li a, are observed as soon as the limestone is brought 
 into the flame. Converted by hydrochloric acid into chlorides ) 
 and brought in this form into the flame, these minerals give the 
 same bands ; and not unfrequently the line Sr is also dis- 
 tinctly seen. This latter appears, however, only for a short 
 time, and is in general best seen when the calcium spectrum 
 begins to fade. 
 
 In this way the lines Na a, Li a, Ka a, Ca a, Ca & and Sr S 
 were found in the spectra of the following limestones : Lime- 
 stone from the Silurian at Kugelbad near Prague, muschelkalk 
 
9 SPECTR UN ANALYSIS. [LECT. 1 1 . 
 
 from Rohrbach near Heidelberg, limestone from the lias at 
 Malsch in Baden, chalk from England. The following lime- 
 stones gave the lines Na a, Li a, Ka a, Ca a, Ca /3, but not the 
 blue strontium band Sr 3 : Marble from the granite near 
 Auerbach, 1 limestone from the Devonian at Gerolstein in the 
 Eifel, carboniferous limestone from Planitz in Saxony, dolomite 
 from Nordhausen in the Hartz, Jura kalk from Streitberg in 
 Franconia. From these few experiments it is evident that a 
 more extended series of exact spectrum analyses, respecting the 
 amount of strontium, lithium, sodium, and potassium which 
 the various limestone formations contain, must prove of the 
 greatest geological importance both as regards the order of 
 their formation and their local distribution, and may possibly 
 lead to the establishment of some unexpected conclusions 
 respecting the nature of the oceans from which these limestones 
 were originally deposited. 
 
 BARIUM. 
 
 . The barium spectrum is the most complicated of the spectra 
 of the alkalies and alkaline earths. It is at once distinguished 
 from all the others by the green lines Ba a and Ba ft (which 
 are by far the most distinct) appearing the first, and continuing 
 during the whole of the reaction. Ba 7 is not quite so distinct, 
 but is still a well-marked and peculiar line. As the barium 
 spectrum is considerably more extended than those of the other 
 metals, the reaction is not observed to so great a degree of 
 delicacy: still 0'3 grm. of chlorate. of barium burnt with milk- 
 sugar gave a distinct band of Ba a which lasted for some time, 
 when the air of the room was well mixed by moving an open 
 umbrella about. Hence we may calculate, in the same manner 
 as was done in the sodium experiment, that about T o T off of a 
 milligramme of barium salt may be detected with the greatest 
 certainty. 
 
 1 According to the method already described, a quantity of nitrate of stron- 
 tium was obtained from 20 grins, of this marble such as to give a complete 
 and vivid strontium spectrum. We have not examined the other limestones 
 in the same way. 
 
APPEND. A.] EXTRACTS FROM KIRCHHOFF AND BUNSEtf. 91 
 
 The chloride, bromide, iodide, and fluoride of barium, as also 
 the hydrated oxide, the sulphate, and carbonate, show the re- 
 action best. Tt may be obtained by simply heating any of 
 these salts in the flame. 
 
 Silicates containing barium which are decomposed by hydro- 
 chloric acid also give the reaction if a drop of hydrochloric 
 acid be added to them before they are brought into the flame. 
 Baryta-harmotome, treated in this way, gives the lines Ca a and 
 Ca/8, together with the bands Baa and Ba/3. Compounds 
 of barium with fixed acids, giving no reaction either when 
 alone or after addition of hydrochloric acid, should be fused 
 with carbonate of sodium as described under strontium, and the 
 carbonate of barium thus obtained examined. If barium and 
 strontium occur in small quantities together with large amounts 
 of calcium, the carbonates obtained by fusion are dissolved in 
 nitric acid, and the dried salt extracted with alcohol : the residue 
 contains only barium and strontium, both of which can almost 
 always be detected. When we wish to test for small traces 
 of strontium or barium, the residual nitrates are converted into 
 chlorides by ignition with sal-ammoniac, and the chloride of 
 strontium is extracted by alcohol. Unless one or more of the 
 bodies to be detected is present in very small quantities, the 
 methods of separation just described are quite unnecessary, as 
 is seen from the following experiment : A mixture of the 
 chlorides of potassium, sodium, lithium, calcium, strontium, and 
 barium, containing at the most T V of a milligramme of each 
 of these salts, was brought into the flame, and the spectra pro- 
 duced were observed. At first the bright yellow sodium line, 
 Na a, appeared with a background formed by a nearly con- 
 tinuous pale spectrum : as soon as this line began to fade, the 
 exactly defined bright red line of lithium, Li a, was seen, and 
 still farther removed from the sodium line the faint red 
 potassium line, Ka a, was noticed ; whilst the two barium lines, 
 Baa, Ba/5, with their peculiar form, became visible in the 
 proper position. As the potassium, sodium, lithium, and 
 barium salts volatilized, their spectra became fainter and fainter, 
 and their peculiar bands one after the other vanished, until 
 
9? SPECTRUM ANALYSIS. [LECT. n. 
 
 after the lapse of a few minutes, the lines Ca a, Ca ft, Sr a, Sr ft, 
 Sr 7, and Sr 8 became gradually visible, and, like a dissolving 
 view, at last attained their characteristic distinctness, colouring, 
 and position, and then, after some time, became pale and dis- 
 appeared entirely. The absence of any one or of several of 
 these bodies is at once indicated by the non-appearance of 
 the corresponding bright lines. 
 
 Those who become acquainted with the various spectra by 
 repeated observation do not need to have before them an exact 
 measurement of the single lines in order to be able to detect the 
 presence of the various constituents ; the colour, relative position, 
 peculiar form, variety of shade and brightness, of the bands are 
 quite characteristic enough to ensure exact results, even in the 
 hands of persons unaccustomed to such work. These special 
 distinctions may be compared with the differences of outward 
 appearance presented by the various precipitates which we 
 employ for detecting substances in the wet way. Just as it 
 holds good as a character of a precipitate that it is gelatinous, 
 pulverulent, flocculent, granular, or crystalline, so the lines of 
 the spectrum exhibit their peculiar aspects, some appearing 
 sharply denned at their edges, others blended off either at one 
 or both sides, either similarly or dissimilarly; or some again 
 appearing broader, others narrower; and just as in ordinary 
 analysis we only make use of those precipitates which are 
 produced with the smallest possible quantity of the substance 
 supposed to be present, so in analysis with the spectrum we 
 employ only those lines which are produced by the smallest 
 possible quantity of substance, and require a moderately 
 high temperature. In these respects both analytical methods 
 stand on an equal footing; but analysis with the spectrum 
 possesses a great advantage over all other methods, inasmuch 
 as the characteristic differences of colour of the lines serve 
 as the distinguishing feature of the system. Most of the pre- 
 cipitates which are valuable as reactions are colourless; and 
 the tint of those which are coloured varies very considerably, 
 according to the state of division and mechanical arrangement 
 of the particles. The presence of even the smallest quantity 
 
APPEND. A.] EXTRACTS FROM KIRCHHOFF AND BUXSEN. 93 
 
 of impurity is often sufficient entirely to destroy the character- 
 istic colour of a precipitate ; so that no reliance can be placed 
 upon nice distinctions of colour as an ordinary chemical test. 
 In spectrum analysis, on the contrary, the coloured bands are 
 unaffected by such alteration of physical conditions, or by the 
 presence of other bodies. The positions which the lines occupy 
 in the spectrum give rise to chemical properties as unalterable as 
 the combining weights themselves, and which can therefore be 
 estimated with an almost astronomical precision. The fact, how- 
 ever, which gives to this method of spectrum analysis an extra- 
 ordinary importance, is that the chemical reactions of matter 
 thus reach a degree of delicacy which is almost inconceivable. 
 By an application of this method to geological inquiries concern- 
 ing the distribution and arrangements already mentioned, we are 
 led to the unexpected conclusion, that not only potassium and 
 sodium, but also lithium and strontium, must be added to the 
 list of bodies occurring only indeed in small quantities, but most 
 widely spread throughout the matter composing the solid body of 
 our planet. 
 
 The method of spectrum analysis may also play a no less im- 
 portant part as a means of detecting new elementary substances ; 
 for if bodies should exist in nature so sparingly diffused that the 
 analytical methods hitherto applicable have not succeeded in 
 detecting or separating them, it is very possible that their pre- 
 sence may be revealed by a simple examination of the spectra 
 produced by their flames. We have had opportunity of satisfy- 
 ing ourselves that in reality such unknown elements exist. We 
 believe that, relying upon unmistakeable results of the spectrum 
 analysis, we are already justified in positively stating that, 
 besides potassium, sodium, and lithium, the group of the alka- 
 line metals contains a fourth member, which gives a spectrum as 
 simple and characteristic as that of lithium, a metal which in 
 our apparatus gives only two lines, namely, a faint blue one, 
 almost coincident with the strontium line Sr 8, and a second 
 blue one lying a little further towards the violet end of the 
 spectrum, and rivalling the lithium line in brightness and dis- 
 tinctness of outline. 
 
94 SPECTRUM ANALYSTS. [LECT. n. 
 
 APPENDIX B. 
 
 BUNSEN AND KIRCHHOFF ON THE MODE OF USING A 
 SPECTROSCOPE. 1 
 
 The apparatus is represented by Fig. 27. On the upper end 
 of a cast-iron foot a brass plate is screwed, carrying the flint- 
 glass prism (a), having a refracting angle of 60. The tube I 
 is also fastened to the brass plate : in the end of this tube near- 
 est the prism is placed a lens, whilst the other end is closed by 
 
 FIG. 27. 
 
 a plate in which a vertical slit has been made. Two arms are 
 also fitted on to the cast-iron foot, so that they are moveable in a 
 horizontal plane about the axis of the foot. One of these arms 
 carries the telescope (/), having a magnifying power of 8, whilst 
 the other carries the tube (g) : a lens is placed in this tube at the 
 
 1 Second Memoir on Spectrum Analysis, Phil. Mag. vol. xxii. 1861, pp. 334 
 498. 
 
APPEND. B.] HOW TO USE A SPECTROSCOPE. 9.5 
 
 end nearest the prism, and at the other end is a scale which can 
 
 be seen through the telescope by reflection from the front surface 
 
 of the prism. This scale is a photographic copy of a millimetre 
 
 scale, which has been produced in the camera of about Jg- the 
 
 original dimensions. 1 The scale is covered with tinfoil, so that 
 
 only the narrow strip upon which the divisions and the numbers 
 
 are engraved can be seen. The upper half only of the slit is 
 
 left free, as is seen by reference to Fig. 28 ; the lower half is 
 
 covered by a small equilateral glass prism, which sends by 
 
 total reflection the light of the lamp 6, Fig. 27, through the slit, 
 
 whilst the rays from the lamp e pass freely through the upper 
 
 and uncovered half. A small screen placed 
 
 above the prism prevents any light from 
 
 ^ passing through the upper portion of the 
 
 slit. By help of this arrangement the ob- -^mmmmmr 
 
 server sees the spectra of the two sources FIG. 28. 
 
 of light immediately one under the other, 
 
 and can easily determine whether the lines are coincident Ot*i S J 
 
 not, 2 
 
 We now proceed to describe the arrangement and mode of 
 using the instrument. 
 
 The telescope f is first drawn out so far that a distant object 
 is plainly seen, and screwed into the ring, in which it is held, 
 care being taken to loosen the screws beforehand. The tube b 
 is then brought into its place, and the axis of B brought into 
 a straight line with that of b. The slit is then drawn out 
 until it is distinctly seen on looking through the telescope, and 
 this latter is then fixed by moving the screws, so that the 
 middle of the slit is seen in about the middle of the field of 
 view. After removing the small spring, the prism is next 
 
 1 This millimetre scale was drawn on a strip of glass, covered with a thin coat- 
 ing of lampblack and wax dissolved in glycerine. The divisions and numbers, 
 which by transmitted light showed bright on a dark ground, were represented in 
 the photograph dark on a light ground. It would be still better to employ, for 
 the spectrum apparatus, a scale in which the marks were light on a dark ground. 
 Such scales are beautifully made by Salleron and Ferrier of Paris. 
 
 2 This apparatus was made in the celebrated optical and astronomical atelier 
 of C. A. Steinheil in Munich. 
 
96 SPECTRUM ANALYSIS. [LECT. n. 
 
 placed on the brass plate, and fastened in the position which is 
 marked for it, and secured by screwing down the spring. If 
 the axis of the tube b be now directed towards a bright surface, 
 such as the flame of a candle, the spectrum of the flame is seen 
 in the lower half of the field of the telescope on moving the latter 
 through a certain angle round the axis of the foot. When the 
 telescope has been placed in position, the tube g is fastened on 
 to the arm belonging to it, and this is turned through an angle 
 round the axis of the foot such that, when a light is allowed to 
 fall on the divided scale, the image of the scale is seen through 
 the telescope /, reflected from the nearer face of the prism. 
 This image is brought exactly into focus by altering the posi- 
 tion of the scale in the tube g ; and by turning this tube on its 
 axis it is easy to make the line in which one side of the divisions 
 on the scale lies parallel with the line dividing the two spectra, 
 and by means of the screw S to bring these two lines to 
 coincide. 
 
 In order to bring the two sources of light, e and e, into posi- 
 tion, two methods maybe employed. One of these depends upon 
 the existence of bright lines in the inner cone of the colourless 
 gas flame, which have been so carefully examined by Swan. If 
 the lamp e be pushed past the slit, a point is easily found at 
 which these lines become visible ; the lamp must then be pushed 
 still further to the left, until these lines nearly or entirely dis- 
 appear; the right mantle of the flame is now before the slit, 
 and into this the bead of substance under examination must be 
 brought. In the same way the position of the source of light e 
 may be ascertained. 
 
 The second method is as follows : The telescope / is so 
 placed that the brightest portion of the spectrum of the flame of 
 a candle is seen in about the middle of the field of view ; the 
 flame is then placed before the ocular in the direction of the axis 
 of the telescope, and the position before the slit determined in 
 which the upper half of the slit appears to be the brightest ; the 
 lamp e is then placed so that the slit appears behind that portion 
 of the 1 flame from which the most light is given off after the 
 introduction of the bead. In a similar way the position of the 
 
APPEND, cv] MAPPING SPECTRA. 97 
 
 lamp ^ is determined by looking through the small prism and 
 the lower half of the slit. 
 
 By means of the screw the breadth of the slit can be regu- 
 lated in accordance with the intensity of the light, and the degree 
 of purity of spectrum which is required. To cut off foreign light, 
 a black cloth, having a circular opening to admit the tube g, is 
 thrown over the prism a and the tubes I and /. The illumina- 
 tion of the scale is best effected by means of a luminous gas flame 
 placed before it : the light can, if necessary, be lessened by placing 
 a silver-paper screen close before the scale. The degree of illu- 
 mination suited to the spectrum under examination can then be 
 easily found by placing this flame at different distances. 
 
 APPENDIX C. 
 
 BUNSEtf ON A METHOD OF MAPPING SPECTKA. 1 
 
 For the purpose of facilitating the numerical comparison of the 
 data of various spectrum observations, we give in Fig. 29, p. 98, 
 graphical representations of the observations which are taken 
 from the guiding lines given in chromolithograph drawings 
 of the spectra published in our former memoirs, and in which 
 the prism was placed at the angle of minimum deviation. The 
 ordinates of the edges of the small blackened surfaces, referred 
 to the divisions of the scale as abscissse, represent the intensity of 
 the several lines, with their characteristic gradations of shade. 
 These drawings were made when the slit was so broad, and the 
 flame of such a temperature, that the fine bright line upon the 
 broad Ca a band began to be distinctly visible. This breadth of 
 the slit was equal to the fortieth part of the distance between 
 the sodium line and the lithium line a. For the sake of 
 perspicuity, the continuous spectra which some bodies exhibit 
 
 i Phil. Mag., Fourth Series, vol. xxvi. p. 247. 
 H 
 
98 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. n. 
 
 S- 
 I- 
 
 5- 
 S-Ej 
 
 _Ej 
 
 8-E: 
 
 s 
 
 S-EE 
 
 ?-EE 
 
 S-EE 
 
 8- 
 
 ' g_= 
 
 8-EE 
 
 o__ZZ 
 
 8-= 
 
 _n i-H <TJ 
 
 g ^ H }zi 
 
APPEND, c.] MAPPING SPECTRA. 99 
 
 are specially represented on the upper edge of the scale, to the 
 divisions of which they are referred as abscissae. In order to 
 render these drawings, which have reference to our instrument, 
 applicable to observations upon the scale of any other .apparatus, 
 which we may call B, it is only necessary to prepare a reduced 
 scale, which is laid upon the several drawings, and used in place 
 of the divided scale given in the figure. The lines marked at the 
 bottom of Fig. 29 serve for the preparation of this new scale : 
 these lines denote the distances between the lines K a, Li a, Na, Tl, 
 Sr 8, Kb a, and K/9, measured according to the scale of our 
 instrument. The position of each of these lines is determined 
 by the edge of the line, which does not change its place on 
 altering the breadth of the slit. The position of these same 
 lines is read off on the scale of the instrument B, and the 
 corresponding number written under each. A series of fixed 
 points on the scale is thus obtained, and the complete divisions 
 for the scale of instrument B are got by interpolating the values 
 of the portions of the scale situated between the fixed points. 
 
 The sodium line is then inserted in this scale, which is pasted 
 upon a straight-edge, and the divisions numbered in tens and 
 fives. If this measure be now laid upon any one of the drawings, 
 so that the sodium line on the measure coincides with the 
 division 50 on the drawing, the scale on the measure will give 
 the position of all the lines in the particular spectrum exactly as 
 they are seen in the photographic scale of the instrument B. 
 When the position of the line under observation has in this way 
 been ascertained, it is easy to assure oneself of its exact identity 
 by means of the small prism on the slit of the spectroscope. 
 
 H 2 
 
LECTURE III. 
 
 Historical Sketch. Talbot, Herschel, Bunsen, and Kirchhoff. Dis- 
 covery of New Elements by means of Spectrum Analysis. Csesium, 
 Rubidium, Thallium, Indium : their History and Properties. 
 Spectra of the Heavy Metals. Examination of the Light of the 
 Electric Discharge. Wheatstone. Volatilization of Metals in the 
 Electric Arc. Kirchhoff, Angstrom, Thalen, and Huggins. Maps 
 of the Metallic Lines. 
 
 APPENDIX A. Spectrum Eeactions of the Kubidium and Csesium 
 Compounds. 
 
 APPENDIX B. Contributions towards the History of Spectrum Ana- 
 lysis. By G. Kirchhoff. 
 
 APPENDIX C. On the Spectra of some of the Chemical Elements. By 
 Wm. Huggins. "With Maps and Tables. 
 
 I PROPOSE to point out to you to-day the properties of 
 the new elementary bodies which have been discovered 
 by means of spectrum analysis, the principles of which 
 we considered in the last lecture. Before passing on to 
 consider this point, I wish to direct your attention, for a 
 few moments, to the history of the subject. 
 
 The experiments of which I gave you an account in 
 the last lecture, and the results derived from these ex- 
 periments, have been carried out chiefly by a German 
 chemist and a German physicist, whose important dis- 
 coveries have made the names of Bunsen and Kirchhoff 
 celebrated throughout the scientific world. 
 
LECT. in.] HISTORICAL SKETCH. 101 
 
 But although these philosophers are the real dis- 
 coverers of this method, because they carried it out with 
 all due scientific accuracy and placed it on the sure 
 foundation upon which it now rests, yet we must not 
 suppose that the ground was before their time abso- 
 lutely untrodden. No great discovery is made all at 
 once. There are always stepping-stones by which such 
 a position is reached, and it is right to know what has 
 been previously done, and to give such credit as is their 
 due to the older observers. 
 
 So long ago as 1752, Thomas Melville, while experi- 
 menting on certain coloured flames, observed the yellow 
 soda flame, although he was unacquainted with its cause. 
 In 1822 Brewster introduced his monochromatic lamp, 
 in which the soda light is used ; the first idea, however, 
 being due to Melville. A simple experiment will prove 
 to you the nature of this monochromatic soda light. I 
 have here the means of producing a very intense soda 
 flame, and I will throw the light on to this screen with 
 painted letters. You will observe that no colour is 
 noticeable in these letters. They appear in various degrees 
 of shade or intensity, but no difference of colour is 
 visible, because the light falling upon them is of a pure 
 yellow colour. Now, if I throw a small quantity of mag- 
 nesium powder into the flame, you will at once notice 
 how brightly the various colours come out. We have 
 here white light containing rays of every degree of 
 refrangibility ; hence the different colours appear, each 
 letter being able to reflect its own peculiar rays. 
 
 Sir John Herschel, in the year 1822, investigated the 
 spectra of many coloured flames, especially of the stron- 
 tium and copper chlorides, and of boracic acid, and he 
 writes in 1827 about this as follows : "The colours thus 
 
102 SPECTRUM ANALYSIS. [LECT. in. 
 
 contributed by different objects to flame afford in many 
 cases a ready and neat way of detecting extremely minute 
 quantities of them." 
 
 Fox Talbot, whose name we know as being so inti- 
 mately connected with the origin of the beautiful art of 
 photography, makes the following suggestions respecting 
 these spectra. Writing in 1826, he says: "The red fire 
 of the theatres examined in the same way gave a most 
 beautiful spectrum, with many light lines or maxima of 
 light. In the red these lines were more numerous, and 
 crowded with dark spaces between them" (these are the 
 strontium lines which you see on the diagram), " besides 
 an exterior ray greatly separated from the rest, and 
 probaMy the effect of the nitre in the composition " (this 
 is really the red potassium line caused by the nitre). 
 " In the orange was one bright line, one in the yellow, 
 three in the green, and several that were fainter." The 
 blue line which he mentions is the blue strontium line 
 which we saw so plainly. " The bright line in the yellow" 
 (our friend sodium) "is caused without doubt by the 
 combustion of sulphur." Talbot got wrong there, as did 
 many of the early observers. They could not suppose 
 that so minute a trace of sodium could produce that 
 yellow light ; and even Talbot says that the yellow line 
 must, be caused in certain cases by the presence of water. 
 He continues : " If this opinion" (about the cause of form- 
 ation of these lines) " should prove correct, and applicable 
 to the other definite rays, a glance at the prismatic 
 spectrum of a flame might show it to contain substances 
 which it would otherwise require a laborious chemical 
 analysis to detect." We cannot even now express the 
 opinion entertained at the present moment more con- 
 cisely than Talbot did in the year 1826. These early 
 
LECT. in.] HERSCHEL, TALBOT, BREfTSTER, ETC. 103 
 
 observers did not, however, determine the exact nature 
 of the substance producing the colour, inasmuch as the 
 extreme sensitiveness of this sodium reaction put them^ 
 off the scent : they could not believe that sodium was 
 present everywhere. 
 
 Both Herschel and Brewster found that the same 
 yellow light was obtained by setting fire to spirits of 
 wine diluted with water, and Talbot also mentions cases 
 in which no soda was, as he thought, present, and yet 
 this yellow line always made its appearance. Hence 
 he says, " The only matter which these substances have 
 in common is water," and he throws out the suggestion 
 that this yellow line is produced by the presence of 
 water. In February 1834 Talbot writes: "Lithia and 
 strontia are two bodies characterized by the fine red tint 
 which they communicate to the flame. The former of 
 these is very rare, and I was indebted to my friend 
 Mr. Faraday for the specimen which I subjected to the 
 prismatic analysis. Now it is very difficult to distinguish 
 the lithia red from the strontia red with the naked eye, 
 but the prism betrays between them the most marked 
 distinction which can be imagined. The strontia flame 
 exhibits a great number of red rays well separated from 
 each other by dark intervals, not to mention an orange 
 and a very definite bright blue ray. The lithia exhibits 
 one single red ray. Hence I hesitate not to say, that 
 optical analysis can distinguish the minutest portions of 
 these two substances from each other with as much 
 certainty as, if not more than, any known method." Still 
 Talbot says further on, that " the mere presence of the 
 substance, which suffers no diminution in consequence, 
 causes the production of a red and green line to appear 
 in the spectrum." 
 
104 SPECTRUM ANALYSIS. [wvi. m. 
 
 Professor William Allen Miller next made some in- 
 teresting experiments in 1845 on the spectra of coloured 
 flame produced by the metals of the alkaline earths, 
 and came still nearer to the result which we now find 
 Bunsen and Kirchhoff arrived at in 1861. Diagrams 
 of these spectra accompany the memoir, but they are 
 not characteristic enough to enable them to be used as 
 distinctive tests for the metals, owing to the fact that 
 a luminous flame was used. Hence the investigations 
 of Miller in 1845 attracted less attention than they 
 deserved. 1 The first person who pointed out this cha- 
 racteristic property of sodium was Professor Swan, in 
 1856, and it is to him that we owe the examination and 
 first accurate determination of the very great sensitive- 
 ness of this sodium reaction. So much then for the 
 history of the method as applied to the detection of the 
 alkalies and the alkaline earths. 
 
 We will now pass on to the consideration of the new 
 elements which have been discovered by spectrum ana- 
 lysis. And, in the first place, I would direct your 
 attention to the new alkaline metals discovered by Pro- 
 fessor Bunsen in 1860. Shortly after he made his first 
 experiments on the subject of spectrum analysis, Bunsen 
 happened to be examining the alkalies left from the 
 evaporation of a large quantity of mineral water from 
 Dtirkheim in the Palatinate. Having separated out aH 
 other bodies, he took some of these alkalies, and found, 
 on examining by the spectroscope the flame which this 
 particular salt or mixture of salts gave off, that some 
 bright lines were visible which he had never observed 
 
 1 See extract in Appendix B from KirchhofFs Contributions to the 
 History of Spectrum Analysis, Phil. Mag., Fourth Series, vol. xxv. 
 p. 250, 1863. 
 
LBCT. in.J CESIUM AND RUBIDIUM. 10f) 
 
 before, and which he knew were not produced either by 
 potash or soda. So much reliance did he place in this 
 new method of spectrum analysis, that he at once set to 
 work to evaporate so large a quantity as forty-four tons 
 of this water in which these new metals, which he termed 
 ccesium and rubidium, were contained in exceedingly 
 minute quantities. 
 
 In short, he succeeded in detecting and separating the 
 two new alkaline substances from all other bodies, and 
 the complete examination of the properties of their com- 
 pounds which he made with the very small quantity of 
 material at his disposal remains a permanent monu- 
 ment of the skill of this great chemist. Both these 
 metals occur in the water of the Durkheim springs. 
 I have here the numbers giving Bunsen's analysis, in 
 1,000 parts, of the mineral water of Durkheim and of 
 Baden-Baden. 
 
 The quantity of the new substance contained in the 
 water from the Dtirkheim springs is excessively small, 
 amounting in one ton to about three grains of the chlo- 
 ride of caesium and about four grains of the chloride of 
 rubidium ; whilst in the Baden-Baden spring we have 
 only traces of the caesium chloride, and a still smaller 
 quantity than in the other spring of the rubidium 
 chloride. From the forty-four tons of water which he 
 evaporated down, Bunsen obtained only about 200 grains 
 of the mixed metals. You will easily appreciate the 
 delicacy and accuracy of a method by which the presence 
 of so minute a trace of the new metals as that contained 
 in the water could be so readily detected. 
 
106 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. in. 
 
 Analysis of 1,000 jmrts of the Mineral 
 
 Water in which 
 
 the new Alkaline 
 
 Metals, Caesium and Rubidium, 
 
 were discovered 
 
 by Bunsen. 
 
 
 Diirkheim. 
 
 Ungemach, at 
 Baden-Baden. 
 
 .Calcium Bicarbonate . . . 
 
 0-28350 
 
 1-475 
 
 Magnesium Bicarbonate . . 
 
 0-01460 
 
 0-712 
 
 Ferrous Bicarbonate . . . 
 
 0-00840 
 
 o-oio 
 
 Manganous Bicarbonate . . 
 
 traces 
 
 traces 
 
 Calcium Sulphate .... 
 
 
 
 2-202 
 
 Calcium Chloride .... 
 
 3-03100 
 
 0-463 
 
 Magnesium Chloride . 
 
 0-39870 
 
 0-126 
 
 Strontium Chloride 
 
 0-00810 
 
 
 
 Strontium Sulphate 
 
 0-01950 
 
 0-023 
 
 Barium Sulphate .... 
 
 
 
 traces 
 
 Sodium Chloride .... 
 
 12-71000 
 
 20-834 
 
 Potassium Chloride .... 
 
 0-09660 
 
 1-518 
 
 Potassium Bromide .... 
 
 0-02220 
 
 traces 
 
 Lithium Chloride . . . . 
 
 0-03910 
 
 0-451 
 
 Rubidium Chloride. . . 
 
 0-00021 
 
 0-0013 
 
 Caesium Chloride .... 
 
 0-00017 
 
 traces 
 
 Alumina 
 
 0-00020 
 
 
 
 Silica 
 
 0-00040 
 
 1-230 
 
 Free Carbonic Acid . . . 
 
 1-64300 
 
 0-456 
 
 Nitrogen 
 
 0-00460 
 
 
 
 Sulphuretted Hydrogen . . 
 
 traces 
 
 
 
 Combined Nitric Acid . . 
 
 
 
 0-030 
 
 Phosphates 
 
 traces 
 
 traces 
 
 Arsenic Acid 
 
 
 traces 
 
 Aminoniacal Salts .... 
 
 traces 
 
 0-008 
 
 Oxide of Copper .... 
 
 
 
 traces 
 
 Organic Matter 
 
 traces 
 
 traces 
 
 18-28028 
 
 29-6393 
 
 Let me show you, in the first place, the colours pro- 
 duced by these two new metals when brought into a non- 
 luminous gas flame. In the last lecture we noticed the 
 beautiful violet tint which the potash flame exhibits. 
 The tint yielded by these two metals is very similar 
 
LECT. in.] SPECTRA OF RUBIDIUM AND CESIUM. 107 
 
 indeed, and in fact, not only in the character of the 
 light which they emit, but in all their chemical pro- 
 perties, the compounds of both the new bodies resemble 
 potassium compounds very closely. Here I bring a small 
 quantity of rubidium salt into the flame, and you observe 
 the beautiful purple colour with which the flame is tinged. 
 Now I throw in. a little caesium salt, and you notice we 
 get a very similar kind of tint, rather more red, but still 
 scarcely to be distinguished from the violet potash flame 
 burning alongside. 
 
 If I next show you the spectra of caesium and rubidium 
 on the screen, and compare them with the spectrum of 
 potassium (see Frontispiece, Nos. 2, 3, and 4), you will 
 see that the spectra of these three metals exhibit (in 
 accordance with their correspondence in other chemical 
 properties) a striking analogy. Each of the three metals 
 possesses a spectrum which is continuous in the middle, 
 showing that under certain circumstances gases may emit 
 light of every degree of refrangibility, and decreasing in 
 intensity towards each end. In the case of potassium the 
 continuous portion is most intense, in that of rubidium 
 less intense, and in the caesium spectrum this luminosity 
 is least. In all three we observe the most intense and 
 characteristic lines towards both the red and blue ends 
 of the spectrum. The metal rubidium, as its name 
 implies, is characterized by two splendid deep red lines 
 (see Frontispiece, No. 3), both less refrangible than the 
 potassium red line ; but the two violet lines are even 
 more characteristic, and serve as the most delicate test of 
 the presence of the metal. No less than the 0*0002 
 part of a milligramme of rubidium can be detected by 
 the spectrum reaction. The caesium spectrum is chiefly 
 characterized by the two blue lines from which it derives 
 
108 SPECTRUM ANALYSIS. [LECT. in. 
 
 its name ; they are remarkable for their brilliancy and 
 sharpness of definition : while it is singular that caesium 
 exhibits no red lines whatever. 
 
 Since the discovery of these two bodies by Bunsen in 
 1860, chemists have been on the look-out for them, and 
 have found both of them in very different situations ; 
 one of them, rubidium, being comparatively widely dis- 
 tributed. The celebrated French waters of Bourbonne- 
 les-Bains contain 0*032 grm. of chloride of caesium and 
 0*010 grm. of chloride of rubidium in one litre of water ; 
 whilst in the well-known mineral springs of Vichy, Gas- 
 tein, Nauheim, Karlsbrunn, and many more, either one 
 or both of the new metals has been discovered. And 
 here the thought strikes one, that the presence of these 
 metals, even in such minute quantities, may possibly exert 
 a not unimportant influence upon the medicinal qualities 
 and effects of the waters. Eubidium has been found to 
 be very widely diffused ; it has been found in beetroot, 
 in tobacco, in the ash of the oak (the Quercus pubescens), 
 in coffee, in tea, and in cocoa : indeed of the new metals 
 it is only rubidium which is found in vegetables and in 
 vegetable products ; whilst both new metals are found in 
 tolerably large quantities in certain minerals, especially 
 in lepidolite and petalite. 
 
 One very interesting example of the occurrence of the 
 metal caesium has been observed in a mineral termed 
 pollux, which was analysed in the year 1846 by the 
 well-known chemist Plattner, and supposed to contain 
 potassium. In calculating out the results of his analysis 
 Plattner invariably found a considerable loss, the cause 
 of which he was unable to account for. Spectrum 
 analysis has now explained this anomaly, for since the 
 discovery of the two new metals it has been found that 
 
LECT. in.] OCCURRENCE OF NEW ALKALIES. 109 
 
 it was not potassium, but the new metal caesium, which 
 was present, of the oxide of which no less than 34 per 
 cent, is contained in this mineral. The want of agree- 
 ment of the former analysis is therefore wholly attri- 
 butable to the difference of the combining weights of 
 these two bodies; that of potassium being only 39*1, 
 whilst caesium is 133 ; and if we use this last number in 
 the calculation, we find that Plattner's analysis comes 
 up exactly, as it ought to do, to 100 parts. So closely 
 indeed are caesium and potassium allied in their chemical 
 characters, that it is only by the discriminating power of 
 spectrum analysis that we have been able to ascertain 
 even the existence of the new metal. 
 
 Having once proved the existence of these two 
 new elementary bodies, Bunsen was of course easily able 
 to find the means of separating them accurately one 
 from the other and from the well-known substance 
 potassium ; and at the present day the chemical his- 
 tory and characters of these two metals and their 
 compounds are as well known as those of the common 
 alkalies. 
 
 The reaction by which Bunsen separated the new 
 metals from potassium can easily be rendered visible to 
 you. I have here a small quantity of rubidium chloride 
 in solution, and here again I have a solution of the 
 double chloride of potassium and platinum. 
 
 The chloride of rubidium and platinum is much less 
 soluble than the corresponding potassium compound, and 
 hence, if I add the potassium double-chloride to this 
 rubidium salt, I shall have a precipitation of the double 
 chloride of rubidium and platinum ; and this will indi- 
 cate to you the mode by which Bunsen separated these 
 two metals from each other. 
 
SPECTRUM ANALYSIS. [LECT. in. 
 
 Here you observe, by pouring in this solution, the 
 liquid at once becomes turbid, and we get a very con- 
 siderable quantity of a heavy yellow granular precipitate 
 of the new rubidium compound. 
 
 It is unnecessary now to enter into the analytical 
 methods by which caesium can be separated from rubi- 
 dium ; it is sufficient to state that the separation is 
 based upon the different solubilities of the tartrates of 
 the new metals, the acid tartrate of caesium being much 
 more soluble than the corresponding rubidium salt. 
 
 The isomorphous relations between the salts of rubi- 
 dium and caesium and those of potassium also point out 
 the striking chemical analogy subsisting between these 
 interesting bodies. 
 
 Shortly after the discovery of these two new alkaline 
 metals the existence of a third new elementary substance 
 was made known by our countryman Mr. Crookes. In 
 the year 1861 he sent to the Exhibition a very small por- 
 tion of a substance which he stated was a new element 
 obtained from a certain seleniferous deposit from a sul- 
 phuric acid manufactory at Tilkerode in the Hartz. This 
 body gives a most beautiful green tint to flame. If I 
 bring a small quantity of this element into the flame, you 
 see that it produces this exquisite green colour. And 
 this was the reaction by which it was discovered. Mr. 
 Crookes proved that this green light was due to some 
 new elementary body ; then he separated out the sub- 
 stance, and gave to it the name thallium, from thallus, 
 a green twig. 
 
 Now the spectrum of thallium is very distinct and 
 specific, consisting of one bright green line. I will show 
 it to you with the electric lamp. Here you see this 
 magnificent green band (Frontispiece, No. 5). The spark- 
 
LECT. in.] THALLIUM AND INDIUM. \H 
 
 spectrum of thallium is rather more complicated, as it 
 exhibits five other lines in addition to the bright one in 
 the green. 1 The line Tla possesses a wave-length of 
 5349 ten-millionths of a millimetre, and when examined 
 with a one-prism instrument appears to be partly coin- 
 cident with one of the barium lines. This apparent 
 coincidence is resolved when examined by a higher mag- 
 nifying power. The chemical properties of this substance 
 are also very remarkable. It stands about half-way 
 between lead and the alkalies, resembling in many of 
 its characters the metal lead, and it has been well de- 
 scribed by Dumas as the " ornithorhynchus " amongst the 
 metals. Thallium can, however, be perfectly separated 
 from the alkalies and lead by means of the insolubility 
 of its chloride and the solubility of its sulphate. The 
 specific gravity of thallium is ITS ; its combining weight 
 is a very high one, 204 ; and it acts as a monad metal, 
 forming an oxide having the formula T1 2 0, and a 
 chloride T1C1. 
 
 The properties of thallium have been examined by a 
 French chemist, M. Lamy, as well as by Mr. Crookes. 
 It has been found to exist in very large quantities in 
 certain varieties of iron pyrites, a substance from which 
 we manufacture almost all our sulphuric acid. 
 
 The metal thallium can be easily obtained in the 
 metallic state from its salts. This I can readily render 
 evident to you all. We can here decompose a solution 
 of the sulphate of thallium by a current of electricity, 
 and then we shall observe the metallic thallium shooting 
 out as a beautiful arborescent growth on the screen. Here 
 you see the crystals of metallic thallium stretching out 
 their long branches all over the screen. 
 
 1 Miller, Proc. Eoy. Soc. 1863, p. 407. 
 
112 SPECTRUM ANALYSIS. [LECT. in. 
 
 The soluble salts of thallium act as a cumulative poi- 
 son : they have been found in large quantities in animals 
 which have been poisoned by this substance. The method 
 for determining or detecting the presence of thallium in 
 such a poisoned animal by means of spectrum analysis is 
 extremely simple. If we had such a means of detecting 
 some of the other metallic poisons as readily as that 
 of thallium, the work of the toxicologist would be 
 extremely easy; except that under these circumstances 
 the very delicacy of the test becomes in itself a danger, 
 as the most minute trace of the poisonous metals which 
 might by chance be present would in this way be as easily 
 detected as a larger quantity. 
 
 There is still one other elementary body of which I 
 have to speak, namely, the metal indium. 
 
 Indium was discovered in 1864 by two German pro- 
 fessors, Eeich and Eichter, of the celebrated Mining- 
 School of Freiberg. It also was detected by the peculiar 
 spectrum, which consists simply of two indigo-coloured 
 lines. These lines are best seen when a bead of an 
 indium compound is held between two electrodes from 
 which a spark passes. The lines In a and In/3 fall 
 respectively upon divisions 107*5 and 140 mm. of the 
 photographic scale of the spectroscope, when Na a = 50 
 and Sr3 = 100'5. (See Frontispiece, No. 6.) It was 
 discovered in certain zinc ores, and has only been found 
 in small quantities. Its chemical and physical characters 
 have recently been carefully examined. It is a silver- 
 white metal, soft, ductile, and compact, melting at 176 C. 
 Its combining weight is 113*4 (0 = 16), and its specific 
 gravity is 7*421 ; and it forms definite compounds, 
 amongst which the trichloride InCl 3 , the yellow trioxide 
 In 2 3 , and the corresponding nitrate and sulphate, are 
 
LECT. III.] 
 
 THALLIUM AND INDIUM. 
 
 113 
 
 the most characteristic. Hence you will see that indium 
 belongs to the triad family of metals. 
 
 I can here show yuu the indigo colour which, indium 
 compounds impart to the flame ; and you now see on the 
 screen that the spectrum of indium consists of two bright 
 indigo-coloured lines, one situated in the blue and one in 
 the violet portion of the spectrum. The wave-length of 
 the blue line is, according to Muller, 4550 ten-millionths 
 of a millimetre. I need scarcely say that there is as yet 
 no notion of any practical employment of any of these 
 new substances, though chemists never can tell what 
 
 FIG. 30. 
 
 important applications of their most recondite discoveries 
 may not arise, even in the immediate future. 
 
 The subject to which I would wish in the next place 
 to direct your attention, is the mode by which we can 
 determine by spectrum analysis the presence of metals 
 proper, or heavy metals. How, for instance, can we 
 ascertain the presence of copper, or of gold, or of silver, 
 or of zinc, or of iron ? how can we volatilize these metals 
 to make them give off the light which is peculiar to each 
 one ? I have here the means of doing this. We have 
 
 i 
 
1 1 4 SPECTRUM ANALYSIS. [LKCT. in. 
 
 again to employ our most valuable agent, electricity. By 
 means of this battery and induction coil I can obtain an 
 electric spark ; and by means of the electric spark I can 
 get what I require, namely, the volatilization of these 
 metals. It is many years since the application of the 
 electric spark to this particular branch of analysis was 
 discovered. The first person who examined the nature 
 of the electric spark was Wollaston, whose name I men- 
 tioned to you in my opening lecture as having first 
 pointed out the existence of these very important dark 
 lines in the solar spectrum. But it was Faraday who 
 first declared that the electric spark consists solely of 
 the material particles of the poles and the medium 
 through which it passes. It was originally supposed that 
 electricity had some existence apart from matter ; but 
 Faraday, by a most elaborate series of experiments, dis- 
 covered that when the electric spark passes from one 
 knob of the electric machine to your hand or knuckle, a 
 quantity of matter passes too, partly consisting of the 
 brass of the pole, and partly consisting of the air and 
 moisture which exist between your knuckle and the brass 
 knob. He speaks, in his experimental researches, of the 
 electric spark as being produced by a current propagated 
 along, and by, ponderable matter, and heated in the 
 same manner, and according to the same laws, as a 
 voltaic current heats and volatilizes a metallic wire. So 
 that what we see and call the spark is really the ignition 
 of the matter which exists in this arc ; and when we take 
 a spark from the electrical machine, the particles of the 
 brass are actually carried over from the one pole to the 
 other, in this case from the pole to the knuckle. When 
 we reflect how short a space of time the spark lasts we 
 shall understand with how great a velocity these particles 
 
LECT. in.] LIGHT OF THE ELECTRIC DISCHARGE. 115 
 
 are driven forward, and we have then only to remember 
 that a great velocity implies a high temperature, in order 
 that we may be able to account for the brightness of the 
 spark. If this is so, it is evident that, when we bring 
 certain different metals in this arc, we must obtain dif- 
 ferent-coloured sparks : thus, if T bring a small quantity 
 of strontium salt into the spark, we shall have a very 
 intensely red light, due to the ignition of the peculiar 
 body strontium which is volatilized between the poles ; 
 and when I take some thallium, we have the green colour 
 characteristic of this metal. 
 
 If we examine the light of such a spark with a spec- 
 troscope, we shall find that two superimposed spectra 
 here present themselves ; the one spectrum produced by 
 the very bright points of light lying close to the poles, 
 and the other by the less luminous portion of the arc 
 lying further from the poles. The spectrum of the bright 
 points is, as we shall see, that of the metal present, 
 whilst the light from the less luminous portion in the 
 centre exhibits the spectrum of the incandescent air, and 
 shows the particular lines produced by the gases existing 
 in the atmosphere, viz. nitrogen, oxygen, and hydrogen (for 
 in the atmosphere we have constantly the vapour of water 
 present). Each gas gives us lines peculiar to itself ; and in 
 some cases, when the quantity of carbonic acid present in 
 the air is considerable, we may even get the carbon lines. 
 
 It was Sir Charles Wheatstone, in the year 1835, who 
 first pointed out that the spectra produced from the 
 sparks of different metals were dissimilar ; and he con- 
 cluded that the electric spark resulted from the volatili- 
 zation, and not from the combustion, of the matter of the 
 poles themselves, for he observed the same phenomena 
 in vacuo and in hydrogen, in which no combustion can 
 
 i 2 
 
116 SPECTR UM ANALYSIS. [LECT. in. 
 
 occur; and in 1835 he writes as follows: "These dif- 
 ferences are so obvious, that one metal may easily be 
 distinguished from another by the appearance of its 
 spark ; and we have here a mode of discriminating 
 metallic bodies more readily than that of chemical exa- 
 
 FIG. 31. 
 
 mination, and which may hereafter be employed for 
 useful purposes." 
 
 You have here a copy of the diagram (Fig. 31) pub- 
 lished in Wheatstone's paper, giving the lines which he 
 saw in the metals. Subsequent research has shown 
 
LECT. II1.J 
 
 WUEATSTONPS METAL LINES. 
 
 117 
 
 that the number of the lines peculiar to each of these 
 metals is very large, although on Wheatstone's diagram 
 but a few of these are noticeable. On this drawing you 
 see some of the bright lines of the metals mercury (Hg), 
 zinc (Zn), cadmium (Cd), bismuth (Bi), tin (Sn), and 
 lead (Pb). The letters placed above and below each 
 bright line indicate its degree of intensity : very bright, 
 bright, faint, very faint. 
 
 It was, however, chiefly through the experiments of 
 the Swedish philosopher Angstrom, that we gained an 
 intimate knowledge of the nature of the electric spark. 
 In the year 1855 Angstrom investigated 'the matter very 
 thoroughly, and pointed out the important fact which 
 I have explained, that the spark yields two superimposed 
 spectra; one derived from the metal of the poles, and 
 the other from the gas or air through which the spark 
 passes. 
 
118 SPECTJl UM ANALYSIS. [LECT. in. 
 
 Perhaps I had better show you, first of all, the beauti- 
 ful spectra of some of these metals, as I can exhibit 
 them to you on a screen ; and then explain to you the 
 nature of the spectra which we see when we look at 
 the spark through such a train of prisms as you have in 
 the large spectroscope on the table. I cannot show you 
 these lines on the screen with anything like the amount 
 of accuracy or delicacy with which we can see them 
 when we throw the image on the retina itself, for then 
 we notice the true spectra. The lines then observed are 
 excessively fine and extremely numerous, and each line 
 possesses a fixed position, and does not interfere with 
 the lines of any other metal. Still I can show you 
 something very beautiful and interesting. I will en- 
 deavour by means of the electric lamp to throw the 
 spectrum of metallic copper on the screen. 1 take a 
 small piece of metallic copper and volatilize it between 
 the incandescent carbon poles, and then you will see the 
 green bands indicative of the presence of this metal. 
 Here you observe these magnificent green bands, which 
 are characteristic of copper ; but when we examine the 
 copper spark by throwing the image into the eye, we get 
 a much more splendid effect, and see the way to a far 
 more delicate method of detecting the presence of copper. 
 In the next place I will take another carbon pole, and 
 bring a small piece of zinc into it, and we shall see that 
 zinc also gives its peculiar and beautiful lines perfectly 
 characteristic of this special metal. If we examine this 
 light by means of an accurate "spectroscope, these broad 
 bands are seen to consist of .masses of bright lines, each 
 one as fine as the most gauzy spider's web. 
 
 If I now take a mixture of zinc and copper, such as 
 brass, we shall not only get the lines of the zinc, but we 
 
LKCT. in.] BANDS OF COPPER AND ZINC. H9 
 
 shall also see the bright copper lines. I have put a small 
 piece of brass on the pole, and when I make the contact 
 I shall volatilize this brass, and the result is a spectrum 
 showing both the copper lines and the zinc lines. You 
 will notice that what I have said with respect to the 
 other metals, the alkaline earths, holds good with this, 
 that the most volatile of the metals burns out first. Now 
 we can still see the less volatile copper, but the zinc lines 
 have died away. In the same way I may show you that 
 cadmium give us a peculiar set of lines. If we volatilize 
 some metallic cadmium, we shall have a series of lines 
 somewhat resembling those of zinc, but not identical 
 with them. There you observe three bands : these are 
 the cadmium lines, something perfectly characteristic 
 and distinct. 
 
 Fox Talbot observed these metallic lines in June 1834, 
 by deflagrating thin sheets of metal by galvanism ; he 
 says : " Gold leaf and copper leaf each afforded a fine 
 spectrum exhibiting peculiar definite rays. The effect of 
 zinc was still more interesting : I observed in this instance 
 a strong red ray, three blue rays, besides several more 
 of other colours." 
 
 I will next show you the spectrum of silver. Here 
 you observe those splendid green lines, and the beautiful 
 purple lines in the distance : the latter are only visible 
 when you look at the most refrangible end for some 
 time. Nothing, surely, can be more magnificent than 
 these spectra ! These green lines are quite different in 
 position and in character from the green copper lines. 
 To exhibit that difference to you, I will put a bit of 
 copper into this silver which is chemically pure and 
 I think you will be able to see that we get the green 
 copper lines distinctly arranged alongside of the green 
 
120 SPECTRUM ANALYSIS. [LECT. in. 
 
 lines of silver. Thus, then, by means of the electric 
 lamp, many of these lines can be rendered visible, 
 although to see others distinctly we must employ a 
 delicate spectroscope, and throw the light directly into 
 the eye of the observer. 
 
 By the examination of the spark-spectrum, chemists 
 are now able to distinguish with the greatest ease between 
 the rarest metals. We are able to detect the difference 
 between erbium and yttrium, and didymium and lan- 
 thanum metals which resemble one another in their 
 properties so closely that it is extremely difficult to 
 separate them from each other by ordinary chemical 
 means. These substances all give distinct lines, and any 
 one of these substances may be detected when mixed 
 with the other : and we thus get a decisive answer as to 
 their presence. 
 
 In order to examine with accuracy the spectra of the 
 heavy metals, an arrangement, represented in Fig. 30, is 
 necessary. This consists of a powerful induction coil 
 used in conjunction with a delicate spectroscope, such as 
 that used by Kirchhoff (see page 62). The light from 
 the spark falls on to the slit, and is refracted by passing- 
 through the prisms. 
 
 For the purpose of intensifying the spark, the ends of 
 the secondary coil are placed in contact with the coat- 
 ings of a large Leyden jar. The electrodes, also of course 
 connected with the poles of the secondary coil, consist 
 of the metals under examination, either in the form of 
 wire, or of irregular pieces held by forceps on a move- 
 able stand. Many precautions must be taken, especially 
 with two sets of electrodes, as it has been found that 
 currents caused by the rapid passage of air between 
 the poles are sufficient to carry over to a second set 
 
LECT. in.] EXAMINATION OF SPARK-SPECTR UM. 121 
 
 of electrodes, placed a,t a distance of a few inches, a 
 very perceptible quantity of the materials undergoing 
 volatilization. 
 
 We are indebted to the labours of Professors Kirchhoff, 
 Angstrom, and Thalen, and Dr. Huggins, for the most 
 accurate sets of maps of the metallic lines which we 
 possess. The positions of the metallic lines have been 
 arranged by Kirchhoff with reference to the dark solar 
 lines, whilst Huggins has used the bright air lines as a 
 constant scale upon which to note the positions of the 
 metal lines ; but both experimenters use an arbitrary 
 scale of divisions by which the lines are designated. 
 Owing to the very large number of the lines of each of 
 the metals, very great care is needed in the discrimination 
 of these spectra ; still, when the eye has been trained, 
 the detection of the individual metal is perfectly certain. 
 The spectra of the following elements were mapped by 
 Kirchhoff:- 
 
 1. Sodium. 9. Strontium. 17. Antimony. 25. Aluminium. 
 
 2. Calcium. 10. Cadmium. 18. Arsenic. 26. Lead. 
 
 3. Barium. 11. Nickel. 19. Cerium. 27. Silver. 
 
 4. Magnesium. 12. Cobalt. 20. Lanthanum. 28. Gold. 
 
 5. Iron. 13. Potassium. 21. Didymium. 29. Ruthenium. 
 
 6. Copper. 14. Rubidium. 22. Mercury. 30. Iridium. 
 
 7. Zinc. 15. Lithium. 23. Silicon. 31. Platinum. 
 
 8. Chromium. 16. Tin. 24. Glucinum. 32. Palladium. 
 
 Copies of Kirchhoff's and Angstrom's maps are given 
 in Plates III., IV., and V., facing Lecture V. ; and a 
 copy of Huggins' maps is given on Plates I. and II. , at 
 the end of this lecture. The tables of reference to the 
 spectrum of each metal are found at the end of Appendix C. 
 
 The maps of two of the experimenters do not agree 
 exactly with each other, because Kirchhoff altered the 
 
122 
 
 SPECTRUM ANALYSIS. 
 
 [LKCT. in. 
 
 position of his prisms several times during the measure- 
 ments, in order to bring the different rays as nearly as 
 possible to the point of minimum deviation, whilst 
 Huggins allowed the position of his prisms to remain 
 unaltered. The spectra of the following metals have 
 been drawn by Huggins : 
 
 1. Sodium. 
 
 7. Thallium. 13. Antimony. 19. Lead. 
 
 2. Potassium. 
 
 8. Silver.. 
 
 14. Gold. 
 
 20. Zinc. 
 
 3. Calcium. 
 
 9. Tullurium. 
 
 15. Bismuth. 
 
 21. Chromium. 
 
 4. Barium. 
 5. Strontium. 
 
 10. Tin. 
 11. Iron. 
 
 16. Mercury. 
 17. Cobalt. 
 
 22. Osmium. 
 23. Palladium. 
 
 6. Manganese. 
 
 12. Cadmium. 
 
 18. Arsenic. 
 
 24. Platinum. 
 
 A very interesting fact is noticed by all the observers, 
 namely, that several of the bright lines of different 
 metals seem to coincide. When, however, these cases 
 of apparent coincidence are narrowly observed, most 
 of the lines are found to show real though slight differ- 
 ences of refrangibility. 
 
 The following still remain as unresolved coincidences 
 in Huggins' map, and future experiments with help of 
 higher magnifying powers must decide whether these and 
 similar coincidences are real or only apparent ; whether 
 the lines in question really fall upon one another, or 
 whether they only lie very close together : 
 
 Zinc and Arsenic . 
 Sodium and Lead 
 Sodium and Barium . 
 
 DIVISION 
 
 . 909 
 . 1000 
 . 1005 
 
 DIVISION 
 
 Tellurium and Nitrogen . 1366 
 Osmium and Arsenic . . 1737 
 Chromium and ^Nitrogen . 2336 
 
 These six are, then, the only cases of coincidence 
 observed by Huggins in examining many hundreds of 
 bright lines of twenty-four elements, and even these 
 may possibly disappear when investigated by a more 
 powerful instrument. 
 
LECT. in.] COINCIDENCE OF METAL LINES. 123 
 
 Thalen has quite recently published 1 an interesting 
 memoir upon the determination of the ivave-lengths of 
 the lines of the metal spectra. In Kirchhoff's and 
 Huggins' maps the bright metal lines are arranged 
 according to an arbitrary scale, but it is of great 
 interest to know the absolute position of each line, and 
 this can only be ascertained by the determination of its 
 wave-length. The spectra of no less than forty-five 
 metals are given in Thalen' s tables, and amongst them 
 are those of many rare metals not previously examined : 
 thus we find the lines of the spectra of glucinum, 
 zirconium, erbium, yttrium, thorinum, uraniun, titanium, 
 tungsten, molybdenum, and vanadium, most accurately 
 mapped. You may judge of the accuracy and value 
 of this method of examination from the fact that each 
 of these rare metals possesses a distinct and numerous 
 set of lines, none of which lines coincide with any 
 belonging to another element, and each of which may 
 therefore be considered as a separate test. 
 
 Thus the extremely rare metal vanadium yields the 
 following bright lines according to Thalen : 
 
 SPECTRUM OF VANADIUM. 
 
 WAVE LENGTH. 2 WAVE LENGTH. 2 
 
 WAVE LENGTH. 2 
 
 
 r 6240-5 
 
 r 5786-0 
 
 T5240-0 
 
 
 6134-4 
 
 5725-0 
 
 Green 1 5233-0 
 
 
 6119-0 
 
 5706-0 
 
 1 5195-0 
 
 Orange < 
 
 6109-5 
 
 5702-5 
 
 15191-5 
 
 
 60890 
 6080-0 Yell W< 
 
 5697-5 
 5668-0 
 
 , 
 
 
 L 6039-0 
 
 5626-0 
 
 
 
 
 5622-5 
 
 
 
 
 5414-0 
 
 
 Violet, 4110-0 
 
 5401-0 
 
 
 1 Annales de Chemie et Physique, Oct. 1869, ser. [4], vol. xviii. 
 p. 202. 2 In ten-millionths of a millimetre. 
 
lL'4 
 
 SP&CT&lfM ANALYSIS. 
 
 [LECT. in. 
 
 SPECTRUM OF VANADIUM (continued). 
 
 WAVE LENGTH. 1 
 
 f 4881 
 
 
 4874-5 
 
 
 48640 
 
 
 4851-0 
 
 Blue < 
 
 4843-0 
 4831-5 
 
 
 4593-0 
 
 
 4585-0 
 
 
 4579-0 
 
 '(^4576-0 
 
 Imli 
 
 WAVE LENGTH. 1 
 "4459-0 
 
 4407-5 
 4406-0 
 44005 
 4395-0 
 4389-0 
 4384-0 
 43790 
 4352-5 
 ^4340-5 
 
 WAVE TiBKGTH. 1 
 
 f4332-5 
 4329-5 
 4310-0 
 41J7-0 
 4292-5 
 4283-5 
 42770 
 4272-0 
 4268-5 
 41100 
 
 To give you a notion of the immense number of these 
 lines, I should like to show you a drawing or two : for 
 this purpose I will throw on the screen an enlarged 
 image of one of Kirchhoff's maps (Plates III. and IV. 
 preceding Lecture V.) Professor Kirchhoff was the first 
 to examine the exact character of these metallic lines, 
 and he drew an accurate map, not only of these metallic 
 lines, but of the dark lines in the spectrum of the sun ; 
 and this is a copy of one of his diagrams, to which I 
 would now briefly allude. The dark lines here represent 
 the dark lines in the sun. With these I have at present 
 nothing to do. We shall devote a subsequent lecture to 
 a detailed discussion of this most remarkable subject. 
 To-day I would simply draw your attention to the short 
 lines at the lower part of the diagram, which indicate to 
 us the positions of the bright metal lines with regard to 
 the fixed dark solar lines, these latter being taken as a 
 sort of inch-rule, by which the positions of the other 
 lines are reckoned. The lines which you see joined by a 
 horizontal line, and marked Fe (for Ferum), are the iron 
 lines ; and I beg you to notice the very large number 
 
 1 In ten millionths of a millimetre. 
 
LSCT. in.] KIIiCllHOFF'S AND HUGGINS' T.IBLKS. 125 
 
 and the very beautifully fine nature of these iron lines. 
 On Kirchhoff 's map each line is accompanied by a letter, 
 being the chemical symbol of the element to which this 
 one belongs ; here an aluminium line, here an antimony 
 line, here a calcium line, here again a number of iron 
 lines connected together ; and so I might go through all 
 these diagrams, showing the number of lines which 
 Kirchhoff has mapped, and this for only a small portion 
 of the spectrum. The one end of this diagram is in the 
 yellow, and the other end in the green ; so that we have, 
 on this map, only a very, very small portion of the 
 metal lines which would be seen if we were looking at 
 the whole length of the visible spectrum. 
 
 I would next illustrate this fact by showing you 
 another beautiful drawing of these metal lines, made by 
 our countryman Dr. Huggins (see Plates I. and II. at 
 the end of this lecture). This map, which is copied from 
 Dr. Huggins' paper in the Philosophical Transactions 
 for 1864, will also give you an idea of the very great 
 number of these metal lines. We have here about twenty 
 metals, and each pair of these horizontal lines includes 
 the spectrum of a particular metal. For instance, if 
 we take silver, here is one line, here three, here two, 
 here a number of other lines: thus we go on through the 
 whole spectrum, and have altogether a great number of 
 silver lines. On the right we have the red end, on 
 the left the blue end of the spectrum, and at the top, 
 for the sake of comparison, are the chief lines of the 
 solar spectrum and the air lines. From this table you 
 may not only form an idea of the large number of 
 metal lines existing, but you will see that the lines of 
 any one metal do not coincide or interfere with those 
 of any other. For facilitating spectroscopic research, 
 
126 SPECTRUM ANALYSIS. [LECT. in. 
 
 Dr. Marshal Watts has compiled a most useful set of 
 tables in his Index of Spectra, in which all the reliable 
 observations of the positions of the bright lines are 
 mapped according to their wave-lengths. 
 
 The lines which are thus easily visible, are by no 
 means all the peculiar rays which such highly heated 
 metallic vapours emit, for Professor Stokes has shown 
 that the bright sparks from poles of iron, aluminium, and 
 magnesium give off light of so high a degree of refran- 
 gibility, that distinct bands are situated at a distance 
 beyond the last visible violet ray, ten times as great 
 as the length of the whole visible spectrum from red to 
 violet ! These bands cannot of course be seen under 
 ordinary circumstances, but when allowed to fall on a 
 fluorescent body, such as paper moistened by quinine 
 solution, they can easily be rendered visible ; or we may 
 photograph them, and make them leave their impression 
 on the sensitive film. In order that these highly refran- 
 gible rays may be seen, no glass lenses or prisms must 
 be used, as the rays of the highest refrangibility cannot 
 pass through glass : quartz, on the other hand, permits 
 them to pass ; hence all the lenses and prisms must be 
 made of quartz. 
 
 In new and interesting subjects like those which now 
 occupy our attention, the mind is very apt to be led 
 away into speculations, which, however engrossing .they 
 may prove, are foreign to the spirit of the exact scientific 
 inquirer. Such speculations might in this case have 
 special reference to the possibility or probability of 
 arriving, by the help of the observations of the bright 
 lines which bodies give us, at some more intimate know- 
 ledge of the composition of the so-called elements. We 
 might speculate as to the connection, for instance, between 
 
LECT. in.] SELECTIVE ABSORPTION. 127 
 
 the wave-lengths of the various bright lines of the metal 
 and the particular atomic weight of the substance ; or 
 we might ask, Can we find out any relation between the 
 spectra of the members of some well-known chemical 
 family, as of the alkaline metals, potassium, sodium, 
 caesium, and rubidium ? Such questions as these natu- 
 rally occur to every one. At present, however, this 
 subject is in such an undeveloped state that these specu- 
 lations are useless, because they are premature, and the 
 data are insufficient ; but doubtless a time will come 
 when these matters will be fully explained, and a future 
 Newton will place on record a mathematical theory of 
 the bright lines of the spectrum as a striking monument 
 of the achievements of exact science. 
 
 In the next lecture I purpose to show how this method 
 of analysis can be applied to the detection of the non- 
 metallic elements, whether they be solid, liquid, or 
 gaseous at the ordinary temperature. 
 
128 SPECTRUM ANALYSIS. [LECT. in. 
 
 LECTURE III. APPENDIX A. 
 
 SPECTRUM REACTIONS OF THE RUBIDIUM AND CAESIUM 
 COMPOUNDS, i 
 
 CESIUM and rubidium are not precipitated either by sulphuretted 
 hydrogen or by carbonate of ammonium. Hence both metals 
 must be placed in the group containing magnesium, lithium, 
 potassium, and sodium. They are distinguished from magnesium, 
 lithium, and sodium, by their reaction with bichloride of platinum, 
 which precipitates them like potassium. Neither rubidium nor 
 caesium can be distinguished from potassium by any of the usual 
 reagents. All three substances are precipitated by tartaric acid 
 as white crystalline powders; by hydrofluosilicic acid as trans- 
 parent opalescent jellies ; and by perchloric acid as granular 
 crystals : all three, when not combined with a fixed acid, are 
 easily volatilized on the platinum wire, &nd they all three tinge 
 the flame violet. The violet colour appears indeed of a bluer 
 tint in the case of potassium, whilst the flame of rubidium is of 
 a redder shade, and that of caesium still more red. These slight 
 differences can, however, only be perceived when the three 
 flames are ranged side by side, and when the salts undergoing 
 volatilization are perfectly pure. In their reactions, then, with 
 the common chemical tests, these new elements cannot be dis- 
 tinguished from potassium. The only method by means of 
 which they can be recognized when they occur together is that 
 of spectrum analysis. 
 
 The spectra of rubidium and caesium are highly characteristic, 
 and are remarkable for their great beauty (Frontispiece, Nos. 
 3 and 4). In examining and measuring these spectra we have 
 
 1 Extract from Professors KirchhofF and Bunsen's Second Memoir on Chemical 
 Analysis by Spectrum Observations (Phil. Mag., vol. xxii. 1861). 
 
APPEND. A.] SPECTRUM OF RUBIDIUM. 129 
 
 employed an improved form of apparatus (Fig. 33), which in 
 every respect is much to be preferred to that described in our 
 first memoir. In addition to the advantages of being more 
 manageable and producing more distinct and clearer images, it 
 is so arranged that the spectra of two sources of light can be 
 examined at the same time, and thus, with the greatest degree 
 of precision, compared both with one another and with the 
 numbers on a divided scale. 
 
 In order to obtain representations of the spectra of caesium 
 and rubidium corresponding to those of the other metals which 
 we have given in our former paper, we have adopted the follow- 
 ing course. 
 
 Fro. 33. 
 
 We have placed the tube g (Fig. 33) in such a position that a 
 certain division of the scale, viz. No. 100, coincided with Fraun- 
 hofer's line D in the solar spectrum, and then observed the position 
 of the dark solar lines A, B, c, D, E, F, G, H, on the scale : these 
 several readings we called A, B, c, &c. An interpolation scale 
 was then calculated and drawn, in which each division corre- 
 sponded to a division on the scale of the instrument, and in which 
 the points corresponding to the observations A, B, c, &c. were 
 placed at the same distances apart as the same lines on our first 
 drawings of the spectrum. By help of this scale, curves of the 
 new spectra were drawn (Fig. 26, p. 67), in which the ordinates 
 express the degrees of luminosity at the various points on the 
 
 K 
 
130 SPECTRUM ANALYSIS. [LECT. in. 
 
 scale, as judged of by the eye. The lithographer then made the 
 designs represented in the Frontispiece from these curves. 
 
 As in our first memoir, so here we have represented only those 
 lines which, in respect to position, definition, and intensity, 
 serve as the best means of recognition. We feel it necessary to 
 repeat this statement, because it has not unfrequently happened 
 that the presence of lines which are not represented in our 
 drawings has been considered as indicative of the existence of 
 new bodies. 
 
 We have likewise added a representation of the potassium 
 spectrum to those of the new metals for the sake of comparison, 
 so that the close analogy which the spectra of the new alkaline 
 metals bear to the potassium spectrum may be at once seen. 
 All three possess spectra which are continuous in the centre, and 
 decreasing at each end in luminosity. In the case of potassium 
 this continuous portion is most intense, in that of rubidium less 
 intense, and in the cesium spectra the luminosity is least. In 
 all three we observe the most intense and characteristic lines 
 towards both the red and blue ends of the spectrum. 
 
 Amongst the rubidium lines, those splendid ones named Eb a 
 and Eb @ are extremely brilliant, and hence are most suited for 
 the recognition of the metal. Less brilliant, but still very cha- 
 racteristic, are the lines Eb S and Eb y. From their position 
 they are in a high degree remarkable, as they both fall beyond 
 Fraunhofer's line A ; and the outer one of them lies in an ultra- 
 red portion of the solar spectrum, which can only be rendered 
 visible by some special arrangement. The other lines, which are 
 found on the continuous part of the spectrum, cannot so well 
 be used as a means of detection, because they only appear when 
 the substance is very pure, and when the luminosity is very 
 great. Nitrate of rubidium and the chloride, chlorate, and per- 
 chlorate of rubidium, on account of their easy volatility, show 
 these lines most distinctly. Sulphate of rubidium and similar 
 salts also give very beautiful spectra. Even silicate and phos- 
 phate of rubidium yield spectra in which all the details are 
 plainly seen. 
 
 The spectrum of caesium is especially characterized by the two 
 
APPEND. A.] SPECTRA OF C^STUM AND RUBIDIUM. 131 
 
 blue lines Cs a and Cs ft : these lines are situated close to the 
 blue strontia line Sr 8, and are remarkable for their wonderful 
 brilliancy and sharp definition. The line Cs 8, which cannot be 
 so conveniently used, must also be mentioned. The yellow and 
 green lines represented on the figure, which first appear when the 
 luminosity is great, cannot so well be employed for the purpose 
 of detecting small quantities of the caesium compounds ; but 
 they may be made use of with advantage as a test of the purity 
 of the caesium salt under examination. They appear much more 
 distinctly than do the yellow and green lines in the potassium 
 spectrum, which, for this reason, we have not represented. 
 
 As regards distinctness of the reaction, the caesium compounds 
 resemble in every respect the corresponding rubidium salts : 
 the chlorate, phosphate, and silicate gave the lines perfectly 
 clearly. The delicacy of the reaction, however, in the case of 
 the caesium compounds, is somewhat greater than in that of the 
 corresponding compounds of rubidium. In a drop of water 
 weighing four milligrammes, and containing only O0002 milli- 
 gramme of chloride of rubidium, the lines Kb a and Kb /3 can 
 only just be distinguished ; whilst 0'00005 milligramme of the 
 chloride of caesium can, under similar circumstances, easily be 
 recognized by means of the lines Cs a and Cs (S. 
 
 If other members of the group of alkaline metals occur 
 together with caesium and rubidium, the delicacy of the reaction 
 is of course materially impaired, as is seen from the following 
 experiments, in which the mixed chlorides contained in a drop 
 of water, weighing about four milligrammes, were brought into 
 the flame on a platinum wire. 
 
 When 0'003 milligramme of chloride of caesium was mixed 
 with from 300 to 400 times its weight of the chloride of 
 potassium or sodium, it could be easily detected. Chloride of 
 rubidium, on the other hand, could be detected with difficulty 
 when the quantity of chloride of potassium or chloride of sodium 
 amounted to from 100 to 150 times the weight of the chloride 
 of rubidium employed. 
 
 0*001 milligramme of chloride of caesium was easily recog- 
 nized when it was mixed with 1,500 times its weight of chloride 
 
 K 2 
 
132 SPECTR UM ANAL YS1S. [LECT. in. 
 
 of lithium ; whilst O'OOl milligramme of chloride of rubidium 
 could not be recognized when the quantity of chloride of lithium 
 added exceeded 600 times the weight of the rubidium salt. 
 
 APPENDIX B. 
 
 CONTRIBUTIONS TOWARDS THE HISTORY OF SPECTRUM 
 ANALYSIS. BY G. KIRCHHOFF. 1 
 
 In my " Kesearches on the Solar Spectrum and the Spectra of 
 the Chemical Elements," 2 I made a few short historical remarks 
 concerning earlier investigations upon the same subject. In 
 these remarks I have passed over certain publications in silence 
 in some cases because I was unacquainted with them, in 
 others because they appeared to me to possess no special 
 interest in relation to the history of the discoveries in question. 
 Having become aware of the existence of the former class, and 
 seeing that more weight has been considered to attach to the 
 'latter class of publications by others than by myself, I will now 
 endeavour to complete the historical survey. 
 
 Amongst those who have devoted themselves to the ob- 
 servation of the spectra of coloured flames, I must in the first 
 place mention Herschel and Talbot. Their names need special 
 notice, as they pointed out with distinctness the service which 
 this mode of observation is capable of rendering to the chemist. 
 For a knowledge of their researches I am mainly indebted to 
 Professor W. Allen Miller, who gave an extract from them in a 
 lecture republished in the number of the Chemical News for 
 19th April, 18(j2. It is there stated that in the volume of 
 the Transactions of the Royal Society of Edinburgh for 1822, at 
 page 455, Herschel shortly describes the spectra of chloride of 
 strontium, chloride of potassium, chloride of copper, nitrate of 
 
 i Communicated to the Phil. Mag., Fourth Series, vol. xxv. p. 250, by Professor 
 Roscoe. 
 
 - Published by Macmillan and Co., Cambridge and London, 1862. 
 
p FEND. B.] KIE CUB OFF'S HISTORICAL SKETCH. 133 
 
 copper, and boracic acid. The same observer says, in his article 
 on Light in the " Encyclopaedia Metropolitan^" 1827, page 438 : 
 " Salts of soda give a copious and purely homogeneous yellow ; of 
 potash, a beautiful pale violet." He then describes the colours 
 given by the salts of lime, strontia, lithia, baryta, copper, and 
 iron, and continues : " Of all salts, the muriates succeed the best, 
 from their volatility. The same colours are exhibited also when 
 any of the salts in question are put (in powder) into the wick of 
 a spirit-lamp. The colours thus communicated by the different 
 bases to flame afford in many cases a ready and neat way of 
 detecting extremely minute quantities of them. The pure earths 
 when violently heated, as has recently been practised by Lieut. 
 Drummond, by directing on small spheres of them the flames of 
 several spirit-lamps, urged by oxygen gas, yield from their 
 surfaces lights of extraordinary splendour, which, when examined 
 by prismatic analysis, are found to possess the peculiar definite 
 rays in excess which characterize the tints of flames coloured by 
 them ; so that there can be no doubt that these tints arise from 
 the molecules of the colouring matter, reduced to vapour and 
 in a state of violent ignition." 
 
 Talbot says : 1 " The flame of sulphur and nitre contains a red 
 ray which appears to me of a remarkable nature. This red ray 
 appears to possess a definite refrangibility, and to be charac- 
 teristic of the salts of potash, as the yellow ray is of the salts of 
 soda, although, from its feeble illuminating power, it is only to 
 be detected with a prism. If this should be admitted, I would 
 further suggest, that whenever the prism shows a homogeneous ray 
 of any colour to exist in aflame, this ray indicates the formation 
 or the presence of a definite chemical compound" Somewhat 
 further on, in speaking of the spectrum of red fire and of the 
 frequent occurrence of the yellow line, he says : " The other lines 
 may be attributed to the antimony, strontia, &c. which enter 
 into this composition. For instance, the orange ray may be the 
 effect of the strontia, since Mr. Herschel found in the flame of 
 muriate of strontia a ray of that colour. If this opinion should 
 be correct, and applicable to the other definite rays, a glance at 
 
 1 Brcwster's Journal of Science, vol. v. 1826; Chemical News, April 27, 1SGL 
 
134 SPECTRUM ANALYSIS. [LECT. TIT. 
 
 the prismatic spectrum of a flame may show it to contain 
 substances which it would otherwise require a laborious chemical 
 analysis to detect." In a subsequent communication l the same 
 physicist, after a striking description of the spectra of lithium 
 and strontium, continues : " Hence I hesitate not to say that 
 optical analysis can distinguish the minutest portions of these 
 two substances from each other with as much certainty as, if 
 not more than, any other known method." 
 
 In these expressions the idea of " chemical analysis by 
 spectrum observations " is most clearly put forward. Other 
 statements, however, of the same observers, occurring in the 
 same memoirs from which the foregoing quotations are taken 
 (but not mentioned by Professor Miller in his abstract), flatly 
 contradict the above conclusions, and place the foundations of 
 this mode of analysis on most uncertain ground. 
 
 Herschel, in page 438 of his article on Light, almost imme- 
 diately before the words quoted above, says : " In certain cases 
 when the combustion is violent, as in the case of an oil-lamp 
 urged by a blowpipe (according to Fraunhofer), or in the upper 
 part of the flame of a spirit-lamp, or when sulphur is thrown 
 into a white-hot crucible, a very large quantity of a definite and 
 purely homogeneous yellow light is produced ; and in the latter 
 case forms nearly the whole of the light. Dr. Brewster has also 
 found the same yellow light to be produced when spirit of wine, 
 diluted with water, and heated, is set on fire." 
 
 Talbot states : " Hence the yellow rays may indicate the 
 presence of soda ; but they nevertheless frequently appear where 
 no soda can be supposed to be present." 2 He then mentions 
 that the yellow light of burning sulphur, discovered by Herschel, 
 is identical with the light of the flame of a spirit-lamp with 
 a salted wick, and states that he was inclined to believe that 
 the yellow light which occurred when salt was strewed upon 
 a platinum foil placed in a flame " was owing to the water of 
 crystallization rather than to the soda : but then," he continues, 
 " It is not easy to explain why the salts of potash, &c. should 
 
 1 Phil. Mag. 1834, vol. iv. p. 114 ; Chemical News, April 27, 1861. 
 
 2 Brcwster's Journal, vol. v. 1826. 
 
APPEND, i).] KLRCHHOFF'S HISTORICAL SKETCH. 135 
 
 not produce it likewise. Wood, ivory, paper, &c., when placed 
 in the gas flame, give off, besides their right flame, more or 
 less of this yellow light, which I have always found the same 
 in its characters. The only principle which these various bodies 
 have in common with the salts of soda is water ; yet I think that 
 the formation or presence of water cannot be the origin of this 
 yellow light, because ignited sulphur produces the very same, a 
 substance with which water is supposed to have no analogy." 
 " It may be worth remark," he adds in a note, " though probably 
 accidental, that the specific gravity of sulphur is 1/99, or almost 
 exactly twice that of water." " It is also remarkable," he con- 
 tinues in the text, " that alcohol burnt in an open vessel, or in 
 a lamp with a metallic wick, gives but little of the yellow light; 
 while, if the wick be of cotton, it gives a considerable quantity, 
 and that for an unlimited time. (I have found other instances of 
 a change of colour in flames, owing to the mere presence of the 
 substance, which suffers no diminution in consequence. Thus a 
 particle of muriate of lime on the wick of a spirit-lamp will 
 produce a quantity of red and green rays for a whole evening 
 without being itself sensibly diminished.)" 1 
 
 In a later portion of the memoir he attributes the yellow 
 line in one place to the presence of soda salts, in another to 
 that of sulphur. Thus, in the above-mentioned statement 
 concerning the spectrum of red fire, he says, " The bright line 
 in the yellow is caused, without doubt, by the combustion of 
 the sulphur." 2 
 
 Hence we must admit that the conclusion that the aforesaid 
 yellow line can be taken as a positive proof of the presence of 
 sodium compounds in the flame can in no way be deduced from 
 Herschel and Talbot's researches. On the contrary, the nume- 
 rous modes in which the line is produced would rather point to 
 the conclusion that it is dependent upon no chemical constituent 
 of the flame, but arises by a process whose nature is unknown, 
 
 1 Brewster's Journal, vol. v. 1 826. 
 
 2 A short statement of Herschel and Talbot's results, as here quoted, was made 
 by me in a lecture at the Royal Institution on April 5, 1862, and reprinted in the. 
 Chemical Netcs for May 10, 1862. H. E. R. 
 
136 SPECTRUM ANALYSIS. [LECT. in. 
 
 which may occur, sometimes more easily, sometimes with diffi- 
 culty, with the most different chemical elements. If we accept 
 such an explanation concerning this yellow line, we must form 
 a similar opinion respecting the other lines seen in the spectrum, 
 which were far more imperfectly examined ; and in this we 
 should be strengthened by the statement of Talbot, that a piece 
 of chloride of calcium by its mere presence in the wick of a flame, 
 and without suffering any diminution, causes a red and a green 
 line to appear in the spectrum. 
 
 The experiments of Wheatstone, 1 Masson, Angstrom, Van 
 der Willigen, and Pliicker upon the spectra of the electric spark 
 or electric light (to which I have already referred in my "Be- 
 searches on the Solar Spectrum and Spectra of the Chemical 
 Elements," Macmillan, London, 1862, p. 8), as well as those of 
 Uespretz, 2 from which the physicist concluded that the posi- 
 tions of the bright lines in the spectrum of the light from a' 
 galvanic battery were unaltered by variation of the intensity of 
 the current, might serve to support the view that the bright 
 lines in the spectrum of an incandescent gas are solely depen- 
 dent upon the chemical constituents of the gas ; but they 
 could not be considered as proof of such an opinion, as the con- 
 ditions under which they were made were, for this purpose, too 
 complicated, and the phenomena occurring in an electric spark 
 too ill understood. The demonstrative power of the above ex- 
 periments as regards the question at issue is rendered less cogent 
 by the difference visible in the colour of the electric light in dif- 
 ferent parts of a Geissler's tube; by the circumstance noticed by 
 Van der Willigen, who obtained different spectra by passing an 
 electric spark from the same electrodes through gas of constant 
 chemical composition, if the density of the gas was varied within 
 sufficient limits ; and lastly by an observation which Angstrom 
 cursorily mentions. This physicist says: 3 "Wheatstone has 
 
 1 Wheatstone not merely experimented with the spark from an electrical 
 machine, but likewise with the voltaic induction-spark. (Report of the British 
 Association, 1835 ; Chemical News, March 23 and March 30, 1861.) 
 
 2 Comptes Piendus, vol. xxxi. p. 419 (1850). 
 
 3 Pogg. Ann. vol. xciv. p. 150 (translated in Phil. Mag. for May 1855). 
 
APPEND. B.] KIRCHHOFF'S HISTORICAL SKETCH. 137 
 
 already noticed that when the poles consist of two different 
 metals the spectrum contains the lines of both metals. Hence 
 it became of interest to see whether a compound of these metals, 
 especially a chemical compound, also gives the lines of both 
 metals, or whether the compound is distinguished by the occur- 
 rence of new lines. Experiment shows that the first supposition 
 is correct. The sole difference noticed is, that certain lines were 
 wanting, or appeared with less distinctness ; but when they were 
 observed, they always appeared in the position in which they 
 occurred in the separate metals." In the following sentence, 
 however, he states, " That in the case of zinc and tin the lines 
 in the blue were somewhat displaced in the direction of the 
 violet end, but the displacement was very inconsiderable." Had 
 such a displacement, however small, really occurred, we must 
 conclude either that the bright lines of the electric spark obey 
 other laws than those of a glowing gas, or that these latter 
 are not solely dependent on the separate chemical constituents 
 of the gas. 
 
 The question at issue respecting the lines of incandescent 
 gases could only be satisfactorily solved by experiments carried 
 out under the most simple conditions such, for instance, as the 
 examination of the spectra of flames. Observations of this kind 
 were made in the year 1845 by Professor W. Allen Miller, but 
 they do not furnish any contribution towards a solution of the 
 question. Dr. Miller has the merit of having first published 
 diagrams of the spectra of flames ; * but these diagrams are but 
 slightly successful, although, in a republication in the Chemical 
 News 2 of the paper accompanying these drawings, Mr. Crookes 
 remarks : " We cannot, of course, give the coloured diagrams 
 with which it was originally illustrated ; but we can assure our 
 readers that, after making allowance for the imperfect state 
 of chromolithography sixteen years ago, 3 the diagrams of the 
 spectra given by Professor Miller are more accurate in several 
 respects than the coloured spectra figured in recent numbers 
 
 1 Phil. Mag. for August 1845. 2 Chemical News, May 18, 1861. 
 
 3 Prof. Miller's diagrams are not printed by chromolithography, but, as is seen 
 on inspection, tinted by hand. H. E. K. 
 
138 SPECTRUM ANALYSIS. [LECT. in. 
 
 of the scientific periodicals." In reply to this ''assurance" 
 of Mr. Crookes I only have to remark that, by way of experi- 
 ment, I have laid Professor Miller's diagrams before several 
 persons, conversant with the special spectra, requesting them 
 to point out the drawing intended to represent the spectrum 
 of strontium, barium, and calcium respectively, and that in no 
 instance have the right ones been selected. 
 
 Swan was the first who endeavoured experimentally to prove 
 whether the almost invariably occurring yellow line may be 
 solely caused by the presence of sodium compounds. In his 
 classical research " On the Spectra of the Flames of the Hydro- 
 carbons" 1 (referred to both in my "Researches" and in the 
 paper published by Bunsen and myself) Swan shows how small 
 the quantity of sodium is which produces this line distinctly ; 
 he finds that this quantity is minute beyond conception, and 
 he concludes : " When indeed we consider the almost universal 
 diffusion of the salts of sodium, and the remarkable energy with 
 which they produce yellow light, it seems highly probable that 
 the yellow line R, which appears in the spectra of almost all 
 flames, is in every case due to the presence of minute quantities 
 of sodium." 
 
 The strict subject-matter of Swan's investigation was the 
 comparison of the spectra of flames of various hydrocarbons. 
 " The result of his comparison has been, that in all the spectra 
 produced by substance, either of the form C 1 H S or of the 
 form C r H B O t , the bright lines have been identical. In some 
 cases, indeed, certain of the very faint lines which occur in 
 the spectrum of the Bunsen lamp were not seen. The bright- 
 ness of the lines varies with the proportion of carbon to hydro- 
 gen in the substance which is burned, being greatest where 
 
 there is most carbon The absolute identity which is thus 
 
 shown to exist between the spectra of dissimilar carbo-hydrogen 
 compounds is not a little remarkable. It proves, 1st, that the 
 position of ths lines in the spectrum does not vary with the 
 proportion of carbon and hydrogen in the burning body as 
 when we compare the spectra of light carburetted hydrogen, CH 2 , 
 
 1 Trans. Roy. Soc. of Edinburgh, vol. xxi. \\. 414. 
 
APPEND. D.] KIRCIIHOFf'S HISTORICAL SKETCH. 139 
 
 olefiant gas, C 2 H 2 , and oil of turpentine, C 20 H 8 ; and 2dly, 
 that the presence of oxygen does not alter the character of 
 the spectrum: thus ether, C 4 H 5 0, and wood spirit, C 2 H 4 2 , 
 give spectra which are identical with those of paraffin, C 20 H 2o , 
 and oil of turpentine, C 20 H 8 . 
 
 " In certain cases, at least, the mechanical admixture of other 
 substances with the carbo -hydrogen compound does not affect 
 the lines of the spectrum. Thus I have found that a mixture 
 of alcohol and chloroform burns with a flame having a very 
 luminous green envelope an appearance characteristic of the 
 presence of chlorine and no lines are visible in the spectrum. 
 When, however, the flame is urged by the blowpipe, the light 
 of the envelope is diminished, and the ordinary lines of the 
 hydrocarbon spectrum become visible." 
 
 In this research Swan has made a most valuable contri- 
 bution towards the solution of the proposed question as to 
 whether the bright lines of a glowing gas are solely dependent 
 upon its chemical constituents ; but he did not answer it posi- 
 tively, or in its most general form; he did not indeed enter 
 upon this question, for he wished to confine his investigation 
 to the spectra of the hydrocarbons, and was only led to the 
 examination of this yellow line by its frequent occurrence 
 in these spectra. 
 
 No one, it appears, had clearly propounded this question 
 before Bunsen and myself; and the chief aim of our common 
 investigation was to decide this point. Experiments which 
 were greatly varied, and were for the most part new, led us to 
 the conclusion upon which the foundations of the "chemical 
 analysis by spectrum observations " now rest. 
 
140 SPECTRUM ANALYSIS. [LECT. in 
 
 APPENDIX C. 
 
 ON THE SPECTRA OF SOME OF THE CHEMICAL ELEMENTS. 
 BY WILLIAM HUGGINS, ESQ. F.R.A.S. 1 
 
 1. I have been engaged for some time, in association with 
 Professor W. A. Miller, in observing the spectra of the fixed stars. 
 For the purpose of accurately determining the position of the 
 stellar lines, and their possible coincidence with some of the bright 
 lines of the terrestrial elements, I constructed an apparatus in 
 which the spectrum of a star can be observed directly -with any 
 desired spectrum. To carry out this comparison, we found no maps 
 of the spectra of the chemical elements that were conveniently 
 available. The minutely detailed and most accurate maps and 
 tables of Kirchhorf were confined to a portion of the spectrum, 
 and to some only of the elementary bodies ; and in the maps of 
 both the first and the second part of his investigations, the elements 
 which are described are not all given with equal completeness 
 in different parts of the spectrum. But these maps were the less 
 available for our purpose because, since the bright lines of the 
 metals are laid down relatively to the dark lines of the solar 
 spectrum, there is some uncertainty in determining their position 
 at night, and also in circumstances when the solar spectrum 
 cannot be conveniently compared simultaneously with them. 
 Moreover, in consequence of the difference in the dispersive 
 power of prisms, and the uncertainty of their being placed 
 exactly at the same angle relatively to the incident rays, 
 tables of numbers obtained with one instrument are not alone 
 sufficient to determine lines from their position with any other 
 instrument. 
 
 Phil. Trans. 1864, p. 1U9. 
 
APPEND, c.] EXTRACTS FROM HUGGINS' RESEARCHES. 141 
 
 It appeared to me that a standard scale of comparison such as 
 was required, and which, unlike the solar spectrum, would be 
 always at hand, is to be found in the lines of the spectrum of 
 common air. Since in this spectrum about a hundred lines are 
 visible in the interval between a and H, they are sufficiently 
 numerous to become the fiducial points of a standard scale to 
 which the bright lines of the elements can be referred. The 
 air spectrum has also the great advantage of being visible, 
 together with the spectra of the bodies under observation, 
 without any increased complication of apparatus. 
 
 2. The optical part of the apparatus employed in these 
 observations consists of a spectroscope of six prisms of heavy 
 glass. The prisms were purchased of Mr. Browning, optician, 
 of the Minories, and are similar in size and in quality of glass 
 to those furnished by him with the Gassiot spectroscope. They 
 all have a refracting angle of 45. They increase in size from 
 the collimator; their faces vary from 17 inch by 1'7 inch to 1/7 
 inch by 2 inches. 
 
 The six dispersing prisms and one reflecting prism were 
 carefully levelled, and the former adjusted at the position of 
 minimum deviation for the sodium line D. The train of prisms 
 was then enclosed in a case of mahogany, marked a in the 
 diagram (Fig. 34), having two openings, one for the rays from 
 the collimator &, and the other for their emergence after having 
 been refracted by the prisms. These openings are closed with 
 shutters when the apparatus is not in use. By this arrangement 
 the prisms have not required cleansing from dust, and their 
 adjustments are less liable to derangement. The collimator I 
 has an achromatic object-glass by Eoss of 1/75 inch diameter, 
 and of 10'5 inches focal length. The object-glass of the 
 telescope, which is of the same diameter, has a focal length of 
 16'5 inches. The telescope moves along a divided arc of brass, 
 marked in the diagram c. The centre of motion of the telescope 
 is nearly under the centre of the last face of the last prism. 
 The eyepiece was removed from the telescope, and the centre 
 of motion was so adjusted that the image of the illuminated 
 lens of the collimator, seen through the train of prisms, remained 
 
142 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. in. 
 
 approximately concentric with the object-glass of the telescope, 
 whilst the latter was moved through an extent of arc equal to 
 the visible spectrum. All the pencils emerging from the last 
 prism, therefore, with the exception of those of the extreme re- 
 frangible portion of the spectrum, are received nearly centrically 
 on the object-glass of the telescope. The total deviation of the 
 light in passing through the train of prisms is, for the ray D, 
 about 198. The interval from A to H corresponds to about 
 21 14' of arc upon the brass scale. 
 
 3. The measuring part of the apparatus consists of an arc of 
 
 FIG. 34. 
 
 brass, marked c in the figure, divided to intervals of 15". The 
 distance traversed by the telescope in passing from one to the 
 other of the components of the double sodium line D is 
 measured by five divisions of 15" each. These are read by a 
 vernier. 
 
 Attached to the telescope is a wire micrometer by Dollond. 
 This records sixty parts of one revolution of the screw for the 
 interval of the double sodium line. Twelve of these divisions 
 of the micrometer, therefore, are equal to one division of the 
 scale upon the arc of brass. The micrometer has a cross of 
 
APPEND, c.] MAPPING THE METAL LINES. 143 
 
 strong wires placed at an angle of 45 nearly with the lines of 
 the spectrum. The point of intersection of these wires may be 
 brought upon the line to be measured by the micrometer screw, 
 or by a screw attached to the arm carrying the telescope. For 
 the most part the observations were read off from the scale, and 
 the micrometer has been only occasionally employed in the 
 verification of the measures of small intervals. The sexagesimal 
 readings of the scale, giving five divisions to the interval of the 
 double line D, have been reduced to a decimal form, the units of 
 which are intervals of 15" ; and these are the numbers given in 
 the Tables. An attempt was made to reduce the measures to 
 the scale of Kirchhoff's Tables, but the spectra are not found 
 to be superposable on his. This is due, in great part, probably 
 to the prisms in his observations having been varied in their 
 adjustment for different parts of the spectrum. The eyepieces 
 are of the positive form of construction. One, giving the power 
 of 15, is by Dollond; the other, of about 35, is by Cook. 
 
 4. The excellent performance of the apparatus is shown by 
 the great distinctness and separation of the finer lines of the 
 solar spectrum. All those mapped by Kirchhoff are easily seen, 
 and many others in addition to these. The whole spectrum is 
 very distinct. The numerous fine lines between a and A are 
 well defined. So also are the groups of lines about and beyond 
 G. H is seen, but with less distinctness. 
 
 As, with the exception of the double potassium line near A, 
 no lines have been observed less refrangible than a, the maps 
 and Tables commence with the line a of the solar spectrum and 
 extend to H. 
 
 The observations are probably a little less accurate and com- 
 plete near the most refrangible limit. Owing to the feebleness 
 of the illumination of this part of the spectrum, the slit has 
 to be widened ; and, moreover, the cross-wires being seen with 
 difficulty, the bisection of a line exactly is less certain. 
 
 5. For all the observations the spark of an induction coil has 
 been employed. This coil has about fifteen miles of secondary 
 wire, and was excited by a battery of Grove's construction, 
 sometimes two, at others four cells having been employed. 
 
144 SPECTRUM ANALYSIS. [LECT. HI. 
 
 Each of these cells has thirty-three square inches of acting 
 surface of platinum. With two such cells the induction spark 
 is three inches in length. A condenser is connected with the 
 primary circuit, and in the secondary a battery of Leyden jars 
 is introduced. Nine Leyden jars, the surface of each of which 
 exposes 140 square inches of metallic coating, were employed. 
 These are arranged in three batteries of three jars each, and 
 the batteries are connected in polar series. 
 
 The metals were held in the usual way with forceps. The 
 nearness of the electrodes to each other, their distance from the 
 slit, and the breadth of the latter were varied, to obtain in each 
 case the greatest distinctness. The amount of separation of 
 the electrodes was always such that the metallic lines under 
 observation extended across the spectrum. The two sets of 
 discharging points were arranged in the circuit in series. 
 
 6. Some delay was occasioned by the want of accordance of 
 the earlier measures, though the apparatus had remained in one 
 place and could have suffered no derangement. These differ- 
 ences are supposed to arise from the effect of changes of 
 temperature upon the prisms and other parts of the apparatus. 
 This source of error could not be met by a correction applied 
 to the zero point of measurement, as the discordances observed 
 corresponded, for the most part, to an irregular shortening and 
 elongation of the whole spectrum. 
 
 The principal air lines were measured at one time of observing, 
 during which there was satisfactory evidence that the values of 
 the measures had not sensibly altered ; and these numbers have 
 been preserved as the fiducial points of the scale of measures. 
 The lines of the spectra of the metals have been referred to the 
 nearest standard air line, so that only this comparatively small 
 interval has been liable to be affected by differences of tem- 
 perature. Upon these intervals the effect of such changes of 
 temperature as the apparatus is liable to be subjected to is not, 
 I believe, of sensible amount with the scale of measurement 
 adopted. Ordinarily, for the brighter portion of the spectrum, 
 the width of the slit seldom exceeded inch : when this 
 width had to be increased in consequence of the feebler illumi- 
 
APPEND, c.] MAPPING THE METAL LINES. 145 
 
 nation towards the ends of the spectrum, the measure of the 
 nearest air line as seen in the compound spectrum was again 
 taken, and the places of the lines of the metal under observation 
 were reckoned relatively to this known line. 
 
 By this method of frequent reference to the principal air lines 
 the measures are not sensibly affected by the errors which might 
 have been introduced from the shifting of the lines in absolute 
 position in consequence of alterations either in the width of the 
 slit, in the place and direction of the discharge before the slit, 
 or in the apparatus from variations of temperature, flexure, or 
 other causes. 
 
 The usual place of the electrodes was about 'V inch from the 
 slit, though occasionally they were brought nearer to the slit. 
 When they are placed in such close proximity, the sparks charge 
 the spectroscope by induction ; but the inconvenience of sparks 
 striking from the eyepiece to the observer may be prevented by 
 placing the hand upon the apparatus, or putting the latter into 
 metallic communication with the earth. 
 
 The spectrum of comparison was received by reflection from a 
 prism placed in the usual manner over one-half of the slit. As 
 the spectrum of the discharge between points of platinum, when 
 these are not too close, is, with the exception of two or three 
 easily recognized lines, a pure air spectrum, this was usually 
 employed as a convenient spectrum of comparison for dis- 
 tinguishing those lines in the compound spectrum which were 
 due to the particular metal employed as electrodes. The 
 measures, however, of all the lines, including those of the air 
 spectrum itself, were invariably taken from the light received 
 into the instrument directly, and in no case has the position of 
 a line been obtained by measures of it taken in the spectrum 
 of the light reflected into the slit by the prism. 
 
 The measures of all the lines were taken more than once ; 
 and, when any discordance was observed between the different 
 sets, the lines were again observed. The spectra of most of the 
 metals were remeasured at different times of observing. In 
 the measurement of the solar lines for their co-ordination with 
 the standard air spectrum, the observations were repeated on 
 
 L 
 
146 SPECTRUM ANALYSIS. [LECT. in. 
 
 several different occasions during the progress of the experiments 
 The line G of the solar table is the one so marked by Kirchhoff. 1 
 When no change in the instrument could be detected, the 
 measures came out very closely accordant, for the most part 
 identical. The discordances due to small alterations in the in- 
 strument itself were never greater than five or six of the units of 
 measurement in the whole arc of 4,955 units. As the apparatus 
 remained in one place free from all apparent derangement, these 
 alterations are probably due to changes of temperature. The 
 method employed to eliminate these discordances has been 
 described. 
 
 Throughout the whole of the bright portion of the spectrum 
 the probable error of the measures of the narrow and well- 
 defined lines does not, I believe, exceed one unit of the scale. 
 
 NOTES TO THE TABLES. 
 
 Upon a re-examination of the Tables I found that it frequently 
 occurred that lines of two or more metals were denoted by the 
 same number. It appeared probable that these lines having a 
 common number were not coincident, but only approximated in 
 position within the limits of one unit of the scale employed ; and 
 besides, there might be small errors of observation. I therefore 
 selected about fifty of these groups of lines denoted by common 
 numbers, and compared the lines of each group, the one with the 
 other, by a simultaneous observation of the different metals to 
 which they belong. Some of the lines were found to be too 
 faint and ill-defined to admit of being more accurately deter- 
 mined in position relatively to each other. 
 
 The following lines appear with my instrument to be coincident: 
 
 Zn, As 909 Na, Ba 1005 0, As 1737 
 Na, Pb 1000 Te, N 1366 Cr, N 2336 
 
 Of a much larger number of groups, the lines were, by careful 
 scrutiny, observed to differ in position by very small quantities, 
 
 1 Untersiichnngen ii. d. Sonnenspectrum, 2 Theil, Taf. iii. Berlin, 1863. 
 
APPEND. C.] 
 
 NOTES TO THE TABLES. 
 
 147 
 
 corresponding for the most part to fractional parts of the unit of 
 measurement adopted in the Tables. These are : 
 
 Sn 459 Ba 621 '5 Te 657 
 Sb458'8 Bi 621 Cd 656 
 
 Bi 837-3 Co 937 
 Sb 837 Sh 937-5 
 
 Sb 1081 Te 1485 Zn 1797 
 Au 1081-5 Fe 1485-3 Pd 1798 
 
 Ca 515 
 Au516 
 
 Ca622 
 Fe 623 
 
 Te545-5 Au643 
 Sb 545 Ca 642 
 Fe 641 -5 
 
 Sn 581 Ca 649 
 Bi 588-5 Sn 649 
 
 Fe 696-2 Cd 889 Au 981 Ca 1256 Tl 1505 Tl 1851 
 Zn 696 Sb 889*5 Sb 981'5 Co 1257 Mnl505'5 Bi 1851'3 
 
 Ca 1031 Fe 1276 Pd 1548 Sb 1900 
 
 Pdl031-5 Ag 1276-3 Fe 1548'2 Pb 1900'3 
 Agl031'2 N 1900 
 
 Pb 1031-1 
 
 Sb 765 As 
 Te 765-3 Mn 903 
 
 Na 818-3 Ca 921-2 Te 1030'3 Fe 1438 
 Ca 818 Tl 921 Te 1438 -3 
 
 Co 921 
 
 Sb 921-1 
 
 Pb 1593-3 
 Fe 1593 
 
 L 2 
 
148 
 
 SPECTRUM ANALYSIS. 
 
 [LECT in. 
 
 TABLE 
 
 Solar. 
 
 Air. 
 
 Na. 
 
 K. 
 
 Ca. 
 
 Ba. 
 
 Sr. 
 
 Mn. 
 
 Tl. 
 
 ^g- 
 
 Te. 
 
 Sn. 
 
 F 
 
 a 322 
 B 449 
 
 C 589-5 
 
 Dl 1000 
 D2 1005 
 
 N 565-52 
 H 589-54 h 
 
 N 629-52 
 
 NO 8072 h, d 
 
 N 9591 
 N 9676 
 N 9754 
 N 9781 
 
 
 4182 s 
 422 B 
 
 
 441-7 s 
 
 3652 g 
 4442 s 
 
 
 
 
 4593 s 
 49H s 
 
 5811 s 
 
 6231 s 
 641 ' s 
 
 667- s 
 
 673' s 
 674- n 
 083- s 
 696- s 
 
 709-' s 
 719- s 
 726- s 
 75S- s! 
 763- s 
 772' s 
 
 
 
 515-7 8 
 
 486-7 g 
 
 523-7 s 
 532-7 s 
 
 4802 s 
 
 
 
 
 
 549-5 s 
 5631 s 
 
 ... 
 
 ... 
 
 ... 
 
 545-34 n 
 
 ... 
 
 727-5 s 
 "63-5 s 
 
 622-5 s 
 6251-5 s 
 637-7 s 
 
 6422 8 
 649-7 s 
 
 6553 s 
 
 599-2 s 
 709-2 s 
 723-2 s 
 
 8131 s 
 8184 s 
 
 5731 8 
 6081 s 
 621-57 s 
 
 5952 s 
 6192 s 
 
 : 
 
 5964 s 
 
 ... 
 
 : 
 
 
 
 
 
 
 
 6451 8 
 
 655 h 
 
 
 ... 
 
 ... 
 
 ... 
 
 6437 s 
 
 
 
 
 
 657-37 s 
 
 7041 s 
 
 6694 s 
 6811 s 
 6841 s 
 692-5 s 
 703-2 s 
 705-5-5 s 
 723 h 
 745-2 s 
 760 h 
 777 h 
 807-5 s 
 8561 s 
 
 
 
 
 
 
 
 
 
 
 
 704 : 2 s 
 
 837 \ h 
 843 / h 
 
 
 
 
 
 7681 h 
 
 690-2 s 
 762-2 s 
 
 6931 s 
 703-5' n 
 
 7352* s 
 765- 33 n 
 
 7743 s 
 
 
 
 8181-5 s 
 8211 s 
 
 8401-5 g 
 
 8433 s 
 
 859-2 s 
 863-2 s 
 
 8472 s 
 8792 s 
 
 
 
 
 
 829= s 
 852- s 
 S69- s 
 9W s 
 937- s 
 053- s 
 995- s 
 
 I 
 
 
 
 
 
 
 
 
 882 h 
 921-2-2 s 
 
 934 h 
 
 
 
 
 
 ... 
 
 8942 s 
 
 
 9081-5 s 
 9251-5 s 
 9431-5 s 
 993-5 s 
 
 
 
 
 924'" h 
 94H h 
 9453 s 
 
 9093-5 s 
 9132-5 s 
 9152-5 s 
 
 Q212 s 
 9606 s 
 
 899-5 s 
 943-5 s 
 
 9171 s 
 9-27-5 n 
 945-36 s 
 9711-5 s 
 
 ::: 
 
 10008 s 
 10058 s 
 
 
 
 
 
 
 ... 
 
 ... 
 
 10051 n 
 
 
 
 
 
 
 
 
 
 
 
 Solar. 
 
 Air. 
 
 Na. 
 
 K. 
 
 Ca. 
 
 Ba. 
 
 Sr. 
 
 Mn. 
 
 Tl. 
 
 Ag. 
 
 Te. 
 
 Sn. 
 
 The character of the lines is indicated as follows : 
 
 A line sharply defined at the edges, and narrow when the slit is narrow, s 
 
 A band of light, denned as a line, but remaining, even with a narrow slit, nebulous at the edges, n. 
 
 A haze of light irresolvable into lines, h. 
 
 Double baud, too close for measurement, d. 
 
 The comparative intensity of the lines is indicated by the smaller figures placed in the position 
 of exponents against the numbers in the Tables. The scale extends from 1 to 10, and includes 
 fractional parts of unity to represent the very faint lines. 
 
APPEND. C.J 
 
 UUGGINS* TABLES. 
 
 143 
 
 rom a to D. (See Plates I. and II.) 
 
 Cd. 
 
 Sb. 
 
 Au. 
 
 Bi. 
 
 Hg- 
 
 Co. 
 
 As. 
 
 Pb. 
 
 Zn. 
 
 Cr. 
 
 Os. 
 
 I'd. 
 
 rt. 
 
 
 3963 n 
 
 
 
 
 
 
 1 
 
 
 
 
 
 
 
 458-51 n 
 
 
 
 
 
 
 
 
 
 
 
 
 
 4753 s 
 
 
 4734 s 
 
 
 
 
 
 
 
 
 
 
 3024 s 
 
 4873 s 
 
 ... 
 
 ... 
 
 
 
 ... 
 
 480 3 s 
 
 
 
 
 
 
 
 501-5 n 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 516-5 s 
 
 
 
 
 
 
 
 
 
 
 
 
 5171 s 
 
 
 
 
 
 
 542-57 s 
 
 
 
 
 
 
 
 
 535-5 s 
 
 
 
 
 
 
 
 
 
 
 
 
 5451 n 
 
 541- 5 s 
 
 5723 s 
 
 
 
 
 
 
 5411 
 
 
 
 
 
 6141 n 
 
 
 531.51 h 
 
 
 
 
 
 577-5 n 
 
 
 
 
 
 
 6201 n 
 
 
 
 
 
 
 
 
 
 
 
 
 U398 n 
 
 
 ... 
 
 6214 s 
 
 ... 
 
 6451 n, d 
 
 ... 
 
 ... 
 
 ... 
 
 621-5 n 
 
 
 
 
 
 6401 n 
 
 
 
 
 
 
 
 
 
 
 
 
 356 s 
 
 
 643-5 s 
 
 
 
 
 
 ... 
 
 6967 s 
 
 640-5 n 
 
 64U s 
 
 
 
 
 
 
 
 
 
 6721 n 
 
 
 
 
 
 
 
 
 
 659-5 s 
 
 
 
 
 
 ... 
 
 ... 
 
 6541 n 
 
 
 
 
 
 6792 h 
 
 
 
 6851 n 
 
 "01-5 S 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 7071 n 
 
 
 
 
 
 685-5 s 
 
 
 
 
 
 
 6971 n 
 
 731-2 g 
 
 
 
 
 
 
 
 689-6 s 
 
 
 
 
 
 
 
 7591 n 
 
 
 
 
 
 
 
 ... 
 
 7191 n 
 
 
 
 
 745-5 s 
 
 
 
 7821 s 
 
 
 741-7 s 
 
 
 
 
 7092 n 
 
 727-5 s 
 
 
 
 
 
 
 
 
 
 762-2 s 
 
 
 
 7392 n 
 
 734-5 s 
 
 
 
 763-2 s 
 
 
 
 
 
 
 
 
 
 7653 n 
 
 
 
 
 
 SI Of? n 
 
 8981 s 
 
 
 8171 n 
 
 
 
 
 ... 
 
 
 7473 s 
 
 
 8267 n 
 
 844 h 8331 n 
 
 
 8555 n 
 
 
 
 837-2 s 
 
 
 ... 
 
 7871 h 
 
 
 837-35 n 
 
 
 
 8503 n 
 
 
 
 8431-5 n 
 
 
 
 
 ... 
 
 796-5 h 
 
 
 8845 n 
 
 863-2 n 
 
 865-7 s 
 
 
 
 
 
 
 
 
 
 8192 n 
 
 
 
 
 891-7 _s 
 
 8702 n 
 
 
 
 S56-7 n 
 
 
 
 
 389- 5- 5 i 
 
 8377 n 
 
 
 P87-5 g 
 
 
 
 
 
 8951 s 
 
 
 
 
 
 3181 I 
 
 8717 n 
 
 
 
 
 
 
 
 
 
 
 
 
 )531 
 
 8S93 n 
 
 
 S<>01 
 
 
 
 908-83 n 
 
 
 9095 n 
 
 
 
 
 913 h 
 
 61 
 
 921- 18 n 
 
 951-5 s 
 
 9391 h 
 
 
 9211 g 
 
 
 9242 n 
 
 
 
 
 
 
 
 937- 52 n 
 
 Q5Q.5 S 
 
 9431 h 
 
 
 9 %) 3-2 s 
 
 
 
 
 
 <)29-7 s 
 
 
 
 
 981-5ln 
 
 981-7 s 
 
 
 ... 
 
 931-5 s 
 
 
 
 
 
 
 
 039 li 
 
 
 988- 53 n 
 
 
 
 
 
 
 
 
 
 
 
 950-5 s 
 
 
 
 
 
 
 985 s g 
 
 
 
 
 
 
 995 i 
 
 958-5 
 
 
 1000-53i 
 
 
 
 
 
 
 10001 n 
 
 10012 g 
 
 
 
 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1005 
 
 
 Cd. 
 
 Sb. 
 
 Au. 
 
 Bi. 
 
 Hg. 
 
 Co. 
 
 As. 
 
 Pb. 
 
 Zn. 
 
 Cr. 
 
 Os. 
 
 Pd. 
 
 "i 
 
150 
 
 SPECTRUM ANALYSIS. 
 
 TLECT. nr. 
 
 TABLE 
 
 Solar, 
 
 Air. 
 
 Na. 
 
 K. 
 
 Ca. 
 
 Ba. 
 
 Sr. 
 
 Mn. 
 
 Tl. 
 
 Ag- 
 
 Te. 
 
 Sn. 
 
 I 
 
 D2 1005 
 
 rr, /1599 
 
 E \1600 
 
 N 1100-5 
 N 11181 
 N 1135-2 
 N 11502 
 N 117H 
 N" 11778 
 N 11801 
 N 11877 
 
 N 1294-5 
 N 1302-5 
 N 13101-5 
 N 1314-5-5 
 N 1319-2 
 N 13491-2 
 
 N 13661 
 
 N 1383-5 
 N 1394-7 
 
 N 1502-2 
 N 1516-2 
 
 N 1537-2 
 
 
 10491 n 
 1065-5 n 
 10731-5 n 
 
 10313-5 s 
 
 10346 s 
 10571 s 
 10961 s 
 
 1061-5 s 
 
 
 
 
 
 1076'lOn 
 
 1011 
 1030 
 1090 
 
 1225 
 
 1236 
 1247 
 1251 
 1261 
 1274 
 1276 
 133S 
 1383 
 1391 
 1400 
 1413 
 1419 
 1421 
 1434 
 1438 
 1445 
 1446 
 1456 
 1459 
 1467 
 14S1 
 1485 
 1486 
 1486 
 1488 
 1532 
 1537 
 1541 
 1545 
 1560 
 1574 
 1582 
 1593 
 1599 
 1600 
 
 1 
 
 ::: 
 
 10552 s 
 1099'.5n 
 
 1031-2-2 s 
 
 1030-3-5 s 
 10352 s 
 
 HUT n 
 11221 s 
 
 
 
 
 
 1102-6 B 
 
 11692 s 
 11741 s 
 
 
 ... 
 
 11191 s 
 
 
 
 
 1207- 5 n 
 
 11517 n 
 12046' n 
 
 12192 s 
 12608 n 
 
 
 
 ::: 
 
 ' 
 
 12031 n 
 12271-5 s,t 
 
 1268-2 s 
 
 1301*2' s 
 13052-5 s 
 13113 s 
 13243 s 
 
 13413' s 
 1349-7 h 
 13593 s 
 13654 s 
 13972-5 s 
 
 1425-2 s 
 14671-5 h 
 
 ... 
 
 13281 n 
 
 1247-5 S 
 1249-5 s 
 12521-5 s 
 12562-5 s 
 1258-5-5 s 
 1260-4 s 
 1265-7 s 
 
 1335-7 s 
 15061 s 
 
 13084 s 
 13271 s 
 
 1351-5 s 
 
 12891* s 
 
 :." 
 
 1223-2 n 
 1227-7 n 
 1240-3 s 
 1257-7 s 
 1276-3-5 s 
 
 12301* 6 
 12704' s 
 
 ... 
 
 ... 
 
 1286-53 s 
 
 ... 
 
 12848 n 
 
 
 
 
 
 
 13291-5 n 
 
 
 
 
 
 
 
 
 
 1376'i' s 
 1413-7 s 
 14281 s 
 1438-7 s 
 1443-7 s 
 14522 s 
 
 13561 s 
 
 13722' s 
 13807 s 
 1421-3 s 
 1435-3 s 
 1446 h 
 
 13574* 8 
 13664 s 
 13964 s 
 
 1438-34 s 
 
 14841 s 
 
 ... 
 
 1456-2 s 
 1473-53 s 
 1505-5-5 s 
 15154 s 
 
 1559 \ . 
 1571 / h 
 
 15059 s 
 
 " 
 
 14854 s 
 
 154S : 23 s 
 
 15623* s 
 
 15062 n 
 15201 h 
 15244 n 
 15761 n 
 
 
 
 
 
 
 
 1599-54 s 
 
 
 
 
 
 
 
 Solar. 
 
 Air. 
 
 Na. 
 
 K. 
 
 Ca. 
 
 Ba. 
 
 Sr. 
 
 Mn 
 
 Tl. 
 
 Ag. 
 
 Te. 
 
 Sn. 
 
APPEND. C.] 
 
 HUG GIFS' TABLES. 
 
 151 
 
 From D to E. (See Plates I. and II.) 
 
 Oft. 
 
 Sb. 
 
 Au. 
 
 Bi. 
 
 Hg. 
 
 Co. 
 
 As. 
 
 Pb. 
 
 Zn. 
 
 Cr. 
 
 Os. 
 
 Pd. 
 
 rt. 
 
 
 
 101H n 
 10252 s 
 
 1026*2 n 
 
 10081 -5 n 
 1019-5 11 
 
 
 
 10153 n 
 
 
 
 1091 s 
 
 1023-3 s 
 1031-5 h 
 
 lose'-*'' s 
 
 1068 h 
 1084'" h 
 
 1127-3 s 
 11291 s 
 1185-5 s 
 
 1199-5 s 
 
 1212-5 s 
 
 1219) h 
 1233 f ' 
 1240-5-5 s 
 124S-5 s 
 1259 -5 -7s, c 
 
 12811-5 s 
 12991 s 
 13031-5 n 
 13311-5 n 
 .\380l-5 s 
 
 1412-5 s 
 14C6 2 s 
 14S2-5 s 
 
 loll' 5 s 
 1548-5 S 
 
 1569 3 S 
 
 1041-5 
 1045-5 
 
 1073 -7 C 
 
 1367-7.. 
 
 1459-5$ 
 1484-5 
 
 15613 J 
 
 
 
 1031-14 g 
 
 
 
 1041 -5 s 
 1057 '5s 
 
 10454 8 
 
 10591 n 
 
 
 
 10421 11 
 
 
 
 ... 
 
 
 1060-3 n 
 
 ... 
 
 
 
 
 
 10811 n 
 
 1081 "5 -6 s 
 
 ... 
 
 1074 h 
 
 ... 
 
 
 1055-5 n 
 10941 n 
 
 1062 -5s 
 111*0-5 s 
 11 22 -5 11 
 
 10811 1, 
 10871 h 
 10901 h 
 
 1093*5 s 
 11411 8 
 
 ::: 
 
 1145-5 n 
 
 11581 n 
 1189 -5n 
 
 110&1 s 
 1199-5 s 
 
 11436 n 
 11973 n 
 
 1083-58 n 
 l]00-58ii 
 
 11772 n 
 
 ... 
 
 1090 -5n 
 
 
 
 
 12037 n 
 
 ... 
 
 
 12121 s 
 10401-5 s 
 
 
 
 12071 h 
 12144 n 
 12201 n 
 
 11:794 n 
 1383*3 n 
 
 1?66* : 5 n 
 
 12931 s 
 1305*8 s 
 
 12521 n 
 
 
 1039 2 s 
 1043-2 s 
 
 1207-5 s 
 1217-5 s 
 1257-7 s 
 
 
 
 
 
 
 1231 -5 n 
 125/-5ii 
 
 12409 
 1279*3 n 
 
 1269-5 n 
 
 ... 
 
 12641 s 
 
 
 
 
 
 
 
 
 
 
 
 ... 
 
 ... 
 
 
 
 
 
 
 12831 n 
 
 
 13222 s 
 
 13611 s 
 14011-5 s 
 1470-5 s 
 14831 s 
 14911 s 
 1496-2 s 
 
 12916 n 
 
 ... 
 
 
 
 1473i0n 
 
 1457* h 
 14713 n 
 
 ... 
 
 1395*1 h 
 1453*1 h 
 
 138510 n 
 
 
 
 
 
 13486 n 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1405-5 s 
 14321-5 s 
 
 14211 -5 n 
 1487-5 n 
 
 1500-52 s 
 1501-52 s 
 1508-2 s 
 15144 s 
 1525 -5 n ,d 
 1534-5 s 
 1539-3 s 
 1543-2 s 
 1549-5 s 
 1573-2 s 
 
 1443*1 n 
 14651 n 
 
 15296 n 
 15771 n 
 
 ... 
 
 1519-5n 
 
 14391-5 s 
 
 1507*5-7 s 
 15101 s 
 
 1532*i* s 
 1567*i' s,d 
 1594-7 s 
 
 151710] 
 15561 n 
 
 1501 
 
 ".'. 
 
 14951 h 
 
 
 
 
 1583-5 n 
 
 1579-2 s 
 1584-2 s 
 15861-5 s 
 1591-5 s 
 
 .'.'.' 
 
 
 ... 
 
 15937 n 
 
 
 
 
 
 Cd. 
 
 Sb. 
 
 Au 
 
 Bi. 
 
 Hg. 
 
 Co. 
 
 As. 
 
 Zn. 
 
 Or. 
 
 Pd. 
 
 Pt. 
 
152 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. in. 
 
 TABLE III. 
 
 Solar, 
 
 Air. 
 
 Na. 
 
 K. 
 
 Ca. 
 
 Ba. 
 
 Sr. 
 
 Mn. 
 
 TL 
 
 Ag. 
 
 Te. 
 
 Sn. 
 
 Fe. 
 
 (1599 
 E 11600 
 
 (1708 
 6 1723 
 (1731-5 
 
 F 2200 
 
 O 1678-5 
 
 O 1699-5 
 N 1713 h 
 N 1718 h* 
 N 1721 h 
 
 1737-3 
 
 N 1860-5 
 
 N 19003 
 N 1929-7 
 N 1941-5 
 N 1951-5 
 N 1956-5 
 N 1960-510 
 N 196710 
 N 1978-5 
 N 1990-3 
 
 20435 
 O 2060-7 
 N 2079-5 
 O 2089 -i> 
 O 2119-5 
 N 2140-5 
 2145-5 
 N 2168-5 
 
 O 2181-5 
 N 2192-3 
 
 ... 
 
 16053 s 
 1609-5 s 
 16121-5 s 
 
 17021 s 
 
 
 
 
 
 
 
 
 1603-5 B 
 1608-5 s 
 1613-3 a 
 1621-3 g 
 1632-3 s 
 16451 a 
 16531 a 
 1662-5 s, d 
 1691-3 s 
 1696-3 s 
 1698-5 s 
 1713-7 s 
 17281 8 
 1731-5 a 
 17533 s 
 1767-7 s 
 1775-5 s 
 1821 h 
 
 ... 
 
 16173 s 
 1638 8 
 16511-5 s 
 16561-5 s 
 16591-5 s 
 16651 s 
 17451 8 
 
 1617-8 8 
 
 
 
 
 
 ... 
 
 16755 n 
 
 1658-5 n 
 
 16572 n 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 
 17474 n 
 
 ... 
 
 ... 
 
 
 17461 n 
 1753 -5n 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 17731 n 
 
 ... 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1817-5 
 
 ... 
 
 18514 n 
 
 ... 
 
 ... 
 
 18213 n 
 
 ... 
 
 ... 
 
 1907-7 s 
 
 ... 
 
 ... 
 
 ... 
 
 18851 a 
 
 ... 
 
 1909-5 n 
 
 ... 
 
 ... 
 
 1935-3 s 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1991 h 
 
 
 
 
 
 
 
 
 
 
 19401-5 s 
 20361-5 s 
 
 
 
 
 
 
 
 
 
 
 .".' 
 
 !.'.' 
 
 20759n 
 
 202U s 
 
 20293 8 
 2060 h 
 21451 s 
 
 21761 5 B 
 
 
 19992 h 
 
 ... 
 
 ... 
 
 
 ... 
 
 21462 s 
 
 
 
 
 
 
 
 '". 
 
 ... 
 
 20921 s 
 2098-7 s, d 
 
 21471 8 
 
 ... 
 
 ... 
 
 ... 
 
 2133% 
 
 
 ... 
 
 ... 
 
 ... 
 
 
 
 2172-7 
 
 
 218Q1-5 s 
 21651 s 
 
 
 
 
 ... 
 
 K. 
 
 
 
 
 
 
 
 
 
 21911 h 
 
 ""* 
 
 Solar. 
 
 Air. 
 
 Na. 
 
 Ca. 
 
 Ba. 
 
 Sr. 
 
 Mn. 
 
 Tl. 
 
 Ag. 
 
 Te. 
 
 Sn. 
 
 Fe. 
 
 * When the induction spark is taken in oxygen, a faint line is seen nearly in the position of 
 the nitrogen line 1718. Since the lines of oxygen have a diminished intensity when the spark 
 passes in air, this line would be too faint to be distinctly observed in the air spectrum, in which 
 it occurs in a position of close proximity to brighter lines of nitrogen. 
 
APPEND. C.] 
 
 HUGO INS' TABLES. 
 
 153 
 
 From E to F. (See Plates I. and II.) 
 
 Cd. 
 
 Sb. 
 
 Au. 
 
 Bi. 
 
 Hg. 
 
 Co. 
 
 As. 
 
 Pb. 
 
 Zn. 
 
 Cr. 
 
 08. 
 
 Pd. 
 
 Pt. 
 
 17471 S 
 184310s 
 
 
 
 
 
 1602-3 8 
 
 
 
 1605-51 a 
 16071 s 
 1619-5 s 
 1626-5 B 
 1640-5 s 
 
 1657-7 s 
 16774 s 
 16803 s 
 1681 -5s 
 
 17492 n 
 1815-7 n 
 
 20971 s 
 
 21561 s 
 
 2175-7 s 
 2181-3 s 
 2198-6 s 
 
 1683'-5 s 
 1859-5 s 
 
 1617-5 s 
 16225 s 
 16421-5 s 
 1674-7 s 
 
 17352 s 
 
 17981-3 s 
 18071 s 
 
 1873-5 s 
 21751 5 s 
 
 16531 s 
 1689 -3 s 
 
 18791 s 
 
 16363 h 
 16011 s 
 
 17153 h 
 17653 h 
 
 16475 g 
 
 167510 n 
 16851 n 
 
 17597 n 
 1787 n 
 
 1662-3 h 
 1777-5. h 
 
 16043 s 
 1617-5 s 
 1619-3 s 
 1622-5 s 
 1626-3 e 
 16423 s 
 1650-5 s 
 16701-5 3 
 1685-5 s 
 1699-5 s 
 1707-6 s 
 1743-5 8 
 1756-5 8 
 1781 n 
 1813 h 
 
 16484 n 
 17371 n 
 
 18145 n 
 
 16851 s 
 16981 n 
 
 1735-5 n 
 
 16261 n 
 1645-6 n 
 
 1743-5 n 
 
 1790-6 n 
 1797-5 n 
 
 1845-5 n 
 18591 n 
 1893-5 n 
 
 2016-5 n 
 20918 n 
 21108 n 
 
 2191-5 n 
 
 18033 h 
 18491 s 
 
 1869-8 s 
 
 18341 n 
 185135 n 
 
 '". 
 
 
 
 1857-5 h 
 1876-3 e 
 1887-3 B 
 
 1925-5 s 
 
 19932 n 
 
 1900 -32 n 
 
 ... 
 
 19002 h 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 19192 h 
 
 
 19791 li 
 
 
 20513 n 
 
 
 20151 h 
 
 20331 h 
 
 2021-3 s 
 
 ... 
 
 2105-5 n 
 21191 n 
 
 2101-5 h 
 
 
 21531 n 
 
 ... 
 
 ... 
 
 21713 n 
 
 
 
 
 
 
 
 
 21863 s 
 
 
 '". 
 
 ... 
 
 
 
 
 
 
 
 
 
 
 
 Cd. 
 
 Sb. 
 
 Au. 
 
 Bi. 
 
 Hg. 
 
 Co. 
 
 As. 
 
 Pb. 
 
 Zn. 
 
 Cr. 
 
 OS. 
 
 Pd. 
 
 Pt. 
 
154 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. in. 
 
 TABLE IV. 
 
 Solar. 
 
 Air. 
 
 Na. 
 
 K. 
 
 Ca. 
 
 Ba. 
 
 Sr. 
 
 Mn. 
 
 Tl. 
 
 Ag. 
 
 Te. 
 
 Sn. 
 
 Fe, 
 
 F2200 
 
 G3597 
 
 H5277 
 
 N 2205-5 
 2213-3. 
 N 2221-3 
 N 23052 
 N 23361 
 N 2350-7 
 O 2502-7 n 
 O 2512-7 n 
 O 2563-5 n 
 O 2597-5 n 
 O 26262 
 N, 26422 d 
 N 26693 
 N 26891 
 N 27071 
 N 27221-5 
 N 27381-5 
 O 27481 
 O 27661 
 N 2856 h 
 N 29041 . 
 N 2978 f n 
 N 30091 
 N 80111 
 N 3056 h 
 O 3086 h 
 N 3144 d 
 N 3174\ , 
 N 3219 f h 
 O 32381 n 
 O 32411 i 
 N 3292 1 
 33951 i 
 O, N 34562 n 
 O 35601 n,d 
 O 3710 h 
 N 3863 h 
 N 8991 h 
 O 40591 
 O 40871 
 N 4145 h 
 O 4232 
 N 42631 n 
 N 4330 h 
 O 43952 
 N" 44731 n 
 N 45051 n 
 O 46151 n 
 O 46391 n 
 N 4821 h 
 N 5077-7 
 
 ... 
 
 226Q2 n 
 
 ... 
 
 ... 
 
 2131 s 
 
 2541 '5s 
 2911-7 s 
 23431 '5 s 
 2410-5 s 
 24271 s 
 24691 s 
 27265 n 
 
 22676 s 
 23 135 s 
 2.i793 s 
 23855 8 
 24015 s 
 24331 g 
 24561 s 
 2492 h 
 
 23792 n 
 24374 n 
 
 
 22451 h 
 2341-5 h 
 2497 h 
 
 25951 n 
 26131 n 
 
 22053 n 
 2777 2 n 
 
 2781-5 
 
 - 
 
 ... 
 
 ;;; 
 
 2459-5 s 
 
 2535-58 
 
 
 
 
 
 27301 n 
 27391 n 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ... 
 
 ... 
 
 2777-5 s 
 2784-3 n 
 2792-2 s 
 
 
 
 
 
 
 
 
 ... 
 
 28569 s 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 2875 1) 
 
 ... 
 
 ... 
 
 :;; 
 
 
 
 
 
 2087-7 s 
 2999-7 s 
 30-21-1 s 
 
 30541 s 
 30971 s 
 310-22 s 
 31141 s 
 31201 s 
 3131-5-3 s 
 31332 s 
 31411 s 
 31801 s 
 32421 s 
 36911 s 
 37491 s 
 37821 s 
 
 
 
 1" 
 
 ... 
 
 29313 n 
 
 '.'.'. 
 
 ... 
 
 " 
 
 30511 h 
 3435-5 n 
 
 29314 n 
 
 32721-5 
 
 33412 
 45321* 
 
 
 
 33282 n 
 
 35911-5 n 
 37622 n 
 
 40823 n 
 
 31243 
 31813 
 
 32122" 
 
 35613" 
 3602-52-5 
 36174 
 36282-5 
 36653 
 36922-5 
 
 39096* 
 
 '." 
 
 31691 s 
 
 3389-5 n 
 3409-5 n 
 
 34S91 n 
 35531 h 
 36045 n 
 
 39525 n 
 
 
 
 
 
 
 
 
 
 
 
 ... 
 
 
 
 
 
 ::: 
 
 36192 n 
 
 
 351)71 * 
 
 36101-3 
 3023 * 
 3645-5 
 372S2 
 37731-5 
 38121-5 
 
 41672 n 
 
 41813 n 
 
 3S703 s 
 
 
 ... 
 
 3779" h 
 
 ... 
 
 43325 i 
 
 
 
 
 
 ... 
 
 
 40091 
 
 401.H 
 
 4-2-211 
 
 
 
 
 
 
 
 
 
 
 44433 n 
 
 E 
 
 47033 h 
 
 ;;: 
 
 42671 
 43231 
 46331 
 40711 
 47811 
 
 Fe. 
 
 
 
 
 
 
 
 45993 n 
 
 
 
 z 
 
 47913 n 
 
 ... 
 
 
 
 
 
 
 5277*" n 
 
 ... 
 
 
 
 
 ... 
 
 Solar. 
 
 Air. 
 
 Na 
 
 K. 
 
 Ca. 
 
 Ba. 
 
 Sr. 
 
 Mn. 
 
 Tl. 
 
 Ag. 
 
 Te. 
 
 Sn. 
 
APPEND. C.] 
 
 HUGGINS' TABLES. 
 
 155 
 
 From F. to H. (See Plates I. and II.) 
 
 
 Cd. 
 
 Sb. 
 
 Au. 
 
 Bi. Hg. 
 
 Co. 
 
 As. 
 
 Pb. 
 
 Zn. 
 
 Cr. 
 
 Os. 
 
 Pd. 
 
 Pt. 
 
 
 22512 n 
 
 
 
 
 
 - 
 
 
 
 2257-5 
 22661 "5 
 
 
 2279-52 
 
 2S571 s 
 2936-5 s 
 999-7 s 
 
 1561 8 
 5251 s 
 
 23158s 
 25626s 
 
 23392 h 
 23772 h 
 23972 n 
 24402 n 
 24883 n 
 
 25293 n 
 26871 h 
 27401 h 
 27632 n 
 
 
 
 
 
 
 
 
 2291-5 
 23264 
 
 2317*1 n 
 
 240*81 n 
 24675 n 
 24531 n 
 25021 n 
 
 2263''5i 
 
 22363 
 
 22862 
 23251 
 2409-5 
 2438-5 
 '2471-5 
 2550-5 
 
 
 
 
 
 24501 
 
 23843 B 
 
 22947 
 246*96 
 
 2336-7 s 
 
 24001 s 
 2406-5 s 
 2435-7 s 
 2452-7 s 
 24741 s 
 
 26191 s 
 2627-7 s 
 26321 -s,d 
 2663-5 s 
 2701-7 s 
 
 
 
 
 
 
 
 
 25594 
 
 
 
 
 
 
 27852 n 
 
 
 
 
 
 
 
 
 
 
 
 28575 n 
 
 
 
 
 
 
 
 29772 n 
 
 
 
 
 2S231 n 
 
 28591 h 
 28971 h 
 
 ... 
 
 ... 
 
 
 
 
 30601 n 
 
 
 ... 
 
 ... 
 
 ... 
 
 
 
 28621 s 
 
 31151 n 
 
 30262-5 s 
 
 ... 
 
 
 29103 s 
 
 ... 
 
 ... 
 
 ... 
 
 740-7 8 
 768-7 3 
 
 861*7 s 
 
 2252 s 
 4211 s 
 
 5831 s 
 36451 s 
 
 37733 s 
 
 3086*7 s 
 963* s 
 
 
 
 
 
 
 32394s 
 
 33591 h 
 
 ... 
 
 ... 
 
 ... 
 
 ... 
 
 0061-5 h 
 
 ... 
 
 
 840-7 s 
 871-7 s 
 887-7 6 
 899-7 s 
 9141 s 
 9271 s 
 0071 s 
 4443 s 
 4651 s 
 4731 s 
 4S91 s 
 6633 s 
 719^ s 
 7973 s 
 
 
 
 
 
 
 
 
 ... 
 
 ... 
 
 
 3152 n 
 
 ... 
 
 
 0972 * h 
 
 ... 
 
 
 
 34464 n 
 
 
 4813 n 
 
 34218 n 
 
 
 
 
 
 
 
 3297 n 
 
 
 ::: 
 
 37563 n 
 38191 n 
 40431 -5 n 
 
 ."' 
 
 5192 n 
 6195 n 
 7785 n 
 
 
 
 
 .'.'' 
 
 '.'.'. 
 
 3811 n 
 4971 n 
 
 7302 n 
 
 ::: 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 8316 n 
 
 ... 
 
 9051 8 
 9511 n 
 
 
 
 ... 
 
 ... 
 
 
 
 
 
 378*4 n 
 
 77*54 n 
 
 3883 n 
 3943 n 
 14371 n 
 
 15231 n 
 
 
 7137 u 
 
 
 
 
 ... 
 
 6033 n 
 
 
 
 
 
 
 1583 n 
 
 
 Sb. 
 
 
 
 Cd. 
 
 Au. 
 
 Bi. 
 
 HS. 
 
 Co. 
 
 A?. 
 
 Pb. 
 
 Zn. 
 
 Cr. 
 
 08. 
 
 Pd. 
 
 Pt. 
 
LECTURE IV. 
 
 Mode of obtaining the Spectra of Gases and other Non-metallic 
 Bodies. Pliicker and Hittorf. Huggins. Influence of Change 
 of Density arid of Temperature. Kirchhoff. Frankland and 
 Lockyer. Variation of the Spectra of certain Metals with Tem- 
 perature. Spectra of Compounds. Double Spectra. Angstrom's 
 Conclusions. Spectrum of the Bessemer Flame. Selective 
 Absorption. Blood Bands. Detection of Colouring Matters. 
 Phosphorescence. Fluorescence. 
 
 APPENDIX A. Description of the Spectra of the Gases and Non- 
 metallic Elements. Can an Element possess more than one Spec- 
 trum ? On the Spectrum of Nitrogen. 
 
 APPENDIX B. On the Effect of increased Temperature upon the 
 Nature of the Light emitted by the Vapour of certain Metals or 
 Metallic Compounds. 
 
 APPENDIX C. Kirchhoff on the Variation of the Spectra of certain 
 Elements. 
 
 APPENDIX D. Ignited Gases under certain circumstances give con- 
 tinuous Spectra. Combustion of Hydrogen in Oxygen under great 
 pressure. 
 
 APPENDIX E. On the Spectrum of the Bessemer Flame. 
 
 APPENDIX F. On the Spectra of Erbium and Didymium Compounds. 
 
 APPENDIX G. Description of the Micro-Spectroscope. 
 
 WE saw in the last lecture that the light of the electric 
 spark consists of rays emitted from the incandescent 
 materials, first of the poles from which the discharge 
 passes, and in the second place of the air or gas surround- 
 ing those poles ; and I would remind you that Angstrom 
 was the first who pointed out that the ordinary spark 
 thus yields a double spectrum. If the density of the 
 
LKCT. IV.] 
 
 SPECTRA OF GASEOUS BODIES. 
 
 157 
 
 gas through which the discharge passes be diminished to 
 a certain point within a few millimetres of a vacuum, 
 the electricity is able to pass through a longer column 
 of gas than it can do under the ordinary atmospheric 
 pressure ; and we thus may obtain this beautiful phe- 
 nomenon of the discharge invacuo, for we see this tube 
 ten feet long, on being rendered nearly vacuous by the 
 air-pump, becomes filled with purple light; though if 
 the whole of the gas be withdrawn no electrical dis- 
 charge whatever can pass. The character of the light thus 
 
 FIG. 35. 
 
 emitted depends then upon the nature of the gas'through 
 which the electric spark or the silent discharge passes. 
 
 If we seal up a quantity of hydrogen gas, of carbonic 
 acid gas, and of nitrogen gas, in separate tubes, and allow 
 an electric spark to pass through these tubes (see Fig. 35), 
 the spark which passes through the hydrogen has a red 
 colour, and that which passes through the nitrogen has a 
 yellow colour, while that which passes through the car- 
 bonic acid gas has a blue colour : and these differences 
 of colour are due simply to the effect of the gas enclosed 
 
158 SPECTRUM ANALYSIS. [LECT. iv. 
 
 in the tube. I can vary the experiment by taking Geiss- 
 ler's tubes (Fig. 36), containing these gases only in very 
 minute quantities, so that the electric discharge can pass 
 through a longer capillary column of gas : we then find 
 that the small quantity of gas in the exhausted tubes 
 becomes heated up to incandescence, and gives off its 
 peculiar rays in a line of brilliantly coloured light. 
 
 I have here a hydrogen vacuum tube, next a tube 
 containing a carbonic acid vacuum, then one containing 
 nitrogen, then one containing chlorine, then one con- 
 taining iodine. I have only to connect these with the 
 induction coil, and the discharge will pass through the 
 whole of these tubes ; and at once you see the variety 
 
 FIG. 36. 
 
 of bright colours obtained, entirely due to the small 
 traces of the various gases which are here present in 
 the tubes. If we examine the character of these lights 
 by means of the spectroscope, we shall obtain the peculiar 
 and characteristic spectra of each of these gases. 
 
 Here are some large tubes, in which we can see the 
 same effects of the ignition of the small quantities of 
 these various gases by means of the electric spark (Figs. 
 37, 38) ; and you observe the beautiful striated appear- 
 ance which the light exhibits a phenomenon which 
 physicists are at present quite unable to explain. 
 
 I regret that it is impossible to exhibit the spectra of 
 these luminous gases on the screen, owing to the slight 
 
LF.CT. iv.] SPECTRUM OF HYDROGEN. 159 
 
 intensity of the light which they emit. I must ask you 
 to be content with my references to diagrams to explain 
 to you the exact character of the light which these gases 
 give off. 
 
 Thus, when we examine the peculiar red colour which 
 this hydrogen-tube exhibits, we find that the spectrum 
 consists of three distinct bright lines ; one bright red line 
 so intense as almost to overpower the others, one bright 
 greenish-blue line, and one dark blue or indigo line. 
 These are exhibited to you in the diagram. (See fig. of 
 hydrogen spectrum, No. 8 on the chrdmolith. plate facing 
 Lecture VI.) The bright red hydrogen line is always 
 seen when an electric spark is passed through moist air : 
 
 FIG. 37. 
 
 this is due to the decomposition of the aqueous vapour 
 which the air contains. If the air be carefully dried by 
 passing it over hygroscopic substances, the red line 
 disappears. Hence the spectroscope can be made a means 
 of testing the presence of moisture. 
 
 A very remarkable fact, and one to which I shall have 
 frequently to refer in the subsequent lectures, is that 
 these three lines of hydrogen are found to be coincident 
 with three well-known dark lines in the sun, of which I 
 spoke to you in the first lecture. This red hydrogen line 
 possesses exactly the same degree of refrangibility as the 
 dark line c in the solar spectrum ; the green hydrogen 
 line corresponds to the well-known solar line r ; whilst 
 
160 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. iv. 
 
 the blue hydrogen line is identical in position with a 
 dark line near G in the sun's spec- 
 trum. 1 We shall see in a subsequent 
 lecture how such coincidences point 
 out to us the existence of hydrogen 
 and other elements in the solar atmo- 
 sphere. 
 
 When a spark is passed through 
 the air, the lines of both nitrogen and 
 oxygen are seen. This air spectrum 
 has been carefully mapped by Dr. 
 Huggins, who employed it as a scale 
 to which to refer the metal lines in 
 his drawings. He observed the lines 
 simultaneously given off from two 
 sets of poles, one set being of gold 
 and the other set of platinum (in order 
 to eliminate any confusion arising 
 from the presence of metal lines) : 
 and he took those lines which were 
 common to both these spectra as being 
 those due to the components of the 
 air. The spectrum thus obtained 
 remains perfectly constant with re- 
 ference to the position and relative 
 characteristics of its lines when other 
 metals are employed as electrodes. 
 It is, however, found that the air 
 spectrum varies as a whole in distinct- 
 ness according to the volatility of the 
 
 38. 
 
 1 Angstrom maps a dark line in the violet portion of the solar spec- 
 trum, and termed by him (h), as coincident with a fourth hydrogen line, 
 which is not seen unless the gas be heated to a very high temperature. 
 
LECT. iv.] CHANGES IN THE SPECTRA OF GASES. 16 J 
 
 metal used as poles, the air being more or less replaced 
 by metallic vapours in the neighbourhood of the elec- 
 trodes. The bright hydrogen lines due to aqueous vapour 
 are, as I have said, seen when the spark is passed through 
 moist air, whilst the spectrum of lightning, as examined 
 by Grandeau and Kundt, has been found to exhibit in 
 addition the nitrogen and hydrogen spectra, also the 
 bright yellow sodium line. 
 
 The nitrogen spectrum is more complicated than that 
 of hydrogen, but still perfectly definite and characteristic. 
 (See No. 9 on the chromolith. plate in Lecture VI.) 
 
 Some very singular observations have been made by 
 Pllicker and Hittorf 1 upon certain changes which the 
 spectra of highly rarefied gases undergo. They find that 
 the spectrum of highly rarefied nitrogen undergoes a 
 change when the intensity of the electric discharge varies ; 
 and they explain this by supposing that nitrogen can 
 exist in various allotropic conditions, resembling for 
 instance oxygen and ozone, their idea being that the 
 changes in the intensity of the electric discharge may 
 cause changes in the allotropic condition of the nitrogen, 
 and that thus a variation in the appearance of the 
 spectrum may be produced. These variations, however, 
 it is important to observe, are not noticed in nitrogen gas 
 when under the pressure of the atmosphere, however 
 much we may increase the intensity of the spark ; and 
 from some experiments to which I shall have again 
 to refer, it would appear that the band spectrum* of 
 nitrogen is only seen when traces of oxygen are pre- 
 sent, so that pure nitrogen has in reality only one 
 spectrum of bright lines, the band spectrum being due to 
 the oxides of nitrogen (see Appendix A). Plucker has 
 1 Plucker and Hittorf, Phil. Trans. 1865, p. 1. 
 M 
 
1 6 2 SPECTR UM ANALYSIS. [LECT. i v. 
 
 also noticed that under certain conditions of increased 
 electrical tension the fine lines of hydrogen are seen to 
 become broader and broader, until at last the hydrogen 
 gas may be made to emit light of every degree of refran- 
 gibility, so that its spectrum becomes continuous. 
 
 These variations which the hydrogen spectrum, as 
 obtained in Geissler's tubes, undergoes when the density 
 of the gas on the one hand and the intensity of the spark 
 on the other are altered, have been carefully examined by 
 Huggins, as well as by Lockyer and Frankland, and by 
 Wtillner. Still the explanation of the so-called double 
 spectrum of nitrogen renders it possible that these dif- 
 ferently constituted hydrogen spectra may be caused by 
 some differences, as yet unperceived, in the chemical 
 nature of the gas which is operated upon, and we shall 
 see in the sequel that this possibility is rendered a 
 probability by independent experiments. It is, how- 
 ever, not improbable that the fact of this broadening of 
 the hydrogen lines may be found to possess important 
 bearings upon the conclusions which spectrum analysis 
 enables us to draw concerning the physical condition 
 of the sun and fixed stars. To this point I will, how- 
 ever, direct your attention on a future occasion. 
 
 In the same way each of the non-metallic elements 
 yields a characteristic spectrum when its vapour is 
 heated to incandescence ; but in the case of some of the 
 elements, such as silicon, the difficulty of obtaining the 
 spectrum is very great. 
 
 In his original memoir on the spectra of the chemical 
 elements Kirchhoff plainly points out that under varying 
 conditions of density, temperature, and thickness of the 
 layer of incandescent gas, the spectrum of the same body 
 must vary in its appearance, some of the lines coming 
 
LEG r. iv.] APPEARANCE OF NEW LINES. 103 
 
 out more brightly under certain circumstances than 
 others, and thus giving a different character to the 
 spectrum. 1 That the change, in a gaseous spectrum, 
 may go so far as to produce a continuous spectrum is 
 also certain. The flames of many gases, such as this 
 blue one of carbonic oxide, burning in the air to form 
 gaseous products of combustion, give continuous spectra ; 
 indeed, we may see the beginning of such a continuous 
 spectrum in every soda flame ; and Dr. Frankland has 
 lately observed that when oxygen and hydrogen gases 
 are inflamed under great pressure, they emit white light 
 and show an unbroken spectrum. From these facts 
 there is no doubt that, when intensely heated and under 
 certain circumstances, gaseous bodies can be made to 
 
 Fro. 39. 
 
 yield continuous spectra, 2 This, however, in no way 
 interferes with the fixity of position of the bright lines, 
 nor can it influence the deductions derived from this 
 fact. 
 
 Several interesting observations have been made with 
 respect to the changes produced in the spectra of some 
 
 1 See Appendix C to this lecture. 
 
 2 See Appendix D to this lecture. 
 
 M 2 
 
164 SPECTR UM ANAL YSIS. [LECT. i v. 
 
 of the metals by increase of temperature. Let me, in 
 the first place, show you that new lines may make their 
 appearance in the spectra of certain elements when the 
 temperature is raised. Thus, for instance, if we heat 
 lithium, either the metal or its salts, in the electric arc, 
 we obtain a splendid blue band having the wave-length 
 of 4605 ten-millionths of a millimetre (see Fig. 39), in 
 addition to the red and orange rays a and & seen in the 
 flame spectrum, showing that the undulations in this 
 particular set of vibrations have become more intense. 
 The same phenomenon is observed in the case of the 
 strontium spectrum, where no less than four new lines (e, 
 vj, K, and X, Fig. 39) make their appearance on increasing 
 the temperature of the incandescent vapour of the metal. 
 Also in the case of sodium four sets of new lines appear 
 when the temperature is increased, in addition to the well- 
 known " D " lines ; and singularly enough, each of these 
 four lines is double. Dr. Watts has shown that the first 
 of these higher sodium lines (wave-length 5889 and 
 5687) become visible at a temperature of 2000 C., whilst 
 the next set (wave-length 5155 and 5152) appear when 
 the temperature rises to about 3000 C. The analogy 
 between the production of these more highly refrangible 
 rays and that of the overtones or harmonics of a vibrat- 
 ing string will occur to all. 
 
 On the other hand, by reducing the temperature, and 
 therefore the intensity of the spark, only the most pro- 
 minent lines of a metallic spectrum may be seen. Thus 
 Lockyer and Frankland have shown that the magnesium 
 (b) lines vary in length and intensity when the electrodes 
 are separated, so that in a certain position one of the four 
 well-known magnesium lines disappears. We shall see the 
 application of this observation in a subsequent lecture. 
 
LECT. iv.] SPECTRA OF COMPOUND BODIES. 165 
 
 The second set of facts with regard to the effect of 
 increased heat has reference to the changes which the 
 spectra of compound bodies undergo when the temperature 
 is increased. These changes are clearly seen in the follow- 
 ing experiments. Let us first put a bead of fused chloride 
 of calcium, a common lime salt, into the colourless gas 
 flame : we observe a peculiar spectrum, which is repre- 
 sented roughly on this diagram, in which the red is sup- 
 posed to be on the right and the blue on the left hand 
 (Fig. 40, No. 1, and Frontispiece, No. 9). If, however, 
 we now pass an electric spark over a bead of chloride 
 of calcium, and then look at the coloured spark, we find 
 that the spectrum thus obtained is not the same as that 
 
 FIG. 40. 
 
 observed in the flame. Here you notice the difference 
 between these two spectra : the lower drawing gives you 
 the spark spectrum, and the upper one what we may 
 call the flame spectrum. This variation can be readily 
 explained. It is a well-known fact that certain chemical 
 compounds, when they are heated up above a given 
 temperature, decompose into their constituent elements, 
 whilst, below that temperature, these compounds are 
 
166 SPECTRUM ANALYSIS. [LECT. iv 
 
 capable of existing in a permanent state. When we once 
 get the spark spectrum, we find that no alteration in the 
 intensity of the spark can then alter the position of those 
 lines. The position of the red lithium line never varies, 
 although the blue line conies out. It naturally strikes 
 every observer that these bands seen in the flame spec- 
 trum are produced by a compound of calcium (say the 
 oxide or chloride), which remains undecomposed at the 
 temperature of the flame. When we increase the tem- 
 perature, as in the spark spectrum, a dissociation of the 
 compound occurs, and we get the true spectrum of the 
 metal. The position of these true metallic lines never 
 alters at all, although, when the intensity of the electric 
 spark is increased, new lines may sometimes make 
 their appearance. Hence we can fully rely upon the 
 spectrum test as a proof of the presence of the particular 
 metal. 
 
 No such change in the character of the spectra is 
 noticed in the case of those metals whose compounds 
 undergo dissociation at low temperatures : thus we do 
 not see any such phenomenon in the alkaline metals, 
 although it is observed in the case of barium, strontium, 
 and calcium; for if I take two beads, one of sodium 
 nitrate and the other of sodium chloride, I obtain in the 
 flame the same sodium spectrum with both salts, because 
 each is decomposed, yielding incandescent sodium vapour. 
 Another fact which bears out the truth of this expla- 
 nation has been observed by Plticker, that, in the case 
 of bodies whose spectra change from bands to lines on 
 increase of temperature, a recombination of the elements 
 occurs on cooling, and the band spectrum of the com- 
 pound reappears. Many other observations crowd upon 
 us to convince us that compound substances capable of 
 
LECT. iv.] SPECTRA OF COMPOUND BODIES. 167 
 
 existing in the state of glowing gas yield spectra different 
 from those of their constituent elements. Thus the 
 spectrum of terchloride of phosphorus exhibits lines 
 differing from those of either phosphorus or chlorine, and 
 the chloride and iodide of copper each yields a distinct 
 set of bands bearing no resemblance to the bright lines 
 of the metal. 
 
 It is here important to learn that a distinguished 
 spectroscopist, Professor Angstrom, 1 does not endorse 
 the conclusions of Plticker and Wiillner respecting the 
 existence of several spectra for one element, inasmuch 
 as the spectra observed in the Geissler's tubes with low 
 intensity are, according to Angstrom, those of compound 
 bodies, arid it is only when the discharge becomes 
 disruptive that the constant spectrum of the element 
 appears. Angstrom doubts the truth, therefore, of reputed 
 dualism in the spectrum of one element ; and he explains 
 the observed changes by supposing that traces of some 
 foreign body are present, and he shows that it is almost 
 impossible to obtain any gas perfectly pure when in 
 an extreme state of rarefaction. Thus, on one occasion, 
 Angstrom rarefied air in a Geissler's tube to the utmost 
 extent attainable by a mercury pump, and on allowing 
 a discharge from an induction coil to pass through, 
 he obtained, (1) the ordinary air spectrum, (2) the fluted 
 spectrum of nitrogen, (3) that of carbonic oxide, (4) the 
 bright lines of chlorine and of sodium. Proceeding to 
 criticise in detail Wtillner's experiments, Angstrom con- 
 cludes that two of the four spectra attributed to hydrogen 
 are really the spectra of the hydrocarbon acetylene and 
 sulphur ; whilst of the other two, one is the true hydro- 
 gen spectrum, and the other the broad band hydrogen 
 1 See Appendix A, Lect. V. 
 
1 6 8 SPECTR UM ANALYSIS. [LECT. iv. 
 
 spectrum which he (Angstrom) discovered in 1853. 
 This conclusion is still further borne out by experiments 
 made at Owens College by Mr. Schuster. 1 In a similar 
 way Angstrom disposes of Wiillner's different oxygen 
 and nitrogen spectra ; the lines of one of the new 
 oxygen spectra are identical with those of carbonic oxide 
 gas, whilst the other beyond doubt is due to chlorine. 
 
 Whilst the pages of this edition are passing through 
 the press, a very important addition has been made to 
 our knowledge of the so-called double spectra of nitro- 
 gen, by Mr. Schuster, 2 working under Professor Balfour 
 Stewart's direction. These experiments go far to confirm 
 the above opinions of Angstrom, for Mr. Schuster has 
 shown, (1) that pure nitrogen gives only one spectrum, 
 (2) that this is the line spectrum, (3) that the fluted 
 spectrum of the first order is due to oxides of nitrogen 
 formed under the influence of the electric spark. When 
 every trace of oxygen is got rid of, by heating a small 
 piece of sodium in the vacuous tube, only the line-spectrum 
 or the true spectrum of nitrogen is invariably obtained, 
 however much the temperature or pressure may vary. 
 When, on the other hand, through leakage or impurity, 
 the smallest quantity of oxygen is present, the band 
 spectrum reappears. 
 
 Wiillner still 3 denies the truth of Angstrom's general 
 statement, but acknowledges that in one case, that of 
 oxygen, he himself has been mistaken ; and that one 
 of the two spectra which he attributed to oxygen, is in 
 reality due to carbon which found its way into the 
 vacuum from the fat used to grease the stop-cocks of 
 his air-pump ! From this we may form an idea of the 
 
 1 See Nature, p. 358, Aug. 20, 1872. 
 
 2 See Appendix A to this lecture. 3 Xov. 1871. 
 
LECT. iv.] SPECTRUM OF CARBON. 169 
 
 difficulty of such investigations ; and thus finding our- 
 selves in the midst of conflicting evidence, even on 
 questions of a fundamental nature, we must endeavour 
 to hold our minds unbiassed until the results of further 
 research render it possible for us to come to a decision. 
 Still, although in the case of oxygen, nitrogen, and 
 hydrogen (bodies which are permanently gaseous) we 
 now conclude that probably each has only one spectrum, 
 it is well to remember that the existence of two spectra 
 for each of the solid elements sulphur and iodine appears 
 to have been satisfactorily established by the experiments 
 of M. Salet. 
 
 The examination of the spectrum of carbon is a subject 
 of much interest as well as of much difficulty. The 
 character of the lines which the blue flame of coal gas 
 and air emits was first described in the year 1856 by 
 Professor Swan. Since that time the various spectra of 
 the carbon compounds have been carefully examined by 
 Dr. Attfield, Dr. W. M. Watts and others ; and it appears 
 that the different compounds of this element, when 
 brought into the condition of luminous gases, either by 
 combustion or when heated up by the electric spark, give 
 no less than four different spectra. 1 Thus this beautiful 
 purple flame of cyanogen gas exhibits a great number of 
 very peculiar lines, which differ in position and in in- 
 tensity from the lines observed in this flame of olefiant 
 gas burning in oxygen. (See fig. of carbon spectra, 
 Nos. 10, 11, on the chromolith. Plate facing Lecture VI.) 
 The causes of these differences in the carbon spectra 
 cannot, as yet, be satisfactorily explained ; at least, it has 
 been shown by Watts that variations in temperature alone 
 do riot account for them, inasmuch as two or more of 
 1 See Appendix E, on the Spectrum of the Bessemer Flame. 
 
170 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. iv. 
 
 the carbon spectra are obtained within the same limits 
 of temperature, so that here also we must wait for in- 
 formation. 
 
 I may mention, in connection with these different 
 carbon spectra, the application of spectrum analysis 
 to the important branch of steel manufacture which 
 has been introduced and is well known under the 
 
 FIG. 41. 
 
 name of the Bessemer process. In this process five 
 tons of cast iron are in twenty minutes converted 
 into cast steel. Steel differs from cast iron in contain- 
 ing less carbon, and by the Bessemer process the 
 carbon is actually burnt out of the molten white-hot 
 
LECT. iv. J SPECTRUM OF THE BESSEMER FLAME. \ ~ \ 
 
 cast iron by a blast of atmospheric air. The arrange- 
 ment employed for this purpose is shown on this 
 diagram (Fig. 41). 
 
 The exact nature of the chemical changes which 
 occur in this most interesting process I cannot at 
 present discuss, but mainly they are as follows : In 
 the first place the graphite which is contained in the pig- 
 iron is converted into combined carbon ; in the second 
 place, we find that the silicon begins to burn off, and 
 that afterwards the combined carbon is oxidized. The 
 following analyses of portions of metal taken out during 
 the operation show this gradual diminution in the 
 silicon and combined carbon, until in the fourth sample 
 we find that from one- to two-tenths of carbon remain, 
 whilst only a few hundredths, or mere traces, of silicon 
 are left. 
 
 ANALYSES SHOWING THE CHEMICAL CHANGES OCCURRING IN 
 
 THE BESSEMER CONVERTER. 
 Samples of Metal taken out at various stages of the operation, viz. : 
 
 (1) Original Pig-iron. (2) Taken out at end of first stage (6 min.). 
 
 (3) ,, ,, boil (12 min.). 
 
 (4) ,, ., blow. 
 
 (5) After addition of Spiegel. 
 
 FUOM THE ATLAS WORKS, SHEFFIELD. 
 
 
 IKON. 
 
 
 
 
 STEEL. 
 
 
 (1) 
 
 (2) 
 
 (3) 
 
 (4) 
 
 (5) 
 
 pliite 
 
 . . 2'570 
 
 
 
 
 
 
 
 Combined Carbon 
 
 . . 1 -000 
 
 3'<!40 
 
 1-640 
 
 0-190 
 
 0-370 
 
 Silicon .... 
 
 . . 2"260 
 
 0-955 
 
 0-470 
 
 trace 
 
 trace 
 
 Phosphorus 
 
 . . 0-o73 
 
 0-070 
 
 0'070 
 
 0-070 
 
 0-059 
 
 Sulphur .... 
 
 . . 0-107 
 
 0-091 
 
 093 
 
 0-093 
 
 0-090 
 
 Manganese . . 
 
 . . 0-410 
 
 trace 
 
 trace 
 
 trace 
 
 truce 
 
 The molten cast iron is run into a large wrought-iron 
 vessel, termed the converter (c), lined with refractory 
 clay. The converter is capable of being turned round 
 on a pivot (A), through which pivot passes a tube in 
 
172 SPECTRUM ANALYSIS. [LECT. iv. 
 
 connection with a powerful blowing apparatus, by means 
 of which air can be thrown into the bottom of the vessel, 
 through a sort of tuyere or blowhole into the molten 
 iron. The oxygen of the air burns out the carbon and 
 silicon which the cast iron contains, and the heated 
 gases issue in the form of a flame (F) from the mouth 
 of the converter during the time that the molten iron is 
 being burned. This flame varies in appearance, and it 
 is of the utmost importance that the operation should be 
 stopped instantly when the proper moment has arrived. 
 If the blast be continued for ten seconds after the proper 
 point has been attained, or if it be discontinued ten 
 seconds before that point is reached, the charge becomes 
 either so viscid that it cannot be poured from -the 
 converter into the ladle (L), from which it has to be 
 transferred to the moulds, or it contains so much carbon 
 as to crumb] e up like cast iron under the hammer. 
 
 Those who are accustomed to work this process are 
 able by the simple inspection of the flame to tell with 
 more or less exactitude when the air has to be turned off. 
 To those who are uninitiated in this peculiar appearance 
 of the flame no difference at all can be detected at 
 the point in which it is necessary to stop, but by the 
 help of the spectroscope this point can be at once ascer- 
 tained .beyond shadow of doubt, and that which pre- 
 viously depended upon the quickness of vision of a 
 skilled eye has become a simple matter of exact scientific 
 observation. The light which is given off by the Bes- 
 semer flame is most intense, indeed a more magnificent 
 example of combustion in oxygen cannot be imagined. 
 A cursory examination of the flame spectrum in its 
 various phases reveals complicated masses of dark ab- 
 sorption bands and bright lines, showing that a variety 
 
LECT. iv.] SPECTRUM OF THE BESSEMER FLAME. 
 
 173 
 
 of substances are present in the flame in the state of 
 glowing gas. 
 
 By a simultaneous comparison of the lines in the 
 Bessemer spectrum with those of well-known substances 
 I was able in the year 1863 to detect the following 
 substances in the Bessemer flame : sodium, potassium, 
 lithium, iron, carbon, hydrogen, and nitrogen. At a cer- 
 tain stage of the operation I found that all at once the 
 lines supposed to be due to carbon disappeared, and we 
 got a continuous spectrum. The workman by experience 
 has learned that this is the moment at which the air 
 must be shut off; but it is only by means of the spec- 
 troscope that this point can be exactly determined. 
 
 The following table gives you a good idea of the 
 changes seen to take place in the flame, (1) as seen by 
 the unaided eye, (2) as seen by the aid of the spectro- 
 scope. 
 
 STAGE. 
 
 TIME. 
 
 APPEARANCE OF 
 FLAME TO EYE. 
 
 APPEARANCE OF SPECTRUM. 
 
 
 About 
 
 
 
 / 
 
 min. 4 sec. 
 
 No flame seen. 
 
 Faint continuous spectrum, due 
 
 | 
 
 
 
 to sparks of burning metal. 
 
 1st. -j 
 
 4 ,, 6 
 
 Small pointed flame. 
 
 Brighter, with yellow sodium 
 
 1 
 
 
 
 line flashing out. 
 
 I 
 
 6 ,, 8 ,, 
 
 Unsteady flame, 
 with explosions. 
 
 Bright continuous, with sodium 
 line permanent. Ked lithium 
 
 
 
 
 line, red and violet potassium 
 
 
 
 
 lines. 
 
 , 
 
 8 10 ,, 
 
 Very bright and 
 
 Bright lines in red, green, and 
 
 
 
 dense flame. 
 
 blue, with preceding spec- 
 
 2d. -| 
 
 
 
 trum. 
 
 1 
 
 10 14 
 
 Flame less dense, 
 
 Bright green lines more dis- 
 
 I 
 
 
 but bright. 
 
 tinct. 
 
 f 
 
 14 16 
 
 Flame diminishing 
 
 Bright green lines become faint. 
 
 
 
 in size and in- 
 
 
 01 
 
 3d. 1 
 
 
 tensity. 
 
 
 I 
 
 16 18 
 
 Flame drops; blow 
 ends. 
 
 Bright green lines suddenly dis- 
 appear, leaving a continuous 
 
 
 
 
 spectrum. 
 
1 74 SPECTRUM ANALYSIS. [LECT. iv. 
 
 No. 2, Fig. 42, represents the general appearance of 
 the Bessemer spectrum towards the close of the " blow," 
 drawn according to the plan proposed by Bunsen (see 
 page 67). The striking analogy between the flame 
 spectrum and that of carbon (No. 1, Fig. 42) renders it 
 at first sight probable that the principal lines of the Bes- 
 semer spectrum are due to carbon in some form ; and this 
 conclusion is strengthened when we find that the lines 
 disappear at the moment when, by chemical analysis, we 
 can show that the carbon has been burnt out. Still it 
 has been stated that the lines are due to the presence 
 of manganese, although they are brightly seen in the 
 working of certain iron ores (such as the Ulverstone 
 
 NO. 1. 
 
 wirniiiiiiii ii!|!ll!l|Tf!lffl iiiiiiiii.fftflliniiiimiiiitt^iiii.i 
 
 2 3 14 5 16 |7 a 19 
 
 NO. 2. 
 
 iMjuufiil^HMp' 
 
 3 I* ' J6 ' 16 ' 
 
 e ' Ir 'I IJ ' Is" jo' In L'' us" 1 'ii4 ; ' lie '' i '"'iir'' iia '' ''i 
 
 NO. 3. 
 
 E 6 F 
 
 Fio. 42. 
 
 beds) which contain scarcely any of this metal. And, 
 singular and at present unaccountable as it may appear, 
 it has lately been shown beyond doubt by Dr. Marshall 
 Watts, that the bright lines in the Bessemer flame are in 
 reality not identical with carbon lines, as we had long 
 believed, but with those of oxide of manganese. Fig. 42a 
 on the opposite page shows this singular fact clearly : 
 No. 1 gives the iron spectrum ; No. 2 that of the 
 Bessemer flame ; No. 3 that of oxide of manganese ; and 
 No. 4 the spectrum of the spiegel flame. Here again 
 we must be content accurately to record ascertained 
 facts, leaving the explanation for a future time. When 
 the spiegeleisen is brought into the converter, a very 
 
IANCANESE 
 0X1 DEI 
 
176 SPECTRUM ANALYSIS. [LECT. iv. 
 
 bright flame issues from the mouth of the vessel, and this 
 flame exhibits a spectrum (No. 4, fig. 42a) which really 
 contains the same lines as that of the Bessemer flame, 
 although the general appearance of the spectrum is com- 
 pletely changed by the alteration of the relative bright- 
 ness of the lines. 
 
 Those who are practically engaged in working this 
 process would like spectrum analysis to do a great deal 
 more ; they would like to be told whether there is any 
 sulphur, phosphorus, or silicon in their steel : questions 
 which unfortunately at present spectrum analysis cannot 
 answer, for this very good reason, that these substances 
 do not appear at all as gases in the flame, but that they 
 either remain unvolatilized in the molten metal, or swim 
 on its surface in the slag of the ore ; and consequently 
 the lines of these bodies are not seen in the spectrum of 
 the flame. 
 
 The next point to which I would direct your atten- 
 tion is one of a slightly different kind. We find that 
 certain substances not only gases, but liquids, and even 
 solid bodies exert at the ordinary temperature of the 
 air a selective absorption power upon white light when 
 it passes through them. In the following lecture I shall, 
 have occasion to show you, in various ways, the absorp- 
 tive effect which glowing sodium vapour exerts upon 
 the particular kind of yellow light which sodium itself 
 gives off; but I would now consider some cases of 
 selective absorption occurring at the ordinary tempe- 
 rature, and just indicate to you a most interesting and 
 important branch of this subject which has been, to a 
 certain extent, worked out, but in which a rich harvest 
 of investigation still remains open. I refer to the ab- 
 sorption spectra obtained by the examination of various 
 
LECT. 1V.J 
 
 SEl, ECTIPE A BSOR P '1 ION. 
 
 17 
 
 coloured gases and liquids, especially of blood and other 
 animal fluids. In the first place, then, it has long been 
 known that certain bodies have at the ordinary tempera- 
 ture the power of selectively absorbing certain particular 
 kinds of light. In Fig. 43 we have a representation of 
 the selective absorption exhibited by two coloured gases : 
 No. 1 shows the dark bands seen when white light passes 
 through the violet vapours of iodine, whilst No. 2 gives 
 the bands first observed by Brewster in the red fumes of 
 nitrogen tetroxide, which have since been shown by Kundt 
 to be identical with those which the liquid tetroxide 
 
 gives. Some coloured gases, such as chlorine, do not 
 give any dark absorption bands ; whilst, on the other 
 hand, certain colourless gases, such as air and aqueous 
 vapour, exert a remarkable power of selective absorption, 
 and exhibit spectra filled with dark lines. I shall return 
 to this subject of the atmospheric lines in a subsequent > 
 lecture. Perhaps the most striking instance of the ( 
 formation of these absorption lines in the case of liquids 
 is the one which I will show you of this colourless 
 solution of a salt of the rare metal didymium. All 
 the didymium salts possess the power of absorbing 
 
1 78 SPECTRUM ANALYSIS. [LECT. iv. 
 
 from white light certain definite rays, so that if I place 
 the solution in the path of our continuous spectrum we 
 get the broad absorption bands by which, as Dr. Gladstone 
 has shown, the presence of didymium can be recognized, 
 when present even in very minute quantities. It is very 
 remarkable that, although these didymium absorption 
 lines are so black, and serve as such a reliable test of the 
 presence of this metal, yet the fraction of the total light 
 which is absorbed is so small that the solution appears 
 colourless. From the recent experiments of Bunsen on 
 this subject we learn that the various didymium com- 
 pounds do not exhibit exactly the same absorption lines, 
 and that if light is allowed to fall upon a crystal, the 
 dark bands also differ according to the direction in 
 which the light passes through (see Appendix F). 
 
 " The differences thus observed," says Bunsen, " cannot 
 as yet be connected with other phenomena. They remind 
 one of the gradual alteration in pitch which the notes 
 from an elastic rod undergo when the rod is weighted." 
 
 Remembering the changes seen by Bunsen in the 
 absorption spectra of didymium, we must accept with 
 great caution any conclusions as to chemical composition 
 derived solely from variation in the absorption spectra. 1 
 Indeed, it has been shown that even experienced ob- 
 servers may be led to false conclusions by relying too 
 implicitly on the complicated absorption bands which 
 certain mixtures may yield. 
 
 1 It has been found that the absorption bands attributed to a new 
 metal contained in zircons are due to a mixture of salts of zirconium 
 and uranium. This mixture appears to afford a most delicate means 
 of detecting the presence of uranium, for bands appear in the mixture 
 which are not seen when the two metals are examined separately in 
 much larger quantities (Sorby). 
 
LECT. IV.] 
 
 SELECTIVE ABSORPTION. 
 
 179 
 
 The solutions of many other coloured metallic salts 
 possess a similar property of yielding definite absorp- 
 tion lines, and Dr. Gladstone finds that with very few 
 exceptions all the compounds of the same base, or acid, 
 have the same effect on the rays of light : thus the 
 chromium salts (both green and purple) exhibit the same 
 form of absorption spectrum (Fig. 44). Fig. 45 shows 
 the bands produced by potassium permanganate solution 
 contained in a wedge-shaped vessel. The right hand cor- 
 responds to the red end of the spectrum, and the letters 
 refer to the position of Fraunhofer's lines. The absorptive 
 
 FIG. 44. 
 
 FIG. 45. 
 
 action of the solution is most powerful at the upper part 
 of each drawing, which represents the spectrum seen 
 where the layer of solution was thickest, and diminishing 
 towards the lower part of the figure. 
 
 There are a variety of other substances which have 
 this selective power : thus here is the absorption spectrum 
 of chlorophyll, the green colouring matter of leaves, and 
 here that of chloride of uranium. 
 
 Another interesting case of the selective absorption of 
 liquids is exhibited to you in these purple solutions con- 
 taining the two colouring matters of madder alizarine 
 
 N 2 
 
180 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. iv. 
 
 and purpurine. Spectrum. No. 4 (Fig. 47) shows the 
 peculiar dark bands of the purple solution of alkaline 
 alizarine, a substance which has lately been artificially 
 prepared from a hydrocarbon (anthracene) contained in 
 
 CHLOROPHYLL 
 
 CHLORIDE OF URANIUM. 
 
 FIG. 46. 
 
 coal-tar, by two German chemists, Messrs. Graebe and 
 Liebermann ; whilst No. 1 gives that of the alkaline 
 solution of purpurine. The bands of artificial alizarine 
 are found to correspond exactly to those of the ' natural 
 
 FIG. 47. 
 
 vegetable colouring matter obtained from the Rubia tinc- 
 torum. The marked difference between the spectrum of 
 purpurine dissolved in carbon disulphide (No. 2, Fig. 47) 
 and that of an etheiial solution (No. 3, Fig. 47) of 
 
LECT. IV.J 
 
 STOKES' S BLOOD BANDS. 
 
 181 
 
 the same body, reminds one of the difference in colour 
 which iodine exhibits when dissolved in chloroform and 
 in alcohol. Professor Stokes, who has examined the 
 spectra of these colouring matters, says : " The cha- 
 racters of these subjects are so marked that I do not 
 know any substance with which either of them could 
 be confounded, even if we restricted ourselves to any 
 one of the solutions yielding the peculiar spectra. Not 
 only so, but these properties enable us to detect small 
 quantities, in the case of purpurine the merest trace, 
 
 DARK BAND IN MAGENTA. 
 
 DARK BANDS IN BLOOD. 
 
 FlG. 48. 
 
 of the substance present in the midst of a quantity of 
 impurities." 1 
 
 If I take a solivtion of blood, and place the cell 
 containing it before the slit, we get these distinct dark 
 absorption bands, due to the presence of the blood (Fig. 
 48). This is the red blood : deoxidized blood gives a 
 different appearance. Here you see the two bands due 
 to the oxy haemoglobin ; whilst this portion of deoxidized 
 blood gives only one black band, somewhat similar, but 
 not identical in position with the dark band in magenta, 
 which I now throw upon the screen. This subject was 
 
 1 Journal of the Chemical Society, vol. xii. p. 21. 
 
182 
 
 SPECTRUM ANALYSIS. 
 
 [LEGT. iv. 
 
 first examined by Professor Stokes, who published a 
 paper on the subject in the Proceedings of the Royal 
 Society for 186 4. From this we learn that " the colouring 
 matter of blood, like that of indigo, is capable of existing 
 in two states of oxidation, distinguishable by a difference 
 of colour and a fundamental difference in the action on 
 the spectrum/' These two forms may be made to pass one 
 into the other by suitable oxidizing and reducing agents, 
 and they have been termed red and purple cruorine. 
 
 E b 
 
 FIG. 49. 
 
 I have here a drawing of Mr. Stokes's diagram of the 
 blood bands. At the top (Fig. 49, No. 1) you see the 
 position of the two bands of the scarlet cruorine, or 
 oxyhsemoglobin. The deoxidized blood is seen in No. 2 
 to have only one dark band. By the action of an acid 
 on blood the cruorine is converted into hsematin, yield- 
 ing a different absorption spectrum ; and this hsematin 
 is capable of reduction and oxidation like cruorine. 
 
LECT. iv.] MICRO-SPECTROSCOPE. 183 
 
 The absorption bands of hsematin are represented in 
 Nos. 3 and 4. 
 
 One very interesting point to which I must refer is 
 the fact that the blood, when it contains very small 
 quantities of carbonic oxide gas in solution, exhibits a 
 very peculiar set of bands. And the poisoning by car- 
 bonic oxide for, as is well known, the poison of burning 
 charcoal is due to this gas can be readily detected by 
 
 FIG. 50. 
 
 the peculiar bands which the blood containing carbonic 
 oxide in solution exhibits ; and hence we have these 
 absorption lines coming out as a most valuable aid in 
 toxological research. 
 
 A valuable suggestion as to the mode of accurately 
 measuring the position of these various absorption bands 
 of the blood-colouring matters has recently been made by 
 Mr. Eay Lancaster, 1 in referring to the numerous and 
 well-marked absorption bands of the red nitrous fumes 
 
 1 Journal of Anatomy and Physiology, vol. iv. p. 119. 
 
184 SPECTRUM ANALYSIS. [LECT. iv. 
 
 N 2 4 (No. 2, Fig. 43) as a fixed scale upon which the 
 places of the blood bands can be easily marked. 
 
 The instrument by which all these beautiful absorption 
 phenomena can be observed with delicacy and accuracy 
 is simply a spectroscope placed in connection with a 
 microscope (Fig. 50). Here we have the instrument. 1 
 The eyepiece contains prisms, so placed as to enable the 
 
 FIG. 51. 
 
 refracted ray to pass in a straight line to the eye. Such 
 spectroscopes are termed direct-vision instruments. This 
 (Fig. 51) is a diagram showing the structure of the eye- 
 piece which I hold in my hand. This is the first lens of 
 the eyepiece ; here is the adjustable slit, for we must 
 
 1 W. Huggins, "On the Prismatic Examination of Microscopic 
 Objects" (Trans. Microscopical Society, May 10, 1865). 
 
LECT. iv.] MICRO-SPECTROSCOPE. 185 
 
 have a line of light in order to get a pure spectrum. 
 When the light passes through the second lens, the 
 rays are rendered parallel ; and then they pass through 
 this compound prism, consisting of three crown-glass 
 prisms placed in one direction and two flint-glass prisms 
 placed in the opposite direction, so that we see the 
 spectrum by looking straight at the source of light, or 
 have a direct-vision spectroscope. In this way, then, 
 the absorption bands can be very beautifully seen ; and, 
 what is important, we cnn, by means of this little move- 
 able mirror, send a ray of light (shown in the dotted 
 line) through the slit at one side of the instrument, which 
 being reflected upwards passes through the prisms along 
 with the other light which comes from the object under 
 the microscope, and so observe the two spectra one above 
 the other : and thus it is that we can detect, for in- 
 stance, the presence of blood. Supposing we wish to 
 know whether a substance is blood which we have in 
 solution : nothing is easier than to place a small quantity 
 of the liquid supposed to be blood on the table of the 
 microscope, and to bring a small quantity of blood in 
 a tube, placed before the slit in the side of the instru- 
 ment, so as to compare the spectrum obtained from 
 the body under examination with that of the body 
 winch we know is really blood. This instrument, which 
 in the hands of Mr. Sorby has taught us how to detect 
 iOTu-th P art of a grain of the red colouring matter in 
 a blood-stain, and by means of which I have seen 
 the characteristic bands in the blood circulating in a 
 frog's foot, is a most beautiful one, and the method of 
 microscopic spectrum analysis must every year become a 
 more and more trusted and valuable means of research 
 in medico-legal investigations. 
 
186 SPECTR UM ANALYSIS. [LECT. i v. 
 
 Before concluding my remarks upon the application of 
 spectrum analysis to the examination of terrestrial matter, 
 I would wish to direct your attention for a moment to 
 an interesting, though as yet but imperfectly understood, 
 source of luminosity namely, the phenomenon of phos- 
 phorescence. We have doubtless most of us observed 
 the beautiful appearance of light in the ocean at night, 
 when the motion of the ship stirs up myriads of brightly 
 shining particles, and the crest of each wave is lighted up 
 with liquid fire. I may produce this phosphorescence 
 artificially, for if I write upon this board in the darkened 
 room with a piece of phosphorus, we see the letters 
 shining with a pale light. In this case certainly, and 
 probably also in that of the infusoria, glowworms, and 
 other animals and plants which phosphoresce, the evolu- 
 tion of light is accompanied by an act of oxidation or 
 slow combustion. But we have also evidence of cases 
 of phosphorescence which depend upon the power of 
 substances to absorb light and to give it out again after 
 lapse of some time. If I expose the powders contained 
 in these tubes to any source of intense light, such as the 
 sunlight or the rays obtained from this burning mag- 
 nesium wire, we shall find that on again darkening the 
 room, the tubes, or rather the substances which they 
 contain, remain visible ; each glowing with a different 
 colour red, green, or blue and exhibiting this phos- 
 phorescence for several hours after their exposure to 
 the light. 
 
 By means of his ingenious phosphoroscope, M. Ed. 
 
 Becquerel 1 has shown that a large number of bodies 
 
 phosphoresce for a very short space of time after they 
 
 are withdrawn from the action of the light. In order to 
 
 1 La Lunricre, vol. i. p. 207. 
 
LECT. IV.] 
 
 PHOSPHORESCENCE. 
 
 187 
 
 show the phosphorescence of this small crystal of fluor- 
 spar, I put it in the small stirrup (a, Fig. 52) placed 
 between the two rotating screens of the phosphoroscope, 
 and set our powerful electric light to shine upon the 
 back of the closed cylindrical box (Fig. 52, A B). From 
 the peculiar construction of the instrument, you cannot 
 
 FIG. 52. 
 
 see the light when by means of the handle I rotate the 
 perforated screens which move inside the fixed box ; for 
 these screens (P P and M M) are so arranged that when 
 the front slit (o) in the box is open that at the back is 
 closed, and vice versd. If 1 now cause the perforated 
 screens to rotate, the crystal will be exposed to the light 
 
188 SPECl'R UM ANALYSIS!, [ LECT. rv. 
 
 placed behind the box for a series of very short spaces of 
 time, and will also be seen by you through the front hole 
 for a series of equally short moments. If I turn the 
 handle slowly, after darkening the room, you do not see 
 the fluor-spar ; but if I increase the speed of rotation 
 so that the times of illumination and of observation do 
 not exceed the ToVoth P ai 't- f a second, you will observe 
 that the crystal glows with a very perceptible amount of 
 light, or in other words it becomes phosphorescent. This 
 crystal of nitrate of uranium produces a more brilliant 
 appearance. But many substances, such as sulphur, 
 quartz, the metals, and liquids, cannot be made thus to 
 phosphoresce. 
 
 Becquerel has carefully examined the spectra of these 
 phosphorescent bodies, and he has found that the light 
 emitted by many of them is of a peculiar kind ; that 
 they, in fact, give broken spectra, or bands of differently 
 coloured rays. Thus on Fig. 53 we have a representation 
 of the phosphorescent spectra of several substances : 
 alumina, when phosphorescent, emits a red light, and its 
 spectrum (No. 1) exhibits four bands between the lines c 
 and H in the solar spectrum ; diamond (No. 3) emits, when 
 phosphorescent, light of many degrees of refrangibility, 
 giving an almost continuous spectrum stretching from B 
 in the red to beyond a in the indigo ; aragonitc (4) also 
 gives a continuous spectrum ; whilst native phosphate of 
 lime (5), fluor-spar (6), and nitrate of uranium (7), each 
 phosphoresces with the emission of a peculiar light, as is 
 seen in the varying character of the above spectra. 
 
 The different rays of the solar spectra possess a very 
 different power of producing phosphorescence. By far 
 the most powerful in this respect are the more refrangible 
 rays. Phosphorescent bodies exposed to the chemically 
 
LECT. IV.] 
 
 FLUORESCENCE. 
 
 lb'9 
 
 active portion of the spectrum emit light which, as we 
 have seen, varies from red to violet, and as a rule depends 
 only upon the nature of the substance. 
 
 FIG. 53. 
 
 Another interesting property which certain substances 
 possess when exposed especially to these blue rays is that 
 of fluorescence. This piece of uranium glass appears self- 
 
190 SPECTR UM ANALYSIS. [LECT. i v. 
 
 luminous when held in the scarcely visible violet rays 
 of our electric lamp ; and this is produced by a change 
 of refrangibility of the light, the emitted rays being 
 always of lower refrangibility than the exciting rays. 
 This phenomenon of fluorescence may be used, thanks to 
 the researches of Stokes, for the purpose of identifying 
 certain substances, such as quinine, or the very inter- 
 esting substance resembling quinine lately discovered 
 in animal fluids and tissues by Dr. Bence Jones ; but 
 the spectra which fluorescent bodies emit are generally 
 continuous, and in this direction it does not therefore 
 seem likely that spectrum analysis will give us much 
 help. 
 
 In the next lecture I hope to bring before you the 
 simple facts upon which Professor Kirchhoff founded 
 his discovery of the chemical composition of the solar 
 atmosphere. 
 
APPEND. A.] SPECTRA OF THE GASES, ETC. 191 
 
 NIVERSITY 
 
 LECTUEE IV. APPENDIX A. 
 
 DESCRIPTION OF THE SPECTRA OF THE GASES AND NON-METAL- 
 LIC ELEMENTS, AND ON THE EXISTENCE OF MORE THAN 
 ONE SPECTRUM FOR EACH ELEMENT. 
 
 THE spectra of the gases are obtained, (1) by passing the 
 electric spark from poles of certain metals whose lines are 
 known, through the gas under the ordinary atmospheric pres- 
 sure ; or (2) by observing the electric discharge passed thro ugh- a 
 capillary tube (Geissler's) containing the gas in a rarefied state. 
 Kirchhoff and Huggins have adopted the first, Pliicker and 
 Hittorf (Phil. Trans. 1865, p. 1) the second method. 
 
 The, Air Spectrum. "The lines given in this spectrum are 
 present with all the electrodes when the spark is taken in air at 
 the common pressure. The lines thus obtained between one set 
 of electrodes of platinum and the other of gold were observed 
 simultaneously. The lines common to both these spectra were 
 measured as those due to the components of the air. The 
 spectrum thus obtained remains invariably constant, with 
 reference to the position and relative characteristics of its lines, 
 with all the metals which have been employed. The air spec- 
 trum varies as a ivhole, however, in distinctness according to 
 the metal employed as electrodes, owing to the difference in the 
 volatility of the metals, the air in and around the electrodes 
 being more or less replaced by the metallic vapours." The air 
 spectrum is made up of the spectra of the following components 
 nitrogen, oxygen, and hydrogen. Grandeau 1 and Kundt 2 have 
 observed the spectrum of lightning ; and, in addition to the 
 nitrogen and hydrogen spectra, have seen the bright yellow 
 sodium line. 
 
 1 Chemical News, ix. t>6. 2 Pogg. Ann. cxxxv. p. 315. 
 
192 SPECTHUM JlULmiZ [LRCT. iv. 
 
 Huggins has employed the air lines (seen on Plates and in 
 the Tables, Appendix 0, Lecture III.) as a scale of reference 
 for recognizing the bright lines of the metals. 
 
 Hydrogen. The spectrum of hydrogen seen under the ordinary 
 pressure consists of four bright lines (see Chromolith. No. 8, 
 facing Lecture VI.). 
 
 H a coincident with Frar.ntiofer'a f 1 in th.j reil. 
 
 H ,, ,, F ,, liluish green. 
 
 H y G in.ligo. 
 
 H 5 line near H violet. 
 
 The lines Ha, H/3, and H? are seen fine and very bright when 
 the gas is rarefied; but if the reduction of pressure be continued, 
 the red line Ha gradually disappears, whilst H/5, though fainter, 
 remains well defined. Pliicker finds that when the intensity of 
 the spark is increased the bands H/3 and Hy begin to broaden ; 
 and when the tension of the gas is increased to 360 mm. and a 
 Leyden jar introduced into the circuit to raise the temperature 
 of the discharge, the bright lines are found to give way to a 
 continuous spectrum. This change from lines to a continuous 
 spectrum is not observed under the ordinary atmospheric pressure. 
 Wiillner has recently shown 1 that by intensifying the discharge 
 through a Geissler's tube containing hydrogen, the tube and the 
 abraded particles of the glass become highly heated, so that first 
 the sodium line and afterwards the calcium lines make their 
 appearance, whilst at last the spectrum becomes continuous, 
 and the sodium line is reversed, giving a dark absorption line. 
 
 In a paper recently published, Wiillner (Phil. Mag. [4] xxxvii.) 
 fully describes the variation of the hydrogen spectrum with the 
 pressure: when the tension of the gas is 135 mm. the tube 
 shines with a white light of insufficient intensify to yield a 
 visible spectrum ; when the pressure is reduced to 100 mm. the 
 light emitted is bluish-white, and gives a continuous spectrum, 
 in which the lines Ha (C) and H/i? (F) stand out. Under a 
 pressure of 70 mm. the light is reddish-white, and the spectrum 
 is continuous with H, a, 0, and 7 visible, and also a series of 
 beautifully shaded bands in the greenish and reddish-yellow. 
 
 1 Pog. Ann. cxxxv. p. 174. 
 
APPEND. A.] SPECTRA OF HYDROGEN AND NITROGEN. 193 
 
 This spectrum becomes more brilliant as the pressure diminishes 
 to 30 mm. Under 21 mm. the lines H, a, /?, and 7 stand out 
 brilliantly, and the shaded bands with the continuous spectrum 
 become less intense. When the pressure is diminished to about 
 8 mm. the bands disappear, and the continuous spectrum becomes 
 almost invisible ; under further rarefaction to 3 or 2 mm. the 
 characteristic lines retain the same brightness, and everything 
 else disappears almost entirely from the spectrum. 
 
 According to Wullner, a still more remarkable change occurs 
 when the hydrogen-tube is exhausted to the extreme limit of 
 a Sprengel's pump : the light then suddenly becomes of a 
 splendid green, like the light of a thallium flame, and the spec- 
 trum is quite changed. The line H a can scarcely be seen, and 
 six splendid green lines appear on an almost black ground. 
 This spectrum is always exhibited when the tube has attained 
 the extreme degree of rarefaction of the Sprengel's pump ; and 
 if the discharge be continued for some time with the tube stop- 
 cock closed, a continuous spectrum appears, but this, on again 
 exhausting (although no change of density in the gas occurs), 
 yields the peculiar line spectrum just described. Wullner has 
 compared this spectrum with that of aluminium (of which metal 
 the electrodes were composed), mercury, and other substances, 
 traces of which might be present and might possibly cause the 
 appearance observed ; but he concludes from the non-coincidence 
 of the green lines with those of the metals, &c., that these former 
 are really due to hydrogen. Wullner concludes that difference 
 of temperature must in the case of hydrogen be regarded as the 
 cause of the essentially different spectra observed, and hence 
 that the emissive power of a substance may materially alter with 
 the temperature. 
 
 Nitrogen. In the spectrum of the electric spark when taken 
 in a current of pure nitrogen, under the ordinary pressure, a few 
 of the lines of common air are wanting, but no new lines appear. 
 The lines of the air-spectrum which remain in nitrogen preserve 
 their relative brightness and their distinctive character. In 
 the Tables these lines are distinguished by the letter N 
 (pp. 148 155). Pliicker and Hittorf have observed some remark- 
 
194 SPECTRUM ANALYSIS. [LECT. iv. 
 
 able changes which the nitrogen spectrum undergoes when the 
 current is intensified. Nitrogen, like other gases, does not allow 
 the induction current to pass when it is in an extreme state of 
 rarefaction ; but when its tension is only a fraction of a millimetre 
 the current passes, and the gas becomes- luminous. At a com- 
 paratively low temperature nitrogen thus ignited emits a golden 
 coloured light, giving a series of bands (see Chrornolith. No. 9, 
 facing Lecture VI.) ; above this point the colour becomes bluish, 
 and a new spectrum of bands appears. If a Leyden jar be 
 enclosed in the circuit, the temperature again rises, and a 
 brilliant white light is emitted, the spectrum again changing to 
 one of bright lines on a dark ground. These lines do not change 
 their position with alteration of temperature, though the bril- 
 liancy of all does not increase in the same ratio. Pliicker desig- 
 nates the spectra consisting of broad bands " spectra of the 
 first order;" whereas those composed of fine bright lines on a 
 dark background are termed " spectra of the second order." The 
 nitrogen spectrum of the second order is doubtless that of the 
 air-spectrum. The differences thus observed are attributed 
 by Pliicker to the existence of allotropic conditions of nitrogen 
 which decompose at high temperatures (for analogous pheno- 
 mena, see Appendix P>, Lecture V.). According to Kundt, the 
 spectrum of lightning varies with the nature of the discharge, 
 the difference being due to the appearance of the two nitrogen 
 spectra ; one of these (viz. the second spectrum of the first 
 kind) is also seen when the discharge of electricity from a point 
 is observed. The discharge of forked lightning gives a spectrum 
 consisting of bright lines, being the nitrogen spectrum of the 
 second order. Wlillner finds that the two different nitrogen 
 spectra cannot be changed one into the other by simply varying 
 the density of the gas, as is the case with oxygen, but that this 
 can only be effected by altering the mode of discharge, as by the 
 introduction of a Leyden jar into the circuit. (For Schuster's 
 explanation of the double nitrogen spectrum, see p. 198.) 
 
 Oxygen. The lines given by this gas are given in Huggins' 
 Tables, and designated by the letter 0. The same experimenter 
 found that some few lines appeared in the spectra of both 
 
APPEND. A.] SPECTRA OF THE NON-METALS. 195 
 
 nitrogen and oxygen. On further examination he finds that 
 the phenomenon is produced by the superposition in the air- 
 spectrum of lines of oxygen and nitrogen. Pliicker, operating 
 as with nitrogen, obtained only one " secondary " spectrum of 
 oxygen, but the lines appeared to expand so as to form a 
 continuous spectrum at a higher temperature. 
 
 Wiillner states that three distinct spectra of oxygen can be 
 obtained with induction currents according as the oxygen has a 
 greater or less density, and he concludes that these different 
 spectra depend on the temperature to which the particles of 
 oxygen are heated. More recently, however (Pogg. Ann. 1871, 
 No. 12), Wiillner admits that two of these reputed oxygen 
 spectra really consist of carbon spectra obtained from the 
 grease used in his air-pump. Wiillner, however, still asserts 
 that the differences observed in the hydrogen spectra are not 
 due to impurities. 
 
 Sulphur. When sulphur burns in the air, or when carbon 
 disulphide burns in nitric oxide, a continuous spectrum is 
 observed. If a little sulphur be introduced into a narrow 
 Geissler's tube, and the air withdrawn, a band spectrum of the 
 first order is seen upon warming the tube and passing the spark 
 through. On continuing to heat the tube, these bands change 
 to bright lines. A figure of these two spectra is given in Pliicker 
 and Hittorf's memoir. Salet has recently COD firmed the above 
 results, and believes that two spectra of sulphur really exist 
 (Comptes Eendus, 1871, No. 9). 
 
 Selenium likewise yields a characteristic spectrum. 
 
 Phosphorus yields a spectrum of the second order when 
 treated like sulphur. The characteristic lines are three bright 
 bands in the green, having the positions 58, 70, and 74 to 75, on 
 the scale of the spectroscope when Na = 50. The green line P/3 
 appears with one prism to be coincident with the green barium 
 line BaS. The green bands may be seen by observing the spectrum 
 of the green spot which makes its appearance in the interior 
 of a hydrogen flame when the slightest trace of a phosphorus 
 compound is placed in contact with the dissolving zinc (Cristofle 
 and Beilstein, Annales de Chimie et de Physique, 4 Sr. iii. 280). 
 
 o 2 
 
196 SPECTIWM ANALYSIS. [LECT. iv. 
 
 Chlorine, Bromine, and Iodine.- When enclosed in Geissler's 
 tubes, each gives a peculiar spectrum of bright lines, which 
 expand, and ultimately form continuous spectra when the tem- 
 perature is increased. Figures of these spectra are given in the 
 memoir above referred to. 
 
 Carbon. The complicated question of the carbon spectra has 
 been carefully investigated by W. M. Watts (Phil. Mag. Oct. 
 1869). He finds that there are four distinct modifications of the 
 spectrum of carbon, or, at any rate, of the spectrum obtained 
 from carbon compounds. 
 
 1. The carbon spectrum No. 1 is obtained when olefiant gas 
 and oxygen are burnt together in an oxyhydrogen jet. This 
 spectrum was first described by Swan, and afterwards by Attfield. 
 It can be obtained from each of the following carbon compounds : 
 olefiant gas, cyanogen, 1 carbonic oxide, carbon disulphide, carbon 
 tetrachloride, amyl alcohol, marsh gas, and naphthalin (No. 10 
 of the Chromolith. facing Lecture VI.), and must, therefore, be 
 produced by carbon vapour. 
 
 2. Carbon spectrum No. 2 is obtained when carbonic oxide 
 or olefiant gases are heated in a Geissler's vacuum tube, when 
 the pressure on the gas does not exceed 12 mm. of mercury. 
 
 3. Carbon spectrum No. 3 is seen in the Bessemer-flame, 
 observed not only in the flame during the process of conversion, 
 but also in the " Spiegel-flame," and in the coke-flame of the 
 converter and of other furnaces. This is not identical with the 
 carbonic oxide spectrum. 
 
 4. The fourth modification of the carbon spectrum is obtained 
 from the induced spark, either from carbonic acid or carbonic 
 oxide, when a Leyden jar is introduced into the circuit. The 
 spectrum thus obtained consists of sharply-defined lines, and 
 not of bands as seen in the former modifications. 
 
 Still more recent experiments by the same author show that 
 the existence of the third of the above carbon spectra is more 
 
 than doubtful. (See Lecture IV., Appendix E.) 
 
 .? 
 
 1 The cyanogen spectrum varies according to its mode of production. No. 11 
 Chromolith. Plate facing Lecture V I. shows the spectrum of the flame of cyanogen 
 burning in air. 
 
APPEND. A.] ON SO-CALLED DOUBLE SPECTRA. 1<J7 
 
 ON THE EXISTENCE OF MOKE THAN ONE SPECTRUM FOR 
 EACH ELEMENT. 
 
 The discussion as to the existence of more than one spectrum 
 for each elementary gas is still being carried on. In a recent 
 communication (Comptes Rcndus, Aug. 7, 1871), Angstrom re- 
 asserts his conclusion that hydrogen and oxygen have each but 
 one spectrum, that of hydrogen being the one found in the sun 
 and stars. He bases his opinion on the difficulty of obtaining 
 any gas perfectly pure in an extreme state of rarefaction ; thus 
 on one occasion he rarefied air in a Geissler's tube as much as 
 possible by a mercurial pump, causing the discharge of a Buhm- 
 korff' 's coil to pass through the tube, and obtained in succession 
 the following spectra : (1) the ordinary air-spectrum ; (2) the 
 fluted spectrum of nitrogen ; (3) that of carbonic oxide ; (4) the 
 lines of chlorine and sodium. If the vacuum has been produced 
 by mercury, the spectrum of this metal may be obtained ; and if 
 the cases are dried by sulphuric acid or anhydrous phosphoric 
 acid, the spectra of sulphur or phosphorus may make their 
 appearance. Angstrom then proceeds to criticise Wullner's 
 four different hydrogen spectra. One of these is the true 
 hydrogen spectrum of fine lines, and this does change into one 
 consisting of bright bands or into a continuous spectrum (as 
 Angstrom himself stated was the case in 1853), when a denser 
 gas is used. The other two of Wullner's hydrogen spectra 
 Angstrom disposes of by showing that the spectrum of acety- 
 lene, as observed by Berthelot, is identical with one, whilst the 
 other is identical with the sulphur spectrum. 
 
 As regards the two new spectra found by Wiillner for oxygen, 
 Angstrom shows that the lines of the one are identical with 
 those of the oxide of carbon spectrum (and this has since been 
 admitted by Wiillner to be the case see Pogg. Ann. 1871, No. 
 12, p. 521), whilst the other, beyond doubt, contains the lines of 
 chlorine. Hence Angstrom concludes that we do not know of 
 any other spectrum of oxygen besides the one discovered by him 
 in 1853, and subsequently accurately examined by Pliicker. 
 The variation observed in the spectra of certain gases by the 
 
198 SPECTRUM ANALYSIS. [LECT. iv. 
 
 action of magnetism Angstrom ascribes, not to the existence of 
 different spectra for one substance, but to the production, by the 
 magnetization, of new compounds or new substances, an action 
 similar to that produced by inserting a Leyden jar or condenser 
 in the circuit. Thus a Geissler's tube gave between the poles of 
 an electro-magnet the ordinary spectrum of carburetted hydrogen, 
 whereas without the intervention of magnetism it gave the 
 carbonic oxide spectrum without the hydrogen lines being 
 visible ; whilst another tube containing hydrogen obtained from 
 water and dried over sulphuric acid, which gave Pliicker's two 
 hydrogen spectra, gave, when under the influence of magnetism, 
 the sulphur lines (believed by Wiillner to be a new hydrogen 
 spectrum), whilst at the same time the carbonic oxide lines 
 were seen near the poles. 
 
 Wiillner has since acknowledged that one of his supposed 
 oxygen spectra was caused by carbon, but does not admit 
 Angstrom's general conclusions. (Pogg. Ann. Bd. cxliv. 520.) 
 
 ON THE SPECTRUM OF NITROGEN. 1 
 
 BY ARTHUR SCHUSTER, STUDENT AT THE PHYSICAL LABORATORY 
 OF OWENS COLLEGE. 
 
 (Communicated ly BALFOUR STEWART, F.RS.) 
 
 1. Introductory. The formation of the different spectra which 
 one gas is said to exhibit when examined under different con- 
 ditions still remains one of the most obscure points of spec- 
 trum analysis. In 1864, when Pliicker and Hittorf published 
 their researches " On the Spectra of Ignited Gases and Vapours, 
 with especial regard to the different spectra of the same ele- 
 mentary gaseous substance," 2 they drew attention to the close 
 resemblance in character of the band spectra which certain metals 
 yield at a comparatively low temperature to the band spectrum 
 of nitrogen and sulphur. Roscoe and Clifton, in their paper " On 
 the Effect of Increased Temperature upon the Nature of the 
 Light emitted by the Vapour of certain Metals or Metallic Com- 
 
 1 Proc. Roy. Soc. 1872. 2 Phil. Trans, vol. civ. p. 1. 
 
APPEND. A.] THE SPECTRUM OF NITROGEN. 199 
 
 pounds/' 1 rendered it probable that the band spectra of the metals 
 belonged really to the oxides. The two spectra of nitrogen 
 were not, however, examined from that point of view ; but on 
 the contrary, they were made the starting-point of new in- 
 vestigations by Wiillner, who came to the conclusion that 
 certain gases may give even more than two different spectra. 
 Angstrom, 2 expressing his doubts about the trustworthiness of 
 Wlillner's experiments, says in a note : " As regards the spectra 
 which are usually attributed to nitrogen, I mention here, as 
 a general fact, that it is my conviction that the fluted bands 
 which are so characteristic of the oxides of metals are never 
 found in spectra of elementary gases." 
 
 I propose to show in the present communication 
 
 (1) That pure nitrogen gives only one spectrum ; 
 
 (2) That this is the line-spectrum ; 
 
 (3) That the fluted spectrum of the flrst order is due to oxides 
 of nitrogen formed under the influence of the electric spark 
 
 2. First Experiment. The first experiment which I made with 
 respect to the spectrum of nitrogen was a repetition of an experi- 
 ment of Secchi, who found that, in different sections of the same 
 tube, three different spectra of nitrogen might be obtained. A 
 vacuum tube was made exactly according to Secchi's descrip- 
 tion, filled with nitrogen and exhausted. To my astonishment, 
 the tube showed, even in its widest parts, only a spectrum of 
 lines. No accurate measurements were taken at the time, but 
 the spectrum was, no doubt, that of the second order described 
 by Pliicker. Suddenly, and while I was looking through the 
 spectroscope, the spectrum changed, and the well-known fluted 
 bands appeared. The first spectrum could now easily be ob- 
 tained by introducing a Leyden jar in the circuit. The spark 
 very soon ceased to pass, and it was then found that the tube 
 was leaking. 
 
 3. The behaviour of this tube at once suggested the idea that 
 the presence of air was necessary for the formation of the fluted 
 spectrum. It is well known that the oxides of nitrogen are 
 
 1 Chem. News, v. 233. 2 Comptes Reudus, Aug. 1871. 
 
200 SPECTRUM ANALYSIS. [LBCT. iv. 
 
 formed on passing an electric spark through air, and the resem- 
 blance which this spectrum bears to the spectra of the oxides of 
 metals rendered this view probable. 
 
 In order to test it, a series of experiments were made, showing 
 that (a) Whenever the fluted spectrum appeared, it could be 
 shown that traces of oxygen were present ; (6) whenever there 
 was a certainty of no oxygen being present, the spectrum 
 of the second order appeared under all pressures and at all 
 temperatures. 
 
 In order to free the nitrogen from every trace of oxygen, 
 I adopted, at Dr. Stewart's suggestion, the plan of heating a 
 small piece of sodium placed in the vacuum tube. This proved 
 in each case perfectly satisfactory; for when every trace of 
 oxygen had thus been absorbed, the line spectrum alone was 
 invariably obtained. The formation of the fluted spectrum does 
 not imply that all the nitrogen in the tube has been oxidized ; 
 it has been remarked by different observers, and especially 
 noticed by Pliicker, that when the spark passes through a 
 mixture of two gases, the spectrum of one only is often seen. 
 
 4. Wave-lengths of the two Spectra. There is no possibility 
 of confounding the two spectra. The fluted spectrum is well 
 known by its beautifully shaded violet bands, but in order to 
 exclude any possibility of error, their position was read off on 
 the reflecting scale of the spectroscope ; the measurements were 
 reduced to wave-lengths, and the following numbers obtained 
 for the least refrangible end of the bands in tenth-metre. 1 
 
 FLUTED SPECTRUM. 
 
 5129 4436 
 
 4981 4390 
 
 4649 4318 
 
 4556 4237 
 
 As the measurements were taken merely for the sake of 
 reference, they do not lay claim to great accuracy. The true 
 spectrum of nitrogen is easily recognized by a very bright 
 green line, followed at a small distance towards the more re- 
 frangible parts by a green band. It also contains some violet 
 
 1 A tenth-metre, according to Angstrom, means a metre divided by 10 10 . 
 
APPEND. A.] THE SPECTRUM OF NITROGEN. 201 
 
 bands which are not shaded. The position of the principal 
 lines was read off; their wave-lengths as determined by Dr. 
 Marshall Watts from the measurements made by Pliicker are 
 as follows : 
 
 LINE SPECTRUM. 
 
 6243 5767 4214 | 
 
 6176 5666 4199 ) 
 
 6087 5164 (the green line) 4184 ) 
 
 6051 4894 4170 i 
 
 5908 4644 
 
 5. Description of Apparatus. The tubes generally used had 
 two pockets, A and B, into which small pieces of metallic sodium 
 
 were introduced by means of the tubes c and r>. The tube c 
 was connected with the receiver containing the nitrogen, whilst 
 the tube D was connected with the air-pump. The nitrogen 
 was generally prepared by the combustion of phosphorus in air. 
 After a few hours' standing, when all the phosphoric acid formed 
 had been absorbed, the gas became quite clear, and was ready 
 for use. 
 
 This mode of preparation, it is true, does not give the nitrogen 
 very pure ; but as my object was to get the nitrogen free from 
 oxygen, and this was easily obtained by means of the absorption 
 by sodium, the method was found sufficient. Other modes of 
 preparing the nitrogen were tried, such as passing air over red- 
 hot copper or the decomposition of ammonia by chlorine, but 
 the same results were invariably obtained. The air-pump used 
 was that of Carre's freezing machine, with which pressures 
 down to two millimetres could be easily obtained. When the 
 pressure was measured, a T-shaped tube was employed, one 
 side of which was connected with the Geissler's tube, the other 
 with the pump ; while the mercury was drawn up in the longer 
 
202 SPECTRUM ANALYSIS. [LKCT. iv. 
 
 part of the tube, its height was read off, and compared with a 
 barometer. I now pass to the description of the experiments. 
 
 6. Method of experimenting. When the air in the vacuum 
 tube had been exhausted, the communication with the receiver 
 containing the nitrogen was opened, and the gas was allowed 
 to pass through it for some time, while the pump was being 
 worked. The tubing connecting the tube with the receiver 
 was then clamped air-tight, and the tube was exhausted. The 
 electric spark in passing through it exhibited a violet colour, 
 and gave the spectrum of fluted bands 
 
 5129 4436 
 
 4981 4390 
 
 4649 4318 
 
 4556 4239 
 
 The sodium was next heated until it presented a clean metallic 
 surface. The light which the tube now emitted was bluish- 
 white, and much fainter than before, and the whole appearance 
 of the spectrum had changed to that of the second order with 
 its characteristic green line. It was, however, found that the 
 pressure in the tube had slightly increased, owing, most likely, 
 to the vapour of the sodium present ; and on bringing the 
 mercury to its former level, the spectrum became brighter, but 
 remained the same in character. New nitrogen was then led 
 into the tube, and, after exhaustion, the old fluted spectrum 
 again appeared. This was, however, at once changed into that 
 of lines by heating the sodium. This process was repeated 
 several times in succession, but invariably with the same result. 
 I have in my possession two tubes, sealed off under 2 mm. 
 pressure, one without sodium, showing the fluted bands, the 
 other containing sodium, showing the spectrum of lines. Two 
 other tubes, sealed off under 15 mm. pressure, show the same 
 thing. I .have repeatedly convinced myself that, from the 
 highest pressure under which the spark of the induction coil 
 passes, to the lowest pressure which I could obtain with an 
 ordinary air-pump, pure nitrogen invariably gave one and the 
 same line-spectrum. Once when I intended to seal a tube off 
 under higher pressure, it was found that the sodium was not 
 
APPEND. A.] SPECTRUM OF THE NITROGEN OXIDES. 203 
 
 sufficient to absorb all the oxygen present, so that a sort of 
 mixture of the two spectra was seen. Such a mixture was 
 often observed by Pliicker and Wiillner at the point where one 
 spectrum changed into the other. It is characterised by the 
 green line of nitrogen and the fluted violet bands at the same 
 time. The tube showing the mixture at 15 mm. pressure was 
 gradually exhausted, but the spectrum remained exactly the 
 same. If the formation of the two spectra depend merely upon 
 the pressure or temperature to which the gas is subjected, how 
 can a mixture of the two spectra indicating a state of transi- 
 tion exist under so entirely different pressures and different 
 temperature ? 
 
 In order to ascertain whether nitrogen, even carefully prepared, 
 contains oxygen, a drop of a solution of iodide of potassium and 
 starch was introduced into the tube. After the spark had passed 
 for a few seconds only, the liquid was coloured blue, showing 
 either the formation of oxides of nitrogen or of ozone ; but, at 
 any rate, the presence of oxygen. 
 
 7. Spectrum of Oxides of Nitrogen. I tried to obtain the 
 spectra of the different oxides of nitrogen. They all give the 
 same fluted spectrum, and I could get no information as to which 
 particular oxide the fluted spectrum is due. This is, however, 
 easily understood, if we remember that it is just as difficult to 
 prepare the oxides of nitrogen free from oxygen as pure nitrogen 
 itself, so that the oxide giving the spectrum in question will 
 always be formed. I have, however, convinced myself that the 
 absorption bands of nitrous acid gas are not coincident with the 
 bright bands of the spectrum, and it is probable that the spec- 
 trum is due to nitric oxide, this being the most stable of all 
 the oxides of nitrogen. 
 
 I may add, that one of the tubes containing the sodium and 
 showing the lines one day cracked, and then at once showed the 
 violet bands. This fact will not be easily explained by the 
 assumption that the fluted spectrum belongs to a lower pressure 
 and lower temperature than the spectrum of lines. 
 
 I propose to subject the different spectra of the remaining 
 gases to a careful examination. 
 
204 SPECTRUM ANALYSIS. [LECT. iv. 
 
 The above experiments were made in the Physical' Laboratory 
 of Owens College, Manchester, and I have to thank Professors 
 Balfour Stewart and Eoscoe for many valuable suggestions. 
 
 APPENDIX B. 
 
 ON THE EFFECT OF INCREASED TEMPERATURE UPON THE NATURE 
 OF THE LIGHT EMITTED BY THE VAPOUR OF CERTAIN METALS 
 OR METALLIC COMPOUNDS. 
 
 BY H. E. EOSCOE AND R. B. CLIFTON. 1 
 
 In a letter communicated to the Philosophical Magazine for 
 January last we stated that, in examining, with Steinheil's form 
 of Kirchhoff and Bun sen's apparatus, the spectra produced by 
 passing the induction spark over beads of the chlorides and 
 carbonates of lithium and strontium, we had observed an 
 apparent coincidence between the blue lithium line, which is 
 seen only when the vapour of this metal is intensely heated, 
 and the common blue strontium line called Sr & We further 
 stated that on investigating the subject more narrowly by the 
 application of several prisms and a magnifying power of 40, 
 we came to the conclusion that the lithium blue line was some- 
 what more refrangible than the strontium $, but that two other 
 more refrangible lines were observed to be coincident in both 
 spectra. Having constructed a much more perfect instrument 
 than we at that time possessed, we are now able to express a 
 definite opinion on the subject, and beg to lay a short notice of 
 our observations before the Society. Our instrument is in all 
 essential respects similar to the magnificent apparatus em- 
 ployed by Kirchhoff in his recent investigations on the solar 
 spectrum and the spectra of the chemical elements. It consists 
 of a horizontal plane cast-iron plate, upon which three of Stein- 
 heil's Munich prisms, each having a refracting angle of 60, are 
 placed; and of two tubes fixed into the plate, one being a 
 telescope having a magnifying power of 40, moveable with a 
 
 1 Proc. Lit. Phil. Soc. Manchester, read April 1, 1862. 
 
APPEND. B.] ACTION OF INCREASED TEMPERATURE. 205 
 
 slow-motion screw about a vertical axis placed in the centre of 
 the plate, and the other being a tube carrying at one end the 
 slit, furnished with micrometer screw, through which the beam 
 of light passed, and at the other end an object-glass for the 
 purpose of rendering the rays parallel. The luminous vapours 
 of the metals under examination were obtained by placing a 
 bead of the chloride or other salt of the metal on a platinum 
 wire, between two platinum electrodes, from which the spark of 
 a powerful induction coil could be passed. In order to obtain 
 a more intense, and therefore a hotter, spark than can be got 
 from the coil alone, the coatings of a Ley den jar were placed in 
 connection with electrodes of the secondary current respectively. 
 When this arrangement was carefully adjusted, the two yellow 
 sodium lines were observed to be separated by an apparent 
 interval of two millimetres, as seen at the least distance of 
 distinct vision. 
 
 The position of the blue line, or rather blue baud, of lithium 
 was then determined with reference to the fixed reflecting scale 
 of Steinheil's instrument, by volatilizing the carbonate of lithium 
 in the first place on a platinum wire between platinum elec- 
 trodes, and secondly on a copper wire between copper electrodes. 
 A bead of pure chloride of strontium was then placed on new 
 platinum and copper wires between two new platinum and 
 copper electrodes, and the position of the blue line Sr 8 read off 
 upon the same fixed scale : a difference of one division on the 
 scale was seen to exist between the positions of the two lines, 
 the lithium line being the more refrangible. The salts of the 
 two metals were then placed between the poles at the same time, 
 arid both the blue lines were simultaneously seen, separated by 
 a space about equal to that separating the two sodium lines. 
 When experimenting with this complete instrument, we were 
 unable to observe any other blue lines in the pure lithium spec- 
 trum than the one above referred to ; we have however noticed 
 the formation of four new violet lines in the intense strontium 
 spectrum, and we now believe that the other two lithium lines 
 mentioned in our letter to the Philosophical Magazine are caused 
 by the presence of the most minute trace of strontium floating 
 
206 SPECTRUM ANALYSIS. [LECT. iv. 
 
 in the atmosphere, and derived from a previous experiment, 
 We have convinced ourselves by numerous observations that the 
 currents of air caused by the rapid passage of the electric spark 
 between the electrodes are sufficient to carry over to a second 
 set of electrodes placed at the distance of a few inches a very 
 perceptible quantity of the materials undergoing volatilization. 
 The greatest precautions must hence be taken when the spectra 
 of two metals have to be compared ; and no separate observa- 
 tions of the two spectra can be relied upon, unless one is made 
 a considerable space of time after the other, and unless all 
 the electrodes which have been once used are exchanged for 
 new ones. 
 
 Kirch hoff, in his interesting Memoir on the Solar Spectrum 
 and the Spectra of the Chemical Elements, 1 noticed in the case 
 of the calcium spectrum that bright lines which were invisible 
 at the temperature of the coal-gas flame became visible when 
 the temperature of the incandescent vapour reached that of the 
 intense electric spark. 
 
 We have confirmed this observation of KirchhofY's, and have 
 extended it, inasmuch as we, in the first place, have noticed that 
 a similar change occurs in the spectra of strontium and barium ; 
 and, in the second place, that not only new lines appear at 
 the high temperature of the intense spark, but that the broad 
 bands, characteristic of the metal or metallic compound at the 
 low temperature of the flame or weak spark, totally disappear 
 at the higher temperature. The new bright lines which supply 
 the part of the broad bands are generally not coincident with 
 any part of the band, sometimes being less and sometimes more 
 refrangible. Thus the broad band in the flame spectrum of cal- 
 cium named Ca/3 is replaced in the spectrum of the intense 
 calcium spark by five fine green lines, all of which are less 
 refrangible than any part of the band Ca/3; whilst, in the place 
 of the red or orange Ca a, three more refrangible red or orange 
 lines are seen (see Fig. 39). The total disappearance in the spark 
 of a well-defined yellow band seen in the calcium spectrum at 
 
 1 Kirchhoff on the Solar Spectrum, &c. Translated by H. E. Eoscoe. (Cam- 
 bridge : Macmillan, 1862.) 
 
APPEND, c.] VARIATION OF SPECTRA. 207 
 
 the lower temperature was strikingly evident. We have assured 
 ourselves, by repeated observations, that, in like manner, the 
 broad bands produced in the flame spectra of strontium and 
 barium compounds, and especially Sr a, Sr {3, Sr 7, Ba a, Ba /3, 
 Ba 7, Ba S, Ba e, Ba //-, disappear entirely in the spectra of the 
 intense spark, and that new bright non-coincident lines appear. 
 The blue Sr 8 line does not alter either in intensity or in position 
 with alterations of temperature thus effected, but, as has already 
 been stated, four new violet lines appear in the spectrum of 
 strontium at the higher temperature. 
 
 If, in the present incomplete condition of this most interesting 
 branch of inquiry, we may be allowed to express an opinion as 
 to the possible cause of the phenomenon of the disappearance 
 of the broad bands and the production of the bright lines, we 
 would suggest that, at the lower temperature of the flame or 
 weak spark, the spectrum observed is produced by the glowing 
 vapour of some compound, probably the oxide, of the difficultly 
 reducible metal ; whereas at the enormously high temperature 
 of the intense electric spark these compounds are split up, and 
 thus the true spectrum of the metal is obtained. 
 
 In conclusion, we may add that in none of the spectra of 
 the more reducible alkaline metals (potassium, sodium, lithium) 
 can any deviation or disappearance of the maxima of light be 
 noticed on change of temperature. 
 
 APPENDIX C. 
 
 KIRCHHOFF ON THE VARIATION OF THE SPECTRA OF CERTAIN 
 ELEMENTS: 1862. 
 
 " I close this section with the following remarks : The position 
 of the bright lines, or, to speak more precisely, the maxima of 
 light in the spectrum of an incandescent vapour, is not dependent 
 upon the temperature, upon the presence of other vapours, or 
 upon any other conditions except the chemical constitution of 
 the vapour. Of the validity of this conclusion Bunsen and 
 1 have assured ourselves by experiments made for that special 
 
208 SPECTRUM ANALYSIS. [LECT. iv. 
 
 object, and I have confirmed it by many observations made 
 with the extraordinary delicate instrument just described. The 
 appearance of the spectrum of the same vapour may, neverthe- 
 less, be very different under different circumstances. Even the 
 alteration of the mass of the incandescent gas is sufficient to 
 effect a change in the character of the spectrum. If the thick- 
 ness of the film of vapour, whose light is being examined, be 
 increased, the luminous intensities of all the lines increase, but 
 in different ratios. By virtue of a theorem which will be con- 
 sidered in the next section, the intensity of the bright lines 
 increases more slowly than that of the less visible lines. The 
 impression which a line produces on the eye depends upon its 
 breadth as well as upon its brightness. Hence it may happen 
 that one line being less bright, although broader, than a second, 
 is less visible when the mass of incandescent gas is small, but 
 becomes more distinctly seen than the second line when the 
 thickness of the vapour is increased. Indeed, if the luminosity 
 of the whole spectrum be so lowered that only the most striking 
 of the lines are seen, it may happen that the spectrum appears 
 to be totally changed when the mass of the vapour is altered. 
 Change of temperature appears to produce an effect similar to 
 this alteration in the mass of the incandescent vapour. If the 
 temperature be raised, no deviation of the maxima of light is 
 observed, but the intensities of the lines increase so differently, 
 that those which are most plainly seen at a high temperature 
 are not the most visible at a low temperature." 
 
 APPENDIX D. 
 
 IGNITED GASES UNDER CERTAIN CIRCUMSTANCES GIVE CON- 
 TINUOUS SPECTRA. COMBUSTION OF HYDROGEN IN OXYGEN 
 UNDER GREAT PRESSURE. 1 
 
 It has long been known that the flames of several gases, such 
 as carbonic oxide, burning in the air to form gaseous products of 
 combustion, give continuous spectra. Dibbits 2 in 1864 pointed 
 
 1 Frankland, Proc. Roy. Soc. xvi. p. 419. 2 Pogg. Ann. cxxii. 497. 
 
APPEND. D.] DIFFERENT CARBON SPECTRA. 209 
 
 out that, when oxygen and hydrogen are burnt in exactly the 
 proportions to form water, a faint continuous spectrum alone is 
 seen, neither the hydrogen nor the oxygen lines being visible. 
 He states that the following gaseous products of combustion, viz. 
 water, hydrochloric acid, sulphur dioxide, and carbon dioxide, 
 exhibit continuous spectra when they are heated to incandes- 
 cence. Frankland has recently shown that, when hydrogen gas is 
 burnt in oxygen gas under a pressure gradually increasing up to 
 twenty atmospheres, the feeble luminosity of the flame becomes 
 gradually augmented, until at a pressure of ten atmospheres the 
 light emitted by a jet about one inch long is amply sufficient to 
 enable an observer to read a newspaper at a distance of two feet 
 from the flame. Examined by the spectroscope, the spectrum of 
 this flame is bright and perfectly continuous from red to violet. 
 A similar increase of luminosity was observed in the case of 
 carbonic oxide gas burning in oxygen under pressure ; and with 
 this gas the spectrum, both when burning under the pressure of 
 the atmosphere and higher pressures, is a continuous one. This 
 has also long been known to be the case with the combustion of 
 carbon disulphide in oxygen or nitric oxide, and with that of 
 arsenic and phosphorus in oxygen. In these combustions Dr. 
 Frankland believes it to be impossible that the continuous spec- 
 trum is due to glowing solid matter, as the temperature at which 
 these products of combustion are volatilized is much below the 
 point at which bodies become luminous, and he expresses the 
 opinion (" Lectures on Coal Gas," see Journal of Gas Lighting, 
 March 1867) that the luminosity of a candle or coal-gas flame 
 is not clue to the incandescence of the particles of solid carbon 
 separated out and heated in the flame, according to the gene- 
 rally received explanation of Davy, but that it is produced by 
 the ignition of highly condensed gaseous hydrocarbons ; and 
 he considers himself supported in this view by the fact that 
 the luminosity of a candle flame diminishes proportionally 
 to the diminution of the atmospheric pressure under which 
 it burns. 1 
 
 However extensively future research may modify the pro- 
 
 1 Frankland, Phil. Trans, vol. cli. p. 629, for 1861. 
 P 
 
210 SPECTR UM ANALYSIS. [LECT. i v. 
 
 position that gases give discontinuous spectra, it is well to 
 remember that the theory of exchanges, upon which the science 
 of Spectrum Analysis is based, does not give us any information 
 as to whether a gas yields a continuous or a broken spectrum. 
 This theory states that a gas or any other body which when 
 incandescent is perfectly transparent to a certain class of rays, 
 cannot emit these rays ; but that it must emit any rays to which 
 it is not perfectly transparent. 
 
 If a glowing gas under great pressure absorbs some of each 
 kind of the rays which fall upon it, it must emit a continuous 
 spectrum. Even under diminished pressure many gases exhibit 
 traces of a continuous spectrum : this is seen clearly in a name 
 coloured by sodium or potassium salt. Kirchhoff has shown that 
 when the temperature or density of a glowing gas is increased 
 and the luminosity of the spectrum becomes more intense, the 
 dark portions of the spectrum must increase in luminosity more 
 rapidly than the bright portions. Hence it does not appear 
 surprising that by increase of temperature and pressure the 
 spectrum originally consisting of bright lines or bands upon a 
 scarcely visible continuous background should gradually change 
 into a spectrum exhibiting all the colours with an equal degree 
 of intensity. 1 
 
 APPENDIX E. 
 
 ON THE SPECTRUM OF THE BESSEMER FLAME. 
 BY W. M. WATTS, D.S.C. 2 
 
 The October number of the Philosophical Magazine con- 
 tains translations of two Papers by Professor Lielegg, giving the 
 
 1 H. St. Claire Deville (Phil. Mag. Fourth Series, vol. xxxvii. p. Ill) explains 
 the increase of luminosity in gases burnt under pressure by the consequent 
 increase of the temperature of the flame, and does not endorse Frankland's views 
 with reference to the source of light in a candle flame. This is in fact the same 
 explanation of the phenomena as that given by Kirchhoff. 
 
 2 Phil. Mag. (4), xxxiv. 437. 
 
APPEND. E.j SPECTRUM OF BESSEMER FLAME. 211 
 
 results of his observations on the spectrum of the Bessemer 
 flame. As these results are published as entirely new, and no 
 mention is made of any prior observations, it is only right that 
 attention should be called to the fact that as long ago as 1862 
 the same results had been obtained by Professor Eoscoe, and 
 were published in the form of a short preliminary notice in 
 the " Proceedings of the Manchester Literary and Philosophical 
 Society" for February 24th, 1863. As the note is extremely 
 short, I venture to transcribe it in full : 
 
 "Professor Pioscoe stated that he had been for some little 
 time, and is still, engaged in an interesting examination of the 
 spectrum produced by the flame evolved in the manufacture of 
 cast steel by the Bessemer process, on the works of Messrs. 
 John Brown and Co. of Sheffield. The spectrum of this highly 
 luminous and peculiar flame exhibits during a certain phase of 
 its existence a complicated but most characteristic series of 
 bright lines and dark absorption bands. Amongst the former the 
 sodium, lithium, and potassium lines are most conspicuous ; but 
 these are accompanied by a number of other, and as yet undeter- 
 mined, bright lines : whilst among the absorption bands those 
 formed by sodium vapour and carbonic oxide can be readily 
 distinguished. Professor Eoscoe expressed his belief that this 
 first practical application of the spectrum analysis will prove of 
 the highest importance in the manufacture of cast steel by the 
 Bessemer process, and he hoped on a future occasion to be in a 
 position to bring the subject before the Society in a more 
 extended form than he was at present able to do." 
 
 In a lecture delivered before the Royal Institution (May 6, 
 1864), a year later than the communication quoted above, Dr. 
 Eoscoe described the Bessemer spectrum more fully, and pointed 
 out the existence of lines produced by carbon, iron, sodium, 
 lithium, potassium, hydrogen, and nitrogen. 
 
 An important practical result of the observations on which 
 these communications were based was the discovery that the 
 exact point of decarbonization could be determined by means 
 of the spectroscope with much greater exactitude than from the 
 appearance of the flame itself, the change in which indicating 
 
 P 2 
 
212 SPECTR UM ANALYSIS. [LECT. i v 
 
 the completion of the process is minute, and requires a length- 
 ened experience to detect with certainty. This method of deter- 
 mining the point at which it is necessary to stop the blast was 
 indeed at that time (1863) in constant use at Messrs. Brown's 
 works at Sheffield, and has since been introduced with equal 
 success by Mr. Eamsbottom (at the suggestion of Dr. Eoscoe) 
 at the London and North-Western Eailway Company's steel- 
 works at Ore we. 
 
 I was at that time acting as inspector to Professor Eoscoe, 
 and in that capacity conducted a lengthened examination of the 
 Bessemer spectrum at the works at Crewe, The results of that 
 investigation were not published at the time, on account of their 
 incompleteness ; and I have since then continued in Glasgow 
 the same research, which has now extended itself into an inquiry 
 into the nature of the various spectra produced by the carbon 
 compounds. These experiments are still incomplete ; but, under 
 the circumstances of the publication of Professor Lielegg's 
 papers, I have put together a few of the more important results 
 obtained in the examination of the Bessemer spectrum. 
 
 The changes which take place in the spectrum from the 
 commencement of the " blow " to its termination are extremely 
 interesting. When the blast is first turned on, nothing is seen 
 but a continuous spectrum. In three or four minutes the sodium 
 line appears flashing through the spectrum, and then becoming 
 continually visible ; and gradually an immense number of lines 
 become visible, some as fine bright lines, others as intensely 
 dark bands ; and these increase in intensity until the conclusion 
 of the operation. The cessation of the removal of carbon from 
 the iron is strikingly evidenced by the disappearance of nearly 
 all the dark lines and most of the bright ones. 
 
 The spectrum is remarkable from the total absence of lines in 
 the more refrangible portion ; it extends scarcely beyond the 
 solar line I. 
 
 No. 2, Fig. 54, represents the general appearance of the Bes- 
 semer spectrum towards the close of the " blow," drawn accord- 
 ing to the plan proposed by Bunsen (see page 67). It must 
 be remarked, however, that at the period of greatest intensity 
 
APPEND. E.J SPECTRUM OF BESSEMER FLAME. 
 
 '213 
 
 almost every bright band is seen to be composed of a great 
 number of very fine lines. 
 
 The occurrence of absorption lines in the Bessemer spectrum 
 is iii itself extremely probable ; and that this is the case appears 
 almost proved by the great intensity of some of the dark lines 
 of the spectrum. It was with this view that the investigation 
 was commenced, with the expectation that the spectrum would 
 prove to be a compound one, in which the lines of iron, carbon, 
 or carbonic oxide, &c. would be found, some as bright lines, 
 others reversed as dark absorption bands. To a certain extent 
 this anticipation has been verified ; but the great mass of the 
 lines, including the brightest in the whole spectrum, have not as 
 yet been identified. 
 
 MITT 
 
 NO. 3. 
 
 I* 116 |M 
 
 iiiiiiiiliiiiliiiiliiiiiiiiiiiiiiliiTiiiin 
 i* 
 
 FIG. 54. 
 
 In dealing with a complicated spectrum like that of the Bes- 
 semer flame, it is indispensable that the spectrum should be 
 actually compared with each separate spectrum of the elements 
 sought. This was the plan actually pursued ; the spectroscope 
 was so arranged that the spectrum of the Bessemer flame was 
 seen in the upper half of the field of view, and the spectrum 
 with which it was to be compared was seen immediately below. 
 In no other way can any satisfactory conclusion be obtained as 
 to the coincidence or non-coincidence of the lines with those of 
 known spectra. 
 
 The spectrum of the Bessemer flame was thus compared with 
 the following spectra : 
 
 (1) Spectrum of electric discharge in a carbonic oxide vacuum. 
 
 (2) Spectrum of strong spark between silver poles in air. 
 
 (3) iron 
 
 (4) iron poles in hydrogen. 
 
 (5) Solar spectrum. 
 
214 SPECTRUM ANALYSIS. [LECT. iv. 
 
 (6) Carbon spectrum oxyhydrogen blowpipe supplied with 
 olefiant gas and oxygen. 
 
 The coincidences observed were, however, but very few, and 
 totally failed to explain the nature of the Bessemer spectrum. 
 The lines of the well-known carbon spectrum (given in No. 1) 
 do not occur at all, either as bright lines or as absorption 
 bands ; nor was any coincidence observed between the lines 
 of the Bessemer spectrum and those of the carbonic oxide 
 vacuum tube. 
 
 The lines of lithium, sodium, and potassium are always seen, 
 and are unmistakeable. 
 
 The three tine bright lines, 73*7, 76'8, and 82, are due to iron. 
 The red band of hydrogen (c) is seen as a black band, more 
 prominent in wet weather. 
 
 After the charge of iron has been blown, it is run into the 
 ladle, and a certain quantity of the highly carbonized spiegel- 
 eisen is run into it. The effect of the addition of the spiegeleisen 
 is the production of a flame which is larger and stronger when 
 the blow has been carried rather far. This flame occasionally 
 gives the same spectrum as the ordinary Bessemer flame ; but 
 more commonly a quite different spectrum (No. 3) is seen, which 
 reminds one at first of the ordinary carbon spectrum, but differs 
 from it very remarkably. 
 
 In the carbon spectrum, which is drawn in No. 1, each group 
 of lines has its strongest member on the left (i.e. less refrangible), 
 and fades gradually away towards the right hand : in the spec- 
 trum of the spiegel flame the reverse is the case ; each group has 
 its brightest line most refrangible, and fades away into darkness 
 on the least refracted side. A comparison of the drawing of the 
 spectrum of the spiegel flame (No. 3) with that of the Bessemer 
 flame (No. 2) will show that they really contain the same lines ; 
 but the general appearance of the spectrum is completely changed 
 by alteration of the relative brightness of the lines. This was 
 shown by direct comparison of the actual spectra. 
 
 There can be no doubt that the principal lines of the Bes- 
 semer spectrum are due to carbon in some form or other. My 
 own belief is that they are due to incandescent carbon vapour. 
 
APPEND. E.] SPECTRUM OF BESSEMER FLAME. 215 
 
 The experiments in which I am at present engaged have already 
 shown the existence of two totally different spectra, each capable 
 of considerable modification (consisting in the addition of new 
 lines), corresponding to alterations in the temperature or mode 
 of producing the spectrum, and each due to incandescent carbon. 
 It is possible that the Bessemer spectrum may prove to be a 
 third spectrum of carbon, produced under different circumstances 
 from those imder which the ordinary carbon spectrum is ob- 
 tained ; and the intensity of the dark bands is more probably 
 due to contrast with the extreme brilliancy of the bright lines 
 than to their actual formation by absorption. 
 
 The most recent observations on the singular spectrum of the 
 Bessemer flame, made by Dr. Marshall Watts, appear to throw 
 entirely new light upon the cause of the lines therein seen. The 
 following contains the result of Dr. Watts's observations, and 
 from them we can now no longer doubt that the peculiar lines 
 are due to the presence of a manganese compound, and not, as 
 was previously and on good ground supposed, to that of carbon. 
 
 FURTHER OBSERVATIONS ON THE SPECTRUM OF THE BESSEMER 
 
 FLAME. 
 
 These observations were made by Dr. W. M. Watts, at the 
 steel-works at Barrow. The " Barrow Haematite Iron and Steel 
 Company " assisted the investigation in the most liberal manner, 
 not only erecting an observatory on the works, but also contri- 
 buting to the expense of the experiments. 
 
 The instrument employed was Browning's Automatic Spectro- 
 scope, of six prisms. The measurements were made by means 
 of a micrometer tangent-screw, giving 2 '94 turns between the 
 lithium orange line and the least refrangible D-line. In some of 
 the later measurements a micrometer eyepiece was employed, fur- 
 nished with two pairs of cross wires. To separate the wires by 
 the same interval requires 12*49 turns of the screw. The method 
 of observation commonly employed was to throw an image of 
 the flame on the slit of the spectroscope by means of a large 
 lens of about 25 centijnetres' focus; and just in front of the 
 
216 SPECTR UM ANALYSIS. [LECT. i v. 
 
 lens was placed a spark-discharger. The spectrum of the flame 
 could thus be obtained simultaneously with that of any metal, 
 or either spectrum could be obtained in the field alone. The 
 wave-length of a line in the Bessemer spectrum was obtained by 
 graphical interpolation (occasionally by calculation) from the 
 known wave-lengths of two metal lines, selected so that the 
 Bessemer line fell between them as closely as possible. The 
 metals employed in the comparison were aluminium, copper, 
 cadmium, iron, lithium, lead, magnesium, manganese, platinum, 
 sodium, thallium, tin, and zinc; besides which, some lines of the 
 air- spectrum were made use of. 
 
 The results of the observations are embodied in Fig. 42 a 
 (page 175), which shows the spectrum on the scale of wave- 
 lengths. With it are given, upon the same scale, the spectra of 
 iron of the flame obtained on adding the spiegel and of oxide 
 of manganese. A comparison of these drawings shows that the 
 spiegel spectrum is essentially the same spectrum as the Bessemer 
 spectrum only further developed and that the Bessemer spec- 
 trum, while containing a few lines of iron, sodium and lithium, 
 is. essentially the spectrum of oxide of manganese. 
 
 No lines certainly known to be produced by carbon have been 
 observed. 
 
 It has been repeatedly affirmed that the Bessemer spectrum is 
 produced by manganese a conclusion which has been denied 
 by many who have observed this spectrum (by Dr. Eoscoe and 
 myself, as well as by many others who have observed this spec- 
 trum), and upon what appeared to be very satisfactory evidence. 
 It was stated loosely, that the spectrum was that of manganese 
 which it certainly is not ; for if the spectrum of the electric 
 spark between manganese poles be observed together with that 
 of the Bessemer flame, it is seen that there is absolutely no 
 single coincidence. Moreover, the spectrum is obtained just as 
 brightly in working iron, which contains scarcely any manganese 
 at all, as with highly manganiferous iron, and is obtained from 
 coke-fires and other furnace-flames in which only traces of 
 manganese can be supposed to be present ; and, most strange of 
 all, repeated observation shows that in 99 blows out of 100 this 
 
APPEND. F.] SPECTRA OF ERBIUM AND DIDYMWM. 217 
 
 spectrum disappears at the time when, as analysis shows, the 
 carbon is completely removed from the iron, and the manganese 
 is not. Nevertheless, simultaneous comparison of the Bessemer 
 spectrum with the spectrum of manganese oxide, shows the 
 coincidence in a manner so entire as to completely convince 
 anyone who sees it, of the identity of the two spectra. This 
 spectrum of manganese oxide is obtained faintly by bringing 
 manganese chloride into a Bunsen flame ; but best and very bril- 
 liantly by bringing manganese chloride, pyrolusite or any man- 
 ganese compound, into the oxyhydrogen flame. Why this 
 spectrum, which is not that of carbon, should disappear at the 
 exact moment when all the carbon is burnt out, is very difficult 
 to understand. Possibly, the point which it is necessary to hit is 
 not that of the complete removal of carbon, but that at which 
 the injurious oxidation of iron begins, viz. when the quantity 
 of manganese becomes too small to combine with the excess of 
 
 APPENDIX F. 
 
 ON THE SPECTRA OF ERBIUM AND DIDYMIUM AND THEIR 
 COMPOUNDS. 
 
 Bunsen 1 has shown that the rare earth erbia is distinguished 
 from all other known substances by a peculiar optical reaction 
 of the greatest interest. This solid substance when strongly 
 heated in the non-luminous gas-flame gives a spectrum contain- 
 ing bright lines, which are so intense as to serve for detecting 
 this substance. This singular phenomenon does not, however, 
 constitute any exception to the law of exchanges ; for Bunsen 
 has shown that the bands of maximum intensity in the emission 
 spectrum of erbia coincide exactly in position with the bands of 
 greatest darkness in the absorption spectrum. A similar inver- 
 sion of the didymium absorption bands has also been observed 
 by Bunsen. 2 
 
 1 Ann. Ch. Pharm. cxxxvii. p. 1. 
 
 2 Ibid, cxxxi. p. 255 ; Phil. Mag. vol. xxviii. p. 246. 
 
218 SPECTR UM ANALYSIS. [LECT. i v. 
 
 Some very interesting observations have also been made by 
 Bunsen upon the absorption spectrum of didymium, 1 from which 
 we learn that the didymium spectrum, and also that of erbium, 
 undergo changes if examined by polarized light according as the 
 ordinary or extraordinary ray be allowed to pass through the 
 crystal. These changes only become visible, however, when a 
 powerful battery of prisms and a telescope .of high magnifying 
 power are employed. According to the direction in which the 
 ray of polarized light is allowed to traverse the crystal of didy- 
 mium sulphate is the position of the dark absorption bands 
 found to vary; whilst the bands produced by the solution of the 
 salt in water are again different. Very remarkable are the small 
 alterations in the position of the dark bands of the didymium 
 salts, dependent upon the nature of the compound in which the 
 metal occurs. These changes are too minute to be seen with a 
 small spectroscope, but are distinctly visible in the larger in- 
 strument. "The differences thus observed in the .absorption 
 spectra of different didymium compounds cannot, in our com- 
 plete ignorance of any general theory for the absorption of light 
 in media, be connected with other phenomena. They remind 
 one of the slight gradual alteration in pitch which the notes 
 from a vibrating elastic rod undergo when the rod is weighted, 
 or of the change of tone which an organ-pipe exhibits when the 
 tube is lengthened." 
 
 From experiments made with erbia and other earths by 
 Huggins and Eeynolds, 2 they conclude that the bright lines 
 seen in the spectra obtained by heating these earths in the oxy- 
 hydrogen flame are due to the partial vaporization of the heated 
 substance. If this is really the case, the only exception to the 
 law of solid bodies giving continuous spectra will disappear. 
 
 1 Phil. Mag. vol. xxxii. 126, p. 177. 
 
 2 Proc. Roy. Soc. xviii. 54tJ. 
 
APPEND, o.] SORBY-BROWNING MICRO-SPECTROSCOPE. 219 
 
 APPENDIX G. 
 
 DESCRIPTION OF THE SORBY-BROWNING MICRO-SPECTROSCOPE. 
 
 The construction of this instrument is represented in Figs. 50 
 (page 183) and 55. The prism is contained in a small tube (a), 
 
 FIG. 55. 
 
 which can be removed at pleasure, and which is shown in section 
 in Fig. 51. Below the prism is an achromatic eyepiece, having 
 an adjustable slit between the two lenses ; the upper lens being 
 furnished with a screw motion to focus the slit. A side slit 
 capable of adjustment admits when required a second beam of 
 light from any object whose spectrum it is desired to compare 
 with that of the object placed on the stage of the microscope. 
 This second beam of light strikes against a very small prism, 
 suitably placed inside the apparatus, and is reflected up through 
 the compound prism, forming a spectrum in the same field with 
 that obtained from the object on the stage. 
 
220 SPECTRUM ANALYSIS. [LECT. iv. 
 
 a is a brass tube carrying the compound direct-vision prism. 
 
 6, a milled head, with screw motion to adjust the focus of the 
 achromatic eye- lens. 
 
 c, milled head, with screw motion to open or shut the slit 
 vertically. Another screw at right angles to c, and which from 
 its position could not be shown in the cut, regulates the slit 
 horizontally. This screw has a larger head, and when once 
 recognized cannot be mistaken for the other. 
 
 d d, an apparatus for holding a small tube, in order that the 
 spectrum given by its contents may be compared with that from 
 any other object placed on the stage. 
 
 e, a square-headed screw opening and shutting a slit to admit 
 the quantity of light required to form the second spectrum. 
 Light entering the round hole near e strikes against the right- 
 angled prism which we have mentioned as being placed inside 
 the apparatus, and is reflected up through the slit belonging to 
 the compound prism. If any incandescent object is placed in a 
 suitable position with reference to the round hole, its spectrum 
 will be obtained, and will be seen on looking through it. 
 
 / shows the position of the field-lens of the eyepiece. 
 
 g is a tube made to fit the microscope to which the instrument 
 is applied. To use this instrument, insert g like an eyepiece 
 in the microscope tube, taking care that the slit at the top of the 
 eyepiece is in the same direction as the slit below the prism. 
 Screw on to the microscope the object-glass required, and place 
 the object whose spectrum is to be viewed on the stage. Illumi- 
 nate with stage mirror if transparent, with mirror and Lieberkiihn 
 and darken well if opaque, or by side-reflector bull's-eye, &c. 
 Remove a, and open the slit by means of the milled head, not 
 shown in cut, but which is at right angles to d d. When the slit 
 is sufficiently open, the rest of the apparatus acts like an ordi- 
 nary eyepiece, and any object can be focussed in the usual way. 
 Having focussed the object, replace a, and gradually close the 
 slit till a good spectrum is obtained. The spectrum will be 
 much improved by throwing the object a little out of focus. 
 
 Every part of the spectrum differs a little from adjacent parts 
 in refrangibility, and delicate bands or lines can only be brought 
 
APPEND. G.] SORBY-BROWNING MICRO-SPECTROSCOPE. 221 
 
 out by accurately focussing their own parts of the spectrum. 
 This can be done by the milled head I. Disappointment will 
 occur in any attempt at delicate investigation if this direction is 
 not carefully attended to. 
 
 When the spectra of very small objects are to be viewed, 
 powers of from J inch to ^stli or higher may be employed. The 
 prismatic eyepiece is shown in section in Fig. 51. 
 
 Blood, madder, aniline red, and permanganate of potash 
 solution, are convenient substances to begin experiments with. 
 Solutions that are too strong are apt to give dark clouds instead 
 of delicate absorption bands. 
 
I* C 69 
 
 67 66 65 
 
 PLATE III. ( 
 
 KIRCHHOFFS MAPS OF THE SOLAR SPECTRU 
 
 63 
 
 60 B 59 
 
 57 
 
 Air 
 
 Tb 
 
 I.IT 
 
 Ii Ca Cfl 
 
 Sn 
 
 101 100 99 98 97 96 95 94 93 
 
 91 90 89 88 87 
 
 Hill 
 
 iilimlmilmilmilmilimlimim 
 
 mil mlmilii 
 
 'null 
 
 \\ iiiilniiliinliHiliiiilinimi'liii limlni 
 
 i li 
 
 iilniilii 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 - 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 i 
 
 ~Sb Te Air jjj 
 
 J5 
 
 T!Y 
 
 
 1 
 
 B, 
 
 Y Y il mil i 
 1 U ill II 
 
 Fe Sb SaFt Sb Xi jjaafj 
 ! ll i ii i i 
 
 _2H 
 
 T j 
 1*1 
 
 IT Y T * T 
 
 Ti 
 
 
 A'fZn J>t 
 
 TbCo JsZn Pb VtiNA&i 
 
 
 $2 131 
 
 130 129 1 
 
 28 127 126 
 
 iHlill II Illlllll 
 
 125 
 
 ll]||||||| ll 
 
 124- 
 | 
 
 III! 
 
 ii 
 
 123 
 
 Hi; 
 
 122 
 
 : 
 
 121 120 
 
 Illllllll hill Mil 
 
 us lie 
 
 Jipillllllllllll III 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 i 
 
 j 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 1 ! 
 
 | 
 
 1 1 
 
 
 ||| | i [ 
 
 l! 
 
 
 1 
 
 
 
 
 I 
 
 
 i 
 
 
 
 1 1 1 
 
 
 III! | 
 
 
 II 
 
 
 1 
 
 
 I i 
 
 T 
 
 nt \ r 
 
 r 
 
 T IT 
 
 in 
 
 
 I 
 
 
 
 r i 
 
 163 162 161 160 159 158 157 
 
 Ij 
 ll!l HI! llllhlll II I I 
 
 Sn 
 
 155 154- 153 ^ 152 151 150 149 I 
 
 I 
 
 Ca 
 
 II II I 
 
 III 4 ! c " 
 
 
 II II I 
 
 An Sr 
 
 II II! 1 1 
 
 fig 
 
at end of book.) 
 
 E. (The portion from A to D mapped ly K. Hofmann.) 
 
 1 52 51 SO 49 48 47 46 45 44 43 42 
 
 40 39 38 
 
 I 
 !ll!li 
 
 93 82 
 
 __ Mlllliliili 
 
 Bl ( 
 
 to 
 
 null 
 
 79 
 
 ill 
 
 
 7 
 
 3 
 : 
 
 Illl!! 
 
 7 , 
 
 hinlii! 
 
 re 
 || 
 
 ,., 
 
 75 
 
 y 
 
 iiii 
 
 '4- 
 
 I i 
 ___ 
 
 73 7 
 
 Z 7 
 
 uJuj 
 
 1 70 C 6S 
 
 iiimiiiliml 111! 
 
 
 
 
 
 
 
 
 
 j 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ; 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 i 
 | i 
 
 
 
 
 
 
 1 
 
 M 
 
 I 
 
 1 1 
 
 1 1 
 
 T 
 
 if 
 
 J 
 
 
 ", 
 
 fr) 
 
 M 
 
 tun ai 
 
 Air 
 
 Al An (LalJi) 
 
 
 
 $r i Ca- Sr 
 
 
 5 114 113 112 III 110 
 
 /. 
 
 n 
 
 D 
 
 107 106 105 104 103 102 101 101 
 
 [mini] 
 
 m 
 
 HI! 
 
 \\ 
 
 Mlllimill 
 
 mlllillill 
 
 \\\ 
 
 
 M'l: 
 
 Liilil 
 
 tji 
 
 ill 
 
 lilimliiiiliiiimiilniminlmm 
 
 Illlllllllllllllllll 
 
 ill _ 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 i 
 
 
 i 
 
 
 
 
 1 
 
 
 
 i 
 
 i 
 i i 
 
 1 1 
 
 1 1! 
 
 
 1 1 
 il 
 
 U 
 
 
 A 
 
 r 
 
 
 F 
 
 } 
 
 W 
 
 / 
 
 JB 
 
 1 ;/ 
 
 ^ 
 
 i 
 i 
 
 T 
 
 Hn 
 
 Jin An JUi i 
 
 1 
 
 
 f 
 
 JW 
 
 145 144 143 142 141 140 139 138 137 138 135 134 133 132 13 
 
 llll 
 
 j 
 
 
 i 
 Ill'llill 
 
 , 
 
 iiiliiiihi 
 
 m | 
 
 | i 
 
 Mil! 
 
 
 v 
 
 bill 
 
 Ill 
 
 u 
 
 1 
 
 Hllllill 
 
 iilmil 
 
 ii 
 
 
 |! 
 
 u 
 
 illl 
 
 Illll 
 
 
 
 - 
 
 
 
 j 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 ii 
 II 
 
 1 1 1 
 
 i 
 
 m In 
 
 
 
 
 
 
 I!! 
 
 
 ! 
 
 i 
 
 ! 
 
 
 a 
 
 n 
 v M 
 
 
 U 1! 
 
 II i 
 
 Y y /t 
 
 1! 
 
 i i 
 
 II 
 
 II 1 
 
 
 i i 
 
 M 1 
 
 J>L Cd 
 
 u r r 
 
 fa H!/ Cu 
 
PLATE IV. 
 
 KIRCHHOFF'S MAPS OF THE SOLAR SPEC 
 
 l3 
 
 M Mill!!! 
 
 
 K, 
 
 2 
 
 19 
 
 Illll 
 
 ll 
 
 I9C 
 
 1 
 
 mi 
 
 i! 
 
 IS 
 
 i ; 
 
 :o 
 
 II 
 
 Hi! 
 
 ja IB; 
 
 ill Illll 
 
 i 
 
 36 
 
 m 
 
 186 1 
 
 Hill lillll 
 
 34 
 
 ;j 
 
 IS 
 
 Illl 
 
 3 
 
 132 181 (80 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 r T LJ 
 
 ' 1 1 Y i ' 
 
 1 1 1 I 1 1 
 
 LL 
 
 M, 
 
 \ 
 
 r Y 
 
 ?25 22C 223 222 221 220 219 218 217 216 215 214 213 212 211 
 
 null 
 
 [U 
 
 _ M 
 
 i in Inn HIM 
 
 ii inilii 
 
 
 ;|j|. 
 
 I ill 
 
 l|l| 
 
 Ilii 
 
 Ulllll 
 
 ll|lll 
 
 linn 
 
 1 III 
 
 IHUlii 
 
 iiii iiiiiiiiiiii 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ! 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 i 
 i 
 
 i 
 
 i 
 
 
 
 
 
 
 1 1 
 
 i 
 
 
 
 1 All Cd 
 
 ! 
 
 1 1 
 
 i 
 
 
 
 
 
 1 
 
 Ni 
 
 
 
 
 
 
 56 
 
 'n Cc 7,n 
 
 255 254 253 252 251 250 249 248 247 246 245 244 243 242 
 
 Jillllillu 
 
 l|l mil 
 
 iliiiiliiiili!ii|iiiilii!iniii!iiiil 
 
 llllllll 
 
 iiliiiNiinliiimiiiii 
 
 Illlllllillllllll 
 
 inliiii 
 
 limn 
 
 Illll 
 
 
 
 
 
 
 
 
 
 
 | j ii II 
 
 
 
 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 : 
 
 i 
 
 1 
 
 
 
 * * 
 
 
 1 I'V if 
 i lih i 
 
 V 
 
 
 K 
 
 
 1 
 
 m 
 
 
 
 Pt ftffjs 
 1 M 
 
 <V It Ba V 
 
 Ce ^ 
 
 I 1 1 
 
 n, 
 
 ^jK) C' (La.J}f) 
 > Sn I 
 
 Co .\ 
 
 e Sn 
 
 287 
 
 282 281 280 279 278 277 276 275 274 273 
 
j at end of book.) 
 
 [ b TO G. ( The latter half mapped by K. ffofmaun. ) 
 
 177 176 f75 t74. 173 172 171 170 169 
 
 13/ 168 165 u 1C* 163 
 
 _U i 1 
 
 Cu 
 
 f 
 
 Ca 
 
 V 
 
 My 
 
 208 207 206 205 204 203 C02 
 
 201 200 199 198 197 196 195 194 
 
 IHJIIIllll 
 
 
 iiliiiiliiiiliiiiliiiili:: 
 
 II! 
 
 jll,! 
 
 h 
 
 || 
 
 INI 
 
 Illllll 
 
 mi 
 
 ! | 
 
 U| 
 
 illl 
 
 Illlll 
 
 iiiilimlm 
 
 111 
 
 L Jill ill 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 J 
 
 
 
 
 
 1 
 
 
 
 ij 
 
 
 
 
 
 
 
 
 
 
 
 I 
 
 1 
 
 
 
 i ' 
 
 
 1 
 
 | 
 
 i 
 
 
 
 
 fe 
 
 Ba 
 
 
 i 
 
 1 S, 1 1 IM ft 
 
 
 1 
 
 
 
 i 
 
 1 I i 1 
 
 Y m r 
 
 239 238 237 236 235 234 233 232 231 230 229 228 227 226 225 
 
 illllll 
 
 in 
 
 HI 
 
 nil" ilu 
 
 i! 
 
 i | 
 
 il 
 
 
 y 
 
 111] 
 
 l ! l 
 
 [njiliiiiliiiiliiiilmmmliiiiliiiilimmiili!!! 
 
 i! 
 
 ml 
 
 Illl 
 
 I 
 
 
 
 
 
 
 
 
 
 _ 
 
 
 
 
 
 
 
 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 il II 
 
 
 
 
 
 
 
 
 
 
 
 'J 
 
 i II 
 
 IT T IT 
 
 II HIM 
 
 
 
 
 
 i 
 
 
 yJ- i y ce Air j 
 
 y Yl 
 
 
 CdZn 
 
 
 \ pi 
 
 (J-tt^i) u 
 
 SIN 
 
 ... Cu A1 Sb!f I 
 
 270 269 268 267 266 265 264 263 262 261 260 259 258 257 256 
 
 Illllll 1 
 
 li 
 
 Illlllll 
 
 Inn 
 
 IP 
 
 null; 
 
 ih 
 
 ii 
 
 mi 
 
 Illllll 
 
 I muni 
 
 i ' ! II 
 
 III 
 
 i i 
 
 mil 
 
 i in 
 
 h 
 
 y 
 
 y 
 
 ;, ' 
 
 Illllll 
 
 i il ml 
 
 
 
 1 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 ' 
 
 i 
 
 i 
 
 T 
 
 i 
 
 ii 
 
 
 y 
 
 
 
 
 
 1 
 
 1 
 
 y 
 
 I 
 
 ~ 
 
 \ Y 
 
 Ait 
 
ANGSTROM'S AND THALEN'S MAPS OF THE SOLAR g 
 
 IS 
 
 Jill 
 
 
 UH 
 
 3 
 
 
 T 
 
 Mill! 
 
 
 31 
 
 | 
 
 31 
 
 
 
 3C 
 
 9 
 
 III 
 
 ill 
 
 3C 
 
 y 
 
 8 307 
 
 Mlllllllll 
 
 III 
 
 [ 
 
 3 
 
 llllll 
 
 35 
 
 ||| 
 
 T 
 
 mi i 
 
 > 
 
 lulu 
 
 ,1,, 
 
 I 
 
 
 
 
 I 
 
 in i 
 
 
 
 " 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 ! 1 
 
 
 1 
 
 
 
 
 | 
 
 
 
 
 
 
 I 
 
 1 
 
 
 || 
 
 
 i i 1 
 
 
 
 i 
 
 
 
 
 
 
 Y y 
 
 Ca 
 
 Mn 
 
 Tt Zl 
 
 n zi 
 
 345 344- 343 342 341 3*0 339 338 337 n 336 335 334 333 
 
 375 374 373 37Z 371 370 36ft 
 
 III! Ill 
 
 ll 
 
 II 
 
 imliiim 
 
 ulii 
 
 i 
 
 nil 
 
 iii| 
 
 li 
 
 iilmilmi 
 
 |i 
 
 !| 
 
 4 
 
 u 
 
 llll 
 
 11 
 
 ii|imii 
 
 Mliiii hi 
 
 Mi! 
 
 Hill 
 
 III 
 
 ilinihi! 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 
 
 
 II 
 
 
 
 
 
 
 
 
 jf 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 l-'e 
 
 
 
 Mn 
 
 406. 405 404 403 402 401 400 
 
 iiiliiiiliiiilinilniiliiiiliin'" 1 
 
 397 396 395 394 383 392 
 
 
 
FROM G TO H 2 . (Drawn to the same scale as Kirchhoffs maps.) 
 
 )8 397 53 23 
 
 Ya Cr Vet Mn Va f - r \- ff 
 
 Bt 56 Hi CuMo 
 
 Illllllll 
 
 ! 
 
 lIllllllMllllllll 
 
 
 ||| 
 
 M 11 MM 
 
 Illllllll 
 
 Ml 
 
 luluu 
 
 Illllll 
 
 il 
 
 llll 
 
 niilini 
 
 II Nil 
 
 III i 
 
 IIP 
 
 M 
 
 III III 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 i 
 
 1 
 
 1 
 
 1 
 
 
 
 
 
 
 
 
 
 II 
 
 
 1 
 
 
 
 
 1 
 
 Y * 1 " 
 
 fe \ 
 
 
 \ \ 
 
 JSr 
 
 Yfc Zi 
 
 358 357 J56 355 354 353 352 351 350* 349 348 347 346 345 
 
 ill 
 
 J L 
 
 in y 
 
 I I 
 
 I I 
 
 TS., 
 
 387 386 385 384 383 382 381 380 379 378 L 377 376 375 
 
LECT. v.J BASIS OF SOLAR CHEMISTRY. 223 
 
 magnesium, and hydrogen, which we know well on this 
 earth, are present in a state of luminous gas. 
 
 In beginning to consider this matter, we shall, how- 
 ever, do well to remember that the subject is still in its 
 infancy ; that it is only within the last few years that we 
 have been at all acquainted with the chemistry of these 
 distant bodies. We must not be surprised to find that 
 some of our questions cannot be satisfactorily answered, 
 and we may expect in several instances to meet with 
 facts to which an explanation is still wanting. 
 
 In the first lecture I pointed out to you that sunlight 
 differs from the light given off by solid and liquid sub- 
 stances, as well as from the light given off by gaseous 
 bodies. If we were experimenting with sunlight now, 
 and if I could throw the solar spectrum on to the screen, 
 instead of this continuous spectrum of the incandescent 
 carbon poles we should find that this bright band was 
 cut up by a series of dark lines or shadows. 
 
 These lines I mentioned to you were first discovered 
 in 1814 by Fraunhofer at least they were first carefully 
 observed by him and have since gone by the name of 
 Fraunhofer's lines. 
 
 Fraunhofer measured the distances (see Fig. 56) 
 between these fixed lines, and he found that the distance 
 from D to E, and from E to F, remained perfectly constant 
 in the sunlight, that they are fixed lines which always 
 appear in sunlight ; and, moreover, as I think I mentioned 
 to you on a previous occasion, he examined the light 
 from the moon and from the planet Venus, and observed 
 the same lines occur in moonlight and in planet-light, 
 which is simply reflected sunlight, arid he found that the 
 relative distances between these lines were the same in 
 light from these three sources. He then examined the 
 
224 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. v. 
 
 light from some fixed stars, from Sirius and others, and 
 he noticed that, although in some of these fixed stars 
 
LETT. V.] 
 
 BASIS OF SOLAR CfffMISTEY. 
 
 225 
 
 certain lines exist which occur in sunlight, yet that other 
 lines, always present in sunlight, are absent from the 
 light of the stars : thus in Procyon and Capella he saw 
 the double solar line D, but other well-known solar lines 
 were wanting. 
 
 So long ago as 1814, Fraunhofer concluded that these 
 lines were caused by some absorptive power exerted in 
 the star or in the sun. 
 
 
 Fm. 57. 
 
 The exact mapping of these lines becomes a matter of 
 very great importance, and, since the time of Fraunhofer, 
 the best maps which have been made of these solar lines 
 are those of KirchhofF and Angstrom. Facsimile drawings 
 of these maps are, with the permission of the authors, 
 given in Plates III., IV., and V. 
 
 I will now project, by means of the oxyhydrogen 
 light, a photograph of one of the diagrams of Professor 
 Kirchhoff upon the screen, and show you the great 
 
 Q 
 
226 SPECTRUM ANALYSIS. [LECT. v. 
 
 number of lines existing in the solar spectrum (see Plate 
 III. facing this Lecture). This is the line D in the 
 yellow, which was noticed by Fraunhofer, and observed 
 by him to be double. Thanks to the kindness of 
 Mr. Browning, I have on the other end of the table a 
 very beautiful instrument, which is so arranged that it 
 enables me to show these double D lines. Reverting 
 again to the map, we see a great number of lines varying 
 in intensity, in depth of shade, as well as in breadth. 
 
 Fro. 58. 
 
 Here we come to E in the blue. I might in the same 
 way show you that throughout the whole length of the 
 spectrum similar groups of dark lines occur. From these 
 diagrams you will, however, form an idea of the enormous 
 number of these lines which exist in the solar spectrum. 
 On Plate IV. you see the lines existing at the blue 
 end of the spectrum, going up as far as G in the blue. 
 Here you observe these dark lines, to which Fraunhofer 
 gave the term G ; and between these we have a very large 
 
LECT. V.] 
 
 BASIS OF SOLAR CHEMISTRY. 
 
 227 
 
 number of lines mapped out with a very great degree of 
 accuracy and care by Professor KirchhofF by means of 
 his delicate spectroscope (Fig. 59). 
 
 In Fig. 57 we have a representation of a still larger 
 spectroscope made by Mr. Browning, for Mr. Gassiot, in 
 which there are nine prisms, and in which the light is 
 actually bent round, so that the incident and emergent 
 beams cross each other's path, as is seen in Fig. 58, giving 
 a plan of the instrument and showing the path of the 
 
 FIG. 59. 
 
 light through the prisms. With this we can see the 
 D lines very beautifully doubled. To both these large 
 instruments means of accurately measuring the distances 
 between any lines are attached. In KirchhofFs spectro- 
 scope a circular divided scale was used, fixed to the head 
 of the micrometer screw by which the telescope was 
 moved. The eyepiece was placed so that the cross 
 wires made angles of 45 with the dark lines : the point 
 
228 SPECTRUM ANALYSTS. [LECT, v. 
 
 of intersection was then brought by means of the 
 micrometer screw to coincide with each of these lines, 
 and the divisions read off. A somewhat similar arrange- 
 ment is seen in the instrument shown in Fig. 57. 
 
 Professor Kirchhoff did not draw the whole spectrum ; 
 he only got as far as G. Since his time, some very beau- 
 tiful drawings have, however, been made by Angstrom, 
 whose name T had to mention in the third lecture as 
 having given us the first notion respecting the true con- 
 stitution of the electric spark. In Plate V. you have a 
 copy of one of Angstrom's drawings made in Upsala, 
 which extend from G to H in the violet. Professor 
 Angstrom has also recently published a complete set of 
 maps of the solar lines, 1 which he terms the normal 
 spectrum, because he lias indicated the positions of the 
 lines according to their ivave-lengths as measured by 
 diffraction, thus rendering his observations indepen- 
 dent of the changeable nature of glass prisms used in 
 Kirchhoff's method. The maps which accompany the 
 memoir are marvels of accurate observation, and the 
 length of the spectrum extends to about eleven feet: each 
 division on the scale represents the ten-millionth part of 
 a millimetre in wave-length. I have already given you 
 (page 30) the wave-lengths of the most prominent of 
 the lines according to Angstrom's measurements. 
 
 I hope you will understand that these dark lines, 
 betokening the absence of certain kinds of rays in the 
 sunlight, not only exist in the visible portions of the 
 spectrum, but also occur in the portions which contain 
 the invisible heating- and chemically-active rays. I 
 cannot show you any of the lines which are found in 
 the ultra-red portion of the spectrum, but I can show 
 1 Spectre normal du Soleil avec Atlas. Upsala, 18G8. 
 
LS3T. V.J 
 
 MEANS OF MEASURING THE LINES. 
 
 229 
 
 you those in the ultra-violet. Thanks to the beautiful 
 researches of Professor Stokes on fluorescence, these lines 
 have become perfectly well known (see Fig. 60). The 
 diagram shows the effect produced on a film of sensitized 
 collodion which was exposed to the action of these ultra- 
 violet rays passing through quartz prisms. The shaded 
 spaces indicate the positions in which the intensity of 
 the rays is small ; they are the Fraunhofer's lines in the 
 ultra-violet sunlight. You see that the lines stretch out 
 a long way beyond the visible portion of the spectrum, 
 that to which the eye is ordinarily sensitive, ending 
 somewhere near the line H. 
 
 FIG. 60. 
 
 In order to point out to you the accuracy with which 
 Professor Kirchhoff has drawn these very difficult maps 
 of the solar lines, I will show you a copy of a very 
 interesting photograph made by Mr. Kutherfurd of New 
 York, who, as many present will be aware, has devoted 
 himself with great success to astronomical photography. 
 Mr. Eutherfurd has photographed those portions of the 
 solar spectrum which are capable of producing a photo- 
 graphic image, for you will remember that it is only the 
 
SPECTRUM ANALYSIS. 
 
 [LECT. v. 
 
 blue and ultra blue rays which are capable of thus acting 
 chemically. You see here (Fig. 61) a copy of one of 
 these photographs compared with Kirchhoff s drawing : 
 at the bottom is Rutherfurd's photograph, and above is 
 Kirchhoff s drawing. Let us compare the two. In the 
 photograph there is this line F, for instance, and you 
 will see that for nearly every line Nature has drawn by 
 means of the light itself there is a corresponding line in 
 KirchhofFs map : this will give you an idea of this philo- 
 sopher's extreme accuracy. When I first saw the photo- 
 
 (') KlRCHHQFFS MAP. 
 
 119 SIS 217 E16 2)5 814 813 218 11 810 
 
 207 208 205 204 203 32 
 
 liiiiliiiiliiiiliiii in null ilimliiiiliiiilimliiiiliiiiliiiilmilii iiilmiliiiilmilimliiiiliiiilm iiiliiiiliiiiliiiiliiiiliiiiliiiiliilniliiiiliiiiliiiiliiiiliiiiliiuliiiliinliii iiilimliii 
 
 iilniiliiii 
 
 RU THERFURDS PHO TOGRAPH. 
 
 FlU. 61. 
 
 graphs which Mr. Rutherfurd was good enough to send 
 me, I really had some difficulty in believing that they 
 had been photographed from the sun itself, so beautifully 
 are they done, and so marvellously do they correspond 
 with KirchhofFs drawing : but on a careful scrutiny you 
 will find some slight differences between them, especially 
 in the relative intensities of the two sets of lines. This 
 is readily understood if we remember that the map 
 represents the variations of light and shade as affecting 
 
LECT. v.] PHOTOGRAPHING THE DARK LIMES. 231 
 
 Kirchhoff s retina, whereas the photograph gives us the 
 variations of the chemically active rays, indicated by 
 decomposition of silver salt and subsequent development 
 of the image. 
 
 Having fully mastered the facts concerning the com- 
 position of sunlight, I must now ask you to pass on to 
 the examination of the first of Kirchhoff s discoveries 
 by which the cause of these singular dark solar lines is 
 explained. So long ago as 1814 Fraunhofer discovered 
 that the dark lines D in the sunlight were coincident 
 with the bright sodium lines. The fact of the coinci- 
 dence of these lines is easily rendered visible if the solar 
 spectrum is allowed to fall into the upper half of the 
 field of our telescope, while the sodium spectrum occu- 
 pies the lower half. The bright lines produced by the 
 metal, as fine as the finest spider's web, are then seen to. 
 be exact prolongations, as it were, of the corresponding 
 solar lines. 
 
 These facts, however, remained altogether barren of 
 consequences, so far as regards the explanation of the 
 phenomena, except to the bold minds of Angstrom, 
 Stokes, and William Thomson ; the last two of whom 
 combining the facts with an ill-understood experiment 
 of Foucault's made in 1849, foresaw the conclusion to 
 which they must lead, and expressed an opinion which 
 subsequent investigations have fully borne out. Clear 
 light was, however, thrown upon the subject by 
 Kirchhoff, in the autumn of 1859. 1 Wishing to test 
 the accuracy of this asserted coincidence of the bright 
 sodium line and the dark solar lines with his very 
 
 1 Berlin. Akad. Bericht. 1859, 662; Phil. Mag. Fourth Series, 
 xix. 193, xx. 1. 
 
232 SPECTRUM ANALYSIS. [LECT. v. 
 
 delicate instrument, Professor Kirchhoff made the fol- 
 lowing very remarkable experiment, which is memorable 
 as giving the key to the solution of the problem con- 
 cerning the presence of sodium and other metals in the 
 sun. " In order/' says Kirchhoff, for I will now give 
 his own words, " to test in the most direct manner 
 possible the frequently asserted fact of the coincidence 
 of the sodium lines with the lines D, I obtained a 
 tolerably bright solar spectrum, and brought a flame 
 coloured by sodium vapour in front of the slit. I then 
 saw the dark lines D change into bright ones. The 
 flame of a Bunsen's lamp threw the bright sodium lines 
 upon the solar spectrum with unexpected brilliancy. 
 In order to find out the extent to which the intensity of 
 the solar spectrum could be increased without impairing 
 the distinctness of the sodium lines, I allowed the full 
 sunlight to shine through the sodium flame, and to my 
 astonishment I saw that the dark lines D appeared with 
 an extraordinary degree of clearness. 
 
 " I then exchanged the sunlight for the Drummond's 
 or oxyhydrogen lime-light, which, like that of all incan- 
 descent solid or liquid bodies, gives a spectrum contain- 
 ing no dark lines. 
 
 " When this light was allowed to fall through a suit- 
 able flame coloured by common salt, dark lines were seen 
 in the spectrum in the position of the sodium lines. 
 
 "The same phenomenon was observed if, instead of 
 the incandescent lime, a platinum wire was used, which 
 being heated in a flame was brought to a temperature 
 near its melting-point by passing an electric current 
 through it. The phenomenon in question is easily ex- 
 plained upon the supposition that the sodium flame 
 absorbs rays of the same degree of refrangibility as 
 
LECT. V.J 
 
 SPECTRUM OF BURNING SODIUM. 
 
 233 
 
 those it emits, whilst it is perfectly transparent for all 
 other rays." 
 
 Kirchhoff had in fact, as far as he had gone, produced 
 artificial sunlight, because he had obtained the two double 
 dark lines in his continuous spectrum. I will try to 
 show the formation of the dark lines of the sodium : for 
 this purpose we will again employ our electric lamp, and 
 I will throw the continuous spectrum of the carbon 
 points on to the screen, and then I will bring into the 
 lower carbon, which is shaped like a cup, a small quanji 
 of metallic sodium: and we shall thus see tjdit $M^ 
 vapour of the sodium has the power of absorbing", the 
 
 
 
 NVl 
 
 N92 
 
 src 
 
 FIG. 62. 
 
 particular kind of light which it emits, and that in 
 place of the bright sodium line we shall have a dark 
 line. There you observe the dark sodium line. As a 
 further illustration I have here a diagram (Fig. 62) repre- 
 senting what is seen when we look at the spectrum of 
 burning sodium with an instrument such as that which 
 Kirchhoff used. At the bottom (No. 2) we have a drawing 
 of the ordinary sodium spectrum, giving us these bright 
 yellow double lines on a dark background, and above (No. 
 1 ) we see a drawing of the spectrum of burning sodium. 
 Instead of two bright yellow lines, we here find we have 
 
234 SPECTRUM ANALYSIS. [LECT. v. 
 
 two intensely black lines upon a bright continuous spec- 
 trum, the " D" light having been absorbed by the sodium 
 vapour. The difference between the intensities of the 
 lights on each side of these lines and in that particular 
 part where the lines fall is so great as to give an actual 
 shadow, which we see as a black line. There is a well- 
 known experiment by which we cast a shadow with a 
 
 luminous object, such as a candle flame : so here, 
 although these black lines are not wholly devoid of light, 
 yet the light is so much less intense than in the sur- 
 rounding parts, that they appear black to us. 
 
 I can illustrate this to you in another way. Here 
 (Fig. 63) we have a large sheet of non-luminous gas flame 
 (bb) burning under a tall chimney (c), and the flame I can 
 
LECT. v.] REVERSAL OF SODIUM SPKCTRUM. 235 
 
 colour by sodium. In front of this I am going to ignite a 
 flame of hydrogen (a), arid I will also place in the hydro- 
 gen flame some sodium compound; so that we shall have 
 two sodium flames burning,. one in front of the other. I 
 want you to notice that the yellow rays passing from this 
 large flame at the back through the hydrogen flame tinged 
 with soda will be absorbed, and that the outer rim of 
 this hydrogen flame, where the temperature is decidedly 
 low, will appear dark ; in fact, it will look just as if the 
 hydrogen flame was smoky, as though we had a smoky 
 cardie burning in front of the large flame. There is no 
 carbon in this flame to produce a smoky appearance. We 
 shall have nothing but pure hydrogen burning. "We will 
 light our hydrogen here, but before you can see the phe- 
 nomenon of absorption I must first make a large soda 
 flame. This I do by burning a little sodium, the fumes 
 of which I waft into the flame. Now you see the large 
 flame has turned yellow, and you will notice that in front 
 we get a smoky flame. It is now very distinct. If, in- 
 stead of a sodium compound, I next place some lithium 
 salt in the flame, no black rim will appear. We shall 
 get the red colour of the lithium flame, but it will not 
 give us any black shadow, because it has no power of 
 absorbing the yellow light. Hence we conclude that the 
 smoky appearance was really caused by the absorption of 
 the yellow " D" light by the sodium vapour in a state of 
 incandescence. 
 
 Here is another most ingenious apparatus devised by 
 my friend Professor Bunsen, for exhibiting a constant 
 black sodium flame absorbing the rays of the same degree 
 of refrangibility as it emits. The little cap of yellow 
 flame (d) which floats from the first burner in front of 
 the larger yellow soda flame (g) absorbs the "D" rays, 
 
236 * SPECTRUM ANALYSIS. [LECT. v. 
 
 and in consequence we have the peculiar phenomenon of 
 a constantly burning black sodium flame (Fig. 64). 
 
 I can also show you in a third way the fact that 
 sodium vapour is opaque to the light which it gives off. 
 
 FIG. 64. 
 
 I have prepared a tube containing some sodium which 
 I can convert into vapour. By heating the tube as I 
 am doing, it will become filled with sodium vapour, and 
 you will see that it is perfectly colourless and trans- 
 
LECT. v.] REVERSAL OF BRIGHT LINES. 237 
 
 parent when we look at it with the white sunlight ; but 
 when we look at it with the yellow sodium light it will 
 appear to be opaque. We shall then see that the tube 
 containing the sodium vapour throws a dark shadow on 
 the screen. [The lights were turned down, and the 
 screen was illuminated with a yellow sodium flame.] 
 Now the tube looks black ; we cannot see through it ; 
 it throws a dark shadow. [Light was again admitted.] 
 Now, by the daylight, it is colourless. This shows us, 
 then, very distinctly, that the sodium vapour is opaque 
 for the rays which itself can emit. 
 
 Thoroughly understanding, then, the nature of the 
 phenomena with which we have to deal, let us follow 
 Kirchhoff to the interesting conclusions which he draws 
 from this experiment. He states that from this fact it 
 appears likely that glowing gases have the power of 
 especially absorbing rays of the same degree of refran- 
 gibility as those they emit ; and that therefore the 
 spectrum of such a glowing gas can be reversed, or the 
 bright lines turned into dark ones, when light of suffi- 
 cient degree of intensity, giving a continuous spectrum, 
 is passed through it. This idea was further confirmed 
 by substituting for the sodium flame the flame coloured 
 by potassium, when dark lines appeared in the exact 
 position of the characteristic bright lines of this metal. 
 Bunsen and Kirchhoff have likewise succeeded in revers- 
 ing the flames of lithium, calcium, strontium, and barium ; 
 whilst Dr. Miller and M. Cornu have also reversed some 
 of the lines in the spectra of copper and other metals. 
 I can here show you the reversal of the red lithium line 
 on the screen. For this purpose I bring on to the carbon 
 pole of the lamp some salt of lithium, together with a 
 piece of metallic sodium. The sodium will reduce the 
 
238 SPECTRUM ANALYSIS. [LECT. v. 
 
 lithium salt to the metallic state, and I can then show 
 you that we have got not only a dark sodium band, but a 
 dark lithium band in the red part of the spectrum. Now 
 the reversed lines of both these metals are clearly seen. 
 
 In speaking of this subject I may mention that Pro- 
 fessor Cornu has l recently made some singular obser- 
 vations respecting the reversal of the lines of certain 
 metals. When endeavouring to obtain photographs of 
 the three magnesium lines situated in the ultra-violet, 
 he found that impressions of five instead of three lines 
 were left on the plate. This he showed was due to the 
 reversal of two of the lines which appeared dark on a 
 light ground, whilst the third line could not be reversed. 
 By using a powerful electric arc, the three bright well- 
 known magnesium lines (b) can be reversed, one coming 
 out after the other. In a similar way Cornu has reversed 
 certain of the lines of the following metals : sodium, 
 thallium, lead, silver, aluminium, cadmium, zinc, and 
 copper. Why some only of the lines of these metals 
 can be reversed, or why none of the lines of such metals 
 as antimony, gold, and bismuth can be reversed, are 
 questions which we are at present unable to answer. 
 
 Generalizing from these facts, Kirch hoff has arrived, 
 by the help of theoretical considerations which I am un- 
 able now to lay before you, at a law, previously partially 
 enunciated by Prevost of Geneva and by Prevostaye and 
 Dessains in France, and extended by Dr. Palfour Stewart 
 in this country, which expresses the relation between the 
 amount of heat of any wave-length which a body receives 
 and that which it emits. This law has been called the 
 law of exchanges. It asserts that the relation between 
 the amount of heat emitted and that which is absorbed at 
 1 Phil. Mag., Sept. 1871. 
 
LECT. v.] THE THEORY OF EXCHANGES. 239 
 
 any given temperature remains constant for all bodies ; 
 and that the greater the amount of heat emitted, the 
 greater must be the amount of heat absorbed. KirchhofF 
 has proved that the same law holds good for light as well 
 as for heat ; that it is as true of the luminous as of the 
 heat-giving rays ; and for rays of different kinds, if we 
 compare the same kind of rays : for instance, if we com- 
 pare red rays emitted with red rays absorbed, or yellow 
 rays emitted with yellow rays absorbed. . From this we 
 see that an incandescent gas which is giving off only cer- 
 tain kinds of light that is, whose power of emission is 
 limited to light of certain definite degrees of refrangi- 
 bility must have the power of absorbing those kinds of 
 light, and those kinds only. This is what we find to be 
 the case with the luminous sodium vapour : it has a very 
 high power of emission for the " D " rays, and it has a 
 proportionately high power of absorption for that kind 
 of light ; but for it alone. And we see that every sub- 
 stance which emits at a given temperature certain kinds 
 of light must possess the power, at that same temperature, 
 of absorbing the same kinds of light. 1 
 
 We must remember, however, that the emissive and 
 absorptive powers of substances can only be compared 
 at the same or nearly the same temperature. This is 
 of very great importance, for it has been supposed that 
 in some cases the law of exchanges does not hold good, 
 the comparison between absorption and radiation not 
 having been made at the same temperature. It must 
 not be assumed that because the bright lines of the 
 incandescent iodine spectrum, for instance, do not corre- 
 
 1 Report on the Theory of Exchanges, by B. Stewart (Brit. Assoc. 
 1861) ; Kirchhoff on the History of the Analysis of the Solar Atmo- 
 sphere (Phil. Mag., Fourth Series, vol. xxv. p. 256). 
 
240 SPECTRUM ANALYSTS. [LECT. v. 
 
 spond to the dark absorption bands of the gas at a much 
 lower temperature, therefore the law is faulty or incorrect. 
 'We must compare the lines at the same temperature. 
 
 Now we know that the same kind of law holds good 
 with the other vibrations known to us the vibrations of 
 the air which we call sound. We are all acquainted with 
 what is called resonance. When we sing a particular 
 note in the neighbourhood of a piano, that same note is 
 returned to us. The particular vibrating string which 
 can emit that note has the power also of absorbing 
 vibrations of that particular kind, when proceeding in a 
 straight line, and emitting them again in all directions. 
 We are not, therefore, without analogy, in the case of 
 sound, for the absorption and emission of the same kind 
 of undulation by the same substance. 
 
 We will now pass to the application of this principle of 
 the reversibility of the spectra of luminous gases to the 
 foundation of a solar and stellar chemistry. How does 
 this principle assist us in our knowledge of the consti- 
 tution of the solar atmosphere ? 
 
 In order to map and determine the positions of the 
 bright lines found in the electric spectra of the various 
 metals, KirchhofF, as I have already stated, employed the 
 dark lines in the solar spectrum as his guides. Judge of 
 his astonishment, when he observed that dark solar lines 
 occur in positions coincident with those of all the bright 
 iron lines ! Exactly as the sodium lines were identical 
 with Fraunhofer's lines r>, so for each of the iron lines, 
 of which Kirchhoff and Angstrom have mapped no less 
 than 460, a dark solar line was seen to correspond. Not 
 only had each iron line its dark representative in the 
 solar spectrum, but the breadth and degree of shade of the 
 two sets of lines were seen to agree in the most perfect 
 
LKCT. v.] COINCIDENCES OF IRON LINES. 241 
 
 manner, the brightest iron lines corresponding to the 
 darkest solar lines. 
 
 To those who have not themselves witnessed this coin- 
 cidence it is impossible to give an adequate idea, by 
 words, of the effect produced on the beholder, when 
 looking into the spectroscope he sees the coincidence of 
 every one of perhaps a hundred of the iron lines with 
 a dark representative in the sunlight, and the idea that 
 iron is contained in the solar atmosphere flashes at once 
 on his mind. 
 
 These hundreds of coincidences cannot be the mere 
 effect of chance ; in other words, there must be some 
 causal connection between these dark solar lines and the 
 bright iron lines. That this agreement between them 
 cannot be simply fortuitous is proved by Kirchhoff, who 
 calculates from the number of the observed coinci- 
 dences, the distance between the several lines, and the 
 degree of exactitude with which each coincidence can be 
 determined the fraction representing the chance or pro- 
 bability that such a series of coincidences should occur 
 without the two sets of lines having any common cause . 
 this fraction he finds to be less than ^^, m \-,-^-^^: 
 or, in other words, it is practically certain that these lilies 
 have a common cause. " Hence this coincidence," says 
 Kirchhoff, "must be produced by some cause; and a 
 cause can be assigned which affords a perfect explanation 
 of the phenomenon. The observed phenomenon may be 
 explained by the supposition that the rays of light which 
 form the solar spectrum have passed through the vapour 
 of iron, and have thus suffered the absorption which the 
 vapour of iron must exert." 
 
 " As this is the only assignable cause of this coincidence, 
 the supposition appears to be a necessary one. These 
 
 R 
 
242 SPECTRUM ANALYSIS. [LECT. v. 
 
 iron vapours might be contained either in the atmosphere 
 of the sun or in that of the earth. But it is not easy 
 to understand how our atmosphere can contain such a 
 quantity of iron vapour as would produce the very 
 distinct absorption lines which we see in the solar 
 spectrum ; and this supposition is rendered still less 
 probable by the fact that these lines do not appreciably 
 alter when the sun approaches the horizon. It does 
 not, on the other hand, seem at all unlikely, owing to 
 the high temperature which we must suppose the sun's 
 atmosphere to possess, that such vapours should be 
 present in it. Hence the observations of the solar 
 spectrum appear to me to prove the presence of iron 
 vapour in the solar atmosphere with as great a degree of 
 certainty as we can attain in any question of natural 
 science." This statement is, I believe, not one jot more 
 positive than the facts warrant. For what does any 
 evidence in natural science amount to, beyond the ex- 
 pression of a probability ? A mineral sent to me from 
 New Zealand is examined by our chemical tests, of which 
 I apply a certain number ; and these show me that the 
 mineral contains iron : and no one doubts that my con- 
 clusion is correct. Have we, however, in this case, proof 
 positive that the body really is iron 1 May it not turn 
 out to be a substance which in these respects resembles, 
 but in other respects differs from, the body which we 
 designate as iron ? Surely. All we can say is, that in 
 each of the many comparisons which we have made, the 
 properties of the two bodies prove identical, and it is 
 solely this identity of the properties which we express 
 when we call both of them iron. 
 
 Exactly the same reasoning applies to the case of 
 the existence of these metals in the sun. Of course the 
 
LECT. v.] METALS IN THE SUN'S ATMOSPHERE. 243 
 
 metals present there, causing these dark lines, may not be 
 identical with those we have on earth ; but the evidence 
 of their being the same is as strong and cogent as that 
 which is brought to bear upon any other question of 
 natural science the truth of which is generally admitted. 
 I do not think I can give you a more clear or succinct 
 account of the development of this great discovery than 
 by quoting from Kirchhoff s admirable memoir the 
 following passage : " As soon as the presence of one 
 terrestrial element in the solar atmosphere was thus 
 determined, and thereby the existence of a large number 
 of Fraunhofer's lines explained, it seemed reasonable 
 to suppose that other terrestrial bodies occur there, and 
 that, by exerting their absorptive power, they may cause 
 the production of other Fraunhofer's lines. For it is 
 very probable that elementary bodies which occur in 
 large quantities on the earth, and are likewise distin- 
 guished by special bright lines in their spectra, will, like 
 iron, be visible in the solar atmosphere. This is found 
 to be the case with calcium, magnesium, and sodium. 
 The number of bright lines in the spectrum of each of 
 these metals is indeed small, but those lines, as well 
 as the dark lines in the solar spectrum with which they 
 coincide, are so uncommonly distinct that the coincidence 
 can be observed with great accuracy. In addition to 
 this, the circumstance that these lines occur in groups 
 renders the observation of the coincidence of these 
 spectra more exact than is the case with those composed 
 of single lines. The lines produced by chromium, also, 
 forma very characteristic group, which likewise coincides 
 with a remarkable group of Fraunhofer's lines : hence I 
 believe that I am justified in affirming the presence of 
 chromium in the solar atmosphere. It appeared of great 
 
 R 2 
 
244 SPECTRUM ANALYSIS. [LECT. v. 
 
 interest to determine whether the solar atmosphere 
 contains nickel and cobalt, elements which invariably 
 accompany iron in meteoric masses. The spectra of 
 these metals, like that of iron, are distinguished by the 
 large number of their lines. But the lines of nickel, and 
 still more those of cobalt, are much less bright than the 
 iron lines ; and I was therefore unable to observe their 
 position with the same degree of accuracy with which 
 I determined the position of the iron lines. All the 
 brighter lines of nickel appear to coincide with dark solar 
 lines ; the same was observed with respect to some of 
 the cobalt lines, but was not seen to be the case with 
 other equally bright lines of this metal. From my own 
 observations I consider that I am entitled to conclude 
 that nickel is visible in the solar atmosphere. I do not, 
 however, yet express an opinion as to the presence of 
 cobalt. Barium, copper, and zinc appear to be present 
 in the solar atmosphere, but only in small quantities ; 
 the brightest of the lines of these metals correspond to 
 distinct lines in the solar spectrum, but the weaker lines 
 are not noticeable. The remaining metals which I have 
 examined viz. gold, silver, mercury, aluminium, cad- 
 mium, tin, lead, antimony, arsenic, strontium, and lithium 
 are, according to my observation, not visible in the 
 solar atmosphere." 
 
 The lines of the following metals have already been 
 proved to have their dark representatives in the sunlight, 
 and their number is each year increased through the 
 accurate observations of astronomers. Thus only a few 
 months ago titanium was added to the list, arid now 
 we learn with surprise that a line of the rare alkaline 
 metal -rubidium has been seen by Professor Young in 
 the solar atmosphere. 
 
LECT. V.] 
 
 KIRCHHOFF'S DISCOVERIES. 
 
 245 
 
 1. Sodium. 
 
 2. Calcium. 
 
 3. Barium. 
 
 5. Iron. 
 
 9. Zinc. 
 
 13. Hydrogen. 1 
 
 6. Chromium. 10. Strontium. 14. Manganese. 
 
 7. Nickel. 11. Cadmium. 15. Aluminium. 2 
 
 12. Cobalt. 16, Titanium. 
 
 4. Magnesium. 8. Copper. 
 
 17. Rubidium. 
 
 The coincidences in the case of none of these metals 
 are so numerous as with iron, of which Angstrom has 
 counted no less than 470 ; still we find no less than 75 
 calcium lines, 57 lines of manganese, 33 nickel lines, and 
 these are so characteristic and distinct as to leave no doubt 
 of the presence of these metals in the solar atmosphere. 
 In the cases of cadmium, strontium, and zinc, there 
 may be some doubt, either because only a few coinci- 
 dences have been observed, or because one or more of 
 the prominent metal lines are not seen in the solar 
 spectrum; but at least 170 titanium lines have been 
 shown by Thalen to be coincident with dark solar lines. 
 The following metals appear to be either altogether 
 absent, or present in a very small quantity, in the solar 
 atmosphere : 
 
 1. 
 
 Gold. 
 
 6. 
 
 Lead.- 
 
 11. 
 
 Glucinium. 
 
 16. 
 
 Iridium. 
 
 2. 
 
 Silver. 
 
 7. 
 
 Antimony. 
 
 12. 
 
 Cerium. 
 
 17. 
 
 Palladium. 
 
 3. 
 
 Mercury. 
 
 8. 
 
 Arsenic. 
 
 13. 
 
 Lanthanum. 
 
 18. 
 
 Platinum. 
 
 4. 
 
 Caesium. 
 
 9. 
 
 Lithium. 
 
 14. 
 
 Didymium. 
 
 19. 
 
 Thallium. 
 
 5. 
 
 Potassium. 
 
 10. 
 
 Silicium. 
 
 15. 
 
 Ruthenium. 
 
 
 
 1 The conclusion that the lines c, F, a line marked 2796 on Kirch- 
 hoff s maps lying near G, and h are due to the absorption of hydrogen 
 in the sun's atmosphere, and are not caused by the presence of aqueous 
 vapour in our own, is proved by the fact that in the spectra of certain 
 stars these lines are altogether wanting, as well as by the fact that 
 these same are frequently seen as bright lines in the sun. 
 
 2 Aluminium has been found by Angstrom to be contained in the 
 solar atmosphere, and two of its lines form a portion of the solar 
 bands H. 
 
240 SPECTRUM ANALYSIS. [LECT. v. 
 
 I will now show you these bright Hues of some of the 
 metals contained iu the solar atmosphere. Here we have 
 the green magnesium lines, and I can point out to you 
 the dark lines in the solar atmosphere which are coinci- 
 dent with these green lines. You see these two dark lines 
 on the upper part in the right-hand corner (Plate IV. in 
 Kirchhoff's map) : these are the bands which Fraunhofer 
 called b, and some of them at least are caused by mag- 
 nesium. Hence you see that the b lines are caused by 
 the presence of iron and magnesium in the solar atmo- 
 sphere. I have written down here a short resume of 
 KirchhofFs experiments and reasoning on this subject. 
 
 Sodium and Iron in the Suns Atmosphere. 
 
 1. The light emitted by luminous sodium vapour is 
 homogeneous. The sodium spectrum consists of one 
 double bright yellow line. 
 
 2. This bright double sodium line is exactly coincident 
 with Fraunhofer's dark double line D. 
 
 3. The spectrum of a Drummond's light is continuous ; 
 it contains no dark lines or spaces. 
 
 4. If between the prism and the Drummond's light a 
 soda flame be placed, a dark double line identical with 
 Fraunhofer's double line D is produced. 
 
 5. If, instead of using Drummond's light, we pass sun- 
 light through the sodium flame, we see that the line D 
 becomes much more distinct than when sunlight alone is 
 employed. 
 
 6. The sodium flame has, therefore, the power of 
 absorbing the same kind of rays as it emits. It is 
 opaque for the yellow D rays. 
 
 7. Hence we conclude that luminous sodium vapour 
 in the sun's atmosphere causes Fraunhofer's dark double 
 
LSCT. v.] EXTRACTS FROM KIRCHEOFF'S MAPS. 247 
 
 line D ; the light given off from the sun's body giving a 
 continuous spectrum. 
 
 8. KirchhofF found that each and all of the bright 
 lines produced in the spectra of certain metals for 
 instance, of iron, magnesium, and chromium coincide 
 exactly with dark lines in the solar spectrum. 
 
 9. Hence it is certain that these bright metallic lines 
 must be connected in some way with the dark solar lines. 
 
 10. The connection is as follows : each of the coinci- 
 dent dark lines in the solar spectrum is caused by the 
 absorption effected in the solar atmosphere by the glow- 
 ing vapour of that metal which gives the corresponding 
 bright line. 
 
 There are a great many very interesting points which 
 I should like to show you with regard to Kircbhoffs map. 
 Here, for instance, is an extract from the tables which 
 accompany these diagrams, complete copies of which are 
 found at the end of this volume. You see in column i. 
 the numbers representing the lines which refer to his 
 arbitrary scale of millimetres on the top line of his 
 drawing. In column II. we have the thickness and dark- 
 ness of the lines, represented respectively by letters, a to 
 g, and by numbers, 1 to 6, a being the smallest and 1 the 
 lightest; whilst column in. gives the metallic lines which 
 are coincident with certain solar lines. For instance, the 
 dark line numbered 1648'S is coincident with a magne- 
 sium line, 1627'2 with a calcium line, 1622%3 with an 
 iron line. Here you see this one line 1653'7 belongs 
 both to iron and to nickel, and 1655*6 is both an iron 
 and a magnesium line. 
 
 It is a singular fact that quite recently it has been 
 noticed by Angstrom and Thalen that many of the lines 
 
248 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. v. 
 
 which had formerly been classed as calcium lines are really 
 due to titanium, a metal which is of but comparatively 
 rare occurrence on the earth. 
 
 Extract from the Index Table of Kirchhoff 's Maps, showing the coinci- 
 dences of the dark /Solar and bright Metallic Lines. 
 
 I. 
 
 n. 
 
 in. 
 
 i. 
 
 n. 
 
 in. 
 
 1621-5 
 
 16 
 
 
 1648-4 
 
 4e 
 
 
 16223 
 
 5c 
 
 Fe 
 
 1648-8 
 
 6/ 
 
 Mg 
 
 1623-4 
 
 56 
 
 Fe 
 
 1649-2 
 
 4e 
 
 
 1627-2 
 
 5/> 
 
 Ca 
 
 1650-3 
 
 66 
 
 
 1628-2 
 
 16 
 
 
 1653-7 
 
 66 
 
 Fe, Ni 
 
 1631-5 
 
 16 
 
 
 1654-0 
 
 4c 
 
 
 1633-5 
 
 4.7 
 
 
 1655-6 
 
 Qe 
 
 Fe, Mg 
 
 1634-1 
 
 % 
 
 Mg 
 
 1655-9 
 
 U 
 
 
 1634-7 
 
 4r/ 
 
 
 1657-1 
 
 56 
 
 
 1638-7 
 
 16 
 
 
 16583 
 
 26 
 
 
 1642-1 
 
 16 
 
 
 1659-4 
 
 1 
 
 
 1643-0 
 
 16 
 
 Ni 
 
 1662-8 
 
 56 
 
 Fe 
 
 1647-3 
 
 5a 
 
 
 
 
 
 Whether these apparently coincident lines will prove 
 to be absolutely identical is a matter which we cannot 
 as yet decide. Kirchhoff thinks it is necessary, for the 
 purpose of settling this question, to use a much more 
 delicate apparatus than even that which he employed. 
 
 Fraunhofer's line D corresponds on KirchhofFs map to 
 the lines 1002 8 and 1006*8; Fraunhofer's E to the lines 
 1523' 7 and 1522*7; and Fraunhofer's I to the lines 
 1633*4, 1648*3, and 1655'0. Kirchhoff observed the 
 traces of many lines and nebulous bands, which the 
 power of even his instrument did not prove adequate to 
 resolve. He adds : "The resolution of these nebulous 
 bands appears to me to possess an interest similar to that 
 of the resolution of the celestial nebulae, and the invest!- 
 
LECT. v.] COINCIDENCES OF IRON LINES. 249 
 
 gation of the solar spectrum to be of no less importance 
 than the examination of the heavens themselves/' It is 
 important to remark that it is by no means the case that 
 all the lines have been identified ; the cause of many of 
 them is known, but a still greater number yet remain 
 for identification. An interesting question suggests 
 itself as to whether some of these as yet non-identified 
 lines may be caused by the presence in the sun of 
 elementary bodies with which we ori this earth are 
 not acquainted ? In thus speculating on the discovery 
 of new solar elements, we must bear in mind that 
 it is just possible that some, or even all the lines, 
 caused by solar absorption may be due to known ele- 
 ments of which we have not yet succeeded in obtaining 
 sufficiently intense spectra to enable us to see all the lines. 
 Thus Kirchhoff only saw about 60 iron lines when 
 he used the electric spark, but Angstrom, by vola- 
 tilizing iron in the electric arc, obtained no less than 
 460 coincidences. I may again remind you, that the 
 well-known double line D is caused by sodium, and we 
 learn from the exact observations of Mr. Huggins, that 
 not only the line D, but several other less distinct lines 
 (seen on the Maps following Lecture IV.), one lying 
 nearly neutral between the D lines, are produced by 
 sodium, in the sun. The line E is an iron line, and 
 the lines c, r, a line near G, and h are hydrogen lines ; 
 the line b is a line of magnesium, and the line H 
 appears from the researches of Angstrom to be at any 
 rate partly produced by calcium. 
 
 Many, however, of the lines frequently seen in the 
 solar spectrum are not due to the presence of metals in 
 the sun, but are caused by the absorption occurring 
 in our own atmosphere. The existence of dark bands 
 
250 SPECTRUM ANALYSIS. [LECT. v. 
 
 caused by atmospheric absorption was first pointed out 
 by Brewster in 1833, and a map of these bands was 
 subsequently published by Sir David Brewster and Dr. 
 Gladstone. Fig. 65 shows the chief of these lines com- 
 pared with the solar lines and the bright lines of nitrogen 
 and oxygen. These telluric or atmospheric lines are 
 most plainly seen when the sun is low on the horizon, 
 because the column of air which the rays have to traverse 
 is then the longest. 
 
 ORDINARY SOLAR SPECTRUM SHOW/NG 
 
 'NSET SHOWING DARK BANDS OF A 
 
 SHOW/NG BRIGHT ATMOSPHERIC L INES. (ANGSTROM 
 
 FIG. 65. 
 
 Some very interesting experiments were made in 1866 
 by the French physicist, M. Janssen : he observed that 
 if light from 16 jets of coal-gas be passed through 
 a long column of steam 37 metres in length, under a 
 pressure of 7 atmospheres, the steam exerts a strong 
 absorptive power, and groups of dark lines appear in the 
 spectrum between the extreme red and the line D. These 
 lines are found to coincide with lines in the solar spectrum 
 which become intense when the sun is near the horizon : 
 
251 
 
 and are therefore due 
 to absorption in the 
 aqueous vapour of our 
 own atmosphere. An 
 accurate map of the 
 telluric lines between 
 D and c, quite recently 
 published by Janssen, 
 is given in Fig. 66. 
 The important results 
 of his researches on 
 this subject are(l) that 
 Brewster's dark bands 
 are resolved into fine 
 lines comparable with 
 Fraunhofer's lines, and 
 (2) that the terrestrial 
 atmosphere produces in 
 the spectrum a system 
 of fine lines, so that 
 the absorptive action 
 exerted by our atmo- 
 sphere is analogous to 
 that of the sun in spite 
 of the enormous differ- 
 ence of temperature. 
 All the dark lines seen 
 in the lower but not 
 found in the upper 
 spectrum (Fig. 66) 
 have a telluric origin, 
 and they have been de- 
 signated by the Greek 
 
252 SPECTRUM ANALYSIS. [LECT. v. 
 
 letters, and are classed in groups according to their 
 position with regard to well-known solar lines. 
 
 I do not know that I can do better in concluding 
 this portion of my subject than give you Professor 
 Kirchhoff's exact opinions, by reading a short extract 
 from his chapter on the " Physical Constitution of the 
 Sun." " In order to explain," he says, "the occurrence 
 of the dark lines in the solar spectrum, we must assume 
 that the solar atmosphere encloses a luminous nucleus, 
 producing a continuous spectrum, 1 the brightness of 
 which exceeds a certain limit. The most probable sup- 
 position which can be made respecting the sun's consti- 
 tution is, that it consists of a solid or liquid nucleus 
 heated to a temperature of the brightest whiteness, sur- 
 rounded by an atmosphere of somewhat lower tempera- 
 ture. This supposition is in accordance with Laplace's 
 celebrated nebular theory respecting the formation of 
 our planetary system. If the matter now concentrated in 
 the several heavenly bodies existed in former times as an 
 extended and continuous mass of vapour, by the contrac- 
 tion of which sun, planets, and moons have been formed, 
 all these bodies must necessarily possess mainly the same 
 constitution. Geology teaches us that the earth once 
 existed in a state of fusion : and we are compelled to 
 admit that the same state of things has occurred in the 
 other members of our solar system. The amount of 
 cooling which the various heavenly bodies have under- 
 
 1 This continuous spectrum is most probably derived from incan- 
 descent solids or liquids, but may, under certain conditions, be given 
 off by luminous gases. Kirchhoff, as will be seen, has carefully 
 guarded himself from expressing a definite opinion as to the exact 
 condition of the luminous portion of the sun's body ; and on this 
 subject, those who have devoted much attention to solar physics are 
 still undecided. 
 
LBCT. v.] PHYSICAL CONSTITUTION OF THE SUN. 
 
 253 
 
 gone, in accordance with the laws of radiation of heat, 
 differs greatly, owing mainly to the difference in their 
 
 
 FIG. 67. 
 
 masses. Thus, whilst the moon has become cooler than 
 the earth, the temperature of the surface of the sun has 
 
 FIG. 63. 
 
 not yet sunk below a white heat. Our terrestrial atmo- 
 sphere, in which now so few elements are found, must 
 have possessed, when the earth was in a state of fusion, 
 
254 SPECTRUM ANALYSIS. [LECT. v. 
 
 a much more complicated composition, as it then con- 
 tained all those substances which are volatile at a white 
 heat. The solar atmosphere at this time possesses a 
 similar constitution." 
 
 Within the last few years our knowledge concern- 
 ing the physical constitution of the sun has received 
 additions second only in importance to the original 
 discovery of Kirchhoff. The spectroscope in this case 
 is again the instrument by which the extraordinary 
 phenomena of solar physics have been revealed, arid the 
 first step towards the extension of our knowledge has 
 been the examination of the light emitted by those 
 remarkable protuberances or red flames which, during 
 a total eclipse, are seen to dart out from the surface 
 of the sun to the enormous height of some 80,000 to 
 90,000 miles. The appearance of the sun during the 
 total eclipse of 1860 is represented by Figs. 67 and 68, 
 which are copies of photographs taken by Mr. De la Rue 
 in Spain during the eclipse. The first one of these was 
 taken immediately after the total obscuration, and the 
 second just previous to the reappearance of the sun. Fig. 
 69 gives a representation of the total eclipse of 186 9, copied 
 from the photographic registrations taken at Burlington 
 in the United States by Dr. Mayer. In this drawing both 
 the prominences and the coronal rays are seen, and the 
 peculiarly indented appearance of the moon's dark limb 
 in the neighbourhood of the prominences is well shown. 
 The existence of these flames proves that the sun's incan- 
 descent atmosphere extends to a very great height above 
 the ordinary and usually visible portion, and it is very 
 remarkable that certain protuberances which were not 
 visible to the naked eye are found in the photograph ; the 
 flames emitting rays of a high degree of refrangibility so 
 
PiirsraiL CONSTITUTION OF THE SUN. 25.5 
 
 weak as not to act upon the retina, although strong 
 enough to produce an image on the sensitive plate. 
 
 A most striking feature of the ' discovery of the nature 
 of the material composing these red protuberances is 
 that it was made independently and nearly simultaneously 
 
 FIG. 69. 
 
 by two observers many thousands of miles apart, namely, 
 by Mr. J. Norman Lockyer in England, and by the French 
 physicist M. Janssen in India. In the autumn of 1866 
 Mr. Lockyer suggested * that it might be possible, by. the 
 
 1 Proc. Roy. Soc., Oct. 11, I860. 
 
256 SPECTRUM ANALYSIS. [LKCT. v. 
 
 use of the spectroscope, to obtain evidence, under the ordi- 
 nary conditions of the solar disc, of the red prominences 
 which had hitherto only been seen during total eclipses. 
 After many fruitless attempts Mr. Lockyer at last, on Oct. 
 20, 1868, succeeded in seeing the prominences with an 
 unobscured sun, and he ascertained that the spectrum 
 of the prominences is discontinuous, consisting of three? 
 bright bands, which he then gave as being 1, absolutely 
 coincident with c ; 2, nearly coincident with F ; 3, near D. 
 The principle adopted by Lockyer, by which these bright 
 lines, proving the gaseous nature of the prominence, 
 were rendered visible, was that of employing a spectro- 
 scope with a heavy battery of prisms, arid possessing 
 a strong dispersive power. The light from the body 
 of the sun, producing an almost continuous spectrum, 
 was in this way much spread out and thereby weak- 
 ened ; whilst the luminous intensities of the monochro- 
 matic rays emitted by the glowing gas were but slightly 
 diminished, and thus the light from the prominences 
 became visible without being interfered with by that 
 emanating from the body of the sun. A simple experi- 
 ment will render this important point clear. If I 
 throw the light from the incandescent carbon points on 
 to the screen by passing the rays through a flint-glass 
 prism, you will observe a short but very bright and 
 perfectly continuous spectrum ; if I next substitute for 
 the glass prism two prisms filled with carbon disulphide, 
 you see that the spectrum becomes very much elongated 
 and its luminous intensity correspondingly diminished, 
 so that now you can distinctly observe the narrow 
 yellow sodium band and many other bright lines due 
 to impurities in the carbon. These lines were present 
 when the glass prism was used, but they were rendered 
 
LECT. v.] LOCKYER AND JANSSEN'S DISCOVERIES. 257 
 
 invisible by the greater brightness of the continuous 
 spectrum. 
 
 Whilst Mr. tockyer was experimenting in England, 
 M. Janssen had been sent out by the French Govern- 
 ment to Guntoor, in India, to observe the spectroscopic 
 appearances presented by the sun on the total eclipse 
 of August 18, 18G8. On that occasion he saw and 
 measured the position of the bright lines above referred 
 to ; but, struck by their intensity, he likewise conceived 
 the idea that they might be seen when the sun was 
 un-eclipsed, and cried out, as he was looking through 
 his telescope, " Je reverrai ces lignes-la ! " On the next 
 morning, as soon as the sun rose out of the bank of 
 clouds which lay on the horizon, he succeeded in his 
 endeavour, he saw the protuberances plainly, and was 
 able to do what he failed to accomplish in the hurry and 
 excitement of the eclipse ; namely, to measure the exact 
 position of the bright lines. " So that," he writes, " the last 
 seventeen days have been to me like a perpetual eclipse." 
 The announcement of M. Janssen's independent obser- 
 vation was received by the French Academy on October 
 26, 1868, a few days after Mr. Lockyer's discovery had 
 been made known to the Royal Society. As regards 
 the claims of priority of this discovery, you will all, I am 
 sure, feel inclined to agree with the following eloquent 
 words of M. Faye when speaking on this subject in the 
 French Academy on October 26, 1868 : 
 
 " Mais au lieu de chercher a partager, et par con- 
 sequent a affaiblir le merite de la decouverte, ne vaut-il 
 pas mieux en attribuer indistinctement Thonneur entier 
 a ces deux homines de science qui ont eu separement, 
 a plusieurs milliers de lieues de distance, le bonheur 
 d'aborder Tintangible et Tinvisible par la voie la plus 
 
 s 
 
258 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. v. 
 
 etonnante peut-etre qus le genie de 1'observation ait 
 jamais concue ? " 
 
 Lockyer's investigations have not only proved that 
 these singular red prominences consist of glowing gaseous 
 hydrogen, but have revealed the existence of an atmo- 
 sphere, chiefly consisting of incandescent hydrogen, 
 extending all round the sun's surface. The prominences 
 are only ]ocal aggregations of this envelope of glowing 
 hydrogen, which extends for 5,000 miles in height, and 
 has been termed the Chromosphere, to distinguish it from 
 the cooler absorbing atmosphere on the one hand, and 
 the light-giving photosphere on the other. Under proper 
 instrumental and atmospheric conditions the spectrum of 
 
 FIG. 70. 
 
 the chromosphere is always visible in every part of the 
 sun's periphery. Fig. 70 gives a representation, taken 
 from one of Mr. Lockyer's drawings, of the spectrum of 
 the edge of the sun's limb, and of that of the outlying 
 chromosphere. The bright lines of hydrogen, sodium, 
 magnesium, and iron are here seen to be coincident with 
 the corresponding dark lines in the solar spectrum placed 
 below. Hundreds of bright chromospheric lines are 
 frequently seen filling up the field of the telescope, and 
 Professor C. A. Young of Dartmouth College has recently 
 most carefully mapped and described no less than 268 
 
LECT. v.] BRIGHT LINES IN THE CHROMOSPHERE. 259 
 
 bright lines in the spectrum of the chromosphere. Of 
 these as many as 20 are due to titanium ; whilst amongst 
 others the bright lines of barium, manganese, chromium, 
 and calcium are clearly seen. These bright lines have 
 been observed by Professor Young in enormous numbers, 
 in the light proceeding from a narrow layer of solar 
 atmosphere lying nearest to the limb. This zone exhi- 
 bited a splendid spectrum, in which all the Fraunhofer's 
 lines were seen to be bright on a dark ground, showing 
 that here the incandescent gases are at a very high 
 temperature. Another observation of the greatest im- 
 portance we likewise owe to Lockyer, viz. that in 
 examining the bright line coincident with Fraunhofer's 
 F, the breadth or strength of the line is seen to expand 
 or increase as the sun's limb is approached, whilst the 
 line coincident with c and that near to D do not suffer 
 any change of breadth. This remarkable fact, placed in 
 connection with an observation of Pllicker and Hittorf 
 (since confirmed by Huggins, Lockyer, and Frankland), 
 viz. that a similar expansion of the F line in the hydrogen 
 spectrum occurs when the pressure of the incandescent 
 hydrogen is considerably increased, suggested the possi- 
 bility of ascertaining the absolute pressure under which 
 the hydrogen of the prominences exists ; and it thus 
 appears probable that the tension at the lowest portion of 
 the chromosphere is very much less than that of our 
 atmosphere, whereas at the higher parts of a prominence 
 the pressure amounts only to a fraction of a millimetre 
 of mercury. 
 
 Lockyer has succeeded in detecting the third (blue) 
 line of hydrogen (viz. 2796 on Kirchhoff's scale), as well 
 as the violet line known as h in the light of the 
 chromosphere ; and we must therefore admit that the 
 
 s 2 
 
260 SPECTRUM ANALYSIS. [LECT. v. 
 
 proof of the existence in the solar envelope of glowing 
 hydrogen is well founded. The nature of the bright yel- 
 low line, more refrangible by 9*7 of Kirchboffs degrees 
 than the line D = 100 6 '8, and now called "D 3 ," remains as 
 yet a mystery. This line, however, appears always most 
 strongly at the lowest, and therefore at the hottest, portion 
 of the prominence or chromosphere ; and it may therefore 
 possibly be a hydrogen line which is only visible when a 
 great thickness of incandescent gas is examined. The 
 different behaviour of the D 3 line and the line r has been 
 used as an argument in favour of the former not being 
 due to hydrogen ; but cases are known in which the well- 
 known hydrogen lines c and F were differently affected 
 at the same moment. At any rate, Lockyer has proved 
 that the ordinary solar spectrum contains a dark absorp- 
 tion line coincident with this bright orange line in the 
 chromosphere. Fig. 70 shows the position of this yellow 
 line; Fig. 76, p. 266, exhibits the appearance of the 
 bright F line, which is seen to thicken out or become 
 wedge-shaped at the point where it touches the ordi- 
 nary solar spectrum. 
 
 By employing a wide slit, with a screen of ruby- 
 red glass, Huggins, Lockyer, .and Zollner succeeded in 
 seeing the form of a prominence, and thus clearly ob- 
 serving the singularly rapid changes in shape as well 
 as in intensity which they undergo. Lockyer de- 
 scribes some of these enormous flames of incandescent 
 hydrogen, 27,000 miles in height, which totally disap- 
 peared in less than 10 minutes ! " During the last few 
 days," he writes, " I have been perfectly enchanted 
 with the eight which my spectroscope has revealed to 
 me. The solar and atmospheric spectra being hidden 
 and the image of the wide slit alone being visible, 
 
LECT. v.] FORMS OF THE PROMINENCES SEEN. 261 
 
 the telescope or slit is moved slowly, and the strange 
 shadow-forms flit past. Here one is reminded by the 
 fleecy, infinitely delicate cloud-forms, of an English 
 hedge-row with luxuriant elms ; here of a densely inter- 
 twined tropical forest, the intimately interwoven branches 
 threading in all directions, the prominences generally 
 expanding as they mount upwards, and changing slowly, 
 indeed almost imperceptibly. By this method the 
 
 smallest details of the prominences, and of the chromo- 
 sphere itself, are rendered perfectly visible and easy of 
 observation." 
 
 Zollner has also made similar observations, and has 
 published striking drawings of some of these protube- 
 rances, which I here have the pleasure of showing you 
 (Fig. 71). These drawings represent one and the same 
 
262 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. v. 
 
 protuberance observed on July 1, 1869, which under- 
 went the singular changes here seen between the hours 
 of 6h. 45' and 7h. 8' A.M., some of which remind one 
 of the outbursts of a volcano, or the eruptive discharges 
 
 FIG. 72. 
 
 FIG. 73. 
 
 of a gey sir. 1 In one case a flickering flame-like motion 
 was observed to pass in a few seconds up and down 
 a horn shooting up to the height of 50,000 miles 
 (Fig. 72) ; whilst other protuberances formed clouds 
 
 FIG. 74. 
 
 FIG. 75. 
 
 which seem to have been shot upwards by a kind of 
 explosion (Figs. 74 and 75). The chromolith on the 
 opposite page, also one of Zollner's drawings, shows still 
 more strikingly the appearance of these prominences, 
 i See Appendix C. 
 
(an! flnni-H f)\ Pivl 7,<>Utiw 
 
 ay Sons i Taylor, Londor 
 
 f-rixiyrafjfacal Mcfjf^ 
 
 01 Z 3 4- S \' <V .V 1C tl 12 13 14- 150CO 
 
 Postixjrn 160' 
 
 Tfie 
 
 Timt.11* '2C* 
 
LECT. v.] SOLAR TORNADOES. 
 
 The startling rapidity with which these gigantic masses 
 of hydrogen appear and disappear proves that currents, 
 storms, and hurricanes are of constant occurrence in the 
 chromosphere. These changes are doubtless brought 
 about there, as in our own atmosphere, by local varia- 
 tions in temperature. "But," as Kirchhoff remarks, 
 "the differences in temperature which produce these 
 winds may amount to thousands of degrees, and there- 
 fore the force of the currents must far exceed that of 
 the most violent terrestrial tornadoes." Both telescopic 
 and spectroscopic observations of phenomena which have 
 long been known as peculiarities of the solar disc fully 
 bear out this conclusion. You will have anticipated me 
 when I say, that I refer to the dark sun-spots and to 
 the bright stripes or faculae which are always more or 
 less visible on the solar surface. 
 
 Astronomers formerly supposed that the sun-spots were 
 holes in the photosphere through which the dark body 
 of the sun was visible. Kirchhoff proved that this 
 theory could not be correct, inasmuch as the interior 
 portion of the sun's body must be white-hot, and he 
 threw out the idea that these spots were clouds float- 
 ing in the solar atmosphere. Subsequent research has 
 somewhat modified these views of KirchhofFs, for Ave 
 now know that the sun-spots are really hollows or cavities 
 in the solar atmosphere where the temperature of the 
 glowing gases has been reduced. These spots look to 
 us black because they give off less light than the 
 surrounding portions of the sun's surface, but they are 
 not therefore non-luminous ; on the contrary, they emit 
 much light though they appear dark, just as a candle- 
 flame looks black when held in front of the much more 
 intensely-heated surface of the lime-light. The telescope 
 
264 SPECTRUM ANALYSTS. [LECT. v. 
 
 lias long ago told us of the gigantic changes, some- 
 times extending over even thousands of millions of 
 square miles, which these spots undergo, but it is the 
 spectroscope which admits us into the secrets of the 
 constitution of these most singular phenomena. This 
 instrument has shown us that the gases of the whole 
 solar atmosphere are constantly in a state of the most 
 violent motion, and has proved that a spot is a region 
 of greater absorption. The faculse, on the contrary, 
 are accompanied by the incandescent vapours of sodium, 
 iron, magnesium, and barium, thrown up by a sort of 
 volcanic action from the lower to the higher regions 
 of the solar atmosphere ; for the bright lines, indicative 
 of the presence of these bodies, occasionally make their 
 appearance, not only at the edge of the sun's disc, but also 
 in the centre of the sun's surface near the bright faculae, 
 or in the hotter ascending currents of the ignited gases. 1 
 Lockyer even describes a cloud of incandescent mag- 
 nesium that he saw floating high up above a prominence, 
 as in Fig. 75. What an insight this single observation 
 gives us into the condition of solar physics ! 
 
 These bright metallic lines, some of which may gene- 
 rally be seen when carefully looked for in the ordinary 
 
 1 The following is a list of the lines seen by Mr. Lockyer in the 
 chromosphere, with the dates of discovery. The lines c and F were 
 first seen by M. Janssen : 
 
 Hydrogen c, Oct. 20, 1868 ; F, Oct. 20, 1868 ; near D, Oct. 20, 
 1868 ; near G, Dec. 22, 1868 ; h, March 14, 1869. 
 
 Sodium D, Feb. 28, 1869. 
 
 Barium 1985-5 (Kirchhoff's scale), March 15, 1869; 2031-2 
 (ditto), July 5, 1869. 
 
 Magnesium and included line b v 6 2 , b y 6 4 , Feb. 21, 1869. 
 
 Other lines Iron, 1474, June 6, 1869; 1515'5, June 6, 1869. 
 
 Bright lines unknown 1529-5, 1567-5, 1613-8, 1871-5, 2054-0; 
 Iron, 2001-5, 2003-4, June 26, 1869. 
 
LECT. v.J CHANGES IN THE CHROMOSPHERE. 265 
 
 solar spectrum, are always thinner than the corresponding 
 Fraunhofer's lines : this is accounted for by the fact that 
 the glowing gases form part of an upward current, and 
 that they therefore are in a condition of extreme tenuity 
 when we know the lines are always thinnest. In the 
 sun-spots, on the other hand, the opposite state of things 
 occurs ; there a downward current draws the cooler gases 
 and vapours into a lower position, where they become 
 condensed, and exert the powerful absorption on the 
 rays of light which we observe in the darkened area of 
 the spot. The lines of sodium, magnesium, and barium 
 accordingly always appear in a spot-spectrum darker 
 and broader than the corresponding Fraunhofer's lines 
 as seen in the ordinary solar spectrum. A simple but 
 very beautiful experiment devised by Frankland and 
 Lockyer will serve to prove to you that the power of 
 absorption, exerted by the vapours of the metals, increases 
 with the density of the vapour. For this purpose I 
 have here a tube filled with hydrogen hermetically 
 sealed, at the bottom of which I have placed a few 
 small pieces of sodium. If I now bring this tube before 
 the slit of our electric lamp, and heat the metallic 
 sodium, you will see a fine black line make its appear- 
 ance on the screen : this line is caused by absorption of 
 the yellow rays by the vapour which is now beginning 
 to come off from the heated metal. As the density of 
 the sodium vapour increases, you observe that the black 
 line assumes a wedge or V shape, the absorption being 
 greatest where the gas is most dense. Here, then, we 
 have a precisely similar phenomenon to that observed by 
 Lockyer in the widening out of the F line seen in the 
 chromosphere and in the sun-spots. 
 
 This arrow-headed form of the bright F line close to 
 
266 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. v. 
 
 the sun's edge is shown in Fig. 76; the upper part of 
 the diagram gives part of the ordinary solar spectrum, 
 whilst on the lower is seen the bright hydrogen line H (3. 
 
 203, 
 
 212,1 
 
 Another most interesting subject has reference to the 
 spectrum of the corona or the halo of silver-white light 
 which surrounds the moon on all sides during a total 
 eclipse of the sun (Fig. 77). 
 
 FIG. 77. 
 
 The spectrum of the corona has recently been made 
 the subject of much careful study ; but as this examina- 
 tion can only be carried out during the short duration of 
 
LECT. v.] SPECTRUM OF THE CORONA. 267 
 
 a total eclipse, and as such total eclipses are not very 
 frequent, our knowledge on this subject is not so pre- 
 cise as that respecting the chromosphere. Nevertheless, 
 thanks to the untiring energy of astronomers and spec- 
 troscopists of all nations who have vied with each other 
 in this great work, we have arrived at certain definite 
 conclusions respecting the corona. 
 
 Major Tennant was the first, in 1868, 1 to observe the 
 spectrum of this outlying luminous zone, and he describes 
 it as a continuous one. The American astronomers Young, 
 Harkness, and Pickering, observing in 1869, confirmed 
 Tennant's conclusions, but some of them saw three bright 
 lines, the brightest of which was situated at 1474 on 
 KirchhofFs scale, and the two others about 1250 and 
 1350 on the same scale. The eclipse of 1870, observed 
 in Southern Europe, confirmed the truth of the American 
 observations: line 1474 was again seen with two other 
 fainter lines on a still fainter continuous spectrum ; whilst 
 the Indian eclipse of December 1871 yielded results of a 
 similar character. The same lines were observed to reach 
 to a height of 20 minutes above the photosphere, whilst 
 at the same time a distinctly radial structure in the corona 
 is seen in the photographs obtained. Another result of 
 this last eclipse in which all the observers agree is, that 
 the atmosphere of incandescent hydrogen, seen in the 
 prominences and in the chromosphere, extends to a much 
 greater elevation than had been previously supposed, 
 giving rise, along with the substance 1474 (whether 
 hydrogen or not), to a fine coronal atmosphere. 
 
 The question as to the exact nature of this glorious 
 silver halo has been, and indeed is still being, keenly 
 debated. Some attribute the whole of the visible lumi- 
 1 See Appendix B. 
 
268 SPECTRUM ANALYSIS. [LECT. v. 
 
 nosity to an enormously extended incandescent solar 
 atmosphere, whereas others would restrict the truly solar 
 portion of the phenomenon to the lower and more highly 
 luminous layers, and explain the outlying luminosity as 
 being produced by terrestrial glare. There is no doubt, 
 however, that one of the bright lines has been traced to 
 a height of about 20 minutes (two-thirds of the solar 
 diameter) above the sun's limb, whilst indications of 
 determinate photographic action have been obtained by 
 Mr. Brothers at a distance of at least two solar diameters. 
 A representation of the photograph obtained at Syracuse 
 in Dec. 1870 by Mr. Brothers is given on the opposite 
 page, and facing p. 270 is found a copy of one of Mr. 
 Da vies' fine photographs obtained in India in Dec. 1871. 
 One singular feature of the eclipse indicated both in the 
 drawings as well as in the photographs of the corona is the 
 series of dark rifts or shadows which, starting out from 
 the moon's surface, spread out like a fan at certain points. 
 
 FIG. 78. 
 
 These rifts have not only been shown to be coincident 
 in photographs of the same eclipse taken at different 
 localities, but are found to be indicated by sketch ers as 
 having been seen by the eye to exist in the same positions 
 as those shown by Nature's drawing in the photographs. 
 Thus in the photographs of 1870 taken at Syracuse 
 (Fig. 78, No. 3) and at Cadiz (No. 2) the riffcs are 
 identical in position with those shown in Professor 
 
LOT. v.] SPECTRUM OF THE CORONA. 269 
 
 Watson's sketch (No. 1) of the same eclipse as seen at 
 Carlentini, which represents the main features of the 
 three pictures. 
 
 We may sum up as follows the evidence which we at 
 present possess concerning the corona : 
 
 The corona is due in great part to the sun. 
 
 (1) Because the whole appearance and structure of the 
 corona indicates a solar origin, and cannot be explained 
 by terrestrial glare. 
 
 (2) Because the brightness at the moon's centre during 
 a total eclipse without cloud is the measure of the greatest 
 possible glare, and the photograph of Mr. Brothers shows 
 how small this is. 
 
 (3) Because the dark rifts are solar phenomena. 
 There is, however, little doubt that, although the 
 
 greater portion of the coronal light is due to incandescent 
 gas, giving the bright lines, a certain part is derived 
 from other sources. Thus a faint continuous spectrum 
 would indicate the presence of incandescent cosmical dust; 
 the appearance of the dark Fraunhofer's lines shows that 
 ordinary solar light is reflected ; whilst the fainter and 
 outlying part may be due to light reflected from our own 
 atmosphere. It is very singular that the positions of 
 these three lines (1250, 1350, and 1474, on KirchhofFs 
 scale) coincide, within the probable errors of observation, 
 with three lines observed by Professor Winlock in the 
 spectrum of the aurora borealis. The line 1474 is due 
 to iron. Can we suppose that Dalton's old speculations 
 as to the nature of the aurora have after all some founda- 
 tion, and that this beautiful phenomenon is due " to the 
 presence of some elastic fluid substance, probably of a 
 ferruginous nature, existing in the higher regions of our 
 atmosphere I " 
 
270 SPECTRUM ANALYSIS. [LECT. v. 
 
 Angstrom T also observed the spectrum of the aurora 
 in the winter of 1867-8 ; he saw only one very bright 
 band, the wave-length of which he finds is 5567 ten- 
 millionths of a millimetre, or at 1259 (between D and E) 
 on KirchhofFs scale, together with traces of two others : 
 but the most interesting discovery which he made on this 
 branch of the subject was, that he succeeded in observing 
 the same bright band in the spectrum of the zodiacal 
 light; and even on a starlight night, when the whole sky 
 seemed almost phosphorescent, Angstrom saw traces of 
 these bands in light from all parts of the heavens. In 
 the last few years several splendid exhibitions of aurora 
 have been witnessed : those who saw the display of 25th 
 October, 1870, can never forget the effect. In this and 
 other auroras the same lines were seen ; thus Winlock in 
 1869 saw five bright lines, one of which is identical in 
 position with the coronal line 1474 (KirchhofT), arid 
 Zollner and others in 1870 observed the same lines. 
 Strangely enough, this band, which links together the 
 apparently unconnected phenomena of the solar corona, 
 the zodiacal light, and the aurora, does not, according 
 to Angstrom, appear to correspond to the lines of any 
 known substance. We must, however, remember that 
 if the terrestrial aurora is caused by particles of the 
 earth's atmosphere, and that if it sometimes occurs at 
 an elevation of more than 100 miles above the earth's 
 surface, it follows that the light has been able to pass 
 through 100 miles of cold atmosphere without being 
 altogether absorbed. The radiating power of the atmo- 
 sphere for these rays must, therefore, be very small, since 
 its absorbent power is also very small. Hence, then, we 
 ought not to be surprised if we cannot reproduce these 
 
 1 See end of Appendix A. 
 
272 SPECTRUM ANALYSIS. [LECT. v. 
 
 LECTURE V APPENDIX A. 
 
 ON THE NORMAL SOLAR SPECTRUM. 
 BY A. J. ANGSTROM. 
 
 A MOST valuable memoir on the Normal Spectrum of the Sun 
 has recently been published by Professor Angstrom, of Upsala, 
 accompanied by an atlas of six magnificent plates, exhibiting 
 the lines in the whole length of the solar spectrum from A to H. 
 The positions of these lines are mapped according to their wave- 
 lengths, which have been calculated from observations most care- 
 fully made with diffraction spectra. The bright metallic lines 
 coincident with those of Fraunhofer are also given. The follow- 
 ing table gives a resumd of the solar lines shown on his maps as 
 produced by known elements : 
 
 Substances. * Substances. Dumber of 
 
 Hydrogen ..... 4 Manganese ..... 57 
 
 Sodium ...... 9 Chromium . 18 
 
 Barium . . . . . .11 
 
 Calcium 75 
 
 Magnesium . . . 4 + 3 (?) 
 
 Aluminium 2 (?) 
 
 Iron 450 
 
 Cobalt 19 
 
 Nickel 33 
 
 Zinc 2 (?) 
 
 Copper .7 
 
 Titanium . 118 2 
 
 The total number of these coincident metallic lines amounts 
 to close upon 800, and this number might be easily increased by 
 using more powerful means of raising the temperature of the 
 substances under examination. "Nevertheless the number already 
 mapped suffices to show that to account for the origin of almost 
 all the more prominent rays in the solar spectrum, and in con- 
 
 1 " Kecherches sur le Spectre Solaire," par A. J. Angstrom j "Spectre normal 
 du Soleil, Atlas de six planches," Upsala, 1868. 
 
 2 The presence of titanium in the solar atmosphere was discovered by Thalen. 
 
APPEND. A.[ ANGSTROM'S NORMAL SOLAR SPECTRUM. 273 
 
 formation of an opinion expressed by me in a former research, 
 we must assume that the substances constituting the chief mass 
 of the sun are without doubt the same substances as exist on 
 our planet. It must, however, not be forgotten that nearly 
 equidistant between F and G there exist certain prominent rays 
 whose nature is as yet unknown : still, any conclusions con- 
 cerning the presence of substances in the sun which are 
 unknown on the earth are certainly premature. We may 
 nevertheless notice as a singular fact, that one of the darkest 
 of these unknown lines coincides with a prominent line in the 
 spectrum of bromine ; but, as chlorine exhibits no coincidences 
 with Fraunhofer's lines, it is not likely that this correspondence 
 is really due to bromine. 
 
 "Aluminium undoubtedly exhibits several bright lines in 
 various parts of the spectrum, but the two lines situated between 
 the two H bands are the only ones which have been observed to 
 be coincident with Fraunhofer's lines. To explain this singular 
 fact it must be remembered that the violet rays of this metal 
 are much the most intense. By observing the ultra-violet rays 
 of this metal it will be possible to ascertain whether these two 
 lines are caused by aluminium, as the ultra-violet bands ought 
 to coincide with the invisible dark lines in the chemically active 
 portion of the solar spectrum. 
 
 " To the two zinc lines which I have indicated on iny map 
 as coincident with dark solar lines I have to add a third, situated 
 at 48097, but two other bright and broad lines of this metal 
 which appear somewhat nebulous do not coincide with Fraun- 
 hofer's lines ; and hence I consider that the presence of zinc in 
 the solar atmosphere is very doubtful. At the same time I may 
 mention that there are also three nebulous bands due to mag- 
 nesium, none of which, are seen in the sun, although the 
 presence of this element in the solar atmosphere does not 
 admit of a doubt. 
 
 " Of all the elements, iron certainly contains the largest 
 number of lines visible in the solar spectrum. The iron lines 
 which are not symmetrically distributed throughout the spec- 
 trum exhibit two maxima; the one situated near E, and the 
 
 T 
 
274 SPECTRUM ANALYSIS. [LECT. v. 
 
 other near G. Some of the iron lines appear to be coincident 
 with those of calcium, but such coincidences are often only 
 apparent. Thus, for example, there is a strong iron line between 
 E and I) (wave-length = 5 22 6 1 ), which is drawn as a single line 
 on both Kirchlioff' s maps and my own. Nevertheless M. Thalen 
 has proved, by increasing the dispersive power of his instrument 
 by using six flint-glass prisms, that this ray is in reality a triple 
 one, and that its constituent lines are produced, one by iron and 
 one by titanium. 
 
 " Among the metalloids, hydrogen is the only one indicated by 
 spectrum analysis as existing in the sun : the other substances, 
 such as oxygen, nitrogen, and carbon, which exist in such large 
 quantities on the earth, can never be discovered in the sun by 
 this process. Still, in spite of the almost complete want of 
 coincidences between the solar lines and those of oxygen and 
 nitrogen, we have no right to pronounce definitively upon the 
 absence of these two bodies in the sun. And for this reason : 
 the air spectrum cannot be observed even between the carbon 
 poles of a battery of fifty cells, and in general is not seen 
 when the electricity passes by what may be termed the elec- 
 trolytic discharge. These spectra need for their production the 
 disruptive discharge, as is seen clearly in the experiments with 
 Geissler's tubes containing these two gases. In fact, when the 
 discharge is accompanied by electrolysis, the spectra obtained in 
 rarefied gases are those of compound bodies ; and thus Pliicker is 
 incorrect in naming these the spectra of the first order : on the 
 contrary, when the discharge becomes disruptive, as by using the 
 condenser, the spectra of the elementary bodies at once become 
 visible. This fact possesses a great degree of importance for the 
 true interpretation of the spectra of the sun and stars, as it 
 points out to us as very probable that the high temperature of 
 the sun is insufficient to produce the brilliant rays of oxygen 
 and nitrogen 
 
 "In a memoir on the double spectra of the elementary bodies, 
 which M. Thalen and I are about to publish, we treat of the 
 important points of this interesting subject. Let it suffice for 
 
 1 TV i>millioutlis of a millimetre. 
 
APPEND. A.] SPECTRA OF THE AURORA BOREALIS. 275 
 
 me here to remark, that the results to which we have arrived in 
 no way bear out the opinion of Pliicker, that one element can 
 give totally different spectra, The exact reverse of this is the 
 truth. By successively augmenting the temperature we find 
 that the intensity of the rays varies in a most complicated 
 manner, and that, accordingly, even new rays can make their 
 appearance if the temperature is sufficiently raised. But, inde- 
 pendently of all these mutations, the spectrum of each substance 
 always preserves its individual character." 
 
 SPECTRA OF THE AURORA BOREALIS AND OF THE ZODIACAL 
 
 LIGHT. 
 
 BY A. J. ANGSTROM. 
 
 "During the winter of 1867-8 I have several times observed 
 the spectrum of the luminous arc which bounds the dark circle, 
 and is always seen in feeble auroras. The light of this arc is 
 almost monochromatic, and exhibits a single brilliant band, 
 situated to the left of the well-known group of calcium lines. 
 By measuring its distance from this group I have determined its 
 wave-length to be = 5567. In addition to this ray, of which 
 the intensity is relatively high, I have also observed, by widen- 
 ing the slit, traces of three very feeble bands situated near 
 to F. Another circumstance gives a greater, and indeed an 
 almost cosmical, importance to this observation of the auroral 
 spectrum. During the month of March 1867 I succeeded in 
 observing the same bright band in the spectrum of the zodiacal 
 light, which was at that time seen of great intensity. Indeed 
 during a starlight night, when the sky was almost phospho- 
 rescent, I found traces of this band visible from all parts of the 
 heavens. It is a remarkable fact that this bright band does not 
 coincide with any of the known rays of simple or compound 
 gases which I have as yet examined." 
 
276 SPECTR UM ANALYSIS. [LECT. v. 
 
 APPENDIX B. 
 
 THE INDIAN TOTAL SOLAR ECLIPSE. 
 
 EXTRACTS FROM THE REPORT OF THE COUNCIL OF THE EOYAL 
 ASTRONOMICAL SOCIETY TO THE FORTY-NINTH ANNUAL 
 GENERAL MEETING. 
 
 Solar Eclipse of 1868, August 18. 
 
 " The results obtained by the different observers are of such 
 nterest and importance that the principal observations which 
 would not otherwise appear in our ' Transactions ' are given in 
 considerable detail in the observers' own words. 
 
 ."It is with great satisfaction that the Council call the 
 attention of the Fellows of the Society to the complete success 
 of their own expedition ; a success for which the Fellows 
 are much indebted to the skill and energy of the Superin- 
 tendent, Major Ten n ant. 
 
 The Astronomical Society's Expedition. 
 
 " It will be in the recollection of our Fellows that at the 
 last anniversary meeting it was stated that preparations had 
 been made at the recommendation of the Council of our Society 
 for the observation of the total eclipse of the sun in India, 
 The Astronomer Royal took a warm interest in the proposed 
 observations, and addressed the Secretary of State for India 
 on the subject. It was ultimately arranged that the expense 
 of the expedition should be borne jointly by the Government 
 of India and the Imperial Government. The superintendence 
 of the expedition was entrusted to Major Tennant. It is with 
 
APPEND. B.] SOLAR ECLIPSE OF 1868. 277 
 
 great satisfaction that the Council is able to anrounce that 
 Major Tennant has been most deservedly and eminently 
 successful. 
 
 " The Ecport of Major Tennant's observations is now in the 
 hands of the Society, and it is intended that it shall appear in 
 the forthcoming volume of the 'Transactions/ fully illustrated 
 with fac -similes of the photographs taken at G untoor, which it is 
 proposed to enlarge photographically, in order that the details 
 of the prominences may be seen more clearly than is possible 
 in the small copies which accompany the paper. Mr. De la 
 Rue, who evinced considerable interest in the expedition, and 
 afforded facilities to Major Tennant for familiarizing himself 
 with astronomical photography before he started, has undertaken 
 to see that the photographs are properly enlarged and copied. 
 
 " It is here proper to state that to Major Tennant is due the 
 credit of having first called attention to the peculiarly favour- 
 able conditions which would be presented by the solar eclipse 
 of August 1.868. 1 
 
 " It is only justice also to mention that, as far as regards the 
 part which England took in the observations, it was mainly 
 attributable to the energetic, active, and untiring zeal of Major 
 Tennant, who happened to be in England on leave during the 
 greater part of 1867, and who devoted much time in promoting 
 the observations which, in spite of many difficulties, have been 
 so successfully undertaken and carried out. 
 
 " It will be recollected that Major Tennant, after consulting 
 with the Astronomer Eoyal and other Fellows of the Society, 
 undertook the following work. It was most comprehensive, and 
 entailed possibly almost too much responsibility for the director 
 of a single expedition. 
 
 " 1. The Determination of the Geographical Position of the 
 Station. This was successfully accomplished by means of a 
 repeating circle, although, in consequence of bad weather, there 
 were not many available days between the arrival of the ob- 
 servers and instruments at G untoor and the clay of the eclipse. 
 
 i Monthly Notices, vol. xxvii. pp. 79, 174. 
 
278 SPECTR UM A NALYSIS. [LECT. v. 
 
 "The position was found to be, latitude K 16 17' 29-23", 
 and longitude E. 5h. 21m. 48'6s. 
 
 " Captain Branfill, RE., subsequently connected the station 
 with the marks of the Great Trigonometrical Survey, and de- 
 duced the following result: Lat. N. 16 IT 34'3", and long. E. 
 5h. 21m. 46'5s. 
 
 " 2. Spectroscopic Observations. These were undertaken by 
 Major Tennant himself, by means of the Sheepshanks equatorial, 
 of 4*6 inches aperture and 5 feet focal length. This had been 
 mounted equatorially by the late Mr. Cooke, and was suitable 
 for all latitudes in the British Isles, but it had to be altered 
 to suit the more southern stations of India. The spectroscope 
 employed with the telescope was made by Messrs. Troughton 
 and Simms, and was provided with a scale of equal parts, which 
 was illuminated by means of a lamp. The addition of this 
 spectroscope threw additional work on the driving clock beyond 
 that for which it was originally calculated, and, in consequence, 
 some difficulties were experienced just at the critical time of 
 observation from the irregularity of its going. 
 
 " In spite, however, of this and other mishaps, Major Tennant 
 was able to carry out his observations, and ascertained, 1st, that 
 the corona only gave the continuous solar spectrum ; 2nd, that 
 the light of the- prominences was resolvable into certain bright 
 lines of definite refrangibility, showing that these appendages 
 consist of gaseous matter at a very high temperature. Major 
 Tennant states that the Great Horn gave a beautiful line in the 
 red, a line in the orange, and one in the green, which appeared 
 multiple, also a line seen with difficulty near F ; he says the red 
 and yellow lines were evidently c and D : the reading of the 
 bright lines coincides with that of the brightest line in &. The 
 line near to F was, in all probability, F itself; E, he says, was 
 certainly not seen by him, and that, as regards the line in the 
 blue, it was useless from his data to speculate upon it. 
 
 " We now have more precise information from the researches 
 of M. Janssen and Mr. Lockyer respecting the position of the 
 bright lines, and the probable nature of the sun's appendages ; 
 but it must be admitted that Major Tennant did this part of his 
 
APPEND. B.] SOLAR ECLIPSE OF 1868. 279 
 
 work well, especially when the scope of the instruments at dis- 
 posal is taken into account. 
 
 " 3. Major Tennant noted the time of first contact of the 
 sun and moon's limbs by means of the repeating circle at 
 6h. 2m. 12*60s. sidereal time, and that of the last contact at 
 8h. 47m. 24-62s. sidereal time. 
 
 " 4. Polariscope. This part of the work was most ably per- 
 formed by Captain Branfill, who joined Major Tennant early 
 in August, and immediately set to work to familiarize him 
 self with the phenomena produced by polarized light in th 
 telescope. This instrument was one of the old collimators o 
 the great transit circle of Greenwich, and was lent by the 
 Astronomer Eoyal. It was mounted on a polar axis, so that 
 with one movement it could be made to follow the apparent 
 motion of the sun ; but it was not provided with a driving clock. 
 To this telescope a polariscope eyepiece had been fitted by 
 Mr. Ladd. The polarizing apparatus comprised several com- 
 binations which could readily and rapidly be substituted one 
 for the other. All these concurred in showing that the promi- 
 nences (the Great Horn was chiefly observed) gave no indication 
 of polarized light ; on the other hand, every arrangement brought 
 out the fact that the light of the corona was polarized in a plane 
 passing through the sun's centre. These observations were 
 therefore fully and successfully carried out. 
 
 " 5. We now come to the photographic observations : these 
 were under the immediate direction of Sergeant Phillips, who is 
 not only a skilled photographer, but also had the advantage (as 
 well as the Sappers who aided him) of working in Mr. Warren 
 De la Kue's observatory at Cranford. The telescope employed is 
 a Newtonian with a silvered-glass mirror, 9 inches in diameter, 
 by With, and specially mounted by Mr. Browning. Preparations 
 had been made for having a very large field, in order that the 
 corona might be depicted as well as the prominences. Unfor- 
 tunately the sun was covered with cunmlo-stratus clouds, which 
 diminished the actinic power of the light of the coron^ so much 
 that it was not recorded. In other respects the photographs (six 
 in number) were eminently successful. 
 
280 SPECTRUM ANALYSTS. [LECT. v. 
 
 Interval. 
 
 No. 1 Exposed at 7' 17 2 : 9 S T. for 1 
 
 58-5 ,, 2 
 
 61-4 ,, 3 
 
 58-1 ,, 4 
 
 63-2 ,, 5 
 
 907 6 
 
 7 11 1-4 
 
 7 19 2-3 
 
 7 20 0-9 
 
 7 21 4-1 
 
 7 22 34-8 
 
 o 
 
 10 
 5 
 1 
 1 
 
 " Paper copies of these, about two inches in diameter, 
 accompany the Report ; and Mr. James, one of Major Tennant's 
 assistants, made excellent drawings of the Great Horn and 
 other prominences seen in the photograph, by means of the 
 microscope. Since the arrival of the memoir Sergeant Phillips 
 has brought safely to England eight sets of transparent copies 
 on glass, which have been distributed to individuals and learned 
 bodies ; amongst others, to the Royal Society and the French 
 Academy of Sciences. On the occasion of a lecture given by 
 Prof. Herschel at the Royal Institution, on January 22, these 
 were shown by means of the electric lamp, and projected on a 
 screen, on a scale of about 5 feet for the moon's diameter. The 
 amount of detail visible under these circumstances was very 
 remarkable. The spiral structure of the Great Horn, to which 
 Major Tennant has called attention, was very evident. This 
 spiral formation Major Tennant ascribes to the confliction of 
 an ascending current and one at right angles to it. Since 
 then, Mr. Warren De la Rue has procured some very beautiful 
 copies, about 6| inches diameter. He has also discussed, 
 graphically, the small paper photographs, and communicated 
 the results to the Society. 1 The diagram accompanying his 
 paper shows fairly the form and relative position of these 
 appendages with respect to the sun. Mr. Warren De la Rue 
 thought that he had detected a rotation of the Great Horn on 
 its axis during the intervals between occurrence of totality 
 at the various stations along the line of the eclipse. He has 
 since been favoured by Prof. Foerster, Director of the Berlin 
 Observatory, with a copy of the first Aden photograph, and 
 informs tlje Council that there does not appear to be any very 
 
 1 Monthly Notices, vol. xxix. p. 73. 
 
APPEND. B.J SOLAR ECLIPSE OF 1868. 281 
 
 great change in the appearance of the Great Horn at Aden and 
 at Guntoor. This comparison of results brings out forcibly the 
 great value of photography for this class of observations, for the 
 most careful and collected observer is liable to make an error 
 in recording eye-observations. 
 
 " In justice, however, to Col. Addison, whom Major Tennant 
 had induced to make observations at Aden, it must be stated 
 that a drawing of the prominences which he sent to Major 
 Tennant led that gentleman to conclude that no change had 
 occurred in them between the epoch of Aden and that of Guntoor. 
 
 " Major Tennant reached Aden on the 25th of January : as 
 this was nearly the first place where observations of the totality 
 could be made, he enlisted the services of Captain Davis, the 
 Peninsular and Oriental Company's agent, and of an old com- 
 panion, Major Napier, RA. Both these gentlemen promised 
 their aid, and he learnt from them that Col. Addison and Major 
 Weir, H.M. 2cl Eoyal Regiment, would be likely to be valuable 
 coadjutors. Unfortunately, the contemplated observations with 
 the polariscope, spectroscope, and intended drawings of the 
 corona were rendered impossible, in consequence of clouds. But 
 the prominences were seen and recorded with great accuracy, as 
 it has been before stated. 
 
 " The Council have every reason to feel satisfied with the steps 
 they took in conjunction with the Astronomer Eoyal in further- 
 ing Major Tennant's views, and in thus securing a most valuable 
 series of observations." 
 
 Lieut. J. HerscheVs Account. Position, Jamkandi. 
 
 " The totality commenced unseen. ' A few seconds more, and 
 the spectrum of diffuse light vanished also, and told me the 
 eclipse was total, but behind a cloud. I went to the finder, 
 removed the dark glass, and waited, how long I cannot say, 
 perhaps half a minute. Soon the cloud hurried over, following 
 the moon's direction, and therefore revealing, first, the upper 
 limb, with its scintillating corona, and then the lower. Instantly 
 I marked a prominence near the needle point, an object so con- 
 
282 SPECTRUM ANALYSIS. [LECT. v. 
 
 spicuous that I felt there was no need to take any precautions to 
 secure identification. It was a long finger-like projection from 
 the (real) lower left-hand portion of the circumference. A rapid 
 turn of the declination screw covered it with the needle point, 
 and in another instant I was at the spectroscope. A single 
 glance, and the problem was solved. 
 
 " ' Its Spectrum. Three vivid lines, red, orange, blue ; no 
 others, and no trace of a continuous spectrum. 
 
 " ' When I say the problem was solved, I am, of course, using 
 language suited only to the excitement of the moment ! It was 
 still very far from solved, and I lost no time in applying myself 
 to measurement. And here I hesitate, for the measurement was 
 not effected with anything like the ease and certainty which 
 ought to have been exhibited. Much may be attributed to haste 
 and unsteadiness of hand, still more to the natural difficulty of 
 measuring intermittent glimpses ; but I am bound to confess 
 that these causes were supplemented by a failure less excusable. 
 I have no idea how those five minutes passed so quickly ! 
 Clouds were evidently passing continually, for the lines were 
 only visible at intervals not for one-half the time certainly 
 and not always bright ; but still I ought to have measured them 
 all. My failure was insufficient illuminating power ; but why, I 
 cannot tell. I never experienced any difficulty of the kind with 
 the nebulae, which required that I should flash in light suddenly 
 over and over again. I had found the hand-lamp the surest 
 way, but it failed me here in great measure. The red line must 
 have been less vivid than the orange, for after a short attempt 
 to measure it I passed on to secure the latter. In this I suc- 
 ceeded to my satisfaction, and accordingly tried for the blue 
 line. Here I was not so successful. The glimpses of light were 
 rarer and feebler, the line itself growing shorter, and what 
 remained of it further from the cross. I did, however, place 
 the cross wires in a position certainly very near the true one, 
 and got a reading before the re-illumination of the field told me 
 that the sun had reappeared on the other limb. These readings 
 were called out, as those on the solar lines had been, to my 
 recorder, and it was only afterwards that I compared them. 
 
APPEND. B.] SOLAR ECLIPSE OF 1868. 283 
 
 " ' I need not dwell on the feelings of distress and disappoint- 
 ment which I experienced on realizing the fact that the long- 
 anticipated opportunity was gone, and, as it seemed to me then, 
 wasted. I seemed to have failed entirely. Almost mechanically 
 I directed the telescope to the brightened limb, to verify the 
 readings of the solar lines, and in doing so my interest was 
 again awakened by the near coincidence, as it seemed, of the 
 line F with the position of the wires ; but a little reflection 
 convinced me that the distance of the former was greater than 
 the error which I might have made in intersecting the blue line. 
 I read F, and then D and c. The following were my readings 
 up and down : 
 
 C. D. b. F. 
 
 ( 1-91 2-96 4-58 5'64 
 
 Before j 1'90 2 "94 4'58 5 '61 
 
 I 1-93 2-98 4-60 5 '65 
 
 I 1-92 2-97 4-58 5'62 
 
 Bright Hues [3 -00] [5 '56] 
 
 After 1-93 3 "00 5 '65 
 
 " ' I consider that there can be no question that the orange 
 line was identical with D, so far as the capacity of the instrument 
 to establish any such identity is concerned. I also consider 
 that the identity of the blue line with F is not established ; on 
 the contrary, I believe that the former is less refracted than F, 
 but not much. With regard to the red line, I hesitate very 
 much in assigning an approximate place ; B and c represent the 
 limits : it might have been near c ; I doubt it being so far as b. 
 I am not prepared to hazard any more definite opinion about 
 it. Its colour was a bright red. This estimate of its place 
 is absolutely free from any reference to the origin of the lines 
 c and F.' 
 
 " The spectrum of the corona does not appear to have been 
 specially examined." 
 
282 SPECTRUM ANALYSIS. [LECT. v. 
 
 spicuous that I felt there was no need to take any precautions to 
 secure identification. It was a long finger-like projection from 
 the (real) lower left-hand portion of the circumference. A rapid 
 turn of the declination screw covered it with the needle point, 
 and in another instant I was at the spectroscope. A single 
 glance, and the problem was solved. 
 
 " ' Its Spectrum. Three vivid lines, red, orange, blue ; no 
 others, and no trace of a continuous spectrum. 
 
 " ' When I say the problem was solved, I am, of course, using 
 language suited only to the excitement of the moment ! It was 
 still very far from solved, and I lost no time in applying myself 
 to measurement. And here I hesitate, for the measurement was 
 not effected with anything like the ease and certainty which 
 ought to have been exhibited. Much may be attributed to haste 
 and unsteadiness of hand, still more to the natural difficulty of 
 measuring intermittent glimpses ; but I am bound to confess 
 that these causes were supplemented by a failure less excusable. 
 I have no idea how those five minutes passed so quickly ! 
 Clouds were evidently passing continually, for the lines were 
 only visible at intervals not for one-half the time certainly 
 and not always bright ; but still I ought to have measured them 
 all. My failure was insufficient illuminating power ; but why, I 
 cannot tell. I never experienced any difficulty of the kind with 
 the nebulse, which required that I should flash in light suddenly 
 over and over again. I had found the hand-lamp the surest 
 way, but it failed me here in great measure. The red line must 
 have been less vivid than the orange, for after a short attempt 
 to measure it I passed on to secure the latter. In this I suc- 
 ceeded to my satisfaction, and accordingly tried for the blue 
 line. Here I was not so successful. The glimpses of light were 
 rarer and feebler, the line itself growing shorter, and what 
 remained of it further from the cross. I did, however, place 
 the cross wires in a position certainly very near the true one, 
 and got a reading before the re-illumination of the field told me 
 that the sun had reappeared on the other limb. These readings 
 were called out, as those on the solar lines had been, to my 
 recorder, and it was only afterwards that I compared them. 
 
APPEND. B.] SOLAR ECLIPSE OF 1868. 283 
 
 " ' I need not dwell on the feelings of distress and disappoint- 
 ment which I experienced on realizing- the fact that the long- 
 anticipated opportunity was gone, and, as it seemed to me then, 
 wasted. I seemed to have failed entirely. Almost mechanically 
 I directed the telescope to the brightened limb, to verify the 
 readings of the solar lines, and in doing so my interest was 
 again awakened by the near coincidence, as it seemed, of the 
 line F with the position of the wires ; but a little reflection 
 convinced me that the distance of the former was greater than 
 the error which I might have made in intersecting the blue line. 
 I read F, and then D and c. The following were my readings 
 up and down : 
 
 c. 
 
 D. 
 
 6. 
 
 P. 
 
 
 f 1-91 
 
 2-96 
 
 4-58 
 
 5-64 
 
 Before 
 
 1-90 
 
 2-94 
 
 4-58 
 
 5-61 
 
 
 1-93 
 
 2-98 
 
 4-60 
 
 5-65 
 
 
 . 1-92 
 
 2-97 
 
 4-58 
 
 5-62 
 
 Bright lines 
 After 1-93 
 
 [3-00] 
 3-00 
 
 
 [5-56] 
 5-65 
 
 " ' I consider that there can be no question that the orange 
 line was identical with D, so far as the capacity of the instrument 
 to establish any such identity is concerned. I also consider 
 that the identity of the blue line with F is not established ; on 
 the contrary, I believe that the former is less refracted than F, 
 but not much. With regard to the red line, I hesitate very 
 much in assigning an approximate place ; B and c represent the 
 limits : it might have been near c ; I doubt it being so far as b. 
 I am not prepared to hazard any more definite opinion about 
 it. Its colour was a bright red. This estimate of its place 
 is absolutely free from any reference to the origin of the lines 
 c and F.' 
 
 " The spectrum of the corona does not appear to have been 
 specially examined." 
 
284 SPECTRUM ANALYSTS. [LECT. v. 
 
 Lieut. Campbell's Report. 
 
 " The instruments in question were as follow : a telescope of 
 3-inch aperture, mounted on a rough double axis, admitting of 
 motions in azimuth and altitude by hand only, unaided by any 
 appliance for clamping and slow motion. The telescope was 
 provided with three eyepieces of magnifying powers 27, 41, 
 and 98 ; and with it were furnished two analysers for polarized 
 light, viz. a double-image prism and a Savart's polariscope. 
 
 " On the first opportunity after the commencement of the 
 total phase of the eclipse I turned on the double-image prism 
 with the eyepiece of 27 magnifying power, as recommended in 
 the Instructions, which gave a field of about 45' diameter. A 
 most decided difference of colour w r as at once apparent between 
 the two images of corona ; but I could not make certain of any 
 such difference in the case of a remarkable horn-like protu- 
 berance, of a bright red colour, situated about 210 from the 
 vertex, reckoned (as I have done in all cases) with reference 
 to the actual, not the inverted image, and with direct motion. 
 I then removed the double-image prism and applied Savart's 
 polariscope, which gave bands at right angles to a tangent to 
 the limb, distinct, but not bright, and with little, if any, appear- 
 ance of colour. On turning the polariscope in its cell, the bands, 
 instead of appearing to revolve on their own centre, passing 
 through various phases of brightness, arrangement, &c., travelled 
 bodily along the limb, always at right angles thereto, and without 
 much change in intensity, or any at all in arrangement. The 
 point at which they seemed strongest was about 140 from the 
 vertex, and I recorded them as black centred. Believing that 
 with a higher power and a smaller field I should find it easier 
 to fix my attention on one point of the corona, and observe the 
 phases of the bands at that point, I changed eyepieces, applying 
 that of 41 power. With this eyepiece the first clear instant 
 showed the bands much brighter than before, coloured, and as 
 tangents to the limb at a point about 200 from the vertex : 
 but before I could determine anything further a cloud shut out 
 the view, and a few seconds later a sudden rush of light told 
 
APPEND. B.] SOLAR ECLIPSE OF 1871. 285 
 
 that the totality was over, though it was difficult to believe 
 that five minutes had flown by since its commencement. I 
 experienced a strong feeling of disappointment and want of 
 success ; the only points on which I can speak with any confi- 
 dence being as follows : 
 
 " (1) When using the double-image prism, the strong differ- 
 ence of colour of the corona, and the absence of such difference 
 in the case of the most prominent red flame. (2) With Savart's 
 polariscope the bands from the corona were decided : with a low 
 power they were wanting in intensity and colour : excepting 
 alternate black and white, making it difficult to specify the 
 nature of the centre: and their position was at right angles 
 to the limb, extending over about 30 of the circumference. 
 When the polariscope was turned, the bands travelled bodily 
 round the limb without other changes in position or arrange- 
 ment, as if, indeed, they were revolving round the centre of 
 the sun as an axis. With a higher power, when a smaller 
 portion of the corona was embraced, the bands were brighter- 
 coloured, and seen in a different position, viz. tangents to 
 the limb. 
 
 " The appearance observed with a low power seems exactly 
 what might be expected supposing the bands to be brightest at 
 every point when at right angles to the limb, in which case the 
 bands growing into brightness at each succeeding point of the 
 limb would distract attention from those fading away at the 
 points passed over as the analyser revolved." 
 
 TOTAL SOLAR ECLIPSE OF DECEMBEE 11, 1871. 
 
 EXTRACT FROM THE FIFTY-SECOND REPORT OF THE COUNCIL OF 
 THE ROYAL ASTRONOMICAL SOCIETY. 
 
 " In the last Annual Eeport will be found a Summary of 
 Observations of the total eclipse of December 1870. The bad 
 weather which prevailed at many of the observing stations 
 rendered the results of this eclipse far less complete than was 
 expected from the careful preparations which had been made. 
 
286 SPECTRUM ANALYSIS. [LECT. v. 
 
 The new information, though a considerable and important gain, 
 was not complete enough to warrant a definite opinion on the 
 several points connected with solar phenomena on which we 
 were seeking to increase our- knowledge. The extent and nature 
 of the coronal light and rays surrounding the eclipsed sun were 
 left so far not conclusively settled as to allow great differences 
 of opinion still to exist. 
 
 " It was, therefore, most fortunate for science that another 
 total eclipse visible in our own possessions, in India and in the 
 north of Australia, would take place during the past year. 
 
 " We rejoice to learn that the weather was favourable at nearly 
 all the observing stations in India, and that very satisfactory 
 observations arid good photographs have been obtained. It is 
 with great regret that we receive a telegram to say that bad 
 weather prevailed in Australia. The reports which have reached 
 the Council are as yet too incomplete for it to be desirable to 
 attempt any discussion of the bearing of the observations on the 
 great questions of the true nature and extent of the coronal 
 light and rays. Such a discussion can only be properly made 
 when the reports of all the observers have been received, and 
 when the valuable photographs of the sun's surroundings obtained 
 at the different stations have been carefully examined and com- 
 pared with each other. "We therefore confine ourselves to giving 
 some of the principal results obtained at each station, as far as 
 they have reached us, in the observers' own words. 
 
 " Colonel Tennant, who through the liberality of Lord Mayo 
 had been able to organize a strong observing party, including 
 Captain Herschel and Mr. Hennessy, selected the old meteor- 
 ological station of Dodabetta, on the highest peak of the Neil- 
 gherries, 8,650 feet above the sea. He telegraphed his principal 
 results in the following words : ( Thin mist ; spectroscope satis- 
 factory. Reversion of lines entirely confirmed. Six good photo- 
 graphs/ In a letter addressed to one of the Secretaries, Colonel 
 Tennant writes : 
 
 " ' I had my attention specially directed to the chromosphere 
 and prominences at the bottom of the moon's limb. They first 
 appeared white, and then changed through pink to red. I am 
 
APPEND. B.] SOLAR ECLIPSE OF 1871. 287 
 
 quite confident that I saw no blue or green tinge. You will 
 remember my suspicion that I do not readily see blue when 
 faint, but I am sure the tint was not strong. My waiting in the 
 moon's centre gave me an opportunity of looking about me, and 
 I saw the two rifts I have spoken of. To me they did not reach 
 the moon's edge, but were separated by some minutes of bright 
 corona. The corona's outer layers were undoubtedly radiated, 
 but not coloured. There were alternate gradations of light ; that 
 is, light and comparative darkness, but certainly no colour. The 
 rays were lost as they neared the moon. The rift at the true 
 vertex of the sun I am sure did not change, nor I believe did 
 any other. Colonel Saxton had made for my object-glass a 
 loose cap of pasteboard, with a two and a half inch aperture? 
 to be used during the sun's presence. This was to have been 
 knocked off just before totality. I forgot this, but I doubt if I 
 should have improved matters ; I used the power 35. 
 
 " ' I had asked Captain Morant, E.E. (to whom I am indebted 
 for a very great amount of assistance), to take a very beautiful 
 reconnoitring telescope by Dallmeyer, which was mounted on 
 a stand. Of 14 inches' focus, it has a power of 15 and 
 an aperture of 175 inches. He (Captain Morant) made two 
 sketches of the corona, which generally confirm, as does his 
 description, all I have described. He expressed himself positive 
 as to the absence of colour and the permanence of rifts, &c., in 
 certain positions (not mine), and only differed in thinking that 
 the shades were of a sepia tinge (brownish), and that the rifts 
 did extend to the moon.' 
 
 " The Madras astronomer, Mr. Pogson, observed at Avenashy. 
 He telegraphed to the Astronomer Eoyal : ' Weather fine ; tele- 
 scopic and camera photographs successful ; ditto polarization ; 
 good sketches ; many bright lines in spectrum.' 
 
 " In a letter to the Astronomer Eoyal, Mr. Pogson writes : 
 " As my telegram informed you, we were upon the whole suc- 
 cessful more so than I ventured to anticipate much less so 
 than I could have wished. With the spectroscope I saw five 
 lines, one bright and fine right across the field, evidently my 
 old Masulipatam friend, which the Americans call 1474. This 
 
288 SPECTR UM ANALYSIS. [LECT. v 
 
 was, I believe, the only bright corona line the only one I saw ; 
 the other four were only part-way across, two in the blue and 
 two near together in the deep red, i. e. where such colours are 
 assuredly seen, and certainly prominence lines. With the 
 Browning reflector, my son and Colonel Eitherdon together got 
 three photographs, all available, but two, as I consider, very good, 
 These show the corona some five or seven minutes in extent, but 
 are all over-exposed. Thirty seconds each was allowed, as sug- 
 gested by Mr. De la Eue ; but I think ten would have been 
 better, and we could have had more views. With a camera four 
 views were taken three very good by Mr. Cruths, a profes- 
 sional. The polarization was, I believe, very good, and will, I 
 think, be valuable and reliable, and the ordinary contacts and 
 some distances and angles of position of the cusps were also 
 carefully secured.' 
 
 " Dr. Janssen has addressed the following letter to the 
 President 
 
 " ' J'aurai 1'honneur d'adresser a la Societe lioyale de Lon- 
 dres un memoire detaille de mes observations de 1'eclipse, mais 
 je profile du depart de ce courrier pour vous informer des prin- 
 cipaux resultats obtenus. Sans entrer dans une discussion 
 qui fera partie de ma relation, je dirai d'abord que la magni- 
 fique couronne observee a Sholoor s'est montree sous un aspect 
 tel qu'il me paraissait impossible d'admettre ici une cause de 
 1'ordre de phenomenes, ou de diffraction, ou de reflexion sur 
 le globe lunaire, ou encore de simple illumination de 1'atmo- 
 sphere terrestre. 
 
 " ' Mais les raisons qui militent en faveur d'une cause objec- 
 tive et circumsolaire, prennent une force invincible quand on 
 interroge les elements lumineux du phenomene. En effet, le 
 spectre de la couronne s'est montre dans mon telescope, non 
 pas continu comme on 1'avait trouve jusqu'ici, mais remar- 
 quablement cornplexe, J'y ai constate : Les raies brillantes, 
 quoique bien plus faibles, du gaz hydrogene qui forme le prin- 
 cipal element des protuberances et de la chromosphere ; 
 
 " ' La raie brillante verte qui a deja etc* signalee en 1869 et 
 1870, et quelques autres plus faibles ; 
 
APPEND. B.] SOLAR ECLIPSE OF 1871. 289 
 
 " ' Des raies obscures du spectre solaire ordinaire, notamment 
 celle du sodium (D). Ces raies sont bien plus difficiles a aper- 
 cevoir. Ces faits prouvent 1'existence de matiere dans le voi- 
 sinage du soleil, matiere qui se manifeste dans les eclipses 
 totales par des phenomenes d'emission, d'absorption, et de 
 polarisation. 
 
 " ' Mais la discussion des faits nous conduit plus loin encore. 
 
 "' Outre la matiere cosmique, independante du soleil, qui doit 
 exister dans le voisinage de cet astre, les observations dernontrent 
 1'existence d'une atmosphere etendue, excessivement rare, a base 
 d'hydrogene, s'e'tendant beaucoup au-dela de la chromosphere 
 et des protuberances, et s'alimentant de la matiere meme de 
 celles-ci, matiere lancee avec tant de violence a travers la photo- 
 sphere ainsi que nous le constatons tous les jours. La rarete de 
 cette atmosphere, a une certaine distance de la chromosphere, doit 
 etre excessive; son existence n'est done point en disaccord avec 
 les observations de quelques passages de cometes pres du soleil. 
 
 " NEILGHERRY, SHOLOOR, 19 Dtcembre, 1871." 
 
 " From the English party sent out at the expense of the 
 Government at the instance of the British Association, the 
 following reports have reached us. Mr. Lockyer, who observed 
 at Bekul, speaking of the corona, says, ' Its rays arranged almost 
 symmetrically, three above and three below two dark spaces or 
 rifts at the extremities of a horizontal diameter. The rays were 
 built up of innumerable bright lines of different lengths, with 
 more or less dark spaces between ; near the sun this structure 
 was lost in the brightness of the central ring. I next tried the 
 spectrum of a streamer above the point at which the sun 
 had disappeared. I got a vivid hydrogen spectrum with 1474 
 (1 assume the point of this line from observation) slightly 
 extended beyond it, but very faint throughout its length com- 
 pared with what I had anticipated, and thickening downwards 
 like F. I was, however, astonished at the vividness of the line 
 c and of the continuous spectrum, for there was no prominence 
 on the slit ; the spectrum was undoubtedly the spectrum of 
 glowing gas. In the Savart, I saw r lines vertical over everything, 
 
 U 
 
290 SPECTRUM ANALYSIS. [LECT. v. 
 
 corona, prominences, dark moon, and unoccupied sky.' With a 
 simple train of prisms Mr. Lockyer saw 'four exquisite rings 
 with projections where the prominences were. In brightness, c 
 came first, then F, then a, and last of all 1474. The rings were 
 nearly all the same thickness, certainly not more than 2' high, 
 and they were all enveloped in a line of impure continuous 
 spectrum.' ' The structure of the corona was simply exquisite 
 and strongly developed. I at once exclaimed, " Like Orion ! " 
 Thousands of interlacing filaments varying in intensity were 
 visible. I saw an extension of the prominence structure in cooler 
 material. This died out somewhat suddenly some 5' or 6' from 
 the sun, and then there was nothing. The great fact was this, 
 that close to the sun, and even for 5' or 6' away from the sun, 
 there was nothing like a ray or any trace of radial structure.' 
 At this station five good photographs were obtained. 
 
 " Commander Maclear observing at the same station says :. ' As 
 totality came on, the light decreased and the lines increased 
 exceedingly rapidly in number and brightness, until it seemed 
 as if every line in the solar spectrum was reversed ; then they 
 vanished, not instantly, but so quickly that I could not make 
 out the order of their going, except that Hydrogen, D, b, and some 
 others between D and b, remained last. Then they vanished, 
 and all was darkness. I then undamped and swept out right 
 and left, but saw nothing ; then went to the direct vision, but 
 saw nothing ; placed the telescope on the moon's limb by the 
 eyepiece, then put in the spectroscope, but the light was not 
 sufficient to show any spectrum ; pointed the telescope carefully 
 first on the dark moon, and then on a bright part of the corona, 
 but no spectrum. I then looked at the corona with the naked 
 eye, saw a bright glory round the moon, stellar form, six-pointed, 
 something like the nimbus painted round a saint's head, ex- 
 tending to a diameter and a half. Looked through the finder 
 and saw the same form, but very much reduced in size and 
 brilliancy; then examined with the 6-inch and eyepiece, and 
 saw nothing but a bright glow round the moon, not much more 
 than the height of the big prominence plainly visible in the 
 outh-east quarter/ 
 
APPEND. B.] SOLAR ECLIPSE OF 1871. 291 
 
 " Professor Eespighi observed at Poodoeottah. He writes : 
 'Towards the end of 1868 a small flint-glass prism was made 
 for me by Signer Merz of Monaco to be fitted to the object-glass 
 of the equatorial of the observatory at Campodoglio. This 
 apparatus, in consequence of the dispersion of the prism and 
 the goodness of the prism and object-glass, was found to be 
 admirably adapted for observing the eclipse in the manner just 
 described (that is, without a slit, so that the several chromatic 
 images of the corona would be simultaneously seen in the same 
 field of view). 
 
 " ' The dispersion of the prism from lines c to H is about 32' ; 
 the free aperture of the object-glass is 4J French inches ; the 
 field of the telescope about 1, with a magnifying power of 40.' 
 ' At the very instant of totality, the chromosphere at the edge 
 which was the last to be eclipsed surmounted for a space of 
 about 50 by two groups of prominences, one on the. right, the 
 other on the left, of the point of contact was reproduced in 
 the four spectral lines c, D 3 , F, G. My attention was mainly 
 directed to the comparison of the forms of the prominences on 
 the four spectral lines, and I was able to determine that the 
 fundamental form, the skeleton or trunk, and principal branches 
 were faithfully reproduced or indicated in the images, their 
 extent being, however, greatest in the red, and diminishing suc- 
 cessively in the other colours down to the line G, on which the 
 trunk alone reproduced. In none of the prominences thus com- 
 pared was I able to distinguish in the yellow image D 3 parts or 
 branches not contained in the red image c. Meanwhile the 
 coloured zones of the corona became continually more marked, 
 one in the red corresponding with the line c, another in the 
 green, probably coinciding with the line 1474 K, and a third in 
 the blue, perhaps coinciding with F. 
 
 tf ' The green zone surrounding tbe disc of the moon was the 
 brightest, the most uniform, and the best defined. The red zone 
 was always distinct and well defined, while the blue zone was 
 faint and indistinct. The green zone was well defined at the 
 summit, though less bright than at the base ; its form was sensibly 
 circular, and its height about 6' or 7'. The red zone exhibited 
 
 U 2 
 
292 SPECTR UM ANALYSIS. [LECT. v. 
 
 the same form arid approximately the same height as the green, 
 but its light was weaker and less uniform. These coloured 
 zones shone out upon a faintly-illuminated ground without any 
 marked trace of colour. If the corona contained rays of any 
 other kind, their intensity must have been so feeble that they 
 were merged in the general illumination of the field. . . . 
 
 " ' The spaces between some of the jets (prominences) were 
 perfectly dark, so that the red zone of the corona appeared to 
 be entirely wanting there. Perhaps, however, this was only 
 an effect of contrast due to the extraordinary brightness of the 
 neighbouring jets. 
 
 " ' The green and red zones were well developed at the western 
 as at the eastern limb, while the blue remained faint and ill- 
 defined. Soon after the appearance of the chromosphere at the 
 western edge there was suddenly projected on the spectrum of 
 the sun's limb, which then appeared beyond that of the moon, 
 a stratum of bright lines, separated by dark spaces, but I could 
 not determine whether they were due to a general or partial 
 reversal of the spectral lines, or to a simple discontinuity in the 
 spectrum.' 
 
 "Captain Tupman, who was stationed at Jaffna, Ceylon, 
 observed the different phenomena as follows : 
 
 " ' 1. The corona extended 40' 50' from the limb of the moon. 
 
 " ' 2. An oblique ray 28' to 30' long, two-thirds up a curve ray 
 like the crook of a boat-hook, 12' long. 
 
 " ' 3. A sharply-defined rift, with sides forming a right angle. 
 
 " ' 4. A.narrow rift, very dark, approaching within 2' or 3' of 
 the prominences, and still distinct 45' from them. 
 
 " ' 5. Another rift opposite to 3. 
 
 " ' 6. Strong radial polarization with a Savart. extending to 
 50' from the sun. The corona polarization was so strong as 
 entirely to overcome the air polarization. The polarization 
 remained visible as radial upon the corona until 25", or perhaps 
 35'', after totality. 
 
 " '7. 1474 K was much the brightest line in the integrating 
 spectroscope. Captain Tyers saw the four lines c, D 3 , 1474 K 4 
 and F ; also Young's bright reversed lines.' " 
 
APP. c.] SPECTROSCOPIC OBSERVATIONS OF THE SUN. 293 
 
 APPENDIX C. 
 
 SPECTROSCOPIC OBSERVATIONS OF THE SUN. 
 1. LOCKYER AND JANSSEN'S DISCOVERY. 
 
 Since this lecture was delivered an observation has been made 
 with respect to the sun only second in interest and importance to 
 the results of KirchhofTs celebrated discovery of the coincidence 
 of the bright iron and dark solar lines and the reversal of the 
 sodium spectrum. The striking nature of this discovery is 
 rendered more evident by its having been made independently 
 by two observers situated thousands of miles apart by 
 M. Janssen in India and Mr. Norman Lockyer in London. No 
 less than six years ago 1 Mr. Lockyer suggested that it might 
 be possible by the use of the spectroscope to obtain evidence of 
 the presence of the red prominences which total eclipses have 
 revealed to us in the solar atmosphere, although they escape all 
 other means of observation at other times. After many fruitless 
 attempts to realize his hopes, Mr. Lockyer at last succeeded, on 
 October 20, 1868, in obtaining the spectrum of a solar promi- 
 nence ; and he thus announces his important observation to the 
 Royal Society, through Dr. Sharpey : 
 
 " SIR, I beg to anticipate a more detailed communication by 
 informing you that, after a number of failures, which made the 
 attempt seem hopeless, I have this morning perfectly succeeded 
 in obtaining and observing part of the spectrum of a solar 
 prominence. 
 
 " As a result I have established the existence of three bright 
 lines in the following positions : 
 
 I. Absolutely coincident with c. 
 II. Nearly coincident with F. 
 III. Near D. 
 
 1 Froo. Roy. Soc., Oct. 11, 1866. 
 
294 SPECTRUM ANALYSIS. [LECT. v. 
 
 " The third line (the one near D) is more refrangible than the 
 two darkest lines by eight or nine degrees of Kirchhoffs scale. 
 I cannot speak with exactness, as this part of the spectrum 
 requires remapping. 
 
 " I have evidence that the prominence was a very fine one. 
 
 " The instrument employed is the solar spectroscope, the funds 
 for the construction of which were supplied by the Government 
 Grant Committee. It is to be regretted that its construction has 
 been so long delayed. 
 
 " I have, &c. 
 
 " J. NORMAN LOCKYEK. 
 
 " The Secretary of the Royal Society." 
 
 M. Janssen was sent by the French Government to observe 
 the total eclipse at Guntoor in India, and on August 18, when 
 examining the bright lines exhibited by the spectra of the 
 prominences visible during the totality, the thought struck him 
 that it might be possible to see these lines when the sun was 
 unobscured, and on trying the experiment on the next day he 
 succeeded in his endeavour, " so that," he writes, " for the last 
 seventeen days I have been working as in a perpetual eclipse." 
 The results of his observations were communicated (Oct. 26, 1868) 
 to the French Academy in the following words : 
 
 " La station de Guntoor a ete sans doute la plus favorisee : le 
 ciel a ete beau, surtout pendant la totalite, et mes puissantes 
 lunettes de pres de trois metres de foyer m'ont permis de 
 suivre 1'etude analytique de tous les phenomenes de 1'eclipse. 
 
 " Immediatement apies la totalite, deux magnifiques protu- 
 berances ont apparu : 1'une d'elles, de plus de trois minutes de 
 hauteur, brillait d'une splendeur qu'il est difficile d'imaginer. 
 L' analyse de sa lumiere m'a imrnediatement montre qu'elle etait 
 formee par une immense colonne gazeuse incandescente, princi- 
 palement composee de gaz hydrogene. 
 
 " L' analyse des regions circumsolaires, oil M. Kirchhoff place 
 1'atmosphere solaire, n'a pas donne des resultats con formes a la 
 theorie formulee par ce physicien illustre ; ces resultats me 
 paraissent devoir conduire a la connaissance de la veritable 
 constitution du spectre solaire. 
 
APP. c.] SPEGTROSCOPIC OBSERVATIONS OF THE SUN. 295 
 
 "Mais le resultat le plus important de ces observations est la 
 decouverte d'urie methode, dont le principe fut con9u pendant 
 1'eclipse meme, et qui permet 1'etude des protuberances et des 
 regions circumsolaires en tout temps, sans qu'il soit ne'cessaire 
 de recourir a Tinterposition d'un corps opaque devant le disque 
 du soleil. Cette methode est fondee sur les proprietes spectrales 
 de la lumiere des protuberances, lumiere qui se resout en un 
 petit nombre de faisceaux tres-lumineux, correspondant a des 
 raies obscures du spectre solaire. 
 
 " Des le lendemain de 1'eclipse la me"thode fut appliquee avee 
 succes, et j'ai pu assister aux phenomenes presentes par une 
 nouvelle eclipse qui a duree toute la journee. Les protuberances 
 de la veille e'taient profondement modifiees. II restait a peine 
 (juelques traces de la grande protuberance et la distribution de 
 la matiere gazeuse etait tout autre. 
 
 "Depuis ce jour jusqu'au 4 septembre, j'ai constamment 
 etudie le soleil a ce point de vue. J'ai dresse des cartes des 
 protuberances, qui montrent avec quelle rapidite (souvent en 
 quelques minutes) ces immenses masses gazeuses se deforment 
 et se d^placent. Enfin, pendant cette periode, qui a ete comme 
 une eclipse de dix-sept jours, j'ai recueilli un grand nombre de 
 faits, qui s'offraient comme d'eux-me"mes, sur la constitution 
 physique du soleil. 
 
 " Je suis heureux d'offrir ces resultats a 1'Academie et au 
 Bureau des Longitudes, pour repondre a la confiance qui m r a ete 
 temoignee et a 1'honneur qu'on m'a fait en me confiant cette 
 importante mission." 
 
 The following abstracts of Mr. Lockyer's various commu- 
 nications to the Eoyal Society give the latest results of his 
 observations, and clearly indicate the important additions to 
 our knowledge of solar physics to which these researches have 
 already led. 
 
296 SPECTRUM ANALYSIS. [LECT. v. 
 
 2. LOCKYER : SPECTROSCOPIC OBSERVATIONS OF THE SUN", NO. II.* 
 
 " The author, after referring to his ineffectual attempts since 
 186 6 to observe the spectrum of the prominences with an 
 instrument of small dispersive power, gave an account of the 
 delays which had impeded the construction of a larger one 
 (the funds for which were supplied by the Government Grant 
 Committee early in 1867), in order that the coincidence in time 
 between his results and those obtained by the Indian observers 
 might not be misinterpreted. 
 
 " Details are given of the observations made by the new 
 instrument, which was received incomplete on the 16th of 
 October. These observations include the discovery, and exact 
 determination of the lines, of the prominence spectrum on the 
 20th October, and of the fact that the prominences are merely 
 local aggregations of a gaseous medium which entirely envelopes 
 the sun. The term chromosphere is suggested for this envelope, 
 in order to distinguish it from the cool-absorbing atmosphere on 
 the one hand, arid from the white light-giving photosphere on 
 the other. The possibility of variations in the thickness of this 
 envelope is suggested, and the phenomena presented by the star 
 in Corona are referred to. 
 
 " It is stated that, under proper instrumental and atmospheric 
 conditions, the spectrum of the chromosphere is always visible 
 in every part of the sun's periphery: its height, and the 
 dimensions and shapes of several prominences, observed at 
 different times, are given in the paper. One prominence, three 
 minutes high, was observed on the 20th October. 
 
 " Two of the lines correspond with Fraunhofer's c and F ; 
 another lies 8 or 9 (of Kirchhoff's scale) from D towards E. 
 There is another bright line, which occasionally makes its 
 appearance near c, but slightly less refrangible than that line. 
 It is remarked that the line near D has no corresponding line 
 ordinarily visible in the solar spectrum. The author has been 
 led by his observations to ascribe great variation of brilliancy to 
 the lines. On the 5th of November a prominence was observed 
 
 1 Proc. Roy. Soc. vol. xvii. p. 131. 
 
APP. c.] SPECTROSCOPIC OBSERVATIONS OF THE SUN. 297 
 
 in which the action was evidently very intense ; and on this 
 occasion the light and colour of the line at F were most vivid. 
 This was not observed all along the line visible in the field of 
 view of the instrument, but only at certain parts of the line, 
 which appeared to widen out. 
 
 " The author points out that the line F invariably expands (that 
 the band of light gets wider and wider) as the sun is approached, 
 and that the c line and the D line do not ; and he enlarges 
 upon the importance of this fact, taken in connection with the 
 researches of Pliicker, Hittorf, and Frankland on the spectrum 
 of hydrogen stating at the same time that he is engaged in 
 researches on gaseous spectra which, it is possible, will enable us 
 to determine the temperature and pressure at the surfaces of the 
 chromosphere, and to give a full explanation of the various 
 colours of the prominences which have been observed at dif- 
 ferent times. 
 
 " The paper also refers to certain bright regions in the solar 
 spectrum itself. 
 
 "Evidence is adduced to show that possibly a chromosphere is, 
 under certain conditions, a regular part of star economy ; and 
 the outburst of the star in Corona is especially dwelt upon." 
 
 3. LOCKYER : SPECTROSCOPIC OBSERVATIONS OF THE SUN, NO. III. 1 
 
 " In my former paper it was stated that a diligent search after 
 the known third line of hydrogen in the spectrum of the chromo- 
 sphere had not met with success. When, however, Dr. Frank- 
 land and myself had determined that the pressure in the 
 chromosphere even was small, and that the widening out of 
 the hydrogen lines was due in the main, if not altogether, to 
 pressure, I determined to seek for it again under better atmo- 
 spheric conditions : and I succeeded after some failures. The 
 position of this third line is at 2796 of Kirchhoff s scale. It is 
 generally excessively faint, and much more care is required to 
 see it than is necessary in the case of the other lines ; the least 
 haze in the sky puts it out altogether. Hence, then, with the 
 
 1 Proc. Roy. Soc., March 4, 1869, vol. xvii. p. 350. 
 
298 SPECTRUM ANALYSIS. [LISCT. v. 
 
 exception of the bright yellow line, the observed spectra of the 
 prominences and of the chromosphere correspond exactly with 
 the spectrum of hydrogen under different conditions of pressure 
 a fact not only important in itself, but as pointing to what may 
 be hoped for in the future. As this yellow line may be possibly 
 caused, as Frankland and I have suggested, by the radiation of 
 a great thickness of hydrogen, it became a matter of importance 
 to determine whether, like the red and green lines (c and F), it 
 could be seen extending on to the limb. . I have not observed 
 this ; it has always in my instrument appeared as a very fine 
 sharp line resting absolutely on the solar spectrum, and never 
 encroaching on it. 
 
 "Dr. Frankland and myself have pointed out, that although 
 the chromosphere and the prominences give out the spectrum 
 of hydrogen, it does not follow that they are composed merely of 
 that substance ; supposing others to be mixed up with hydrogen, 
 we might presume that they would be indicated by their selec- 
 tive absorption near the sun's limb. In this case the spectrum 
 of the limb would contain additional Fraunhofer lines. I have 
 pursued this investigation to some extent with, at present, 
 negative results ; but I find that special instrumental appliances 
 are necessary to settle the question, and these are now being 
 constructed. If we assume, as already suggested by Dr. Frank- 
 land and myself, that no other extensive atmosphere besides the 
 chromosphere overlies the photosphere, the darkening of the 
 limb being due to the general absorption of the chromosphere, 
 it will follow : 
 
 " 1. That an additional selective absorption near the limb is 
 extremely probable. 
 
 " 2. That the hydrogen Fraunhofer lines indicating the absorp- 
 tion of the outer shell of the chromosphere will vary somewhat 
 in thickness : this I find to be the case to a certain extent. 
 
 " 3. That it is not probable that the prominences \vill be 
 visible on the sun's disc. 
 
 " In connection, with the probable chromospheric darkening 
 of the limb, an observation of a spot on February 20th is of 
 importance. The spot observed was near the limb, and the 
 
APP. c.J SPECTROSCOPIC OBSERVATIONS OF THE SUN. 299 
 
 absorption was much greater than anything I had seen before ; 
 so great, in fact, was the general absorption, that the several 
 lines could be only distinguished with difficulty, except in the 
 very brightest region. I ascribe this to the greater length of 
 the absorbing medium in the spot itself in the line of sight, 
 when the spot is observed near the limb, than when it is ob- 
 served in the centre of the disc another indication of the great 
 general absorbing power of a comparatively thin layer, on rays 
 passing through it obliquely. I now come to the selective 
 absorption in a spot. I have commenced a map of the spot- 
 spectruin, which, however, will require some time to complete. 
 In the interim, I may state that the result of my work up to the 
 present time in this direction has been to add magnesium and 
 barium to the material (sodium) to which I referred in my 
 paper in 1866, No. I. of the present series ; and I no longer 
 regard a spot simply as a cavity, but as a place in which princi- 
 pally the vapours of sodium, barium, and magnesium (owing to 
 a downrush) occupy a lower position than they do ordinarily in 
 the photosphere. I do not make this assertion merely on the 
 strength of the lines observed to be the thickest in the spot- 
 spectrum, but also upon the following observations on the 
 chromosphere made on the 21st and 28th ultimo. 
 
 " On both these days the brilliancy of the F line taught me 
 that something unusual was going on ; so I swept along the 
 spectrum to see if any materials were being injected into the 
 chromosphere. On the 21st I caught a trace of magnesium; 
 but it was late in the day, and I was compelled to cease ob- 
 serving by houses hiding the sun. 
 
 " On the 28th I was more fortunate. If anything, the evi- 
 dences of intense action were stronger than on the 21st ; and after 
 one glance at the F line, I turned at once to the magnesium lines. 
 I saw them appearing short and faint at the base of the chromo- 
 sphere. My work on the spots led me to imagine I should find 
 sodium- vapour associated with the magnesium ; and, on turning 
 from b to D, I found this to be the case. I afterwards reversed 
 barium in the same way. The spectrum of the chromosphere 
 seemed to be full of lines, and I do not think the three sub- 
 
300 SPECTRUM ANALYSIS. [LECT. v. 
 
 stances I have named accounted for all of them. The observa- 
 tion was one of excessive delicacy, as the lines were short, arid 
 very thin. The prominence was a small one, about twice the 
 usual height of the chromosphere; but tha hydrogen lines 
 towered high above those due to the newly injected materials. 
 The lines of magnesium extended perhaps one-sixth of the 
 height of the F line, barium a little less, and sodium least of all. 
 
 " We have, then, the following facts : 
 
 " 1. The lines of sodium, magnesium, and barium, when ob- 
 served in a spot, are thicker than their usual Fraunhofer lines. 
 
 "2. The lines of sodium, magnesium, and barium, when 
 observed in the chromosphere, are thinner than their usual 
 Fraunhofer lines. 
 
 "For some time past I have been engaged in endeavouring to 
 obtain a sight of the prominences, by using a very rapidly oscil- 
 lating slit ; but although I believe this method will eventually 
 succeed, the spectroscope I employ does not allow me to apply 
 it under sufficiently good conditions, and I am not at present 
 satisfied with the results I have obtained. 
 
 " Hearing, however, from Mr. De la Eue, on February 27th, 
 that Mr. Huggins had succeeded in anticipating me by using 
 absorbing media and a wide slit (the description forwarded to 
 me is short and vague), it immediately struck me, as possibly it 
 had struck Mr. Huggins, that the wide slit is quite sufficient 
 without any absorptive media ; and during the last few days I 
 have been perfectly enchanted with the sight which my spectro- 
 scope has revealed to me. The solar and atmospheric spectra 
 being hidden, and the image of the wide slit alone visible, the 
 telescope or slit is moved slowly, and the strange shadow-forms 
 flit past. Here one is reminded, by the fleecy, infinitely delicate 
 cloud films, of an English hedgerow with luxuriant elms ; here, 
 of a densely intertwined tropical forest, the intimately inter- 
 woven branches threading in all directions, the prominences 
 generally expanding as they mount upwards, and changing 
 slowly, indeed almost imperceptibly. By this method, the 
 smallest details of the prominences and of the chromosphere 
 itself are rendered perfectly visible and easy of observation." 
 
APPEND, c.] THE REJ) FLAMES. SO I 
 
 4. LOCKYEE: SPECTROSCOPIC OBSERVATIONS OF THE SUN, NO. IV. 1 
 
 "The following observations were made on April llth, 1869, 
 near a fine spot situated not very far from the sun's limb : 
 
 " 1. Under certain conditions, the c and F lines may be ob- 
 served bright on the sun ; and in the spot-spectruin also, as in 
 prominences or in the chromosphere. 
 
 " 2. Under certain conditions, although they are not ob- 
 served as bright lines, the corresponding Fraunhofer's lines 
 are blotted out. 
 
 " 3. The accompanying changes of refrangibility of the lines 
 in question show that the absorbing material moves upwards 
 and downwards as regards the radiating material, and that these 
 motions may be determined with considerable accuracy. 
 
 " 4. The bright lines observable in the ordinary spectrum are 
 sometimes interrupted by the spot-spectrum, i.e. they are only 
 visible in those parts of the solar spectrum near, and away from, 
 spots. 
 
 " 5. The c and F lines vary excessively in thickness over and 
 near a spot ; and on the llth, in the deeper portion of the spot, 
 they were much thicker than usual." 
 
 5. ON A POSSIBLE METHOD OF VIEWING THE RED FLAMES WITHOUT 
 AN ECLIPSE. BY WILLIAM HUGGINS, F.R.S. 2 
 
 " In the report of my Observatory at the last anniversary 
 (p. 88 of the last volume), it is stated that ' during the Jast two 
 years numerous observations have been made for the purpose of 
 obtaining a view of the red prominences seen during a solar 
 eclipse. If these bodies are gaseous, their spectra would consist 
 of bright lines. With a powerful spectroscope, the light reflected, 
 from our atmosphere near the sun's edge would be greatly re- 
 duced in intensity by the dispersion of the prisms, while the 
 bright lines of the prominences, if such be present, would remain 
 but little diminished in brilliancy. This principle has been 
 
 i Proc. Roy. Soc., April 14, 1869, vol. xvii. p. 415. 
 
 3 Monthly Notices of the Royal Astronomical Society, Nov. 13, 1868. 
 
302 SPECTRUM ANALYSIS. [LECT. v. 
 
 carried out by various forms of prismatic apparatus, and also by 
 other contrivances, but hitherto without success.' The obser- 
 vations of the eclipse of August last having shown the position 
 in the spectrum of the bright lines of the red flames, Mr. Lockyer 
 and M. Janssen succeeded independently, by a similar method, 
 in viewing the spectra of these objects. 
 
 "My object in this note is to describe one of the 'other con- 
 trivances ' mentioned in the report. 
 
 " The apparatus consisted of screens of coloured glasses and 
 other absorptive media, by which I was able to isolate portions 
 of the spectrum. It appeared highly probable, that if the parts 
 of the spectrum which then alone remained were identical with 
 those in which the bright lines of the flames occur, these objects 
 would become visible. 
 
 " For this inquiry I obtained a great variety of coloured glasses 
 and other absorptive media. I first examined them with a prism 
 to learn the absorptive power which they exercised on different 
 parts of the spectrum. I then combined them in various ways. 
 These glasses were sometimes employed before the eye, but more 
 frequently by projecting the image of the sun's edge upon a 
 screen, after the light had been sifted by the coloured media. In 
 making these experiments, means were taken that the whole of 
 the sun's image should be got rid of, in order that the eye, kept 
 in comparative darkness, might be more sensitive to the greatly 
 feebler illumination of the objects sought for. As I had no 
 knowledge of the position in the spectrum of the bright lines, 
 it would have been by accident only if I had succeeded in 
 obtaining a view of the flames. 
 
 " Now that the positions of these lines are known, this method 
 appears to be very promising. Perhaps the light about the red 
 line at c will be most easily isolated. I have a deep ruby glass 
 which cuts off all the spectrum except the extreme red. I have 
 since the observations only been able to make one attempt, when 
 the state of the atmosphere was unfavourable. 
 
 " It is obvious that by this method the form and appearance 
 of these flames could be observed, and the objects measured 
 with accuracy." 
 
APPEND, c.] ZOLLNER ON PROTUBERANCES. 303 
 
 G. NOTE ON A METHOD OF VIEWING THE SOLAR PROMINENCES 
 WITHOUT AN ECLIPSE. BY WILLIAM HUGGINS, F.R.S. 1 
 
 "Last Saturday, February 13, 1869, I succeeded in seeing a 
 solar prominence so as to distinguish its form. A spectroscope 
 was used; a narrow slit was inserted after the train of prisms 
 before the object-glass of the little telescope. This slit limited 
 the light entering the telescope to that of the refrangibility of 
 the part of the spectrum immediately about the bright line 
 coincident with c. The slit of the spectroscope was then widened 
 sufficiently to admit the form of the prominence to be seen. 
 The spectrum then became so impure that the prominence could 
 not be distinguished. A great part of the light of the refrangi- 
 bilities removed far from that of c was then absorbed by a piece 
 of deep ruby glass. The prominence was then distinctly seen." 
 
 7. EXTRACT FROM ZOLLNER DESCRIPTION OF PROTUBERANCKS. 2 
 
 (See Figs. 71 to 75.) 
 " One of the most remarkable forms is that shown in Fig. 72. 
 
 O 
 
 I scarcely believed my eyes when I noticed in this one the flicker- 
 ing motion of a flame. This motion was, however, slower in 
 proportion to the dimensions' of the protuberance than that of a 
 large mass of ordinary flame. The time needed for the propa- 
 gation of this flame-wave from the base to the point of the pro- 
 minence amounted to about from two to three seconds. .Fig. 
 71 exhibits good examples of the rate of change which the 
 form and intensity of these prominences undergo. The time at 
 which each form was observed is given underneath each figure. 
 Most of the prominences exhibit forms analogous to those of 
 the various clouds and mists occurring in our atmosphere ; of 
 these, the cumulus type is the commonest. The flame-like pro- 
 tuberance Fig. 72 is an exception to the ordinary form ; and in 
 the forms of Figs. 73, 74, and 75, it is almost impossible to help 
 believing that the masses which are seen to rise from the sun's 
 surface are immediately connected with the cloudy portions 
 which float above, and one is forcibly reminded of the pheno- 
 mena of the eruptions of volcanoes or gey sirs." 
 
 1 Proc. Roy. Soc. vol. xvii. p. 302. 2 Pogg. Ann. cxxxvii. p. 624. 
 
3U4 SPECTRUM ANALYSIS. [LECT. v. 
 
 APPENDIX D. 
 
 PRELIMINARY CATALOGUE OF THE BRIGHT LINES IN THE 
 SPECTRUM OF THE CHROMOSPHERE. 
 
 BY C. A. YOUNG, PH.D., PROFESSOR, OF ASTRONOMY IN 
 DARTMOUTH COLLEGE. 
 
 The following list contains the bright lines which have been 
 observed by the writer in the spectrum of the chromosphere 
 within the past four weeks. It includes, however, only those 
 which have been seen twice at least; a number observed on 
 one occasion (Sept. 7th) still await verification. 
 
 The spectroscope employed is the same described in the Jour- 
 nal of the Franklin Institute for November 1870; but certain 
 important modifications have since been effected in the instru- 
 ment. The telescope and collimator have each a focal length 
 of nearly 10 inches, and an aperature of | of an inch. The 
 prism-train consists of five prisms (with refracting angles of 
 55) and two half-prisms. The light is sent twice through the 
 whole series by means of a prism of total reflection at the end 
 of the train, so that the dispersive power is that of twelve 
 prisms. The instrument distinctly divides the strong iron line 
 at 1961 of KirchhofFs scale, and separates /3 (not b) into its 
 three components. Of course it easily shows everything that 
 appears .on the spectrum maps of Kirchhoff and Angstrom. 
 The adjustment for "the position of minimum deviation" is 
 automatic ; i. e., the different portions of the spectrum are 
 brought to the centre of the field of view by a movement which 
 at the same time also adjusts the prisms. 
 
 The telescope to which the spectroscope is attached is the 
 new Equatorial recently mounted in the Observatory of the 
 College by Alvan Clark and Sons. 
 
 It is a very perfect specimen of the admirable optical work- 
 
APPEND. D.J BRIGHT LINES IN THE SPECTRUM. 305 
 
 manship of this celebrated firm, and has an aperture of 94 
 inches, with a focal length of 12 feet. 
 
 In the table the first column contains simply the reference 
 number. An asterisk denotes that the line affected by it has 
 no well-marked corresponding dark line in the ordinary solar 
 spectrum. 
 
 The second column gives the position of the line upon the 
 scale of KirchhofFs map determined by direct comparison 
 with the map at the time of observation. In some cases an in- 
 terrogation mark is appended, which signifies not that the exist- 
 ence of the line is doubtful, but only that its precise place could 
 not be determined, either because it fell in a shading of fine 
 lines, or because it could not be decided in the case of some 
 close double lines which of the two components was the bright 
 one ; or finally because there were no well marked dark lines 
 near enough to furnish the basis of reference for a perfectly 
 accurate determination. 
 
 The third column gives the position of the line upon Ang- 
 strom's normal atlas of the solar spectrum. In this column an 
 occasional interrogation mark denotes that there is some doubt 
 as to the precise point of Angstrom's scale corresponding to 
 Kirchhoff' s. There is considerable difference between the two 
 maps, owing to the omission of many faint lines by Angstrom 
 and the want of the fine gradations of shading observed by 
 Kirchhoff, which renders the co-ordination of the two scales 
 sometimes difficult, and makes the atlas of Kirchhoff far supe- 
 rior to the other for use in the observatory. 
 
 The numbers in the fourth column are intended to denote 
 the percentage of frequency with which the corresponding 
 lines are visible in my instrument. They are to be regarded as 
 only roughly approximative ; it would of course require a much 
 longer period of observation to furnish results of this kind 
 worthy of much confidence. 
 
 In the fifth column the numbers denote the relative brilliance 
 of the lines on a scale where 100 is the brightest and 1 the 
 faintest. These numbers also, like those in the preceding 
 column, are entitled to very little weight. 
 
 X 
 
308 SPECTRUM ANALYSIS. [LECT. v. 
 
 railroad. He constantly saw from this position the stratum, 
 first mentioned by Secchi, which gives a continuous spectrum ; 
 and he finds this to extend from 0"'5 to 0"'75 beyond the 
 sun's limb. Young has also determined the position of 165 
 new bright lines in the chromosphere, in addition to the 103 
 described in the foregoing paper. One of these lines appears 
 coincident with a line 778'3 on Kirchhoff's scale, marked 
 " Bu," and signifying the rare platinum-like metal Ruthenium, 
 and not, as Young supposes, the new alkaline metal Rubidium. 
 Hence the remarks made on pp. 244-5, Lecture V., as to the 
 existence of Rubidium in the sun must be considered as incor- 
 rect, and the word Ruthenium must be substituted. It is, 
 however, very doubtful how far the existence of this latter 
 metal in the solar atmosphere can be inferred from this single 
 coincidence. 
 
 Even both the lines H in the violet were seen by Young to be 
 reversed on the sun's disc and around a spot of any size, and 
 over an area two or three times as great as the penumbra of the 
 spot. In Professor Young's own observatory, at an elevation of 
 600 feet above the sea, he is unable to see any of these peculiar 
 phenomena, and hence we understand the great importance of 
 placing a solar observatory on some elevated situation in as 
 good climate as on the Himalayas or the Andes. 
 
 APPENDIX E. 
 
 PROFESSOR BALFOUR STEWART ON RADIATION AND 
 ABSORPTION. 1 
 
 We have hitherto chiefly confined our remarks to the radia- 
 tion of carbon at different temperatures ; and taking that 
 substance as a type of solids, and comparing its radiation with 
 
 1 Lessons in Elementary Physics, par. 301 307. 
 
APPEND. E.] RADIATION AND ABSORPTION. 309 
 
 that from incandescent gases, we have found a very great and 
 striking difference between the two classes of spectra, that of 
 carbon being continuous, while those of gases are discontinuous. 
 "We shall now endeavour to connect the radiative properties of 
 bodies with their absorptive properties. 
 
 Let us begin with the temperature of boiling water, or 100 
 Cent. Let us now, therefore, suppose that we have a large 
 thermometer at this temperature hung up in a room, having the 
 temperature of melting ice. The thermometer will lose heat in 
 two ways : by convection on account of the air which surrounds 
 it, and which is continually carried off and renewed, and also 
 by radiation. But in order to confine our thoughts to the latter 
 process, let us suppose that the chamber is a vacuum. Now, in 
 the first place, let the outside of the glass bulb of the thermo- 
 meter be coated with a thin coating of polished silver, and let 
 us ascertain how much heat it radiates in one minute. Next 
 let the bulb be coated with lamp-black, the same experiment 
 being repeated, that is to say, the thermometer at 100 Cent, 
 being allowed to cool for one minute in a vacuum chamber of 
 0. It will be found that the bulb now radiates in a minute 
 very much more heat than it did when coated with silver. 
 Next let the glass bulb be left uncovered, &nd the thermometer 
 will still be found to radiate almost as much as when the bulb 
 was covered with lamp-black. Finally, let it be covered with 
 white paper, and its radiation will still be found to be almost 
 equally great. We are thus entitled to say that at 100 Cent, a 
 blackened surface, or one of glass or white paper, radiates much 
 more than a surface of polished silver, and we may thus con- 
 struct a table of the comparative radiating powers of bodies 
 heated to 100 Cent., at the top of which we may put a lamp- 
 black surface, a surface of glass, and one of white paper, and 
 much lower down one of silver, which is a very bad radiator. 
 Our table of radiating substances for heat of low temperature 
 will therefore stand thus : 
 
 ( Lamp-black surface. 
 Good Radiators . . . . ! Glass. 
 
 V White paper. 
 Bad Radiator . Polished silver. 
 
3 1 SPECTRUM ANALYSIS. [LECT. v. 
 
 Suppose now that the thermometer is at 0, and is carried 
 into a vacuum chamber of the temperature of 100, this being 
 the reverse of the previous process. In the first place, let the 
 bulb, as before, be coated on the outside with a coating of silver ; 
 it will absorb a certain quantity of heat in one minute ; observe 
 how much. Next, blacken the bulb with lamp-black, repeat 
 the experiment, and measure the. absorption which takes place 
 in one minute as before ; the absorbing power of the thermo- 
 meter will now be considerably increased. Again, if the coating- 
 be entirely removed, and nothing left above the glass bulb, it 
 will be found that the absorbing power of the glass bulb is 
 almost as great as that of the blackened bulb, and the same 
 result will be obtained if the bulb be covered with white paper. 
 We may thus construct a table of the comparative absorbing 
 powers of various bodies for heat of 100, at the head of which 
 we may place a ] amp-black surface, a surface of glass, and one 
 of white paper, and much further down one of polished silver. 
 
 Our table of bodies which absorb heat of 100 will therefore 
 stand thus : 
 
 f Lamp-black surface. 
 Good Absorbents . . . . ! Glass. 
 
 I White paper. 
 Bad Absorbent .... Polished silver. 
 
 If these two tables, the one of radiators and the other of 
 absorbents, be now compared together, they will be found to be 
 identical; so that the blackened thermometer at 100 will, in 
 the first case, cool much more rapidly than the silvered one 
 when transferred to the chamber at 0, on account of its superior 
 radiation, and will also, in the second case, starting from 0, 
 become heated much more rapidly than the silvered one when 
 transferred to a chamber of 100. In fine, good radiators are also 
 good absorbents, lad radiators lad absorbents. It is worthy of 
 remark, before proceeding further, that surfaces behave very 
 differently in their absorbing power for different rays. White 
 paper and glass, as we have seen, are both very strong absor- 
 bents of low temperature heat, while both of them are manifestly 
 non- absorbents of luminous rays. 
 
APPEND. E.I RADIATION AND ABSORPTION. 311 
 
 Extending now these considerations to visible rays proceeding 
 from bodies of high temperature, they furnish us with some 
 very interesting and instructive experiments, which will now be 
 described. 
 
 Experiment 1. Take a porcelain plate of black and white 
 pattern (the black of the pattern will of course be a strong 
 absorbent of luminous rays, while the white will be a less 
 powerful absorbent). Heat it to a good red or white heat in 
 the fire, arid when so heated take it out and rapidly carry it to 
 a dark place ; the black will appear much more brilliant than 
 the white, presenting a very curious reversal of the pattern. 
 
 Experiment 2. Take a piece of polished platinum foil, and 
 make an ink mark upon it. Bring this foil to a red heat with the 
 flame of a Bunsen's burner in a dark room, and the ink mark 
 will shine out much more brightly than the polished platinum. 
 
 Experiment 3. Make a white mark on a black poker with a 
 piece of chalk ; when heated to a good red heat, examine it in 
 the dark, and the chalk will shine out less brightly than the 
 rest of the poker. 
 
 These experiments might be multiplied indefinitely, all tending 
 to show that bodies which, when cold, are good absorbents, are, 
 when hot, good radiators ; and the observation may be extended 
 to plates of various thicknesses as well as to mere surfaces. 
 Thus a polished plate of rock-salt absorbs very little heat of 
 low temperature (Art. 295), and when heated to 100 Cent, it is 
 found also to give out very little heat. In like manner a piece 
 of transparent colourless glass which absorbs very little light 
 will, when heated in the fire, and quickly examined in the dark, 
 be found to give out very little light ; while on the other hand, 
 a piece of opaque glass treated in the same way will give out a 
 great deal of light. In like manner a film or stratum of air is 
 well known to absorb little light or heat of any kind, and so 
 when heated it hardly gives out any. 
 
 We may now generalize our conclusions by the statement 
 that opaque and non-reflecting solid or liquid particles are at once 
 good radiators and good absorbents for most kinds of rays ; while, 
 on tlw rfher hand, polished metallic surfaces, and more especially 
 
312 SPECTR UM ANALYSIS. [LECT. v. 
 
 films of gas, such as air, absorb and radiate very little either of 
 light or heat. 
 
 It has been mentioned incidentally that surfaces or plates do 
 not behave in the same manner with regard to different kinds 
 of rays : let me now dwell at greater length on this point, for it 
 is perhaps the most important of the whole subject. White 
 paper, it was seen, was a strong absorbent for heat of low tem- 
 perature, while it is evidently not so for luminous rays, for the 
 very reason that it appears white. In like manner the un- 
 covered glass of the bulb of a thermometer was found to be a 
 strong absorbent for low temperature heat, but it is evidently 
 not so for luminous rays. To prove this, we have only to hold 
 a thermometer in the sun, and we shall be dazzled with the 
 light reflected from its bright mercurial surface, which only 
 reaches the eye after it has twice passed through the glass. 
 
 Even within the limits of the visible spectrum we have, as a 
 common occurrence, substances which absorb certain rays and 
 allow others to pass. For what is it that makes the leaves of 
 plants appear green? Is it not that they absorb all the various 
 constituents of sunlight except the green which they allow to 
 be reflected? In fine, all coloured substances are substances 
 which behave in a partial manner with respect to the visible 
 rays, and if we had no such partial absorption, we should be 
 deprived of one great source of beauty in nature. 
 
 Coloured glasses afford a very familiar illustration of this 
 selective or partial absorption. A green glass absorbs all, or 
 nearly all, the red rays which fall upon it, allowing the green 
 to pass ; on the other hand, a red glass absorbs nearly all the 
 green, and allows the red to pass. 
 
 Thus we see that surfaces or plates which behave in one way 
 with respect to dark rays, may behave differently with regard 
 to luminous ones ; nay further, a substance that behaves in one 
 way with regard to a luminous ray of one colour, may behave 
 in a different way with regard to a luminous ray of another 
 colour. We have stated generally, that good radiators are good 
 absorbents ; but in view of the fact that bodies select or choose 
 the rays which they absorb, this statement must be extended, 
 
APPEND. E.] RADIATION AND ABSORPTION. 313 
 
 and we now assert that bodies when cold absorb the same kind of 
 rays that they give out when heated. 
 
 It will be desirable to give, in the first place, some experi- 
 mental proofs of this before attempting to explain the principles 
 upon which the statement rests. 
 
 Experiment 1. Eock salt when heated to 100 gives out that 
 peculiar kind of heat which is greedily absorbed by a cold plate 
 of rock salt. To prove this, heat a thin plate of rock salt to 
 100, and allow the heat from it to fall upon an appropriate 
 instrument for measuring such heat, but only after it has passed 
 through a cold plate of the same material : now this cold plate 
 will be found to have stopped at least three quarters of the 
 heat which falls upon it, while it will only stop a very small 
 percentage of any other kind of heat. 
 
 Experiment 2. Red glass stops the green rays. Now heat a 
 piece of ruby-coloured glass to a white heat in the fire ; if ex- 
 amined in the dark it will be found to give out a greenish light, 
 being the same sort of light that it absorbs. Next, heat a piece 
 of green or blue glass, which absorbs red rays, and its light, 
 when viewed in the dark, will be found to be particularly red, 
 being, as before, the kind of light which it absorbs when cold. 
 
 Experiment 3. Make a spectrum of the electric light after 
 the method already described, and hold burning sodium between 
 the electric lamp and the slit ; it will be found to produce a 
 comparatively dark band in the spectrum. Next, stop the electric 
 discharge while the sodium is left still burning ; the same band 
 will now appear luminous, that is to say, the sodium, which 
 being comparatively cold when compared to the temperature of 
 the electric light stops one of its rays, gives out, when heated, 
 this very ray on its own account. All these experiments tend 
 to show, as a matter of fact, that bodies, when cold, or com- 
 paratively so, absorb the same rays which they give out 
 when heated. 
 
 Our readers must now permit us to transport them in imagi- 
 nation to a white-hot chamber, kept uniformly at this tempera- 
 ture : such, for instance, as one of those chambers in which glass 
 vessels are annealed. We will suppose it to be shut in closely 
 
314 SPECTR UM ANALYSIS. [LECT. v. 
 
 with walls on all sides, with the exception of a small opening 
 through which we can either introduce anything into the 
 chamber, or, if we choose, see what is going on inside. 
 
 Let us introduce polished platinum marked with ink, or coal, 
 or black and white porcelain, or red glass, or green glass, or 
 transparent glass, or black glass. When left sufficiently long, 
 until they have acquired the temperature of the walls of the 
 chamber, if we look in through the small hole, we shall see no 
 apparent difference between the light coming from these various 
 substances and that from the walls of the chamber, in fact, every- 
 thing will appear to be of the same uniform white heat. If, 
 however, we hastily withdraw these various substances, and, 
 without allowing them time to cool, examine them in the dark, 
 we shall find, as already mentioned, a great variety in the 
 appearances which they present; the colourless glass and the 
 polished platinum will give out very little light, the coal and 
 the black of the porcelain a great deal. 
 
 These two facts may be reconciled with one another in the 
 following manner. Let us take the transparent glass ; this gives 
 out very little light on its own account, but, on the other hand, 
 it stops very little of that which reaches the eye from the white- 
 hot wall behind it, being eminently transparent for such light. 
 If we suppose that the rays from the wall are as much recruited 
 by the light given out by the glass on its own account as they 
 are absorbed by its substance, then we shall have an explanation 
 of the fact that the combined radiation of the glass and the wall 
 is no greater than the wall itself, had there been no glass there. 
 The polished platinum, in like manner, gives out little light on 
 its own account, but when in the white-hot chamber, it reflects 
 copiously the light which reaches it from the walls, so that, to 
 an observer viewing it through the small opening, it will have 
 so completely supplemented its deficient radiation by its great 
 reflection, that altogether it will appear equally bright with the 
 wall itself. 
 
 Applying this explanation to the various substances which we 
 have introduced into the white-hot chamber, we see at once 
 why they cause no change in the intensity of the light that 
 
APPEND. E.] RADIATION AND ABSORPTION. 315 
 
 reaches the eye placed at the opening. For although, no doubt, 
 it is only in the case of the black substance, such as coal or 
 black porcelain, that all the light comes from the substance 
 itself, yet, in the other case, what the substance wants in 
 radiating power, it makes up by allowing to pass either through 
 its substance, as in the case of transparent glass, or from its 
 surface, as in the case of polished platinum and white porcelain, 
 what is deficient in its own radiation. 
 
 But let us now further consider for a moment the red and 
 green glass which we have introduced into this chamber. As we 
 view them from the opening, we are at a loss to distinguish 
 which is the red and which is the green, they have so absolutely 
 and entirely lost their colour. Nor have we far to seek for an 
 explanation of this. The red glass absorbs the whitish or 
 greenish rays from the heated chamber behind it, but, in return, 
 it gives out on its own account an equal amount of rays, and 
 these of precisely the same kind as it has absorbed, so that the 
 light from the wall behind, in passing through the glass, is just 
 as much recruited as it is absorbed, and this equality holds for 
 every individual kind of ray which goes to compose this light, 
 and thus it happens that the combined radiation of the walls 
 and the red glass is precisely the same both in quantity and in 
 quality as if there were no glass. 
 
 The same principles apply to the green glass. It absorbs the 
 reddish rays from the wall, but it gives out an equivalent both 
 in quality and quantity for the rays which it absorbs, so that the 
 absorption is virtually cancelled, and the combined result of wall 
 and green glass is, as before, the same as if there were no glass. 
 We thus see that all substances of all kinds, when placed in a 
 room of uniform temperature, and allowed to remain until they 
 have attained the temperature of the enclosure, will absorb just 
 as much as they give out, and that this equality between absorp- 
 tion and radiation will hold good for every individual ray of 
 which the heterogeneous radiation of the heated walls is composed. 
 (By individual rays, we mean the various rays into which the 
 whole radiation may be split up by means of the spectroscope.) 
 All that we have now said has been built upon the hypothesis 
 
316 SPECTR UM AN Air SIS. [LECT. v. 
 
 that the substances are in an enclosure, let us say a white-hot 
 one, of the same temperature as themselves, and if we cannot 
 easily command such a field of white heat, yet the centre of a 
 good fire is a very near approximation ; and if we introduce into 
 such a fire a number of pieces of variously coloured glass, and 
 exclude from the room all sunlight or gaslight, we shall find 
 their colour vanish when once they have reached the temperature 
 of the fire. 
 
 APPENDIX F. 
 
 ON THE HARMONIC RATIOS OBSERVED IN THE WAVE-LENGTHS 
 OF THE LINES OF CERTAIN SPECTRA. 
 
 The question as to whether the lengths of vibration of the 
 various bright lines of an element stand in any simple or har- 
 monic relation to one another, or to some one fundamental 
 vibration, has been discussed by many writers. The most im- 
 portant of all simple ratios hitherto found in the spectra of 
 incandescent gases are those noticed by G. J. Stoney 1 for the 
 spectrum of hydrogen. Taking as the starting-point the very 
 exact measurements of Angstrom, and making the necessary 
 corrections for the dispersion in air, Stoney finds that the three 
 lines, Ji, F, c, may be considered harmonics of one vibration, 
 %hose wave-length would be 013127714 of a millimeter. In 
 the following table the first column gives the observed wave- 
 lengths (in Xth metres), reduced to vacuo ; the second gives the 
 order of the harmonic, or the number by which the supposed 
 fundamental wave-length must be divided in order to give the 
 wave-length of the respective line; the third gives the calculated 
 values; and the last column gives the differences between the 
 calculated and observed values. 
 
 1 Philosophical Magazine, vol. xli. p. 294. 
 
APPEND, p.] ON HARMONIC RATIOS. 3 i 7 
 
 OBSERVED. ORDER OF HARMONIC. CALCULATED. DIFF. 
 
 7t = 4102'37 32 4102-41 + 0'04 
 
 ^=4862-11 27 486212 -O'Ol 
 
 (7=6563-93 20 6563'86 -0'07 
 
 The line near o cannot be regarded as a harmonic of the 
 above vibration, but its wave-length is to that of F exactly in 
 the ratio of 25 : 28. 
 
 Another singular set of ratios in the magnesium spectrum 
 was pointed out by Soret. In examining the ultra-violet portions 
 of this spectrum, Mascart found two groups of triple lines, which 
 exactly resembled in general appearance the well-known group 
 of lines in the green coincident with the group of solar lines &. 
 Soret has shown that these three lines may be regarded as the 
 20th, 27th, and 31st harmonic of one fundamental group (that 
 is, if the wave-lengths of the lines in the supposed fundamental 
 spectrum are represented by unity, the wave-lengths of the 
 higher lines would be represented by J^, Jy, and J r ). The first 
 column of the following table gives the wave-length of the least 
 refrangible ray of each group, the first of which was measured 
 by Angstrom, the second by Cornu, and the third by Mascart. 
 
 OBSERVED. ORDER OF HARMONIC. CALCULATED. DIFF. 
 
 5183' 20 51817 -1-3 
 
 3837-8 27 3838 -2 +0'4 
 
 3335- 31 3343- +8'0 
 
 Similar relations have been shown by Soret to exist for some 
 lines in the cadmium spectrum ; whilst strontium also exhibits 
 many lines whose wave-lengths stand in simple ratios to each 
 other, and the spectra of bismuth, lithium, calcium, thallium, 
 and gold, likewise show simple ratios in certain of their lines, 
 so that in the spectra hitherto examined there is nothing to con- 
 tradict the theory that the periodical motions of the particles of 
 a . gas are of comparatively long period, and that the lines we 
 see in the spectra are only the harmonics of these fundamental 
 vibrations. Still it must be confessed that up to the present 
 time but little has been done towards securing a positive and 
 satisfactory experimental foundation for such a theory. For if 
 
318 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. v. 
 
 we grant that the striking coincidences between the observed 
 and calculated values in the case of hydrogen can hardly be 
 fortuitous, and if it appears almost impossible that it is by 
 mere chance that the three characteristic groups of magne- 
 sium lines exist in one spectrum, we are still far from 
 possessing anything like clear evidence of the truth of the 
 harmonic theory. 
 
 It is perhaps worthy of mention, as bearing on this subject, 
 that the wave-lengths of the solar lines L, o, Q, are, within the 
 limits of observational error, half those of the lines A, B, c 
 is seen from the following table. 
 
 A. 
 
 B. 
 
 
 
 A 
 
 OBSERVED BY 
 
 OBSERVER. 
 
 A 
 
 2, 
 
 MASCART. 
 
 Angstrom . . . 
 
 7612-1 
 
 3806-0) 
 
 3819-0 L. 
 
 Vander Willigen 
 
 7633-6 
 
 3816-8 J 
 
 
 Fraunhofer 
 
 6878-5 
 
 3439 -2 v 
 
 
 Ditscheiner . 
 
 6878-1 
 
 3439-0 ( 
 
 3440-1 0. 
 
 Ditto . . . 
 
 6883-3 
 
 3441 -6 [ 
 
 
 
 
 Angstrom . . . 
 
 6874-9 
 
 3437-4J 
 
 
 Fraunhofer . . 
 
 6556-3 
 
 3278-1 v 
 
 
 Ditscheiner . . 
 
 6566-6 
 
 3283-3 ( 
 
 3285-6 Q. 
 
 Ditto . . . 
 
 6571-1 
 
 3285 -6 [ 
 
 
 Angstrom . . . 
 
 6567-7 
 
 3283-8 ) 
 
 
 Another singular observation, which is of interest when con- 
 sidering this question, was recently made by M. Cornu. 1 In 
 endeavouring to photograph the three ultra-violet magnesium 
 lines, Cornu, using a powerful battery and induction coil, failed 
 to obtain a satisfactory photographic image of the lines. After 
 a long exposure, the impression of five lines instead of three 
 was obtained, and it appeared that the two least refrangible of 
 the lines had been reversed, and they therefore appeared dark on 
 a broad, light background. The most refrangible line of this 
 ultra-violet group could not be reversed. Now turning to the 
 corresponding triple group in the green, Cornu was able to 
 obtain a sharp photographic image of the most refrangible line, 
 whilst the two least refrangible lines were reversed ; thus 
 
 1 Phil. Mag., vol. xlii. p. 237. 
 
APPEND. F.] ON HARMONIC RATIOS. 319 
 
 the two triple groups, one in the green and the other in the 
 ultra-violet, behave, as regards the ease with which they can be 
 reversed, in an exactly similar manner. It would, therefore, 
 appear that only those vibrations which are harmonics of a 
 much longer wave-length are reversed at the same time. 
 
LECTUKE VI. 
 
 Planet and Moon light. Stellar Chemistry. Huggins and Miller. 
 Spectra of the Fixed Stars. Difficulties of Observation. Methods 
 employed. Variable Stars. Double Stars. Temporary Bright 
 Stars. Nebulae. Comets. Motion of the Stars (Huggins). 
 Determinations of Velocity of Solar Storms (Lockyer). 
 
 APPENDIX A. Extract from a Memoir " On the Spectra of some of 
 
 the Fixed Stars." 
 APPENDIX B. On the Spectrum of Mars, with some Remarks on the 
 
 Colour of that Planet. 
 APPENDIX C. On the Occurrence of Bright Lines in Stellar 
 
 Spectra, and on the Spectra of Variable Stars. 
 APPENDIX D. Further Observations on the Spectra of some of the 
 
 Stars and Nebulae, with an attempt to determine therefrom 
 
 whether these bodies are moving towards or from the Earth, also 
 
 Observations on the Spectra of the Sun and of Comet II. 1868. 
 APPENDIX E. On the Spctrum of the Great Nebula in Orion, and 
 
 on the motions of some Stars towards or from the Earth. 
 APPENDIX F. Researches on Gaseous Spectra in relation to the 
 
 Physical Constitution of Sun, Stars, and Nebulae. 
 APPENDIX G. Tables of the Dark Lines from Kirchhoff's Drawings. 
 
 Explanation of Angstrom and Thalen's Tables. Notice of 
 
 Browning's new Automatic Spectroscope. 
 
 IN the last lecture I endeavoured to point out to you the 
 principles upon which Professor Kirchhoff arrived at the 
 remarkable conclusion that certain metals well known on 
 earth are contained in the solar atmosphere. I have 
 to-day to bring before you facts which are still more 
 
OQ 
 
 It 
 
 CO 
 
 LLl 
 Q. ^ 
 CO 
 
 HVlOg 
 
 SBSi 
 
 XS aoNVMQ -HVJLS a^^a 
 
 I NO A3 3 
 
LECT. vi.J HAVE TEE PLANETS ATMOSPHERES? 321 
 
 interesting, with regard to the chemical composition of 
 the stars and the nebulae ; and if in the former lectures 
 I had to couple the names of two great German philo- 
 sophers, I have to-day to bring before your notice the re- 
 searches of three distinguished English men of science 
 Dr. Huggiris, Dr. Miller, and Mr. Lockyer to whom we 
 are indebted for a great part of our knowledge of celestial 
 chemistry. 
 
 Although the moon and planets, shining by borrowed 
 light, do not reveal to the spectroscope the nature of the 
 material of which they are composed, like the sun and 
 stars, yet something may be learned by an examination 
 of the spectra of these bodies. You will remember that 
 some of the dark lines in the solar spectrum are caused by 
 absorption in our own atmosphere : now if an atmosphere 
 of a similar kind exist round the moon or planets, the 
 atmospheric absorption lines must appear more intense 
 in the light reflected from these luminaries than they do 
 in the light which passes through our air alone. With 
 regard to the moon, the observations of Dr. Huggins and 
 Dr. Miller have been negative. No signs of a lunar 
 atmosphere presented themselves. A still more delicate 
 means of ascertaining whether the moon possesses an 
 atmosphere was employed by Dr. Huggins. On January 
 4th, 1865, he observed the spectrum of a star at the 
 moment the dark edge of the moon passed over it. If 
 an atmosphere existed in the moon, the observer would 
 see the starlight by refraction after the occupation 
 had occurred just as the setting sun is visible to us 
 after it has actually disappeared below the horizon. 
 The variously coloured rays are, however, differently 
 refrangible ; and if any atmosphere existed round the 
 moon, the red rays being least so would die out soonest, 
 
 Y 
 
322 SPECTRUM ANALYSIS. [LECT. TI. 
 
 and the spectrum of the star would be seen progressively 
 to diminish in intensity, beginning from the red end. 
 Dr. Huggins observed nothing of this kind, all the rays 
 of the stellar spectrum disappearing simultaneously : and 
 the conclusion must be drawn that the moon is devoid 
 of any appreciable atmosphere. 
 
 In the spectrum of Jupiter lines are seen which 
 indicate the existence of an absorptive atmosphere about 
 this planet. These lines plainly appeared when viewed 
 simultaneously with the spectrum of the sky, which at 
 the time of observation reflected the light of the setting 
 sun. One strong band corresponds with some terrestrial 
 atmospheric lines, and probably indicates the presence 
 of vapours similar to those which float about the earth. 
 Another band has no counterpart amongst the lines of 
 absorption of our atmosphere, and tells us of some gas or 
 vapour which does not exist in the earth's atmosphere. 
 From observations upon Saturn it appears probable that 
 aqueous vapour exists in the atmosphere of this planet, 
 as well as in that of Jupiter. In Venus no intensifying 
 of the atmospheric lines could be observed ; but some 
 remarkable groups of lines, corresponding to those seen 
 when the sun is low, were noticed on the more refran- 
 gible side of the line " D," in the Mars spectrum ; and 
 these indicate the existence of matter similar to that 
 occurring in our own atmosphere. The red colour which 
 distinguishes this planet appears not to be caused by 
 absorption in its atmosphere, as the light reflected from 
 its polar regions is free from the ruddy tint peculiar 
 to the other portions of the planet. Padre Secchi and 
 M. Janssen have likewise made similar observations, and 
 they also conclude that in all probability the vapour of 
 water exists in the planetary atmospheres. 
 
LECT. vi.] HAVE THE PLANETS ATMOSPHERES? 
 
 323 
 
 The absorption- spectrum of the far distant planets 
 Uranus and Neptune have recently been examined, the 
 former by Dr. Huggins, the latter by Padre Secchi. 
 The general appearance of the spectrum of Uranus is 
 represented by Fig. 79 ; the narrow spectrum placed 
 above that of the planet shows the relative positions of 
 the chief solar lines, and of two of the strongest absorp- 
 tion-bands produced by our atmosphere, viz. the group of 
 lines a little more refrangible than D, and that midway 
 from c to D. The numbers give the wave-lengths in 
 million ths of a millimetre. 
 
 C D I 1 F 
 
 05 64, 63 62 61 60 59 58 57 56 55 5t S3 SB 51 50 49 48 
 
 Huggins describes the spectrum as being faint and 
 continuous without any part being wanting from c to o. 
 Of the six very remarkable absorption-lines seen in 
 Uranus one appears to be coincident with the F line of 
 hydrogen, but there is no strong line in the spectrum of 
 Uranus in the positions of the strongest air lines, ,viz. 
 the double nitrogen line. The spectrum of Neptune 
 appears to resemble to a certain extent that of Uranus, 
 it being characterized by three dark bands, one in the 
 blue, one near b, and one between b and D ; moreover, 
 
 Y -2 
 
324 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. VI, 
 
 the red end of the spectrum appears to be altogether cut 
 off, and this absence of red light will probably account 
 for the blue tint of this planet. 
 
 I must now pass on to the subject proper of this day's 
 discourse, which is to consider the properties of the light 
 from the fixed stars. The more we learn about this 
 subject, the more I think we must be surprised at the 
 
 FIG. 80. 
 
 accuracy of the observing powers of those philosophers 
 who have given us this information. By means of this 
 beautiful instrument (made by Mr. Browning, and a 
 fac-simile of the one used by Dr. Huggins, Fig. 80) we 
 have been placed in possession of facts respecting the 
 composition of the atmospheres, and the physical consti- 
 tution of these stars, as accurate as the knowledge we 
 
LECT. vi.J DIFFICULTIES OF THE OBtiKK NATIONS. 325 
 
 possess concerning the composition of the solar atmo- 
 sphere. It would be impossible for me to give you, even 
 if time permitted, an accurate description of the method 
 employed by Dr. Huggiris. (See Appendix A.) Suffice it 
 to say, that at the end of his telescope he has placed this 
 spectroscope, containing two prisms (h h) ; and that, by 
 very accurate adjustment, he is able to bring the image 
 of the star on the slit of his spectroscope (d). You may 
 imagine how difficult these observations are, when you 
 remember that the light of the star emanates from a 
 point, that is to say, the star has no sensible magnitude ; 
 that the image of the star has to be kept steady upon a 
 slit only the rro part of an inch in "breadth ; and, more- 
 over, that the effect of the earth's motion has to be 
 counteracted. When you add to this, that the amount 
 of light which even the brightest stars give is excessively 
 feeble, that this line of light must be still further weakened 
 by being spread out by a cylindrical lens (a) into a band ; 
 and when you remember that in our climate, on a few 
 only of those nights in which the stars appear to the 
 naked eye to shine brilliantly, is the air steady enough to 
 prevent the flickering and confusion of the spectra, fatal 
 to these extremely delicate observations, I think you 
 will easily understand how exceedingly difficult these 
 researches must have been, and I am sure you will ac- 
 knowledge the debt of gratitude which the world owes to 
 those gentlemen who, by devoted labours, have brought 
 the subject to this interesting issue. 
 
 In order to get a knowledge of the chemical compo- 
 sition of the stars, or to ascertain what chemical elements 
 are present in them, it is necessary to use excessively 
 delicate arrangements, by which not only the light from 
 the star is allowed to pass through the prisms and to 
 
326 SPECTRUM ANALYSIS. [LEW. VI - 
 
 be received on the retina, but also that emitted by the 
 various substances, the presence or absence of which' in 
 the stellar atmosphere it is desired to ascertain. These 
 rays must pass together with the beam of starlight, or 
 rather over or under the starlight, into the eyepiece, 
 through the same prism, so that we may be able to 
 compare the position of the dark lines in the stellar 
 spectrum with that of the bright lines in the spectrum 
 
 FIG. 80 a. 
 
 of the body under examination. For this purpose a 
 very ingenious arrangement is attached to a part of the 
 telescope-spectroscope. It consists of a moveable mirror 
 (/, Fig. 80), placed above the slit of the spectroscope, 
 by means of which the light of the spark passing from 
 the metallic poles, held between metal holders, is reflected 
 by the small prism (e) placed on the slit into the optical 
 arrangement, and is received into the eye, the metal 
 spectrum being ranged close above that derived from the 
 
LKCT. vi.] SPECTRA OF THE FIXED STARS. 32J 
 
 star ; so that the coincidence or otherwise of the two sets 
 of lines can be accurately observed. In this way alone 
 is it possible to arrive at any trustworthy conclusion re- 
 specting the composition of the stars, and the existence 
 of certain metals in the stellar atmospheres. An im- 
 proved and compact form of spark condenser, as manu- 
 factured by Mr. Browning, is shown in Fig. 80 a. It is 
 of very simple construction, and may be employed either 
 for burning the metals or for getting the spectra of 
 gases. There are only two connections needed, one at 
 each end of the box ; and thus the arrangements are 
 much simplified. 
 
 The first result which we have to notice, then, is that 
 the spectra of various stars differ very widely indeed from 
 one another. As I mentioned to you, Fraunhofer in the 
 year 1814 showed that the stellar spectra were not the 
 same, and that they did not contain the same lines as 
 the spectrum of the sun. I have here coloured draw- 
 ings which will indicate to you, to begin with, the 
 different nature of these stellar spectra : but these 
 drawings do not pretend to give the exact positions 
 of the various lines in the spectra, but only approxi- 
 mately to represent their general appearance. Here 
 (see Nos. 1 and 2 on the Chromolith. Plate facing this 
 lecture), for example, is a picture of the spectra of the 
 two stars composing ft Cygni, in each of which, as you 
 see, the arrangement of the lines is totally different ; 
 and moreover the arrangement of the lines here is quite 
 different from that of the lines in the solar spectrum. 
 
 Dr. Huggins specially describes the spectra of two 
 particular stars, of which we have here an exact diagram 
 (Fig. 81). The upper drawing represents the spectrum 
 of Aldebaran. and the lower of Betelgeux, the star known 
 
328 
 
 SPECTRUM ANALYSIS. 
 
 [LKCT. vi. 
 
 as a in the constellation of Orion. This drawing is made 
 
 on a similar plan to Kirchhoff 's diagrams of the dark lines 
 
 
LECT. vi.] SPECTRA OF ALUEBARAN AND a ORIONIS. 329 
 
 in the solar spectrum. The longer lines represent the 
 dark bands in the stellar spectrum, the shorter ones 
 beneath represent the bright lines of the metals with 
 which the star spectrum was compared, the symbols of 
 the elements thus examined being added. In the first 
 place, then, the result at which we have arrived is that 
 the constitution of the starlight, although riot identical 
 with the light givdn off by the sun, is yet similar that 
 is to say, the light of a fixed star gives off a continuous 
 spectrum, interspersed by dark shadows or bands ; and 
 hence the conclusion we come to is that the physical 
 constitution of the fixed stars is similar to that of our 
 sun, that their light also emanates from intensely 
 white-hot matter, and passes through an atmosphere of 
 absorbent vapours in fact, that the stars are suns of 
 different systems. We find, for instance, in these two 
 particular stars to which I am now referring, the D line 
 caused by sodium exists : the three lines which we know 
 as b are produced by luminous vapour of magnesium. 
 The lines of these substances exactly agree in position 
 with the dark stellar lines ; hence both sodium and 
 magnesium are present in the atmosphere of these far 
 distant stars. We also find in Aldebaran that two 
 hydrogen lines, c and r, are present ; but if we look at 
 the spectrum of a Orionis, we find that the hydrogen 
 lines c and F are wanting. Hence we come to the con- 
 clusion that hydrogen is present in the atmosphere of 
 the sun and in that of Aldebaran, but that it is wanting 
 in that of Betelgeux. And so I might show you that 
 silver is not present in Aldebaran, nor seen in a Orionis, 
 but that four bright lines of calcium, also seen in the 
 sun's spectrum, are present in both stars. The lines 
 observed in these two stars are at least seventy in 
 
330 SPECTRUM ANALYSIS. [LECT. vi. 
 
 number, and Hugging and Miller have found that in 
 Aldebaran we have evidence of the presence of no less 
 than nine elements : namely (1) hydrogen, giving the 
 lines c and F ; (2) the metal sodium, giving the double 
 line D ; (3) magnesium, giving the lines b ; (4) calcium, 
 giving four lines ; (5) iron, giving four lines, and E ; 
 (6) bismuth, giving four lines (bismuth is not found in 
 the sun) ; (7) tellurium, four lines; (8) antimony is also 
 found, three lines ; and (9) mercury, four lines. Thus 
 the element tellurium, whose name implies a purely 
 earthly origin, is found in the star, although it does 
 not exist in the sun, and is very rare on this earth. 
 There are only two stars Betelgeux, to which I have 
 just referred, and another star called fi Pegasi in which 
 the hydrogen lines are wanting ; all the other stars 
 contain hydrogen. 
 
 We have, then, now arrived at a distinct understand- 
 ing of the physical condition of the fixed stars : they 
 consist of a white-hot nucleus, giving off a continuous 
 spectrum, surrounded by an incandescent atmosphere, 
 containing the absorbent vapours of the particular metals. 
 These results are interesting, as bearing on Laplace's 
 nebular theory, because they show that the visible 
 universe is mainly composed of the same elementary 
 constituents, although certain of the stars differ from 
 one another widely in their chemical constitution. 
 
 The next question to which the attention of the 
 observers was directed was the different character of 
 the light produced by the stars. It is well known that 
 the stars are variously coloured : some shine with a bright 
 white light, others with a yellow light, others with a blue 
 light. Could spectrum analysis give any explanation of 
 the variety of colours exhibited by these different stars ? 
 
LKCT. vi.] COLOURED AND DOUBLE STARS. 331 
 
 This is proved to be possible, as I shall show you by 
 reference to some diagrams from Huggins' drawings, 
 for most of what I have to say to-day will be the result 
 of his investigations. Here we have, in the first place,- 
 the spectrum of a white star, of the star which we all 
 well know as Sinus. In this coloured drawing (No. 3 
 on the Chromolith. facing the beginning of this lecture) 
 we find a representation of what Dr. Huggins observed 
 in the spectrum of Sirius : you will notice that we 
 have a continuous spectrum with dark lines, and we 
 find that these dark lines or shadows are interspersed 
 pretty generally throughout the length of the spectrum, 
 so that, when all the light enters the eye at once, it 
 produces upon the retina the effect of white light. 
 
 We next take an orange-coloured star, known as 
 a Herculis, which is a double star. Here (Chromolith. 
 No. 4) we have a totally different spectrum, and the lines 
 which are most marked in this spectrum exist in the 
 green, blue, and deep red. The light is comparatively 
 free from shadows in the yellow and orange portion : 
 and hence; the light from the red, green, and blue 
 portions of this star being weakened, the star shines with 
 a yellow light. This, then, illustrates to us the expla- 
 nation given by spectrum analysis of the cause of these 
 differently coloured stars in the heavens. We have, 
 however, yet to learn the nature of the substances which 
 produce many of these dark bands in the stellar spectra, 
 and cause the peculiar colour which the stars exhibit. 
 
 Another very interesting and well-known astronomical 
 fact next attracts our attention, viz. the existence of 
 certain twin or double stars. It appears that amongst 
 these twin. stars, which invariably differ in colour, the 
 blue, green, and purple stars are faint telescopic stars, 
 
332 SPECTRUM ANALYSIS. [LECT. vi. 
 
 never found alone, but associated under the protectiou, 
 as it were, of a brighter red or orange star. Does the 
 same explanation which has been given of the variety 
 of the differently coloured stars also apply to these 
 double stars ? 
 
 We have here (No. 2 on the Chroraolith.) a diagram 
 of the combined spectra of the two double stars existing 
 in /5 Cygni above, the orange star ; below, the blue 
 star. This one is orange because there are so many 
 dark lines in the blue and red, whilst there are none at 
 all in the orange portion of the spectrum. In the blue 
 star, on the other hand, we have a vast number of very 
 fine lines existing in the red and in the orange, and a 
 much smaller number existing in the blue : hence the 
 light of this star produces upon the retina the effect of 
 blue light. Padre Secchi 1 observing under the clear skies 
 of Rome has investigated the spectra of many hundred 
 stars. He finds it possible to arrange all these stars in 
 four groups, each characterized by a special form of spec- 
 trum. Group 1 contains the white stars, Sirius, a Lyrae, 
 Vega, &c., whose spectra are especially characterized by 
 four black lines, coincident with those of hydrogen. 
 Group 2 consists of the yellow stars, having spectra 
 intersected by numerous fine lines resembling those of 
 our sun : in this group Secchi reckons Pollux, Capella, 
 7 Aquilse, and our sun. The third group contains the 
 red and orange stars, a Orionis, a Herculis, Pegasi, &c., 
 the spectra of which are divided into eight or ten parallel 
 columnar clusters of alternate dark and bright bands, 
 increasing in intensity towards the red. Group 4 is 
 made up of the small red stars, whose spectra are distin- 
 guished by a succession of three bright zones, increasing 
 
 1 Astronomische Nachrichten, Jan. 28, 1869. 
 
LKCT. vi. J VARIABLE STARS. 333 
 
 in intensity towards the violet. Out of 316 stars 
 examined, Secchi found that 164 belonged to the first 
 type and 140 to the second, whilst the few remaining 
 constituted the third and fourth classes. 
 
 A very interesting and remarkable observation was 
 made in the month of May 1866. All at once, in the 
 constellation of the Northern Crown, a star, which was 
 entirely or almost entirely unknown, and which was at 
 any rate a star of very small size, suddenly blazed out, 
 and attained a magnitude almost equal to that of the 
 largest stars seen in the heavens. The examination of 
 the spectrum of this particular star naturally excited 
 the liveliest interest, and Huggins and Miller were 
 fortunate enough to be able to investigate at frequent 
 intervals this very remarkable phenomenon by means 
 of Dr. Huggins' spectroscope, and to their astonishment 
 found that this star, of which I here show you a diagram 
 (Chromolith. No. 6), differed altogether in its character 
 from the ordinary stellar spectra, inasmuch as superposed 
 on, or in addition to, the ordinary stellar spectrum which 
 you see exhibited here (viz. one consisting of dark lines 
 upon a bright ground), there were, in this particular 
 star, bright lines. Now what do bright lines indicate 1 
 They indicate the presence of certain gaseous bodies ; and 
 the result of the examination of the position of these par- 
 ticular bright lines, which you see here, showed them to 
 be coincident with the bright lines produced by hydrogen. 
 
 As this star made its appearance suddenly, so it soon 
 gradually began to diminish in brilliancy, and at last 
 died out, returning, as it were, to its original telescopic 
 dimensions of about the tenth magnitude. How was this 
 diminution of the brightness of the star to be explained ? 
 The cause of the diminution was revealed to us by the 
 
334 SPECTRUM ANALYSIS. [LECT. vi. 
 
 spectroscope, inasmuch as these bright lines were found 
 to dwindle and fade away, and it was observed after 
 a lapse of twelve days, when the star had diminished 
 in brilliancy from the second to the eighth magnitude, 
 that these bright lines became quite invisible. I had the 
 good fortune to see through Dr. Huggins' telescope the 
 very spectrum the drawing of which is now cast upon 
 the screen. The lines when I happened to see them had, 
 however, nearly faded away ; but they were still visible. 
 The conclusion to which we must come with regard to 
 this violent outburst is that it was probably due to a 
 rapid ignition of hydrogen, of a similar kind to, though 
 enormously larger than, the sudden outbreaks of incan- 
 descent gases seen in the red prominences of our sun. 1 
 
 1 Mr. Baxend ell's careful estimates of the varying brightness of this 
 star (Manch. Proc. Nov. 27, 1866) led him to conclude that the 
 intensity of its light on August 20th, when it reached its minimum, 
 was only yi^th part of that emitted at its maximum on May 12th. 
 From the recent observations of Lockyer and Janssen (see Lecture V.) 
 we learn that the red prominences in the sun are also caused by glowing 
 hydrogen, so that we have a new reason for believing that the sun 
 may belong to the family of variable stars. The question at once 
 suggests itself to the mind, Could a similar conflagration burst out in 
 our system ? Of the effects there can be no doubt. The intensity of 
 the sun's rays being increased nearly eight-hundredfold, our solid 
 globe would be dissipated in vapour almost as soon as a drop of water 
 in a furnace. The temperature in the sunlight would rise at once to 
 that only attainable in the focus of the largest burning-glass, and all 
 life in our planet would instantly cease. In thus speculating on such 
 a possible termination to our terrestrial history, it must be well under- 
 stood that the probability of such an event occurring is undoubtedly 
 infinitely small, and that the researches of geologists do not lead us to 
 suppose that any approach to such an occurrence has ever taken place 
 in former geologic ages, although it is not irrational to suggest that 
 certain geological indications of secular variations of terrestrial tem- 
 perature may have been produced by changes occurring in the heating 
 power of the sun. 
 
LECT. vi.] NATURE OF THE NEBULAR LINES. 335 
 
 An analogous increase of light has been observed in 
 other stars ; ] and Padre Secchi, the Roman astronomer, 
 has ascertained that several very small stars also exhibit 
 bright bands, and therefore have a constitution similar 
 to T Coronae : but he has not ascertained the accurate 
 position of these lines ; and it is therefore only in the case 
 of the star examined by Dr. Huggius that we are really 
 able to indicate the possible cause of the phenomenon. 
 
 From these observations you see that the stars possess 
 chromospheres of ignited hydrogen, and you will not fail 
 to draw the inference, already pointed out by astronomers 
 on other grounds, that our sun belongs to the family of 
 variable stars. 
 
 It is interesting to notice that the spectra of fixed 
 stars contain, like the solar light, invisible chemically 
 active rays. The spectrum of Sirius has been photo- 
 graphed by Dr. Huggins. The intensity of the light 
 of this star is, according to the best measurements, 
 the eooooooooo part of that of the sun : and although 
 probably not less in size than sixty of our suns, it is 
 estimated to be at the enormous distance of more than 
 130,000,000,000,000 miles; and yet even this immense 
 distance does not prevent us registering the chemical 
 intensity of the rays which left Sirius twenty-one years 
 ago (Miller) : and Mr. Lockyer has recently shown that 
 in the spectrum we have probably a means of deter- 
 mining the atmospheric pressure in the last layer of its 
 chromosphere. 
 
 The next point to which Dr. Huggins directed his 
 
 attention was the examination of those most interesting 
 
 and singular astronomical phenomena, the nebulae. The 
 
 first nebula which Dr. Huggins examined with his spec- 
 
 1 See Appendix C, " On Variable Stars." 
 
336 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. vi. 
 
 troscope was one of that class of luminous bodies 
 termed planetary nebuloe, in the constellation Draco. 
 On the 20th of August, 1864, Dr. Huggins turned his 
 telescope on to this particular nebula. I am afraid I 
 cannot give you any idea of the delicacy of such obser- 
 vations. Those, however, of my audience who have seen 
 such a planetary nebula through a telescope will know 
 that the light which those bodies give off is less than 
 that given off by perhaps even the smallest fixed star ; 
 and the difficulty of obtaining a spectrum and of exa- 
 mining the nature of this light is therefore exceedingly 
 
 Spark 
 
 FIG. 81 a. 
 
 ' ' : 
 
 great. 1 What, however, was Dr. Huggins astonishment, 
 on bringing the image of this nebula on to the slit of 
 his spectroscope, to observe that he no longer had to do 
 with a class of bodies of the nature of stars ! that instead 
 of having a band of light intersected by dark lines, indi- 
 cating the physical constitution of the body to be that 
 corresponding to the sun and stars, he found the light from 
 this nebula consisted simply of three isolated bright lines, 
 
 1 Dr. Huggins gives an idea of the extreme faintriess of the more 
 distant nebula?,. "The light of some of those visible in a moderately 
 large instrument has been estimated to vary from r ^ to ^feo of 
 the light of a single sperm candle consuming 158 grains of material 
 per hour, viewed at a distance of a quarter of a mile ; that is, such a 
 candle a quarter of a mile off is 20,000 times more brilliant than the 
 nebula ! " 
 
LECT. vi.] NATURE OF THE NEBULAR LINES. 337 
 
 of which we have here (Fig. 8 la, and in No. 7 of the 
 Chromolith.) a very rough representation. If the spec- 
 trum of this nebula had been continuous, it would have 
 been very difficult to see it. It was only because the 
 light given off consisted of three bright lines that he 
 was enabled to examine this spectrum at all. You 
 will have already anticipated me in the conclusion that 
 these most curious bodies do not consist of a white-hot 
 nucleus, enveloped in an atmosphere, passing through 
 which the light is absorbed, giving us dark lines ; but, 
 on the contrary, that these nebulae are in the condition 
 of luminous gases, and that it really is nebulous matter 
 with which we have here to do. 
 
 FIG. 82. 
 
 The history of these nebulae is one into which I cannot 
 enter. You all know that the names of Herschel and of 
 Rosse are associated with the most accurate and careful 
 examination of these particular bodies, and that it is 
 especially to the late Lord Rosse that we are indebted 
 for the very careful examination, by means of his mag- 
 nificent telescope, of these most singular bodies. It now 
 became a matter of the very greatest interest to examine 
 the character of the light given off by the other nebulae. 
 I will indicate to you the appearance of some of these 
 
 z 
 
338 SPECTRUM ANALYSIS. [LECT. vi. 
 
 nebulae, though very roughly, by means of the drawings. 
 The nebula in Aquarius is seen in Fig. 82. The 
 drawing of this nebula gives you but a faint notion of 
 its appearance in the telescope. I may also show you 
 another nebula (Fig. 83) having a spiral form, and whose 
 spectrum exhibits a fourth bright line. Dr. Huggins 
 then found, on examining the character of the lines 
 which these nebulae give off, that the spectrum was like- 
 wise distinguished by the same three distinct bright 
 lines. The questions will occur to every one, Do all the 
 nebulae give similar spectra ? and especially, Do those 
 
 FIG. 84. 
 
 .which the telescope had certainly resolved into a close 
 aggregation of bright points give gaseous spectra ? 
 
 Dr. Huggins has examined the spectra of about 
 seventy nebulae, and he finds that these can be divided 
 into two great groups. One group (about one-third of 
 the whole number) consists of the nebulae giving spectra 
 of three bright lines similar to those which I have shown 
 you, or else containing only one or two of these bright 
 lines. " Of these seventy nebulae, about one-third belong 
 to the class of gaseous bodies : the light of the remain- 
 
LBCT. VI.] 
 
 CONSTITUTION OF THE NEBULAS. 
 
 339 
 
 ing nebulae and clusters becomes spread out by the prism 
 into a spectrum which is apparently continuous." To 
 the class of nebulae giving continuous spectra the well- 
 known nebula in Andromeda belongs. This singularly 
 shaped body is visible to the naked eye (Fig. 84), and 
 is not ^infrequently mistaken for a comet. It was 
 observed as early as the year 1612, by Simon Marius. 
 The spectrum of this nebula, though apparently con- 
 tinuous, possesses some curious characteristics, the whole 
 of the red and a portion of the orange being wanting, 
 
 FIG. 85. 
 
 besides the brighter parts exhibiting an unequal and 
 mottled appearance. 
 
 It next becomes a most important point to ascertain 
 the chemical nature of the three bright lines in the 
 spectra of the gaseous nebulae. Dr. Huggins finds that 
 the brightest of the lines of the nebula coincides with the 
 strongest of the lines which are peculiar to nitrogen, whilst 
 the faintest of the lines was found to coincide with the 
 green line (F) of hydrogen. The middle line of the three 
 does not coincide with a line of any known element. 
 
340 SPECTRUM ANALYSIS. [LECT. vi. 
 
 The upper part of this drawing (Fig. 85) is intended to 
 represent a portion of the solar spectrum. Here you see 
 the dark line F, due to hydrogen, and the lines formed by 
 magnesium, corresponding with the letter b. Below are 
 the lines corresponding with some of the bright lines 
 of hydrogen, barium, nitrogen, and magnesium, whilst 
 between them are the three lines observed in these 
 nebulae (Fig. 85). Now it may be asked, " How is it, 
 if one of these three lines is due to hydrogen, and 
 another to nitrogen, that the other well-known lines 
 of these elements are not present in the spectra of the 
 nebulae ? Can we come to the conclusion that nitrogen 
 and hydrogen are contained in the nebulae, when we only 
 see two out of the many characteristic lines ? Why do 
 not the others appear?*' With regard to this point, Dr. 
 Huggins has recently shown that if the intensity of the 
 light coming from glowing nitrogen be diminished to a 
 certain point, only one line is seen ; and if you diminish 
 the intensity of the hydrogen spectrum, this one blue 
 line (F) alone becomes visible. 1 We may therefore safely 
 follow in Dr. Huggins' steps, and take all his conclusions 
 as being the result not only of careful experimentation, 
 but of philosophic caution, for in all these new and 
 difficult subjects that is an absolute necessity. I think 
 we may be well satisfied to adopt his decision, that in 
 fact nitrogen and hydrogen do exist in the nebulae, and 
 that the cause of the non-appearance of the other lines is 
 simply to be ascribed to the fact which I have already 
 endeavoured to point out to you, that the light coming 
 from these nebulae is of such excessively slight intensity. 
 I am almost afraid to take up your time in exhibiting 
 
 1 This fact has since been observed by Padre Secchi and Messrs. 
 Lock} r er and Franldand. 
 
LECT. vi.] NEBULA IN ORION. 341 
 
 to you many of these diagrams ; still I must not omit to 
 show you one of the well-known nebulae in the sword- 
 handle of Orion (see Fig. 86), which was discovered by 
 no less a personage than the astronomer Huyghens in 
 1656. I will read to you Sir John Herschel's description 
 of this nebula, " The general aspect of the less luminous 
 and cirrous portion is simply nebulous and irresolvable ; 
 but the brighter portion immediately adjacent to the 
 trapezium forming the square front of the head is shown 
 with the eighteen-inch reflector broken up into masses, 
 
 FIG. 86. 
 
 whose mottled and curdling light evidently indicates, by 
 a sort of granular texture, its consisting of stars, arid 
 when examined under the great light of Lord Kosse's 
 reflector, or the exquisite defining power of the great 
 achromatic at Cambridge, U.S., is evidently perceived to 
 consist of clustering stars. There can therefore be little 
 doubt as to the whole consisting of stars too minute to 
 be discerned individually, even with those powerful aids, 
 but which become visible as points of light when closely 
 adjacent in the more crowded parts." 
 
342 SPECTRUM ANALYSIS. [LECT. vi. 
 
 It becomes a matter of the greatest interest to learn 
 the conclusions to which the spectroscope leads us, con- 
 cerning the nature of these resolvable portions of this 
 nebula. Here you have Dr. Huggins' own words on 
 this important subject. "The results of telescopic 
 observation on this nebula seem to show that it is suit- 
 able for observation as a crucial test of the correctness 
 of the usually received opinion, that the resolution 
 of a nebula into bright stellar points is a certain and 
 trustworthy indication that the nebula consists of discrete 
 stars after the order of those which are bright to us. 
 Would the brighter portions of the nebula adjacent 
 to the trapezium, which have been resolved into stars, 
 present the same spectrum as the fainter and outlying 
 portions ? In the brighter parts would the existence 
 of closely aggregated stars be revealed to us by a con- 
 tinuous spectrum, in addition to that of the true gaseous 
 matter ?" The answer of the spectroscope comes to 
 us in no doubtful tone. " The light from the brightest 
 parts of the nebula near the trapezium was resolved by 
 the prisms into three bright lines, in all respects similar 
 to those of the gaseous nebula. . . . The whole of this 
 great nebula, as far as lies within the power of my in- 
 strument, emits light which is identical in its characters ; 
 the light from one part differs from the light of another 
 in intensity alone. " 
 
 The conclusion is obvious, that the close association 
 of points of light in a nebula can no longer be accepted 
 aa proof that the object consists of true stars. These 
 luminous points, in some nebulae at least, must be re- 
 garded as portions of matter, denser probably than the 
 outlying parts of the great nebulous mass, but still 
 gaseous. Another point of interest here presents itself 
 
LECT. vi.] SPECTRA OF COMETS. 343 
 
 with regard to the opinions entertained of the enormous 
 distances of the nebulae, founded upon the remoteness at 
 which these supposed star-clusters must exist, as they 
 cannot be resolved into stars by the most powerful 
 telescopes. Such opinions, it is clear, cannot now be 
 upheld, at least with respect to those nebulae which 
 have been proved to be gaseous. 
 
 Carrying on his observations still further, to well- 
 known distant clusters of stars, a representation of which 
 I will throw upon the screen, Dr. Huggins has found 
 that even some of those which were supposed to be well- 
 authenticated masses of stars do not really consist of 
 stars, for the light given off by , these clusters is also 
 identical in character with the light given off by the 
 true nebulae. Hence we must be careful in drawing our 
 conclusions respecting the existence of these bodies as 
 groups of far-distant suns, because we find that the light 
 which some of them give out is not the kind of light 
 which such far-distant fixed stars must emit. Still the 
 spectra of most of the resolvable nebulae are found to be 
 continuous, and therefore the light from these may be 
 considered as probably proceeding from systems of stars. 
 
 The true nature of comets is involved in even greater 
 obscurity than that of the nebulae. Dr. Huggins has 
 examined some of these singular bodies, and the result 
 of his observations leaves us even in greater uncertainty 
 respecting their character. A small comet which made 
 its appearance in 1866 and 1867 was first examined: 
 the spectrum of this was a faint continuous one, on 
 which bright lines were visible. Brorsen's comet was 
 next examined : it is a recurring comet, having a period 
 of rotation of 5^ years, and its spectrum consisted of 
 three bright bands, the central one of which lay between 
 
344 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. vi. 
 
 F and 6, and in addition a very faint continuous spectrum 
 was seen. These observations settled the physical cha- 
 racter of the comet : it consists of a mass of glowing 
 
 Solar , 
 F b 
 
 b E 
 
 o 
 
 /ceo 
 
 -H 
 
 9t>c 
 
 Carbon. Spark taken in Olive Oil. 
 
 Carbon. Spark taken in Olefiant Gfas. 
 
 Comet II. 1868. 
 
 Brorseris Coviet, 1868. 
 
 FIG. 87, 
 
 gas, and is self-luminous, a portion only feebly reflecting 
 the sunlight. From the drawing (Fig. 87) it will be 
 seen that the light from Brorsen's comet differs from the 
 
LKCT. vi.] SPECTRA OF COMETS. 345 
 
 light emitted by the nebulae, inasmuch as the lines in the 
 comet spectrum are not identical in position with the 
 lines yielded by the nebulae. Nor, in fact, are these 
 particular lines roughly represented here identical in 
 position with the bands of any known substance. (See 
 Fig. 87.) At the bottom of the diagram the lines of the 
 nebulae are given ; next we have the spark spectra of 
 nitrogen, hydrogen, magnesium, and sodium ; at the top 
 we see the solar lines ; and between these lie the par- 
 ticular lines of the comet : hence this comet contains 
 something not found in the nebulae, whose lines do not 
 coincide with any substance known on earth, so far as 
 examination has yet proceeded. So that w^^ially 
 not yet know of what this comet consists, 
 observations, I am sure you will all admit^ 
 to us subjects of the deepest interest. 
 
 We are entirely at a loss to know how such a body as 
 the comet can be self-luminous : the mass of the comet, 
 I believe, is astronomically speaking inappreciable. We 
 do not know whether there is as much matter in this 
 comet as would fill this room, or as much as would fill 
 one's hat ; and this amount of matter is spread over an 
 enormous space. The diameter of this comet has been 
 determined for me by Mr. Baxendell, who tells me that 
 it is about 60,700 miles an immense space over which 
 to spread so small an amount of substance. 
 
 How matter in this attenuated form can be kept up 
 ai; the high temperature necessary for the gas to become 
 incandescent is a subject on which we cannot at present 
 even speculate. 
 
 Dr. Huggins has also published an account of his 
 observations on the second comet of 1868, known as 
 Winnecke's comet, a drawing of which is seen in Fig. 88. 
 
346 
 
 SPECTRUM ANALYSIS. 
 
 [LEUT. vi. 
 
 Spectroscopic investigation has shown that this comet 
 contains luminous carbon, or carbon compounds : m its 
 spectrum, together with that of Brorsen's comet, is seen 
 
 FIG. 88. 
 
 in Fig. 87. This gives that modification of the carbon 
 spectrum which we obtain when the electric spark is 
 passed through olefiant gas, the coincidence of the bright 
 
LECT. VI. 
 
 CARBON IN COMETS. 
 
 347 
 
 lines of Winnecke's comet with those of the spark taken 
 in olefiant gas being clearly seen. In order to obtain an 
 exact comparison of the lines of the comet with those 
 of incandescent olefiant gas, the arrangement shown in 
 Fig. 89 was employed. This consists of a glass bottle, a, 
 converted into a gasholder containing the olefiant gas. 
 This was connected with the glass tube, b, through which 
 the gas passed, and into which two platinum wires, e and 
 
 FIG, 89, 
 
 f, had been soldered. This tube being then placed before 
 the mirror of the spectroscope c, the light of the spark, 
 passing through the gas in the tube by means of the wires, 
 was reflected into the instrument d, and its spectrum 
 was seen immediately below that of the comet The two 
 sets of bands were not only found to agree precisely 
 in position, but they corresponded in their general cha- 
 racters, and in their relative brightness, Hence we can 
 
348 SPECTRUM ANALYSIS. [LECT. vi. 
 
 scarcely doubt that carbon is really the cause of these 
 bright lines ; but whether the carbon is present in the free 
 state in the comet, or in the state of combination, cannot 
 be as yet definitively decided : nor can we explain how 
 carbon can be transformed into the gaseous state, or heated 
 so as to become luminous, unless indeed it be present in 
 the form of a hydrocarbon which becomes ignited or 
 enters into combination with some other constituent of 
 the comet by the action of the sun's heat. That carbon 
 is an element widely distributed throughout the uni- 
 verse we learn from the fact that it has been detected in 
 considerable quantities in the extra-terrestrial matter of 
 meteoric stones. This observation gains a further interest, 
 as it appears probable that the orbits of many comets 
 are identical with the paths of the recurring meteors. 
 Hence an intimate connection doubtless exists between 
 the comets and falling stars, so that meteorites may 
 perhaps consist of condensed cometary matter. These 
 observations have received further confirmation from 
 the fact that two comets appearing in 1871, one that 
 of Encke and another discovered by Winnecke, have each 
 been shown by Huggins to give a spectrum of three 
 bright bands again corresponding to the carbon lines. 
 / I have still to speak of another result of these in- 
 teresting experiments of Dr. Huggins. Not only are 
 we in a position thus to determine the constitution of the 
 stars and of the nebulae, but, strange as it may appear, 
 we can actually, by these observations, get some ideas 
 respecting the relative motions of these bodies and our 
 earth. It is impossible in the time at my disposal to 
 explain to you the mode in which philosophers or 
 physicists have arrived at the conclusion, originally pro- 
 pounded by Doppler in 1841, that, when a luminous 
 
LECT. vi.] MOTION OF THE STARS. 34<) 
 
 body is approaching another very rapidly, the kind of 
 light which' is received on the retina from that body 
 moving at a very great speed differs in some respects 
 from the light which the retina would receive were that 
 body at rest. An illustration from sound may perhaps 
 render this matter more plain. If in a railway train 
 you listen to the whistle of the engine of another train 
 which is meeting you, you will notice that as the two 
 trains approach the pitch of the note of the whistle alters. 1 
 This is because (owing to the sound being produced by 
 the vibration of the particles of the air), when the two 
 trains are approaching each other, the waves of sound 
 are, as it were, forced together and fall more rapidly 
 upon the ear than they would do if the two trains were 
 in a state of rest. The same thing happens with regard 
 to light. If the one object which is luminous is approach- 
 ing the retina very rapidly, the vibrations causing light 
 will fall more frequently on the retina than if the bodies 
 were at rest; and then the position of the dark lines will 
 be shifted in the direction of the most refrangible rays ; 
 whilst, if the bodies were separating, the shifting would 
 take place in the direction of the red or least refrangible 
 rays. Dr. Huggins has actually found that in some of 
 these stars there is a slight disturbance in the position 
 of the hydrogen line F : he first proved that it is really 
 hydrogen which is present, and then he showed that there 
 is a slight deviation observed between the hydrogen line 
 and the line existing in the star ; and hence he comes to 
 the conclusion that there is motion of recession between 
 the earth and what we call a " fixed star." Here you see 
 
 1 An exact experiment of this kind was made in 1845 by Ballot 
 of Utrecht, in which the alteration of tone for a given velocity was 
 determined. 
 
350 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. vi. 
 
 a diagram (Fig. 90) showing the slight deviation which 
 the line F exhibits in Sirius' light. You see that the 
 narrow line of hydrogen from the vacuum-tube does not 
 coincide with the middle of the Sirius F line, but crosses 
 it at a distance from the middle, which maybe repre- 
 sented by saying that the want of coincidence is appa- 
 rently equal to about one-third or one-fourth of the 
 interval separating the two D lines. Hence the F line 
 has been distinctly deviated towards the red rays, and 
 the vibrations proceeding from the star must have been 
 retarded in their passage ; or, in other words, there is a 
 
 Hydrogen at 
 Atmospheric 
 pressure 
 
 XclarSpectm m 
 Line F 
 
 Spectrum of 
 Sirius 
 
 Hydrogen in 
 Vacuum tube 
 
 FlG. 90. 
 
 motion of recession between our earth and Sirius of such 
 a nature that the wave-length of the F ray has been 
 increased by the 0'109 millionth part of a millimetre. 
 The velocity of this recession can easily be calculated. 
 Light travels at the rate of 185,000 miles per second ; 
 the wave-length of the F line is 486*5 millionths of a 
 millimetre : now the velocity with which the two bodies 
 move away from each other stands to the velocity of 
 light in the same proportion as the observed difference 
 of wave-length does to the wave-length of the particular 
 ray ; or 
 
 486-5 : 0-109 : : 185000 : x = 414. 
 
LECT. vi.] MOTION OF THE STARS ASCERTAINED. 351 
 
 Hence we conclude that this motion of recession between 
 the earth and the star Sinus is 41 '4 miles per second, or 
 that if the earth were stationary, instead of moving in its 
 orbit, as it did at the time of the experiment, away from 
 Sirius, there would be a proper motion of recession of 
 the star of twenty-nine miles per second. 
 
 Astronomers have, as you are aware, long ago shown by 
 telescopic observation that the whole of our solar system 
 is moving in space in the direction of the constellation 
 Hercules. Such observations can, however, only be made 
 when the motion to be noticed is at right angles to the 
 line of vision, whilst the deductions which I have just de- 
 scribed as being made with the spectroscope can only be 
 arrived at when the motion is in the direction of the line of 
 vision. We see, therefore, that by a happy combination of 
 these two methods we are enabled to ascertain the actual 
 rate of motion of the stars in space. Before we can, 
 however, attain an exact knowledge of these motions, the 
 delicacy of our spectroscopes must be much improved. 
 This has already been partially accomplished by Zollrier 
 in his reversing spectroscope, by means of which a dis- 
 placement equal to the ~- Q part of the distance between 
 the D lines can be seen. With this instrument Zollner 
 expects not only to be able to measure the proper motion 
 of the stars, but he has even rendered visible the shifting 
 in the Fraunhofer's lines which must occur from the 
 rotation of the sun on its axis, and thus he is able to 
 distinguish between those which are really solar lines and 
 those caused by absorption in our own atmosphere, which 
 naturally cannot exhibit a shifting in position from the 
 motion of the sun on its axis. The amount- of deviation 
 for a point on the solar equator as observed in this way 
 by Dr. Vogel was found to vary from 0*014 to 0*015 
 
352 SPECTRUM ANALYSIS. [LECT. vi. 
 
 millionth of a millimetre, corresponding to a velocity of 
 from 0'35 to 0*42 geographical mile in the second, the 
 generally accepted velocity being 0*27 mile. 1 
 
 Dr. Huggins has recently 2 communicated to the 
 Royal Society some further observations made with a 
 new and magnificent instrument upon this most inter- 
 esting subject. He finds, not only that his previous 
 conclusions respecting the proper motion of Sirius 
 are confirmed, but by his improved and more delicate 
 methods of measurement he has succeeded in ascer- 
 taining that many other so-called fixed stars are in fact 
 moving, some towards and some away from our planet. 
 Thus Sirius, Betelgeux, Rigel, Castor, Regulus, 8 Ursae 
 Major, and others which are situated in a part of the 
 heavens opposite to Hercules, towards which the sun is 
 advancing, are moving from the earth, whilst stars such 
 as Arcturus, Vega, and a Cygni, situated in the neigh- 
 bourhood of this region, show a motion of approach. 
 These drifting motions of certain stars had previously 
 been considered by Mr. Procter; and now spectroscopic 
 investigation shows that such drifting towards and away 
 from our system does really occur. One of the most re- 
 markable instances pointed out by Mr. Procter is that four 
 stars (/3, y, 8, and e) of the Great Bear have a community 
 of proper motions, whilst a and rj of the same constellation 
 have a proper motion in the opposite direction. Now 
 spectroscopic analysis shows that the stars /5, <y, 8, e, and 
 f have a common motion of recession, whilst the star 
 a is seen to be approaching the earth. 
 
 In the last lecture we learnt that the solar atmosphere, 
 and especially the outlying portion, chiefly consisting of 
 hydrogen gas, is constantly most violently agitated by 
 i Phil. Mag. Jan. 1872. 2 June 13, 1872. 
 
LECT. vi. J CYCLONES IN THE SUN. 353 
 
 storms of white-hot hydrogen, which blow with such 
 fierceness that, compared with these, our most destruc- 
 tive tornadoes are mere summer breezes. We saw also 
 that these storms give rise to the peculiar appearances 
 which we observe on the solar surface, viz. the sun-spots 
 and the faculse. Lockyer has determined the velocity 
 with which the glowing hydrogen rushes forwards or 
 backwards in these storms by observing the peculiar 
 alterations in breadth and position which the F line 
 exhibits. These alterations in refrangibility can only be 
 seen when the motion is one of approach to or of reces- 
 sion from the observer's eye ; and hence upon the sun's 
 disc we can only observe an upward or downward mo- 
 tion, whilst in the chromosphere or on the sun's limb we 
 may obtain evidence of lateral or cyclonic movements, 
 although we cannot there see any upward or downward 
 currents. Now, in looking at the sun's surface through 
 his spectroscope, Lockyer saw the line F sometimes ap- 
 pear as a dark line, and sometimes flash out as a bright 
 line on a darker ground. In the former case the F 
 line is seen to be bent and in several places shifted 
 towards the red end of the spectrum, whilst at other 
 points a displacement towards the violet end is noticed. 
 Sometimes the line disappears altogether, and before it 
 vanishes it is seen to swell or bulge out, or to terminate 
 in a knotty bulbous form. Then it again becomes in- 
 visible as the slit passes over the faculae, especially when 
 they are near some small spots, and again is seen to 
 swell out several times in the course of a few seconds, 
 then to shift towards the violet, and lastly to appear 
 as a straight bright line, without any thickening, over 
 a small spot. 
 
 These variations in the position and darkness or lumi- 
 
 A A 
 
354 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. vi. 
 
 nosity of the F line are attempted to be represented in 
 Fig. 91, giving the appearance of a spot-spectrum: the 
 dark horizontal lines show that a general absorption 
 occurs where the spots are darkest. In the neighbour- 
 hood of one of these spots a facula is situated; and there 
 the F line is seen to be bright and bulbous. 
 
 The other Fraunhofer's lines are, as you see, repre- 
 sented by vertical lines in the drawing (Fig. 91). These 
 serve, according to Lockyer, as milestones 1 by which 
 to measure the velocity, upwards or downwards, with 
 which these eruptive masses of hydrogen are moving, for 
 these shiftings and twistings of the F line are of course 
 nothing else than rapid alterations in the wave-length of 
 the F rays. 
 
 Red.<-= F -> Violet. 
 
 FIG. 91. 
 
 Deviation of the F line in a Spot- Spectrum (Lockyer). 
 
 If, therefore, a shifting towards the violet is observed 
 equal to the i \ - part of a millimetre (see No. 1, Fig. 
 92), this shows that the incandescent hydrogen is rushing 
 upwards with a velocity of thirty-eight miles per second ; 
 whilst a like deviation towards the red, as in No. 3 
 in the figure, proves that a downward current is blowing 
 with an equal velocity. Sometimes the bright line is 
 seen at the violet side of its normal position, whilst a 
 
 1 Still alterations of wave-length have also been detected in the 
 sodium, iron, and magnesium lines in a spot-spectrum. 
 
LECT. VI.] 
 
 CYCLONES IN THE SUN. 
 
 355 
 
 dark line is found shifted towards the red : this proves 
 that an upward rush of intensely-heated incandescent 
 hydrogen occurs on the one side, and a downward rush 
 of cool absorbing gas on the other. 
 
 The lateral motions near the limb are observed by 
 means of the shifting of the bright lines in the spectrum 
 of the chromosphere. The velocity of these cyclones is 
 almost incredible. Lockyer observed such a circular 
 storm on the 14th March, 1869 (No. 2, Fig. 92). The slit 
 of his spectroscope was about ~ of an inch in width ; 
 and as the diameter of the image of the sun cast by his 
 telescope was only 0'94 of an inch, he could observe a 
 strip on the sun's surface some 1,800 miles wide. 
 
 1. 2. 3. 
 
 FIG. 92. 
 
 If we now assume that the solar circular storm spreads 
 over a width of 1,500 miles and is moving at a fearful 
 rate, we must be able by help of the spectroscope to dis- 
 tinguish between those portions which move towards us 
 and those portions which are moving in the opposite 
 direction. The drawing (Fig. 92) shows that this is 
 indeed the case. When the slit was placed upon the 
 centre of this cyclone, the bright line which, in fact, is a 
 
 A A 2 
 
356 SPECTRUM ANALYSIS. [LECT. vi. 
 
 continuation of the dark F line, was seen to be shifted 
 to a distance which corresponds to a velocity of forty 
 miles per second. When the slit was directed towards 
 the edge of the storm, it was clear that on the one side 
 the current was moving towards us, and on the other side 
 away from us, because the deviation in the first case was 
 towards the violet, and in the second towards the red 
 end of the spectrum. The great rapidity with which the 
 prominences appear and disappear shows that the hydro- 
 gen gas of which these flames are composed is often in 
 a state of the most violent eruption, From the obser- 
 vation of the F line in a prominence on May 12, 1869, 
 the following conclusions were drawn : (1) a portion of 
 this flame was in a position of rest as regards us, as is 
 seen from the fact that near the photosphere the bright 
 F line was exactly coincident with the ordinary dark line 
 F of the solar spectrum ; (2) the bright continuation of 
 this line being displaced in a slanting direction towards 
 the violet end of the spectrum shows that a portion of 
 the hydrogen was moving towards the earth, but with 
 different velocities, the upper layers moving more rapidly 
 than the lower portions. Lockyer on this occasion saw 
 the F line triple, and the greatest lateral displacement 
 of the line corresponded to the enormous velocity of 120 
 miles per second ! A still more striking instance of the 
 almost incredible velocities which occur in the move- 
 ments in the solar atmosphere was observed by Professor 
 Young of Dartmouth College on 7th Sept., 1871. At 
 noon on that day he noticed an enormous protuberance 
 of hydrogen cloud on the eastern limb of the sun. It 
 had remained with little change since the noon of the 
 preceding day. It was made up mostly of filaments 
 nearly horizontal with its lower surface at a height of 
 
LECT. vi.] CONCLUSION. 357 
 
 some 15,000 miles ; but was connected with the layer of 
 red hydrogen by three or four vertical columns, brighter 
 and more active than the rest. Eeturning to the tele- 
 scope half-an-hour later, Professor Young found, in place 
 of the quiet cloud, a mass of detached vertical masses 
 rapidly ascending. Some of them had already reached 
 a height of 100,000 miles, and they continued to rise, with 
 a motion almost perceptible to the eye, until in ten 
 minutes the uppermost were more than 200,000 miles 
 above the solar surface ; the velocity of ascent was there- 
 fore 166 miles per second ! 
 
 These spectroscopic results become, if possible, still 
 more interesting when they are combined with telescopic 
 observations. On April 21, 1869, Lockyer was observ- 
 ing a spot near the sun's limb, and at 7h. 30m. A.M. a 
 protuberance in full activity was seen in the field of 
 view. The hydrogen lines were very bright, and, as the 
 spectrum of the spot was visible at the same time, it was 
 easy to see that the red flame was moving more quickly 
 than the spot, and that the prominence was fed, so to 
 speak, from the preceding edge of the spot. The violent 
 eruption had torn up a portion of the upper layer of the 
 photosphere beyond the usual limits of the chromosphere, 
 and high up in the hydrogen flame floated a cloud of 
 magnesium vapour! At 8h. 30m. there was comparative 
 quiet, but after an hour had elapsed the action had 
 commenced afresh, and the existence of a violent cyclone 
 was plainly seen. On the same day, and nearly at the 
 same time, a photograph of the sun was taken at Kew, 
 in which the violent changes observed by Lockyer could 
 be clearly traced, the limb of the sun being torn away 
 exactly at the place where the spectroscope had shown a 
 cyclone was situated. 
 
358 SPECTRUM ANALYSIS. [LEOT. vi. 
 
 Who could have dreamt ten years ago that we should 
 so soon attain such an insight into the processes of crea- 
 tion ? And yet, great though the results of spectrum 
 analysis already are, they are but a tithe of the numerous 
 questions which this branch of discovery has opened up, 
 questions of such number and magnitude, that many 
 generations of men will pass away before they are all 
 satisfactorily answered. 
 
 In conclusion, I may say that I feel it would be idle in 
 me to attempt to add any words as to the importance and 
 grandeur of the subjects which in these lectures I have 
 so imperfectly brought before you. I leave the facts to 
 speak for themselves, and I have only to thank you most 
 heartily for the kind attention with which you have 
 honoured me. 
 
APPEND. A.] EXTRACT FROM HUOGINS AND MILLER. 359 
 
 LECTURE VI. APPENDIX A. 
 
 EXTRACT FROM A MEMOIR ON THE SPECTRA OF SOME OF 
 THE FIXED STARS. 1 
 
 BY W. HUGGINS, F.R.A.S., AND W. MILLER, M.D., LL.D., 
 TREAS. AND V.P.R.S. 2 
 
 I. Introduction. 
 
 1. The recent discovery by^Kirchhoff of the connection between 
 the dark lines of the solar spectrum and the bright lines of 
 terrestrial flames, so remarkable for the wide range of its appli- 
 cation, has placed in the hands of the experimentalist a method 
 of analysis which is not rendered less certain by the distance 
 of the objects the light of which is to be subjected to examina- 
 tion. The great success of this method of analysis as applied 
 by Kirchhoff to the determination of the nature of some of the 
 constituents of the sun rendered it obvious that it would be an 
 investigation of the highest interest, in its relation to our know- 
 ledge of the general plan and structure of the visible universe, 
 to endeavour to apply this new method of analysis to the light 
 which reaches the earth from the fixed stars. Hitherto the 
 knowledge possessed by man of these immensely distant bodies 
 has been almost confined to the fact that some of them, which 
 observation shows to be united in systems, are composed of 
 matter subjected to the same laws of gravitation as those which 
 rule the members of the solar system. To this may be added 
 the high probability that they must be self-luminous bodies, 
 analogous to our sun, and probably in some cases even tran- 
 
 1 Phil. Trans. 1864. 
 
 2 The late Professor of Chemistry, King's College, London. 
 
360 SPECTRUM ANALYSIS. [LECT. vi. 
 
 scending it in brilliancy. Were they not self-luminous, it would 
 be impossible for their light to reach us from the enormous 
 distance at which the absence of sensible parallax in the case 
 of most of them shows they must be placed from our system. 
 
 The investigation of the nature of the fixed stars by a pris- 
 matic analysis of the light which comes to us from them, 
 however, is surrounded with no ordinary difficulties. The light 
 of the bright stars, even when concentrated by an object-glass 
 or speculum, is found to become feeble when subjected to the 
 large amount of dispersion which is necessary to give certainty 
 and value to the comparison of the dark lines of the stella spectra 
 with the bright lines of terrestrial matter. Another difficulty, 
 greater because it is in its effect upon observation more injurious, 
 and is altogether beyond the control of the experimentalist, 
 presents itself in the ever-changing want of homogeneity of the 
 earth's atmosphere through which the stellar light has to pass. 
 This source of difficulty presses very heavily upon observers who 
 have to work in a climate so unfavourable in this respect as our 
 own. On any but the finest nights the numerous and closely 
 approximated fine lines of the stellar spectra are seen so fitfully 
 that no observations of value can be made. It is from this 
 cause especially that we have found the inquiry, in which for 
 more than two years and a quarter we have been engaged, more 
 than usually toilsome ; and indeed it has demanded a sacrifice of 
 time very great when compared with the amount of information 
 which we have been enabled to obtain. 
 
 2. Previously to January 1862, in which month we commenced 
 these experiments, no results of any investigation undertaken 
 with a similar purpose had been published. With other objects 
 in view, two observers had described the spectra of a few of 
 the brighter stars, viz. Fraunhofer in 1823, 1 and Donati, whose 
 memoir, " Intorno alle Strie degli Spettri stellari," was published 
 in the " Annali del Museo Florentine" for 1862. 
 
 Fraunhofer recognized the solar lines D, E, b, and F in the 
 spectra of the moon, Venus, and Mars : he also found the line D 
 in Capella, Betelgeux, Procyon, and Pollux ; in the two former 
 1 Gilbert's Annalen, vol. Ixxiv. p. 374. 
 
APPEND. A ] EXTRACT FROM HUG GINS AND MILLER. 361 
 
 he also mentions the presence of b. Castor and Sirius exhibited 
 other lines. Donati's elaborate paper contains observations upon 
 fifteen stars ; but in no case has he given the positions of more 
 than three or four bars, and the positions which he ascribes to the 
 lines of the different spectra relatively to the solar spectrum do 
 not accord with the results obtained either by Fraunhofer or by 
 ourselves. As might have been anticipated from his well-known 
 accuracy, we have not found any error in the positions of the 
 lines indicated by Fraunhofer. 
 
 3. Early in 1862 we had succeeded in arranging a form of 
 apparatus in which a few of the stronger lines in some of the 
 brighter stars could be seen. The remeasuring of those already 
 described by Fraunhofer and Donati, and even the determining 
 the positions of a few similar lines in other stars, however, 
 would have been of little value for our special object, which was 
 to ascertain, if possible, the constituent elements of the different 
 stars. We therefore devoted considerable time and attention to 
 the perfecting of an apparatus which should possess sumcient 
 dispersive and defining power to resolve such lines as D and b 
 of the solar spectrum. Such an instrument would bring out the 
 finer lines of the spectra of the stars, if in this respect they 
 resembled the sun. It was necessary for our purpose that the 
 apparatus should further be adapted to give accurate measures 
 of the lines which should be observed, and that it should also be 
 so constructed as to permit the spectra of the chemical elements 
 to be observed in the instrument simultaneously with the spectra 
 of the stars. In addition to this, it was needful that these two 
 spectra should occupy such a position relatively to each other 
 as to enable the observer to determine with certainty the coin- 
 cidence or non-coincidence of the bright lines of the elements 
 with the dark lines in the light from the star. 
 
 Before the end of the year 1862 we had succeeded in con- 
 structing an apparatus which fulfilled part of these conditions. 
 With this some of the lines of the spectra of Aldebaran, 
 a Orionis, and Sirius were measured ; and from these measures, 
 diagrams of these stars, in greater detail than had then been 
 published, were laid before the Eoyal Society in February 1863. 
 
362 SPECTRUM ANALYSIS. [LECT. vi. 
 
 After the note was sent to the Society, we became acquainted with 
 some similar observations on several other stars by Butherfurd, in 
 Sillimaris Journal for 1863. 1 About the same time figures of a 
 few stellar spectra were also published by Secchi. 2 In March 
 1863 the Astronomer Eoyal presented a diagram to the Eoyal 
 Astronomical Society, in which are shown the positions of a few 
 lines in sixteen stars. 3 
 
 Since the date at which our note was sent to the Eoyal 
 Society our apparatus has been much improved, and in its 
 present form of construction it fulfils satisfactorily several of the 
 conditions required. 
 
 II. Description of the Apparatus, and Methods of Observation 
 
 employed. 
 
 4. This specially constructed spectrum apparatus is attached 
 to the eye end of a refracting telescope of 8 inches aperture and 
 10 feet focal length, which is mounted equatorially in the 
 observatory of Mr. Huggins at Upper Tulse Hill. The object- 
 glass is a very fine one, by Alvan Clark of Cambridge, Massa- 
 chusetts ; the equatorial mounting is by Cooke of York ; and 
 the telescope is carried very smoothly by a clock motion. 
 
 As the linear spectrum of the point of light which a star 
 forms at the focus of the object-glass is too narrow for the 
 observation of the dark lines, it becomes necessary to spread out 
 the image of the star; and to prevent loss of light, it is of 
 importance that this enlargement should be in one direction 
 only ; so that the whole of the light received by the object-glass 
 should be concentrated into a fine line of light as narrow as 
 possible, and having a length not greater than will correspond to 
 the breadth of the spectrum (when viewed in the apparatus), just 
 sufficient to enable the eye to distinguish with ease the dark 
 lines by which it may be crossed. No arrangement tried by us 
 has been found more suitable to effect this enlargement in one 
 
 1 Vol. xxxv. p. 71. 
 
 2 Astronomische Nachrichten, No. 1405, March 3, 1863. 
 
 3 Monthly Notices, Roy. Astron. Soc. vol. xxiii. p. 190. 
 
APPEND. A.] APPARATUS EMPLOYED. 3(J3 
 
 direction than a cylindrical lens, which was first employed for 
 this purpose by Fraunhofer. In the apparatus by which the 
 spectra described in our " Note " of February 1863 were ob- 
 served the cylindrical lens employed was plano-convex, of 0*5 
 inch focal length. This was placed within the focus of the 
 object-glass, and immediately in front of the slit of the 
 collimator. 
 
 The present form of the apparatus is represented in Fig. 78 
 (page 324), where the cylindrical lens is marked a. This is 
 plano-convex, an inch square, and of about 14 inches focal 
 length. The lens is mounted in an inner tube &, sliding within 
 the tube c, by which the apparatus is adapted to the eye end 
 of the telescope. The axial direction of the cylindrical surface 
 is placed at right angles to the slit d, and the distance of the lens 
 from the slit within the converging pencils from the object-glass 
 is such as to give exactly the necessary breadth to the spectrum. 
 
 In consequence of the object-glass being over-corrected, the 
 red and especially the violet pencils are less spread out than 
 the pencils of intermediate refrangibility ; so that the spectrum^ 
 instead of having a uniform breadth, becomes slightly narrower 
 at the red end, and tapers off in a greater degree towards the 
 more refrangible extremity. 1 
 
 In front of the slit d, and over one-half of it, is placed a 
 right-angled prism e, for the purpose of reflecting the light 
 which it receives from the mirror /, through the slit. In the 
 brass tube c are two holes : by one of these the light is allowed 
 to pass from the mirror to the reflecting prism e; and by means 
 of the other access to the milled head for regulatiog the width 
 
 1 The experiment was made by so placing the cylindrical lens that the axial 
 direction of its convex cylindrical surface should be parallel with the direction of 
 the slit. The line of light is in this case formed by the lens ; and the length of 
 this line, corresponding to the visible breadth of the spectrum, is equal to the 
 diameter of the cone of rays from the object-glass when they fall upon the slit. 
 With this arrangement, the spectrum appears to be spread out, in place of being 
 contracted at the two extremities. Owing to the large amount of dispersion to 
 which the light is subject, it was judged unadvisable to weaken still further the 
 already feeble illumination of the extremities of the spectrum ; and in the exami- 
 nation of the stellar spectra the position of the cylindrical lens with its axis at 
 right angles to the slit, as mentioned in the text, was therefore adopted. 
 
364 SPECTRUM ANALYSIS. [LBCT. VT. 
 
 of the slit is permitted. Behind the slit, and at a distance equal 
 to its focal length, is placed an achromatic collimating lens, g, 
 made by T. Eoss : this has a diameter of 0'6 inch and a focal 
 length of 4J inches. These proportions are such that the lens 
 receives the whole of the light which diverges from the linear 
 image of the star, when this is brought exactly within the jaws 
 of the slit. 
 
 A plano-concave cylindrical lens of about 14 inches negative 
 focal length was also tried. The slight advantage which this 
 possesses over the convex form is more than balanced by the 
 inconvenience of the increased length given to the whole 
 apparatus. The dispersing portion of the apparatus consists of 
 two prisms, li, each having a refracting angle of about 60 : they 
 were made by T. Ross, and are of very dense and homogeneous 
 flint glass. The prisms are supported upon a suitable mounting, 
 which permits them to be duly levelled and adjusted. Since 
 the feebleness of the light from the stars limits the observa- 
 tions for the most part to the central and more luminous 
 portions of the spectrum, the prisms have been adjusted to 
 the angle of minimum deviation for the ray D. A cover of 
 brass, k, encloses this part of the apparatus; and by this 
 means the prisms are protected from accidental displacement 
 and from dust. 
 
 The spectrum is viewed through a small achromatic telescope, 
 I, furnished with an object-glass of 0'8 inch diameter and 6*75 
 inches focal length. This telescope has an adjustment for level 
 at m. The axis of the telescope can be lowered and raised, and 
 the tube can be also rotated around the vertical axis of support 
 at n. At the focus of the object-glass are fixed two wires, 
 crossing at an angle of 90. These are viewed, together with the 
 spectrum, by a positive eyepiece, p, giving a magnifying power 
 of 57 diameters. As the eyes of the two observers do not 
 possess the same focal distance, a spectacle lens, corresponding 
 to the focal difference between the two, was fitted into a brass 
 tube, which slipped easily over the eyepiece of the telescope, 
 and was used or withdrawn as was necessary. 
 
 This telescope, when properly adjusted and clamped, is carried 
 
APPEND. A.] APPARATUS EMPLOYED. 365 
 
 by a micrometer screw, q, which was constructed and fitted to 
 the instrument by Cooke and Sons. The centre of motion about 
 which it is carried is placed approximately at the point of 
 intersection of the red and the violet pencils from the last 
 prism: consequently it falls within the last face of the prism 
 nearest the small telescope. All the pencils therefore which 
 emerge from the prism are, by the motion of the telescope, 
 caused to fall nearly centrically upon its object-glass. The 
 micrometer screw has 50 threads to an inch ; and each revolution 
 is read to the hundredth part, by the divisions engraved upon 
 the head. This gives a scale of about 1,800 parts to the interval 
 between the lines A and H of the solar spectrum. During the 
 whole of the observations the same part of the screw has been 
 used ; and the measures being relative, the inequalities, if any, 
 in the thread of this part of the screw do not affect the accuracy 
 of the results. The eye lens for reading the divisions of the 
 micrometer screw is shown at s. 
 
 The mirror / receives the light to be compared with that of 
 the star spectrum, and reflects it upon the prism c, in front of 
 the slit d. This light was usually obtained from the induction 
 spark taken between electrodes of different metals, fragments of 
 wires of which were held by a pair of small forceps attached to 
 the insulating ebonite clamp r. Upon a movable stand in the 
 observatory was placed the induction coil, already described by 
 one of us, 1 in the secondary circuit of which was inserted a 
 Leyden jar, having 140 square inches of tinfoil upon each of its 
 surfaces. The exciting battery, which, for the convenience 
 of being always available, consisted of four cells of Smee's 
 construction, with plates 6 inches by 3, was placed without the 
 observatory. Wires, in connection with this and the coil, were 
 so arranged that the observer could make and break contact at 
 pleasure without removing his eye from the small telescope. 
 This was the more important, since, by tilting the mirror /. it 
 is possible, within narrow limits, to alter the position of the 
 spectrum of the metal relatively to that of the star. An 
 arrangement is thus obtained which enables the observer to be 
 
 1 Phil. Trans. 1864, p. 141. 
 
366 SPECTRUM ANALYSIS. [LECT. vi. 
 
 assured of the perfect correspondence in relative position in the 
 instrument of the stellar spectrum and the spectrum to be 
 compared with it. 
 
 5. The satisfactory performance of this apparatus is proved 
 by the very considerable dispersion and admirably sharp 
 definition of the known lines in the spectra of the sun and 
 metallic vapours. When it is directed to the sun, the line D is 
 sufficiently divided to permit the line within it, marked in 
 Kirchhoff s map as coincident with nickel, to be seen. The 
 close groups of the metallic spectra are also well resolved. 
 
 When this improved apparatus was directed to the stars, a 
 large number of fine lines was observed, in addition to those 
 that had been previously seen. In the spectra of all the 
 brighter stars which we have examined the dark lines appear to 
 be as fine and as numerous as they are in the solar spectrum. 
 The great breadth in the lines in the green and more refrangible 
 parts of Sirius and some other stars, as seen in the less perfect 
 form of apparatus which was first employed, and which band- 
 like appearance was so marked as specially to distinguish them, 
 has, to a very great extent, disappeared ; and though these lines 
 are still strong, they now appear, as compared with the strongest 
 of the solar lines, by no means so abnormally broad as to 
 require these stars to be placed in a class apart. No stars 
 sufficiently bright to give a spectrum have been observed to be 
 without lines. The stars admit of no such broad distinctness of 
 classification. Star differs from star alone in the grouping and 
 arrangement of the numerous fine lines by which their spectra 
 are crossed. 
 
 6. For the convenience of reference and comparison, a few 
 of the more characteristic lines of twenty-nine of the elements 
 were measured with the instrument. These were laid down to 
 scale, in order to serve as a chart, for the purpose of suggesting, 
 by a- comparison with the lines measured in the star, those 
 elements the coincidence of the lines of which with stellar lines 
 was probable. 
 
 For the purpose of ensuring perfect accuracy in relative 
 position in the instrument between the star spectrum and the 
 
APPEND. A.] APPARATUS EMPLOYED. 367 
 
 spectrum to be observed simultaneously with it, the following 
 general method of observing was adopted: The flame of a 
 small lamp of alcohol, saturated with chloride of sodium, was 
 placed centrally before the object-glass of the telescope, so as 
 to furnish a sodium spectrum. The sodium spectrum was then 
 obtained by the induction spark, and the mirror / was so 
 adjusted that the components of the double line D, which is 
 well divided in the instrument, should be severally coincident in 
 the two spectra. The lamp was then removed, and the telescope 
 directed to the sun, when Fraunhofer's line D was satisfactorily 
 observed to coincide perfectly with that of sodium in the 
 induction spark. Having thus ascertained that the sodium lines 
 coincided in the instrument with the solar lines D, it was of 
 importance to have assurance from experiment that the other 
 parts of the solar spectrum would also accurately agree in 
 position with those corresponding to them in the spectrum of 
 comparison. When electrodes of magnesium were employed, 
 the components of the triple group characteristic of this metal 
 severally coincided with the corresponding lines of the group 5 ; 
 c and F also agreed exactly in position with the lines of 
 hydrogen. The stronger of the Fraunhofer lines were measured 
 in the spectra of the moon and of Venus, and these measures 
 were found to be accordant with those of the same lines taken 
 in the solar spectrum. 
 
 Before commencing the examination of the spectrum of a 
 star, the alcohol-lamp was again placed before the object-glass 
 of the telescope, and the correct adjustment of the apparatus 
 obtained with certainty. The first observation was whether the 
 star contained a double line coincident with the sodium line D. 
 When the presence of such a line had been satisfactorily 
 determined, we considered it sufficient in subsequent observa- 
 tions of the same star to commence by ascertaining the exact 
 agreement in position of this known stellar line with the 
 sodium line D. 
 
 Since from flexure of the parts of the spectrum apparatus 
 the absolute reading of the micrometer might vary when the 
 telescope was directed to stars differing greatly in altitude, tlie 
 
368 SPECTRUM ANALYSIS. [LECT. vi. 
 
 measure of the line in the star which was known to be 
 coincident with that of sodium was always taken at the 
 commencement and at the end of each set of measures. The 
 distances of the other lines from this line, and not the readings 
 of the .micrometer, were then finally registered as the measures 
 of their position; and these form the numbers given in the 
 Tables, from which the diagrams of the star spectra have been 
 laid down. 
 
 The very close approximation, not unfrequently the identity, 
 of the measures obtained for the same line on different occasions, 
 as well as the very exact agreement of the lines laid down from 
 these measures with the stellar lines subsequently determined 
 by a direct comparison with metallic lines, the positions of 
 which are known, have given the authors great confidence in the 
 minute accuracy of the numbers and drawings which they have 
 now the honour of laying before the Society. 
 
 APPENDIX B. 
 
 ON THE SPECTRUM OF MARS, WITH SOME REMARKS ON THE 
 COLOUR OF THAT PLANET. 
 
 BY WILLIAM HUGGINS, ESQ., F.R.S. 
 
 On several occasions during the late opposition of Mars I 
 made observations of the spectrum of the solar light reflected 
 from that planet. 
 
 The spectroscope which I employed was the same as that of 
 which a description has appeared in my former papers. 1 Two 
 
 1 "On the Spectra of some of the Fixed Stars." (Phil. Trans. 1864, p. 415.) 
 During my prismatic researches I have tried, and used occasionally, several other 
 arrangements for applying the prism to the telescope. Some of these instruments 
 are fitted with compound prisms, which give direct vision. I have not found 
 any apparatus equal in delicacy and in accuracy to that which is referred to 
 in the text. 
 
APPEND. B.] ON THE SPECTRUM OF MAKS. 369 
 
 instruments were used, one of which is furnished with a single 
 prism of dense glass, which has a refracting angle of 60. The 
 other instrument has two similar prisms. 
 
 In a paper " On the Spectra of some of the Fixed Stars," by 
 myself and Dr. W. A. Miller, we state that on one occasion 
 several strong lines of absorption were seen in the more refran- 
 gible parts of the spectrum of Mars. 
 
 During the recent more favourable opportunities of viewing 
 Mars I again saw groups of lines in the blue and indigo 
 parts of the spectrum. However, the faiutness of this portion 
 ef the spectrum, when the slit was made sufficiently narrow 
 for the distinct observation of the lines of Fraunhofer, did 
 not permit me to measure with accuracy the position of the 
 lines which I saw. For this reason I was unable to deter- 
 mine whether these lines are those which occur in this part 
 of the solar spectrum, or whether any of them are new lines 
 due to an absorption which the light suffers by reflection from 
 the planet. 
 
 I have confirmed our former observation, that several strong 
 lines exist in the red portion of the spectrum. Fraunhofer's c 
 was distinctly seen, and its identity determined by satisfactory 
 measures with the micrometer of the spectrum apparatus. From 
 this line the spectrum, as far as it can be traced towards the less 
 refrangible end, is crossed by dark lines. One strong line was 
 satisfactorily determined by the micrometer to be situated from 
 c at about one-fourth of the distance from c to B. As a similar 
 line is not found in this position in the solar spectrum, the line 
 in the spectrum of Mars may be accepted as an indication of 
 absorption by the planet, and probably by the atmosphere which 
 surrounds it. The other lines in the red may be identical, at 
 least in part, with B and A, and the adjacent lines, of the solar 
 spectrum. 
 
 On February 14 faint lines were seen on both sides of Frauri- 
 hofer's D. The lines on the more refrangible side of D were 
 stronger than the less refrangible lines. These lines occupy 
 positions in the spectrum apparently coincident with groups of 
 lines which make their appearance when the sun's light traverses 
 
 B B 
 
370 SPECTRUM ANALYSIS. [LECT. vi. 
 
 the lower strata of the atmosphere, and which are therefore 
 supposed to be produced by the absorption of gases or vapours 
 existing in our atmosphere. The lines in the spectrum of Mars 
 probably indicate the existence of similar matter in the planet's 
 atmosphere. I suspected that these lines were most distinct in 
 the light from the margin in the planet's disc ; but this observa- 
 tion was to some extent uncertain. That these lines were not 
 produced by the portion of the earth's atmosphere through which 
 the light of Mars had passed was shown by the absence of similar 
 lines in the spectrum of the moon, which at the time of observa- 
 tion had a smaller altitude than Mars. 
 
 I observed also the spectra of the darker portions of the 
 planet's disc. The spectrum of the dark zone beneath the 
 southern polar spot appeared as a dusky band when com- 
 pared with the spectra of the adjoining brighter parts of 
 the planet. This fainter spectrum appeared to possess a uni- 
 form depth of shade throughout its length. This observation 
 would indicate that the material which forms the darker parts 
 of the planet's surface absorbs all the rays of the spectrum 
 equally. These portions should be therefore neutral, or nearly 
 so, in colour. 
 
 I do not now regard the ruddy colour of Mars to be due to an 
 elective absorption ; that is, an absorption of certain rays only so 
 as to produce dark lines in the spectrum. 
 
 Further, it does not appear to be probable that the ruddy tint 
 which distinguishes Mars has its origin in the planet's atmo- 
 sphere, for the light reflected from the polar regions is free from 
 colour, though this light has traversed a longer column of atmo- 
 sphere than the light from the central parts of the disc. It is in 
 the central parts of the disc that the colour is most marked. If 
 indeed the colour be produced by the planet's atmosphere, it 
 must be referred to peculiar conditions of it which exist only in 
 connection with particular portions of the planetary surface. The 
 evidence we possess at present appears to support the opinion 
 that the planet's distinctive colour has its origin in the material 
 of which some parts of its surface are composed. Mr. Lockyer's 
 observation, that the colour is most intense when the planet's 
 
APPEND. B.] ATMOSPHERE OF MARS. 371 
 
 atmosphere is free from clouds, obviously admits of an inter- 
 pretation in accordance with this view. 
 
 This opinion appears to receive support from the photometric 
 observations of Seidel and Zollner, some of the results of which 
 I will briefly state. 
 
 These observations show that Mars resembles the moon in 
 the anomalous amount of variation of the light reflected from it 
 as it increases and decreases in phase ; also in the greater bril- 
 liancy of the marginal portions of its disc. Further, Zollner has 
 found that the albedo of Mars, that is, the mean reflective power 
 of the different parts of its disc, is not more than about one- 
 half greater than that of the lunar surface. Now these optical 
 characters are in accordance with telescopic observation, that in 
 the case of Mars the light is reflected almost entirely from the 
 true surface of the planet. Jupiter and Saturn, the light from 
 which has evidently come from an envelope of clouds, are, on the 
 contrary, less bright at the margin than at the central part of the 
 disc. These planets have an albedo, severally, about four and 
 three times greater than that of the moon. 1 
 
 The anomalous degradation in the brightness of the moon at 
 the phases on either side of the full, as well as the greater bril- 
 liancy of the limb, may be accounted for by the supposition of 
 inequalities on its surface, and also by a partly regular reflective 
 property of its superficial rocks. Zollner has shown that if 
 these phenomena be assumed empirically to be due to inequali- 
 ties, then the angle of mean elevation of these inequalities must 
 be taken as 52. On the same hypothesis the more rapid changes 
 of Mars would require an angle of 76. 2 
 
 It appears to be highly probable that the conditions of sur- 
 face which give rise to these phenomena are common to the 
 moon and to Mars. The considerations referred to in a former 
 paragraph suggest that these superficial conditions represent 
 peculiarities which exist at the true surface of the planet. 
 In this connection it is of importance to remark that the 
 
 1 Photometriselie Untersuchungeu, von Dr. J. C. Zollner; Leipzig, 1865. 
 
 2 Ibid. pp. 113, 128. 
 
 B B 2 
 
372 SPECTRUM ANALYSIS. [LECT. vi. 
 
 darker parts of the disc of Mars gradually disappear, and the 
 coloured portions lose their distinctive ruddy tint as they 
 approach the limb. 
 
 The observations of Sir J. Herschel 1 and Professor G. Bond 2 
 give a mean reflective power to the moon's surface, similar to 
 that from a "grey, weathered sandstone rock." Zollner has 
 confirmed this statement. According to him, 
 
 The albedo of the Moon = '1736 of the incident light. 
 
 Mars ='2672 
 
 ,, Jupiter ='6238 
 
 ,, Saturn ='4981 ,, ,, 
 
 ,, "White Paper ='700 ,, ,, 
 
 ,, White Sandstone = '237 ,, ,, 
 
 From this table it appears that Mars takes in for its own use 
 7328 of the energy which it receives as light. Jupiter's cloudy 
 atmosphere, nearly as brilliant as white paper, rejects more than 
 six-tenths of the light which falls upon it. Therefore, less than 
 four-tenths of the light which this distant planet receives is alone 
 available for the purposes of its economy. 
 
 The photographic researches of Mr. De la Eue and others 
 show that the rays of high refrangibility, which are spe- 
 cially powerful in producing chemical action, are similarly 
 affected. 3 At present we know nothing of the reflective power 
 of the planets for those rays of slower vibration which we 
 call heat. 
 
 1 "Outlines of Astronomy," p. 272. 
 
 2 " On the Light of the Moon and Jupiter," Memoirs Amer. Academy, vol. iii. 
 p. 222. In the same Memoir Prof. G. Bond estimates the albedo of Jupiter to be 
 greater than unity. This estimate would require the admission that Jupiter 
 shines in part by native light. (Ibid. p. 284. ) 
 
 3 Prof. G. Bond states that "the Moon, if the constitution of its surface 
 resembled that of Jupiter, would photograph in one- fourteenth of the time it 
 actually requires." (Ibid. p. 223.) 
 
APPE.VD. c.J VARIABLE STARS. 
 
 APPENDIX C. 
 
 ON THE OCCURRENCE OF BRIGHT LINES IN STELLAR SPECTRA, 
 AND ON THE SPECTRA OF VARIABLE STARS. 
 
 11 The spectrum of 7 Cassiopeiae appears to be, in some respects 
 at least, analogous to that of T. Coronas. In addition to the bright 
 line near the boundary of the green and blue observed by 
 Father Secchi, there is a line of equal brilliancy in the red, and 
 some dark lines of absorption. The two bright lines are narrow 
 and defined, but not very brilliant. Micrometrical measures 
 made by Dr. Huggins of these lines show that they are doubtless 
 coincident in position with Fraunhofer's C and F, and with tw r o 
 of the bright lines of luminous hydrogen. In these stars part 
 of the light must be emitted by gas intensely heated, though not 
 necessarily in a state of combustion. The nearly uniform light 
 of 7 Cassiopeiae suggests that the luminous hydrogen of this 
 star forms a normal part of its photosphere." Notices, Royal 
 Astronomical Society, vol. xxvii. p. 131. 
 
 " Mir a Cceti, which gives a spectrum apparently identical, 01 
 nearly so, with a Orionis, was examined when at its maximum 
 brilliancy, and on several subsequent occasions, after it had 
 commenced its downward course. At the time the star was 
 waning in brightness there was thought to be an appearance of 
 greater intensity in several of the groups, but a continued series 
 of observations is desirable before any opinion is hazarded as 
 to the cause of the variation in brightness which has procured 
 for this object the title of 'Wonderful.' At Mr. Baxendell's 
 request the variable p Coronae was examined when at its 
 maximum, but without any successful result. . . . Dr. Huggins 
 has confirmed the observation of MM. Wolf and Piaget so far 
 as to the presence of bright lines in the three small stars 
 described by them. He has not determined the positions of 
 these lines." Ibid. vol. xxviii. p. 87. 
 
374 SPECTR UM ANALYSIS. [LECT. vi. 
 
 APPENDIX D. 
 
 FURTHER OBSERVATIONS ON THE SPECTRA OF SOME OF THE STARS 
 AND NEBULAE, WITH AN ATTEMPT TO DETERMINE THEREFROM 
 WHETHER THESE BODIES AR.E MOVING TOWARDS OR FROM 
 THE EARTH; ALSO OBSERVATIONS ON THE SPECTRA OF THE 
 SUN AND OF COMET II. 1868. 1 
 
 BY WILLIAM HUGGINS, ESQ. F.R.S. 
 
 I. Introduction. 
 
 In a paper " On the Spectra of some of the Fixed Stars," 2 by 
 myself and Dr. W. A. Miller, Treas. R.S., we gave an account 
 of the method by which we had succeeded during the years 1862 
 and 1863 in making trustworthy simultaneous comparisons of 
 the bright lines of terrestrial substances with the dark lines in 
 the spectra of some of the fixed stars. We were at the time 
 fully aware that these direct comparisons were not only of value 
 for the more immediate purpose for which they had been under- 
 taken, namely, to obtain information of the chemical constitution 
 of the investing atmospheres of the stars, but that they might 
 also possibly serve to tell us something of the motions of the 
 stars relatively to our system. If the stars were moving towards 
 or from the earth, their motion, compounded with the earth's 
 motion, would alter to an observer on the earth the refrangibility 
 of the light emitted by them, and consequently the lines of ter- 
 restrial substances would no longer coincide in position in the 
 spectrum with the dark lines produced by the absorption of the 
 vapours of the same substances existing in the stars. 
 
 The apparatus employed by us was furnished with two prisms 
 of dense flint glass, each with a refracting angle of 60, and 
 permitted the comparisons to be made with so much accuracy 
 
 * Phil. Trans. 1868, p. 529. 2 Ibid. 1864, p. 413. 
 
APPEND. D.] EXTRACTS FROM HUG GINS. 375 
 
 that the displacement of a line, or of a group of lines, to an 
 amount smaller even than the interval which separates the 
 components of Fraunhofer's D, would have been easily detected. 
 We were therefore in possession of the information that none of 
 the stars, the lines in the spectra of which we had compared 
 with sufficient care, were moving in the direction of the visual 
 ray with a velocity so great, relatively to that of light, as to shift 
 a line through an interval corresponding to a difference of wave- 
 length equal to that which separates the components of D. To 
 produce an alteration of refrangibility of this amount a velocity 
 of about 169 miles per second would be required. The following 
 stars, with some others, were observed with the requisite accu- 
 racy : Aldebaran, a Orionis, /3 Pegasi, Sirius, a Lyree, Capella, 
 Arcturus, Pollux, Castor. 
 
 It appeared premature at the time to refer to these negative 
 results, as it did not seem to be probable that the stars were 
 moving with velocities sufficiently great to cause a change of 
 refrangibility which could be detected with our instrument. The 
 insufficiency of our apparatus for this very delicate investigation 
 does not, however, diminish the trustworthiness of the results 
 we obtained respecting the chemical constitution of the stars, as 
 the evidence for the existence or otherwise of a terrestrial 
 substance was made to rest upon the coincidence, or want of 
 coincidence, in general character as well as position of several 
 lines, and not upon that of a single line. 
 
 According to the undulatory theory, light is propagated with 
 equal velocity in all directions, whether the luminous body be 
 at rest or in motion. The change of refrangibility is therefore 
 to be looked for from the diminished or increased distance the 
 light would have to traverse if the luminous object and the 
 observer had a rapid motion towards or from each other. The 
 great relative velocity of light to the known planetary velocities 
 and to the probable motions of the few stars of which the parallax 
 is known, showed that any alterations of position which might 
 be expected from this cause in the lines of the stellar spectra 
 would not exceed a fraction of the interval between the double 
 line D, for that part of the spectrum. 
 
376 SPECTRUM ANALYSIS. [LECT. vr. 
 
 I have devoted much time to the construction and trial of 
 various forms of apparatus with which I hoped to accomplish 
 the detection of so small an amount of change of refrangibility. 
 The difficulties of this investigation I have found to be very 
 great, and it is only after some years that I have succeeded in 
 obtaining a few results which I hope will be acceptable to the 
 Koyal Society. 
 
 The subject of the influence of the motions of the heavenly 
 bodies on the index of refraction of light had already, at the 
 time of the publication of our paper in 1864, occupied the 
 attention of Mr. J. 0. Maxwell, F.R.S., who had made some 
 experiments in an analogous direction. In the spring of last 
 year, at my request, Mr. Maxwell sent to me a statement of his 
 views and of the experiments which he had made. I have his 
 permission to enrich this communication with the clear state- 
 ment of the subject which is contained in his letter, dated June 
 10, 1867 
 
 In 1841 Doppler showed that since the impression which is 
 received by the eye or the ear does not depend upon the intrinsic 
 strength and period of the waves of light and of sound, but is 
 determined by the interval of time in which they fall upon the 
 organ of the observer, it follows that the colour and intensity of 
 an impression of light, and the pitch and strength of a sound, 
 will be altered by a motion of the source of the light or of the 
 sound, or by a motion of the observer, towards or from each 
 other. 1 
 
 Doppler endeavoured by this consideration to account for the 
 remarkable differences of colour which some of the binary stars 
 present, and for some other phenomena of the heavenly bodies. 
 That Doppler was not correct in making this application of his 
 theory is obvious from the consideration that, even if a star could 
 be conceived to be moving with a velocity sufficient to alter 
 its colour sensibly to the eye, still no change of colour would 
 be perceived, for the reason that beyond the visible spectrum, at 
 both extremities, there exists a store of invisible waves which 
 
 1 " Ueber das farbige Licht der Doppolsterne und einiger anderer Gestirne des 
 Himinels." (Bohm. Gesell. Abh. ii. 1841-42, S. 465.) 
 
APPEND, i).] EXTRACTS FROM HUGGINS. 377 
 
 would be at the same time exalted or degraded into visibility 
 to take the place of the waves which had been raised or lowered 
 in refrangibility by the star's motion. No change of colour, 
 therefore, could take place until the whole of those invisible 
 waves of force had been expended, which would only be the 
 case when the relative motion of the source of light and the 
 observer was several times greater than that of light. 
 
 In 1845 Ballot published a series of acoustic experiments 
 which support Doppler's theory in the case of sound. In the 
 same paper Ballot advances several objections to Doppler's 
 application of his theory to the colours of the stars. 1 
 
 This paper was followed by several papers by Doppler in 
 reply to the objections which were brought against his con- 
 clusions. 2 
 
 In 1847 two memoirs were published by Sestini on the colours 
 of the stars in connection with Doppler's theory. 3 
 
 More recently, in 1866, Klinkerfues 4 published a memoir on 
 the influence of the motion of a source of light upon the refran- 
 gibility of its rays, and described therein a series of observations 
 from which he deduces certain amounts of motion, in the case 
 of some of the objects observed by him. 
 
 The method employed by Klinkerfues has been critically 
 discussed by Dr. Sohncke. 5 
 
 It may be sufficient to state that, as Klinkerfues employs an 
 achromatic prism, it does not seem possible, by his method of 
 observing, to obtain any information of the motion of the stars ; 
 for in such a prism the difference of period of the luminous 
 
 1 " Akustische Versuche auf der Niederlandischen Eisenbalm nebst gelegent- 
 Kohen Bemerkungen zur Theorie des Herrn Prof. Doppler ;" Pogg. Ann. B. Ixvi. 
 S. 321. 
 
 2 See Pogg. Ann. B. Ixxxi. S. 270, and B. Ixxxvi. S. 371. 
 
 3 "Memoria sopra i Color! delle Stelle del Catalogo de Baily osservati dal 
 P. Band. Sestini." Roma, 1847. 
 
 4 " Fernere Mittheilungen iiber den Einfluss der Bewegung der Lichtquelleauf 
 die Brechbarkeit eines Strahls." Von W. Klinkerfues, Nachr. K. G. der W. zu 
 Gottingen, No. 4, S. 33. 
 
 " Ueber den Einfluss der Bewegung der Lichtquelle auf die Brechung, kritische 
 Bemerkungen zu der Entdeckung des Herrn Prof. Klinkerfues." Von Herrn 
 Dr. Sohncke, Astrou. Nachr. No. 1646. 
 
378 SPECTRUM ANALYSIS. [LECT. vi. 
 
 waves would be as far as possible annulled. It is, however, 
 conceivable that his observations of the light when travelling 
 from. E. to W., and from W. to E., might show a difference in the 
 two cases, arising from the earth's motion through the ether. 
 
 Father Secchi has quite recently called attention to this 
 subject. 1 In his paper he states that he has not been able to 
 detect any change of refrangibility in the case of certain stars, of 
 an amount equal to the difference between the components of 
 the double line D. These results are in accordance with those 
 obtained by myself and Dr. Miller in 1868, so far as they refer 
 to the stars which had been examined by us. . . . 
 
 II. Description of Apparatus. 
 
 All the experiments were made with my refractor by Alvan 
 Clark, of 8 inches aperture and 10 feet focal length, which is 
 mounted equatorially, and carried very smoothly by a clock 
 motion. As even on nights of unusual steadiness the lines in 
 the spectra of the stars are necessarily, for several reasons, more 
 difficult of minute discrimination of position than are those of 
 the solar spectrum, it is important that the apparatus employed 
 should give an ample amount of dispersion relatively to the 
 degree of minuteness of observation which it is proposed to 
 attempt. 
 
 In 1866 I constructed a spectroscope for the special objects of 
 research described in this paper, which was furnished with three 
 prisms of 60 of very dense flint glass. The solar lines were 
 seen with great distinctness. I found, however, that, in order to 
 obtain a separation of the lines sufficient for my purpose, an 
 eyepiece magnifying ten or twelve diameters was necessary. 
 Under these circumstances the stellar lines were not seen in the 
 continued steady manner which is necessary for the trustworthy 
 determination of the minute differences of position which were 
 to be observed. After devoting to these observations the most 
 favourable nights which occurred during a period of some 
 months, I found that if success was to be obtained it would 
 
 1 Comptes Rendus, 2 Mars, 1868, p. 398. 
 
APPEND. D.] DESCRIPTION OF APPARATUS. 379 
 
 probably be with an apparatus in which a larger number of 
 prisms and a smaller magnifying power were employed. 
 
 The inconvenience arising from the pencils, after passing 
 through the prisms, crossing those from the collimator, when 
 more than three or four prisms are employed, and also, in part, 
 the circumstance that I had in my possession two very fine 
 direct-vision prisms on Amici's principle, which had been made 
 for me by Hofmann of Paris, induced me to attempt to combine 
 in one instrument several simple prisms with one or two 
 compound prisms which give direct vision. An instrument 
 constructed in this way, as will be seen from the following 
 description, possesses several not unimportant advantages. 1 
 
 a is an adjustable slit ; b an achromatic collimating lens of 4*5 
 inches focal length ; c represents the small telescope with which 
 the spectrum is viewed. The train of prisms consists of two 
 compound prisms, d and e, and three simple prisms /, g, h. 
 Each of the compound prisms contains five prisms, cemented 
 together with Canada balsam. The shaded portions of the 
 diagram represent the position of the two prisms of very dense 
 flint glass in each compound prism. The compound prism 
 marked e is much larger than the other, and is permanently 
 
 1 An apparatus in many respects superior to the one here described has been 
 constructed since. October 1868. 
 
380 SPECTRUM ANALYSIS. [LECT. vi. 
 
 connected with the telescope c, with which it moves. These 
 compound prisms, which were made specially to my order by 
 Hofmann, are of great perfection, and produced severally a 
 dispersion fully equal to two prisms of ordinary dense flint 
 glass. The prisms/ and g were cut for me from a very fine 
 piece of dense glass of Guinand by Messrs. Simms, and have 
 each a refracting angle of 60. The prism h was made by Mr. 
 Browning from the dense flint glass manufactured by Messrs. 
 Chance : this prism has a refracting angle of 45. The great 
 excellence of all these prisms is shown by the very great 
 sharpness of definition of the bright lines of the metals when 
 the induction spark is taken before the slit, even when con- 
 siderable magnifying power is employed on the small telescope 
 with which the spectrum is viewed. The instrument is provided 
 with a second collimator, of which the object-glass has a focal 
 length of 18 inches. 
 
 The compound prism e is so fixed that it can be removed at 
 pleasure, when the total dispersive power of the instrument is 
 reduced from about six and a half prisms of 60 to about 
 four and a half prisms of 60. The facility of being able to 
 reduce the power of the instrument has been found to be of 
 much service for the observation of faint objects, and also on 
 nights when the state of the atmosphere was not very favourable. 
 
 The telescope with which the spectrum is viewed is carried by 
 a micrometer screw, which, however, has not been employed for 
 taking measures of the spectra, but only for the purpose of 
 setting the telescope to the part of the spectrum which it is 
 intended to observe. This precaution is absolutely necessary 
 when nebulas are observed which emit light of two or three 
 refrangibilities only. 
 
 For the purpose of the simultaneous comparisons of the light 
 of the heavenly bodies with the lines of the terrestrial elements, 
 the slit was provided, in the usual way, with a small prism 
 placed over one half of it, which received the light reflected 
 upon it from a small mirror placed opposite the electrodes. The 
 plan of observation formerly employed, and which is described 
 in the paper " On the Spectra of some of the Fixed Stars," was 
 
APPEND. D.] DELICATE STAR SPECTROSCOPE. 381 
 
 adopted to ensure perfect accuracy of relative position in the 
 instrument between the star spectrum and the spectrum to be 
 compared with it, since it is possible, by tilting the mirror, to 
 alter within narrow limits the position of the spectrum of the 
 terrestrial substance relatively to that of the star. Before 
 commencing an observation, a small alcohol-lamp, in the wick 
 of which bicarbonate of soda was placed, was fixed before the 
 object-glass of the telescope, and then the mirror and the 
 electrodes were so adjusted that the components of the double 
 line D were exactly coincident in both spectra. 
 
 This plan was soon found to be very inconvenient, and even 
 in some degree untrustworthy for the more delicate comparisons 
 which were now attempted. An unobserved accidental dis- 
 placement of the spark, or of the mirror, might cause the two 
 spectra to differ in position by an amount equal to the whole 
 extent of want of coincidence which it was proposed to seek for 
 in this investigation. The observations of many nights have 
 been rejected, from the uncertainty as to the possible existence 
 of an accidental displacement. 
 
 Another inconvenience, so great as even to seem to diminish 
 the hope of ultimate success, was found to arise from the diffi- 
 culty of bringing the lower margin of the star spectrum 
 into actual contact with the upper margin of the spectrum 
 of the light reflected into the instrument. The lines in the 
 spectra of the stars are not, on ordinary nights, so steady 
 and distinct as are those of the solar spectrum. Under these 
 difficult circumstances, it is very desirable, as an assistance to 
 the eye in its judgment of the absolute identity or otherwise of 
 the position of lines, that the bright lines of comparison should 
 not merely meet the dark lines in the star spectrum, but that 
 they should overlap them to a small extent. When the two 
 spectra are so arranged as to be in contact, the eye is found to 
 be influenced to some extent by the apparent straightness or 
 otherwise of the compound line formed by the coincident, or 
 nearly coincident, lines in the two spectra. Owing to the 
 unavoidable shortness of the collimator, the lines in a broad 
 spectrum are slightly curved. From this cause the determinu- 
 
382 SPECTRUM ANALYSIS. [LECT. vi. 
 
 tion of the identity of lines in spectra which are in contact 
 merely is rendered more difficult, and it may be less trust- 
 worthy. 
 
 The difficulties of observation which have been referred to 
 were in the first instance sought to be overcome by placing the 
 spark before the object-glass of the telescope. In some respects 
 this method appears to be unexceptionable, but there are dis- 
 advantages connected with it. The bright lines, under these 
 circumstances, extend across the star spectrum, and make the 
 simultaneous observation of dark lines, which are coincident, 
 or nearly so, with them, very difficult. When the spark is 
 taken between electrodes, the consequent disturbance of the air 
 in front of the object-glass is unfavourable to good definition. 
 An important disadvantage arises from the great diminution in 
 the brightness of the spark from the distance (10 feet) at which 
 it is placed from the slit ; since in consequence of its nearness 
 to the object-glass the divergence of the light from it is dimi- 
 nished in a small degree only by that lens. It is obvious that, by 
 means of a lens of short focal length placed between the spark 
 and the object-glass, the light from the spark might be rendered 
 parallel, or even convergent ; but the adjustment of such a lens, 
 so that the pencils transmitted by it should coincide accurately 
 in direction with the optical axis of the telescope, would be very 
 troublesome. When two Leyden jars, connected as one jar, were 
 interposed, and the spark was taken in air between platinum 
 points, there was visible in the spectroscope only the brightest 
 of the lines of the air spectrum, namely, the double line belong- 
 ing to nitrogen, which corresponds to the principal line in the 
 spectra of the gaseous nebulae. When a vacuum-tube contain- 
 ing hydrogen at a low tension was placed before the object- 
 glass, the line corresponding to F was seen with sufficient dis- 
 tinctness, but the line in the red was visible with difficulty. 
 Some observations, however, have been made with the spark 
 arranged before the object-glass. 
 
 The following arrangement for admitting the light from the 
 spark appeared to me to be free from the objections which have 
 been referred to, and to be in all respects adapted to meet the 
 
APPEND. D.] DIFFICULTIES OF OBSERVATION. 383 
 
 requirements of the case. In place of thesm all prism, two 
 pieces of silvered glass were securely fixed before the slit at an 
 angle of 45. In a direction at right angles to that of the slit 
 an opening of about T V inch was left between the pieces of glass 
 for the passage of the pencils from the object-glass. By means 
 of this arrangement the spectrum of a star is seen accompanied 
 by two spectra of comparison, one appearing above and the other 
 below it. As the reflecting surfaces are about 0'5 inch from the 
 slit, and the rays from the spark are divergent, the light reflected 
 from the pieces of glass will have encroached upon the pencils 
 from the object-glass by the time they reach the slit, and the 
 upper and lower spectra of comparison will appear to overlap to 
 a small extent the spectrum formed by the light from the object- 
 glass. This condition of things is of great assistance to the eye 
 in forming a judgment as to the absolute coincidence or otherwise 
 of lines. For the purpose of avoiding some inconveniences 
 which would arise from glass of the ordinary thickness, pieces of 
 the thin glass used for the covers of microscopic objects were 
 carefully selected, and these were silvered by floating them upon 
 the surface of a silvering solution. In order to ensure that 
 the induction spark should always preserve the same position 
 relatively to the mirror, a piece of sheet gutta-percha was fixed 
 above the silvered glass : in the plate of gutta-percha, at the 
 proper place, a small hole was made of about 20- inch in diameter. 
 The ebonite clamp containing the electrodes is so fixed as to 
 permit the point of separation of these to be adjusted exactly 
 over the small hole in the gutta-percha. The adjustment of the 
 parts of the apparatus was made by closing the end of the 
 adapting tube, by which the apparatus is attached to the tele- 
 scope, with a diaphragm with a small central hole, before which 
 a spirit-lamp was placed. When the lines from the induction 
 spark, in the two spectra of comparison, were seen to overlap 
 exactly, for a short distance, the lines of sodium from the light 
 of the lamp, the adjustment was considered perfect. The 
 accuracy of adjustment has been confirmed by the exact coinci- 
 dence of the three lines of magnesium with the component lines 
 of I in the spectrum of the moon. 
 
384 SPECTRUM ANALYSIS. [LECT. vi. 
 
 In some cases the spectra produced by the spark are incon- 
 veniently bright for comparison with those of the stars and 
 nebulas. If the spark is reduced in power below a certain point, 
 many of the lines are not then well developed. The plan, 
 therefore, was adopted of diminishing the brightness of the 
 spectrum by a wedge of neutral-tint glass, which can be moved 
 at pleasure between the plate of gutta-percha and the silvered 
 mirror. 
 
 Two eyepieces were employed with the apparatus ; the one 
 magnifying four diameters, and the other six diameters. . . . 
 
 III. Observations of Nebulce. 
 
 For the greater convenience of reference and of comparison, 
 the spectrum of 37 H. IV. Draconis from my paper " On the 
 Spectra of some of the Nebula}" 1 has been added (Fig. 85, 
 p. 339). The spectrum of this nebula may be taken as 
 characteristic, in its general features, of the spectra of all the 
 nebulae which do not give a continuous spectrum. At present I 
 have determined satisfactorily the general characters of the spec- 
 tra of about seventy nebulae. This number forms but a part of 
 the much larger list of nebulae which I have examined, but in 
 the case of many of these objects their light was found to be too 
 feeble for a satisfactory analysis. Of the seventy nebulae about 
 one-third give a spectrum of bright lines. The proportion which 
 is indicated by this examination, of the nebulae which give a 
 spectrum of bright lines to those of which the spectrum is con- 
 tinuous (namely, as one to two), is probably higher than would 
 result from a wider observation of the objects contained in such 
 catalogues as those of Sir John Herschel and Dr. D'Arrest, since 
 many of the objects which I examined were specially selected, 
 on account of the probability (which was suggested by their form 
 or colour) that they were gaseous in constitution. 
 
 All the differences which I have hitherto observed between 
 the spectra of the gaseous nebulae may be regarded as modifica- 
 tions only of the typical form of spectrum which is represented 
 
 1 Phil. Trans. ]864, p. 438. 
 
APPEND. D.J CHARACTER OF THE NEBULAE. 385 
 
 iii the diagram, since they consist of differences of relative in- 
 tensity, of the deficiency of one or two lines, or of the presence 
 of one or two additional lines. It is worthy of remark that, so 
 far as the nebulae have been examined, the brightest of the three 
 lines, which agrees in position in the spectrum with the brightest 
 of the lines of the spectrum of nitrogen, is present in all the 
 nebulae which give a spectrum indicative of gaseity. It is a 
 suggestive fact that should, not be overlooked, that in no nebula 
 which has a spectrum of bright lines has any additional line 
 been observed on the less refrangible and brighter side of the 
 line common to all the gaseous nebulae. 
 
 The faint continuous spectrum, which in some cases is also 
 seen, has been traced in certain nebulae, by its breadth, to a 
 distinct brighter portion of the nebula which it is convenient 
 still to distinguish by the term " nucleus," though at present we 
 know nothing of the true relation of the bright points of the 
 nebulae to the more diffused surrounding portions. 
 
 It must not be forgotten that when gases are rendered 
 luminous there may usually be detected a faintly luminous con- 
 tinuous spectrum. In the case of several of the nebulae, such 
 as the annular nebula of Lyra and the Dumb-bell nebula, no 
 existence of even a faint continuous spectrum has been yet 
 certainly detected. 
 
 The determination of the position in the spectrum of the three 
 bright lines was obtained by simultaneous comparison with the 
 lines of hydrogen, nitrogen, and barium. The instrument which 
 I employed had two prisms, each with a refracting angle of 60> 
 and the positions of the lines were trustworthy within the limits 
 of about the breadth of the double line D. 
 
 The objects which I proposed to myself, in attempting a re- 
 examination of some of the nebulae with the large instrument 
 described in this paper, were to determine, first, whether any of 
 the nebulae were possessed of a motion which could be detected 
 by a change of refrangibility ; secondly, whether the coincidence 
 which had been observed of the first and the third line with a 
 line of hydrogen and a line of nitrogen would be found to hold 
 good when subjected to the test of a spreading out of the spec- 
 
 C C 
 
38G SPECTRUM ANALYSIS. [LECT. vi. 
 
 trum three or four times greater than that under which the 
 former observations were made. It would not, it seemed, be 
 difficult, in the case of the detection of a want of coincidence, to 
 separate the effects of the two distinct sources referred to, from 
 both, of which equally a minute difference of refrangibility 
 between the nebular lines and those of terrestrial substances 
 might arise. The probability is very great indeed that, in all the 
 nebulae which give the kind of spectrum of which I am speaking, 
 the two lines referred to are to be attributed to the same two 
 substances, and that therefore, in all these, nebulae, they were 
 originally of the same degree of refrangibility. On the other 
 hand, it is not to be supposed that nebulas situated in different 
 positions in the heavens would have a similar motion relatively 
 to the earth. An examination of several nebulae would therefore 
 show to which of these causes any observed want of coincidence 
 was to be attributed. 
 
 The great Nebula in Orion. In my description of this nebula 1 
 I stated that the light from all the parts of this strangely diver- 
 sified object, which were bright enough to be observed with my 
 instrument, was resolved into three bright lines similar to those 
 represented in the diagram. 
 
 On the present occasion I applied myself in the first place to 
 as careful a comparison as possible of the brightest line with the 
 corresponding line of the spectrum of nitrogen. 
 
 My first observations were made with the light from the in- 
 duction spark taken in pure nitrogen sealed in a tube at a tension 
 a little less than that of the atmosphere, which was reflected into 
 the instrument, as in my former series of observations, by means 
 of a mirror and a small prism. The precaution was taken to 
 verify the accuracy of the position of the spectrum of comparison 
 relatively to that of the nebula, by placing a small lamp before 
 the object- glass in the way already described. 
 
 The coincidence of the line in the nebula with the brightest 
 of the lines of nitrogen, though now subjected to a much more 
 severe trial, appeared as perfect as it did in my former observa- 
 tions. I expected that I might discover a duplicity in the line 
 
 1 Proc. Roy. Soc. vol. xiv. p. 39. 
 
APPEND. D.] THE GREAT NEBUL.i IN ORION. 387 
 
 in the nebula corresponding to the two component lines of the 
 line of nitrogen ; but T was not able, after long and careful scru- 
 tiny, to see the line double. The line in the nebula was narrower 
 than the double line of nitrogen : this latter may have appeared 
 broader in consequence of irradiation, and it was much brighter 
 than the line in the nebula. 
 
 The following observations are suggestive in connection with 
 the point under consideration. Electrodes of platinum were 
 placed before the object-glass in the direction of a diameter, so 
 that the spark was as nearly as possible before the centre of the 
 lens. The spark was taken in air. I expected to find the spec- 
 trum faint, for the reasons which have been stated in a previous 
 paragraph ; but I was surprised to find that only one line was 
 visible in the large spectroscope when adapted to the eye end of 
 the telescope. This line was the one which agrees in position 
 with the line in the nebula ; so that under these circumstances 
 the spectrum of nitrogen appeared precisely similar to the spectra 
 of those nebulae of which the light is apparently monochromatic. 
 This resemblance was made more complete by the faintness of 
 the line ; from which cause it appeared much narrower, and the 
 separate existence of its two components could no longer be 
 detected. When this line was observed simultaneously with 
 that in the nebula, it was found to appear but a very little 
 broader than that line. When the battery circuit was com- 
 pleted, the line from the spark coincided so accurately in position 
 with the nebular line that the effect to the eye was as if a sudden 
 increase of brightness in the line of the nebula had taken place. 
 In order to make this observation, and to compare the relative 
 appearance of the lines, the telescope was moved so that the 
 light from the nebula occupied the lower half only of the slit. 
 The line of the spark was now seen to be a very little broader 
 than the line of the nebula, and appeared as a continuation of it 
 in an unbroken straight line. These observations were repeated 
 many times on several nights. 
 
 An apparent want of coincidence, which would be represented 
 by 0-02 division of the head of the micrometer screw would be 
 about the smallest difference that could be observed under the cir- 
 
 c c 2 
 
388 SPECTRUM ANALYSIS. [LECT. vi. 
 
 cumstances under which these observations were made. At the 
 part of the spectrum where this line of nitrogen occurs the angular 
 interval measured by '02 division of the micrometer corresponds 
 to a difference of wave-length of '0460 millionth of a millimetre. 
 
 At the time the comparisons were made the earth was receding 
 from the part of the heavens in which the nebula is situated by 
 about half its orbital velocity. If the velocity of light be taken 
 at 185,000 miles per second, and the wave-length of the nitrogen 
 line at 500 ! 80 millionths of a millimetre, the effect of half the 
 orbital motion would be to degrade the refrangibility of the line 
 by 0*023, an alteration of wave-length which would correspond 
 to about O'Ol of the large micrometer head, an interval too small 
 to be detected. 
 
 We learn from these observations, that if the line be emitted 
 by nitrogen, the nebula is not receding from us with a velocity 
 greater than ten miles per second ; for this motion, added to that 
 of the earth's orbital velocity, would have caused a want of 
 coincidence that could be observed. Further, that if the nebula 
 be approaching our system, its velocity may be as much as twenty 
 miles or twenty-five miles per second ; for part of its motion of 
 approach would be masked by the effect of the motion of the 
 earth in the contrary direction. 
 
 The double line in the nitrogen spectrum does not consist of 
 sharply defined lines, but each component is nebulous, and re- 
 mains of a greater width than the image of the slit. 1 The 
 breadth of these lines appears to be connected with the condi- 
 tions of tension and of temperature of the gas. Pliicker 2 states 
 that when an induction spark of great heating power is employed 
 the lines expand so as to unite and form an undivided band. 
 Even when the duplicity exists, the eye ceases to have the power 
 to distinguish the cornponeDt lines, if the intensity of the light 
 be greatly diminished. 
 
 Though I have been unable to detect duplicity in the corre- 
 
 1 Secchi states that with his direct spectroscope this line in the annular nebula 
 in Lyra appears double. As the image of the nebula is viewed directly, after 
 elongation by the cylindrical lens, and without a slit, it is probable that the two 
 lines may correspond to the two sides of the elongated annulus of the nebula. 
 
 2 PhiL Trans. 1S63, p. 13. 
 
APPEND. D.] THE GREAT NEBULA IN ORION. 389 
 
 spending line in the nebula, it might possibly be found to be 
 double if seen under more favourable conditions: I incline to the 
 belief that it is not double. 1 
 
 In my Tables of the lines of the air 2 I estimated the bright- 
 ness of each of the components of the double line in the 
 spectrum of nitrogen at 10, and the components of the double 
 line next in brightness in the orange at 7 and 5, and those of a 
 third double line on the less refrangible side of D at 6 and 4. 
 It was with reference to these two double lines next in apparent 
 brilliancy that I wrote, 3 in speaking of the line in the nebula, 
 " If, however, this line were due to nitrogen, we ought to see 
 other lines as well ; for there are specially two strong double 
 lines in the spectrum of nitrogen, one at least of which, if they 
 existed in the light of the nebulae, would be easily visible." 
 
 As the disappearance of the whole spectrum of nitrogen, with 
 the exception of the one double line, was unexpected, though, 
 indeed, in accordance with my previous estimations, I examined 
 the spectrum of nitrogen with a spectroscope furnished with one 
 prism with a refracting angle of 60, in which the whole of the 
 spectrum from c to G is included in the field of view, I then 
 moved between the eye and the little telescope of the spectro- 
 scope a wedge of neutral-tint glass corrected for refraction by an 
 inverted similar wedge of crown glass, and which I had found 
 to be sensibly equal in absorbing power on the different parts 
 of the visible spectrum. As the darker part of the wedge was 
 brought before the eye, the two groups in the orange were quite 
 extinguished, while the lines in the green still remained of con- 
 siderable brightness. The line which under these circumstances 
 remained longest visible, next to the brightest line, was one more 
 refrangible at 2669 of the scale of my map. This observation 
 was made with a narrow slit. When the induction spark was 
 looked at from a distance of some feet with a direct-vision prism 
 held close to the eye, I was surprised to observe that the double 
 line in the orange appeared to me to be the brightest in the 
 spectrum ; and when the neutral-tint wedge was interposed, this 
 
 1 " On the Spectra of the Chemical Elements," Phil. Trans. 1864, p. 141. 
 
 2 Phil. Trans. 1864, p. 141. 3 Ihid. p. 443. 
 
390 SPECTRUM ANALYSIS. [LBCT. vi. 
 
 line in the orange remained alone visible, all the other lines 
 being extinguished. 
 
 When, however, in place of the simple prism a small direct- 
 vision spectroscope provided with a slit was employed, I found 
 it to be possible, by receding from the spark, to find a position 
 in which the double line in the green, with which the line in the 
 nebula coincides, was alone visible, and the spectrum of the 
 spark in nitrogen resembled that of a monochromatic nebula. 
 
 It is obvious that, if the spectrum of hydrogen were reduced in 
 intensity, the line in the blue, which corresponds to that in the 
 nebula, would remain visible after the line in the red and the lines 
 more refrangible than F had become too feeble to affect the eye. 
 
 It therefore becomes a question of much interest whether the 
 one, two, or three, or four lines seen in the spectra of these 
 nebulae represent the whole of the light emitted by these bodies, 
 or whether these lines are the strongest lines only of their spectra, 
 which, by reason of their greater intensity, have succeeded in 
 reaching the earth. Since these nebulae are bodies which have 
 a sensible diameter, and in all probability present a continuous 
 luminous surface, or nearly so, we cannot suppose that any lines 
 have been extinguished by the effect of the distance of these 
 objects from us. 
 
 If we had evidence that the other lines which present them- 
 selves in the spectra of nitrogen and hydrogen were quenched on 
 their way to us, we should have to consider their disappearance 
 as an indication of a power of extinction residing in cosmical 
 space, similar to that which was suggested from theoretical con- 
 siderations by Cheseaux, and was afterwards supported on other 
 grounds by Olbers and the elder Struve. Further, as the lines 
 which we see in the nebulas are precisely those which experiment 
 shows would longest resist extinction, at least so far as respects 
 their power of producing an impression on our visual organs, we 
 might conclude that this absorptive property of space is not 
 elective in its action on light, but is of the character of a general 
 absorption acting equally, or nearly so, on light of every degree 
 of refrangibility. Whatever may be the true state of the case, 
 the result of this re-examination of the spectrum of this nebula 
 
APPEND. D.] THE GREAT NEBULA IN ORION. 391 
 
 appears to give increased probability to the suggestion that 
 followed from my former observations, namely, that the sub- 
 stances hydrogen and nitrogen are the principal constituents of 
 the nebulae of the class under consideration. 
 
 I now pass to observations of the third line of the nebular 
 spectrum, the one which I found to coincide with the line of 
 hydrogen which corresponds to Fraunhofer's F. The substance 
 in the nebulse which is indicated by this line appears to be sub- 
 ject to much greater variation in relative brilliancy, or to be more 
 affected by the conditions under which it emits light ; for while 
 the brightest line is always present, the line of which I am 
 speaking seems to be wholly wanting in some nebulae, and to be 
 of different degrees of relative brightness in some other nebulse. 
 
 In the nebula of Orion this line is relatively stronger than in 
 37 H. IV. Draconis, and some other nebulse. I have suspected 
 that the relative brightness of this line varies slightly in different 
 parts of this nebula. It may be estimated perhaps in the nebula 
 of Orion at about the brightness of the second line. The second 
 line suffers in apparent brilliancy from its nearness to the 
 brightest line, and may, without due regard to this circumstance, 
 be estimated as brighter than the third line. 
 
 In order to compare the position of the line with that of the 
 corresponding line in the spectrum of hydrogen, I employed a 
 vacuum-tube containing hydrogen at a very small tension, which 
 was placed before the object-glass of the telescope. Under 
 these conditions the line appears narrow when the slit is narrow, 
 without any sensible nebulosity at the edges. The character of 
 the line is altered, as has been shown by Pllicker, when hydrogen 
 at the atmospheric pressure is employed : the line then expands 
 into a nebulous band of considerable width, even with a very 
 narrow slit. Such a condition of the line is obviously unsuitable 
 for the delicate comparisons which it was proposed to attempt. 
 
 The narrow, sharply-defined line of hydrogen, when the 
 vacuum-tube was before the slit, was observed to coincide per- 
 fectly in position with the third line of the nebula. This 
 observation, which shows the coincidence of these lines with an 
 accuracy three or four times as great as my former observations, 
 
392 SPECTRUM ANALYSIS. [LECT. vi. 
 
 increases in the same ratio the probability that the line in the 
 nebula is really due to luminous hydrogen. 
 
 I suspect that, although the third line in this nebula may 
 impress the eye as strongly as the second line, yet it is not so 
 narrow and well denned as that line. If this suspicion be 
 correct, this condition of the line might indicate that the 
 hydrogen exists at a rather greater tension than that in the so- 
 called vacuum-tubes, but that it is not nearly so dense as would 
 correspond to the atmospheric pressure at the surface of the 
 earth. As, however, the character of the lines of hydrogen is 
 also greatly modified by temperature, it is not possible to reason 
 with any certainty as to the state of things in this distant object, 
 the light of which we have now under examination. 
 
 I am still unable to find any terrestrial line which corresponds 
 to the middle line. I have made the additional observation that 
 the line in the nebula is in a very slight degree less refrangible 
 than the line of oxygen at 2060 of the scale of my map. It is 
 in a rather larger degree less refrangible than the strong line of 
 barium at 2075 of my scale. 
 
 Several other nebulae have been observed with the large spec- 
 troscope : I prefer, however, to re-examine these objects before 
 I publish any observations of them. 
 
 IV. Observations of Stars. 
 
 The chief difficulties which I have had to encounter have 
 arisen from the unsteadiness of our atmosphere. There is 
 sufficient light from stars of the first and second magnitude for 
 the large spectroscope described in this paper, and, so far as the 
 adjustments of the instrument are concerned, the lines in the 
 spectra of the stars would be well defined. Unless, however, the 
 air is very steady, the lines are seen too fitfully to permit of any 
 certainty in the determination of coincidences of the degree of 
 delicacy which is attempted in the present investigation. I have 
 passed hours in the attempt to determine the position of a single 
 line, and have then not considered that the numerous observa- 
 tions which I had obtained were possessed, even collectively, of 
 
APPEND. D.] OBSERVATIONS OF STARS. 393 
 
 sufficient weight to establish with any certainty the coincidence 
 of the line with the one compared with it. 
 
 I prefer, therefore, to reject a large number of observations 
 which appear unsatisfactory from this cause, and to give in this 
 place a very few of the most trustworthy of the observations 
 which I have made. 
 
 Sirius. The brilliant light of this star and the great intensity 
 of the four strong lines of its spectrum make it especially 
 suitable for such an examination. The low altitude of this star 
 in our latitude limits the period in which it can be successfully 
 observed to about one hour on each side of the meridian. 
 
 I have confined myself to comparisons of the strong line in 
 the position of F with the corresponding line of the spectrum 
 of hydrogen. My first trials were made with hydrogen at the 
 ordinary atmospheric pressure : the width of the band of 
 hydrogen, under these circumstances, was greater than the line 
 of Sirius. This line in Sirius, from some cause, is narrower 
 relatively to the length of the spectrum, when considerable dis- 
 persion and a narrow slit are employed, than when the image 
 of the star, rendered linear by a cylindrical lens, is observed with 
 a single prism. 1 (See Fig. 90, p. 350.) 
 
 When the large spectroscope was employed, I estimated the 
 breadth of the line to be about equal to that of the double line 
 D. In Kirchhoff's map the line F of the solar spectrum is 
 represented as a little more than one-fourth of the interval 
 separating the lines D. When the spectroscope attached to the 
 telescope was directed to the moon, the line F appeared even 
 narrower than it is represented in Kirchhoff's map ; I estimated 
 it at about one-sixth of the apparent breadth of the corresponding 
 line in the spectrum of Sirius. The character of the line agrees 
 precisely with the line of hydrogen under certain conditions of 
 tension and temperature. 
 
 As it was obviously impossible to determine with the required 
 accuracy the coincidence of the line of Sirius when the much 
 broader band of hydrogen at the ordinary pressure was compared 
 with it, I employed a vacuum-tube fixed before the object-glass. 
 
 1 See Phil. Trans. 1864, p. 42. 
 
394 SPECTRUM ANALYSIS. [LECT. vi. 
 
 In all these observations the slit used was as narrow as possible. 
 The air at the time of the present observations was more 
 favourable than usual, and the line in Sirius was seen with great 
 distinctness. The line from the spark appeared in comparison 
 very narrow, not more than about one-fifth of the width of the 
 line of Sirius. When the battery circuit was completed, the line 
 of hydrogen could be seen distinctly upon the dark line of 
 Sirius. The observation of the comparison of the lines was 
 made many times, and I am certain that the narrow line of 
 hydrogen, though it appeared projected upon the dark line in 
 Sirius, did not coincide with the middle of the line, but crossed 
 it at a distance from the middle, which may be represented by 
 saying that the want of coincidence was apparently equal to 
 about one-third or one-fourth of the interval separating the 
 components of the double line D. I was unable to measure 
 directly the distance between the centre of the line of hydrogen 
 and that of the line in the spectrum of Sirius, but several very 
 careful estimations by means of the micrometer give a value for 
 that distance of (HMO of the micrometer head. This value is 
 probably not in error by so much as its eighth part. 
 
 Comparisons on many other nights were also made, sometimes 
 with the vacuum-tube before the object-glass, and sometimes 
 with the vacuum-tube placed over the small hole in the gutta- 
 percha plate. On all these occasions the numerous compari- 
 sons which were made gave for the line in Sirius a very slightly 
 lower refrangibility than that of the line of hydrogen, but on 
 no one occasion was the air steady enough for a satisfactory 
 determination of the amount of difference of refrangibility. 
 
 I have not been able to detect any probable source of error 
 in this result, and it may therefore, I believe, be received as 
 representing a relative motion of recession between Sirius and 
 the earth. 
 
 The probability that the substance in Sirius by which this 
 line is produced is really hydrogen is strengthened almost to 
 certainty by the consideration that there is a strong line in the 
 red part of the spectrum which is also coincident with a strong 
 line of hydrogen. There is a third line more refrangible than F, 
 
APPEND. D.] EXPANSION OF LINE F. 395 
 
 which appears to coincide with the line of hydrogen in that part 
 of the spectrum. 
 
 As the line in Sirius is more expanded than that of the 
 vacuum-tube, it seemed of importance to have proof from experi- 
 ment that this line of hydrogen, when it becomes broad, expands 
 equally in both directions. I made the comparisons of the 
 narrow line of the vacuum-tube with the more expanded band 
 which appears when denser hydrogen is employed. For this 
 purpose the intersection of the wires of the eyepiece was brought, 
 as nearly as could be estimated, upon the middle of the expanded 
 line which is produced by dense hydrogen. The vacuum-tube 
 was then arranged before the slit, when the narrow line which it 
 gives was observed to fall exactly upon the point of intersection 
 of the wire. Under these terrestrial conditions the expansion of 
 the line may be considered to take place to an equal amount in 
 both directions. There is very great probability that a similar 
 equal expansion takes place under the conditions which determine 
 the absorption of light by this gas in the atmosphere of Sirius, 
 for the reason that the nebulosity at the edges of the line in the 
 spectrum of that star is sensibly equal on both sides. 
 
 I made some attempts to compare the strong line at c with 
 the corresponding line of hydrogen; but when the large spec- 
 troscope was employed, though the lines could be seen with 
 tolerable distinctness, they were not bright enough to admit of 
 a trustworthy determination of their relative position. When 
 one of the compound prisms was removed, the lines were much 
 more easily seen, but under these circumstances the amount of 
 dispersion was insufficient for my present purpose. 
 
 The lines of Sirius which, in conjunction with Dr. Miller, I 
 had compared with those of iron, magnesium, and sodium, are 
 not sufficiently well seen in our latitude for comparison when a 
 powerful train of prisms is employed, such as is necessary for 
 this special inquiry. 
 
 From these observations it may, I think, be concluded that 
 the substance in Sirius which produces the strong lines is really 
 hydrogen, as was stated by Dr. Miller and myself in our former 
 paper. Further, that the aggregate result of the motions of the 
 
396 SPECTR UM ANALYSIS. [LECT. vi. 
 
 star and the earth in space, at the time when the observations 
 were made, was to degrade the refrangibility of the line in Sirius 
 by an amount corresponding to 0'040 of the micrometer screw. 
 Now the value of the wave-lengths of 0*01 division of the 
 micrometer at the position of F is 0*02725 millionth of a 
 millimetre. 1 The total degradation of refrangibility observed 
 amounts to 0'109 millionth of a millimetre. If the velocity of 
 light be taken at 185,000 2 miles per second, and the wave-length 
 of F at 486'50 millionths of a millimetre (Angstrom's value is 
 486'52, Ditscheiner's 48649), the observed alteration in period 
 of the line in Sirius will indicate a motion of recession existing 
 between the earth and the star of 414 miles per second. 
 
 Of this motion a part is due to the earth's motion in space. 
 As the earth moves round the sun in the plane of the ecliptic, it 
 is changing the direction of its motion at every instant. There 
 are two positions, separated by 180, where the effect of the 
 earth's motion is a maximum ; namely, when it is moving in 
 the direction of the visual ray, either towards or from the star. 
 At two other positions in its orbit, at 90 from the former 
 positions, the earth's motion is at right angles to the direction 
 of the light from the star, and therefore has no influence on its 
 refrangibility. 
 
 The effect of the earth's motion will be greatest upon the light 
 of a star situated in the plane of the ecliptic, and will decrease 
 as the star's latitude increases, until, with respect to a star 
 
 1 The value in wave-lengths of the divisions of the micrometer for different 
 parts of the spectrum was determined by the aid of the tables of the wave- 
 lengths corresponding to every tenth line of Kirchhoff's map by Dr. Wolcott 
 Gibbs (Silliman's Journal, vol. xliii. January 1867). A paper on the same 
 subject by the Astronomer Eoyal, presented to the Royal Society, is not yet in 
 print. The Astronomer Royal's paper is contained in the Philosophical Trans- 
 actions for 1868, Part I. p. 29. The wave-lengths computed by him differ 
 slightly from those assigned to KirchhofFs numbers by Dr. Gibbs at the part of 
 the spectrum under consideration in the text. The difference is due in part to 
 the employment, by the Astronomer Royal, of Ditscheiner's later measures. 
 These give for F the higher value of 486'87. October 1868. 
 
 2 The new determination of the value of the solar parallax by observations of 
 Mars requires that the usually received velocity of light, 192,000 miles per second, 
 should be reduced by about the one twenty-seventh part. The velocity, when 
 diminished in this ratio, agrees nearly with the result obtained by Foucault from 
 direct experiment. 
 
APPEND. D.] PROPER MOTION OF SIRIUS. 397 
 
 situated at the pole of the ecliptic, the earth's motion during the 
 whole of its annual course will be perpendicular to the direction 
 of the light coming to us from it, and will be therefore without 
 influence on its period. 
 
 That part of the earth's resolved motion which is in the direc- 
 tion of the visual ray, and which has alone to be considered in 
 \ this investigation, may be obtained from the following formula : 
 
 Earth's motion towards star = v. cos \. sin (I I'), 
 
 where v is the earth's velocity, I the earth's longitude, I' the 
 star's longitude, and X the star's latitude. 
 
 At the time when the estimate of the amount of alteration of 
 period of the line in Sirius was made the earth was moving 
 from the star with a velocity of about twelve miles per second. 
 
 There remains unaccounted for a motion of recession from the 
 earth amounting to 2 9 '4 miles per second, which we appear to be 
 entitled to attribute to Sirius. 
 
 [ It may be not unnecessary to state that the solar motion in 
 
 space, if accepted as a fact, will not materially affect this result, 
 since, according to M. Otto Struve's calculations, the advance of 
 the sun in space takes place with a velocity but little greater 
 than one-fourth of the earth's motion in its orbit. If the apex 
 
 [ of the solar motion be situated in Hercules, nearly the whole of 
 
 it will be from Sirius, and will therefore diminish the velocity 
 to be ascribed to that star. 
 
 It is interesting, in connection with the motion of Sirius 
 deduced from these prismatic observations, to refer to the 
 remarkable inequalities which occur in the rather larger proper 
 motion of that star. In 1851 M. Peters 1 showed that the 
 variable part of the proper motion of Sirius in right ascension 
 
 [.' might be represented by supposing that Sirius revolves in an 
 
 elliptic orbit, round some centre of gravity without itself, in a 
 period of 50-093 years. This hypothesis has acquired new 
 interest, and seems indeed to have received confirmation from 
 direct observation by Alvan Clark's discovery of a small com- 
 panion to Sirius. 
 
 1 Astron. Nachrichten, No. 748. 
 
398 ' SPECTRUM ANALYSIS. [LECT. vi. 
 
 Professor Safford 1 and Dr. Auwers 2 have investigated the 
 periodical variations of the proper motion of Sirius in decli- 
 nation, and they have found that these variations, equally with 
 those in right ascension, would be reconcilable with an elliptic 
 orbital motion round a centre not in Sirius. The close coinci- 
 dence of the observed positions of the new satellite with those 
 required by theory seems to show that it may be the hypothetical 
 body suggested by Peters, though we must then suppose it to 
 have a much greater mass relatively to Sirius than that which 
 its light would indicate. 
 
 At the present time the proper motion of Sirius in declination 
 is less than its average amount by nearly the whole of that part 
 of it which is variable. May not this smaller apparent motion 
 be interpreted as showing that a part of the motion of the star 
 is now in tine direction of the visual rail ? This circumstance 
 is of much interest in connection with the result arrived at in 
 this paper. 
 
 Independently of the considerations connected with the vari- 
 able part of the star's proper motion, it must not be forgotten 
 that the whole of the motion which can be directly observed by 
 us is only that portion of its real motion which is at right angles 
 to the visual ray. Now it is precisely the other portion of it, 
 which we could scarcely hope to learn from ordinary observations, 
 which is revealed to us by prismatic investigations. By com- 
 bining the results of both methods of research we may perhaps 
 expect to obtain some knowledge of the real motions of the 
 brighter stars and nebulae. 
 
 It seems therefore desirable to compare with the result 
 obtained by the prism the motion of Sirius which corresponds 
 to its assumed constant proper motion. The values adopted by 
 Mr. Main, 3 and inserted by the Astronomer Koyal in the 
 Greenwich "Seven-year Catalogue," are - 0"'035 in RA. and 
 + l"-24 in N.P.D. 
 
 1 Proceedings of the American Academy, vol. vi. ; also Astron. Notices, Ann. 
 Arbor, No. 28 ; Monthly Notices, vol. xxii. p. 145. 
 
 2 Astron. Nachrichtfen, No. 1506 ; Monthly Notices, vol. xxii. p. 148, and 
 vol. xxv. p. 39. 
 
 3 Memoirs of the Royal Astronomical Society, vol. xix. 
 
APPEND. D.J SPECTRUM OF COMET II. 1868. 399 
 
 The parallax of Sirius from the observations of Henderson, 
 corrected by Bessel, = 0"150. A recent investigation by 
 Mr. C. Abbe 1 gives for the parallax the larger value of 0"'27. 
 If the radius of the earth's orbit be taken at its new value of 
 91,600,000 miles, the assumed annual constant proper motion 
 in N.P.D. of 1" ; 24 would indicate, with the parallax of 
 Henderson, a velocity of Sirius of twenty-four miles nearly per 
 second ; with the larger parallax of Mr. Abbe, a velocity of 43*2 
 miles per second. It may be that in the case of Sirius we have 
 two distinct motions ; one peculiar to the star, and a second 
 motion which it may share in common with a system of which 
 it may form a part. 
 
 Observations and comparisons, similar to those on Sirius, have 
 been made on a Canis Minoris, Castor, Betelgeux, Aldebaran, 
 and some other stars. I reserve for the present the results 
 which I have obtained, as I desire to submit these objects to a 
 re-examination. It is seldom that the air is sufficiently favourable 
 for the successful prosecution of this very difficult research. 
 
 V. Observations of Comet II. 1868. 
 
 On June 13 a comet was discovered by Dr. Winnecke, and 
 also independently the same night by M. Becquet, Assistant 
 Astronomer at the Observatory of Marseilles. 
 
 I was prevented by buildings existing near my observatory 
 from making observations of this comet before June 22. On 
 that evening the comet was much brighter than Brorsen's comet, 
 a description of the spectrum of which I recently presented to 
 the Eoyal Society, 2 and it gave a spectrum sufficiently distinct 
 for measurement and comparison with the spectra of terrestrial 
 substances. 
 
 Telescopic Appearance of the Comet. A representation of the 
 comet as it appeared on June 22 at 11 P.M. is given in Fig. 
 88, p. 346. The comet consisted of a nearly circular coma, 
 
 1 Monthly Notices of the Royal Astronomical Society, vol. xxviii. p. 2. 
 2 Proc. Roy. So.;, vol. xvi. p. 386. 
 
400 SPECTR UM ANALYSIS. [LECT. vi. 
 
 which became rather suddenly brighter towards the centre, 
 where there was a nearly round spot of light. The diameter 
 of the coma, including the exterior faint nebulosity, was about 
 6''20". The tail, which was traced for more than a degree, was 
 sharply defined on the following edge, but faded so gradually 
 away oh the opposite side that no limit could' be perceived. No 
 connection was traced between the tail and the brighter central 
 part of the coma. The circular form of the coma was uninterrupted 
 on the side of the tail, which appeared as an extension of the 
 faint nebulosity which formed the extreme margin of the coma. 
 
 The bright roundish spot of light in the centre, when exa- 
 mined with eyepieces magnifying from 200 to 600 diameters, 
 presented merely a nebulous light without a denned form. 
 
 Spectrum of the Comet. When a spectroscope furnished with 
 two prisms of 60 was applied to the telescope, the light of the 
 comet was resolved into three very broad bright bands, which 
 are represented in the diagram. (Fig. 87.) 
 
 In the two more refrangible of these bands the light was 
 brightest at the less refrangible end, and gradually diminished 
 towards the other limit of the bands. This gradation of light 
 was not uniform in the middle and brightest band, which 
 continued of nearly equal brilliancy for about one-third of its 
 breadth from the less refrangible end. This band appeared to 
 be commenced at its brightest side by a bright line. 
 
 The least refrangible of the three bands did not exhibit a 
 similar marked gradation of brightness. This band, though of 
 nearly uniform brilliancy throughout, was perhaps brightest 
 about the middle of its breadth. 
 
 These characters, which are peculiar to the light emitted by 
 the cometary matter, must be distinguished from some appear- 
 ances which the bands assumed in consequence of the mode of 
 distribution of the light in the coma of the comet. The two 
 more refrangible bands became narrower towards their most 
 refrangible side, as well as diminished in brightness. This 
 appearance was obviously not due to any dissimilarity of the 
 light in the parts of the coma, but to the circumstance that, as 
 the light of the coma became brighter towards the centre, it was 
 
APPEND. D.] SPECTRUM OF COMET II. 1868. 401 
 
 emitted by a smaller area of the cometary matter. The strong 
 light of the central spot could be traced the whole breadth of 
 the band ; but the light surrounding this spot, in proportion as 
 it became fainter and broader, was seen for a shorter distance, 
 so that the light from the faintest parts near the margin of the 
 coma was visible only at the brightest side of the band. Since 
 in the least refrangible band a similar gradation of light did 
 not take place, this band appeared of nearly the same width 
 throughout. 
 
 The increasing brightness of the coma up to the brilliant spot 
 in the centre showed itself in this band as a bright axial line 
 fading off gradually in both directions. 
 
 On this evening I took repeated measures of the positions of 
 these bands with the micrometer attached to the spectroscope. 
 These measures give the following numbers for the commence- 
 ment and termination of the three bands on the scale adopted in 
 the diagram : 
 
 First band j ' Second band ' Third band 
 
 I could not resolve the bands into lines. When the slit 
 was made narrower, the bands became smaller both in breadth 
 and length, from the invisibility of the fainter portions. I 
 suspected, however, the presence of two or three bright lines in 
 the bright central part of the middle band near its less refran- 
 gible limit. This part would consist chiefly of light from the 
 blight central spot. 
 
 As has been stated, the middle band commences probably witl, 
 a bright line ; for the limit of the band is here abrupt and dis- 
 tinct. On the contrary, the exact point of commencement and 
 termination of the other bands could not be observed with 
 certainty. 
 
 I could perceive no other bands, nor light of any kind beyond 
 the three bands, in the parts of the spectrum towards the red 
 and the violet. 
 
 When the marginal portions of the coma were brought upon 
 the slit, the three bands of light could still be traced. When, 
 however, the spectrum became very faint, it appeared to me to 
 
 D D 
 
402 SPECTR UM ANALYSIS. [LECT. vi. 
 
 become continuous ; but the light was then so very feeble, that 
 it could not be traced beyond the three bands towards the violet 
 or the red. 
 
 On this evening I observed the spectrum of the cornet in a 
 larger spectroscope, which gives a dispersion equal to about five 
 prisms. In this instrument the middle band was well seen. It 
 retained its nebulous, unresolved character, and the abrupt 
 commencement, as if by a bright line, already mentioned, was 
 distinctly seen. 
 
 .For convenience of comparison, the spectrum of Brorsen's 
 comet, and that of the gaseous nebulae, have been added to the 
 diagram, Fig. 87. The spectrum of Brorsen's comet consisted 
 of three bright bands and a faint continuous spectrum. These 
 bands appeared, as represented in the diagram, narrower than 
 those of the comet now under examination. It is not possible 
 to say to what extent this circumstance may be due to 
 the much feebler light of this comet. Though the bands of 
 Brorsen's comet fall within the limits of position occupied by 
 the broad bands of Comet II., they do not correspond to the 
 brightest parts of these bands. In the middle band I suspected 
 two bright lines which appeared shorter than the band, and may 
 be due to the nucleus. Brorsen's comet differed from the two 
 small comets which I had previously examined l in the much 
 smaller relative proportion of the light which forms a continuous 
 spectrum. In Brorsen's comet the bright middle part of the 
 coma seemed to emit light similar to that of the nucleus ; in the 
 other comets the coma appeared to give a continuous spectrum. 
 The three comets resembled each other in the circumstance 
 that the light of the central part was emitted by the cometary 
 matter, while the surrounding nebulosity reflected solar light. 
 
 It will be seen in the diagram that the bands of Brorsen's 
 comet and those of Comet II. occupy positions in the spectrum 
 widely removed from those in which the lines of the nebulae 
 occur. The spectra of gaseous nebulae consist of true lines, 
 which become narrow as the slit is made narrower. 
 
 1 Comet I. 1866, Proceedings, vol. xv. p. 5 ; and Comet 1867, Monthly Notices 
 of Royal Astronomical Society, vol. xxvii. p. 288. 
 
APPEND. D.] SPECTRA OF COMETS I. AND II. 403 
 
 The following day I carefully considered these observations 
 of the comet, with the hope of a possible identification of its 
 spectrum with that of some terrestrial substance. The spectrum 
 of the comet appeared to me to resemble some of the forms of 
 the spectrum of carbon which I had observed and carefully 
 measured in 1864. On comparing the spectrum of the comet 
 with the diagram of these spectra of carbon, I was much inter- 
 ested to perceive that the positions of the bands in the spectrum, 
 as well as their general characters and relative brightness, agreed 
 exactly with the spectrum of carbon when the spark is taken in 
 olefiant gas. 
 
 These observations on the spectrum of carbon were under- 
 taken in continuation of my researches " On the Spectra of the 
 Chemical Elements." 1 I have not presented them to the Royal 
 Society, as they are not so complete as I hope to make them. 
 
 Though the essential features of the spectrum of carbon 
 remained unchanged in all the experiments, certain modifications 
 were observed when the spectrum was obtained under different 
 conditions. One of those modifications, which was referred 
 to in my paper " On the Spectra of the Chemical Elements," 2 
 may be mentioned here. One of the strongest of the lines of 
 carbon is a line in the red a little less refrangible than the 
 hydrogen line, which corresponds to Fraunhofer's c. Now this 
 line is not seen when the carbon is subjected to the induction 
 spark in the presence of hydrogen. Two of the other modifica- 
 tions of the spectrum of carbon are given in Fig. 87. The first 
 spectrum represents the appearance of the spectrum of carbon 
 when the induction spark, with Leyden jars intercalated, was 
 taken between the points of wires of platinum sealed in glass 
 tubes, and placed almost in contact in olive-oil. In this spectrum 
 are seen the principal strong lines which distinguish carbon. The 
 shading of fine lines which accompanies the strong lines cannot 
 be accurately represented; on account of the small size of the 
 diagram. A spectrum essentially the same is produced when 
 the spark is taken in a current of cyanogen. It may be 
 mentioned that when the heating power of the spark was 
 
 1 Phil. Trans. 1864, p. 139. 2 ibid. p. 145. 
 
 D D 2 
 
404 SPECTRUM ANALYSIS. [LBCT. vi. 
 
 reduced below a certain limit, though the decomposition of the 
 oil still took place, the carbon was not volatilized, and the 
 spectrum was continuous. 
 
 The third spectrum in the diagram represents the modification 
 of this typical spectrum when the induction spark is taken in 
 a current of olefiant gas. The highly-heated vapour of carbon 
 emits light of the same refrangibilities as in the case of the 
 oil ; but the separate strong lines, with a similar power of 
 spark, were no longer to be distinguished. The shading, 
 when the carbon was obtained from the olefiant gas, was not 
 composed of numerous fine lines, but appeared as an unresolved 
 nebulous light. 
 
 Of course in all these experiments the lines of the other 
 elements present were also seen, but they were known, and 
 could therefore be disregarded. 
 
 In the case of the spark in olefiant gas, the three bands in the 
 diagram constitute the whole spectrum, with the exception of a 
 faint band in the more refrangible part of the spectrum. 
 
 It was with the spectrum of carbon, as thus obtained, that the 
 spectrum of the comet appeared to agree. It seemed, therefore, 
 to be of much importance that the spectrum of the spark in ole- 
 fiant gas should be compared directly in the spectroscope with 
 the spectrum of the comet. The comparison of the gas with the 
 comet was made the same evening, June 23. 
 
 My friend Dr. William Allen Miller visited the observatory 
 on this evening, and kindly took part in the following obser- 
 vations. 
 
 The general arrangements of the apparatus with which the 
 comparison was made is shown in the following diagram (Fig. 94). 
 A glass bottle converted into a gasholder, a, contained the 
 olefiant gas. This was connected by means of a flexible tube &, 
 into which were soldered two platinum wires. The part of the 
 tube in front of the points of the wires had been cut away, and 
 the surfaces carefully ground. A small plate of glass closed 
 the opening, being held in its place by a band of vulcanized 
 india-rubber. This tube was arranged in its proper position, 
 before the small mirror of the spectroscope c, by which the light 
 
APPEND. D.] CARBON IN COMETS. 495 
 
 of the spark was reflected into the instrument, and its spectrum 
 was seen immediately beneath the spectrum of the comet. The 
 spectroscope employed was furnished with two prisms of 60. 
 
 The brightest end of the middle band of the cometic spectrum 
 was seen to be coincident with the commencement of the corre- 
 
 FIG. 94. 
 
 sponding band in the spectrum of the spark. As this limit of 
 the band was well defined in both spectra, the coincidence could 
 be satisfactorily observed up to the power of the spectroscope, 
 and may be considered to be determined within about the dis- 
 tance which separates the components of the double line D. As 
 the limits of the other bands were less distinctly seen, the same 
 amount of certainty of exact coincidence could not be obtained. 
 We considered these bands to agree precisely in position with the 
 bands corresponding to them in the spectrum of the spark. 
 
 The apparent identity of the spectrum of the comet with that 
 of carbon rests not only on the coincidence of position in the 
 spectrum of the bands, but also upon the very remarkable 
 resemblance of the corresponding bands in their general cha- 
 racters, and their relative brightness. This is very noticeable 
 
406 SPECTRUM ANALYSIS. [LECT. vi. 
 
 in the middle band, where the gradation of brightness is not 
 uniform. This band in both spectra remained of nearly equal 
 brightness for the same proportion of its length. 
 
 On a subsequent evening, June 25, I repeated these com- 
 parisons, when the former observations were fully confirmed in 
 every particular. On this evening I compared the brightest 
 band with that of carbon in the larger spectroscope, which gives 
 a dispersion of about five prisms. 
 
 The remarkably close resemblance of the spectrum of the 
 comet to the spectrum of carbon necessarily suggests the 
 identity of the substances by which in both cases the light was 
 emitted. 
 
 It may be well to state that some phosphorescent and fluo- 
 rescent bodies give discontinuous spectra, in which the light 
 is restricted to certain ranges of refrangibility. There are, 
 however, several considerations which seem to oppose the idea 
 that the light of comets can be of a phosphorescent character. 
 Phosphorescent bodies are usually so highly reflective that the 
 phosphorescence emitted by them is not seen so long as they are 
 exposed to light. This comet was still in the full glare of the 
 sun, and yet the continuous spectrum corresponding to reflected 
 solar light was of extreme feebleness compared with the three 
 bright bands which we have under consideration. The pheno- 
 menon of phosphorescence seems to be restricted to bodies in 
 the solid state, a condition which is not apparently in accordance 
 with certain phenomena which have been observed in large 
 comets, such as the outflow of the matter of the nucleus and the 
 formation of successive envelopes. 
 
 There are, indeed, some phenomena of fluorescence, such as 
 that of a nearly transparent liquid becoming an object of some 
 brightness by means of the property which it possesses of ab- 
 sorbing the nearly invisible rays of the spectrum, and dispersing 
 them in a degraded and much more luminous form, which are 
 less obviously inconsistent with cometary phenomena than are 
 those of phosphorescence. 
 
 The violent commotions and internal changes which we witness 
 in comets when near the sun seem, however, to connect the great 
 
APPEND. D.] LUMINOSITY OF COMETS. 407 
 
 brightness which they then assume more closely with the part 
 of the solar force we call heat. There is also to he considered the 
 fact of the polarized condition of the light of the tail and some 
 parts of the comce of comets, which shows that a part of their 
 light is reflected. 
 
 The observations of the spectrum of Comet II. contained in 
 this paper, which show that its light was identical with that 
 emitted by highly-heated vapour of carbon, appear to be almost 
 decisive of the nature of cometary light. The great fixity of 
 carbon seems indeed to raise some difficulty in the way of 
 accepting the apparently obvious inference of these prismatic 
 observations. Some comets have approached the sun sufficiently 
 near to acquire a temperature high enough to convert even car- 
 bon into vapour. 1 Indeed for these comets a body of great fixity 
 seems to be necessary. In the case of comets which have been 
 submitted to a less fierce glare of solar heat, it may be suggested 
 that this supposed difficulty is one of degree only ; for we do not 
 know of any conditions under which even a gas, permanent at 
 the temperature of the earth, could maintain sufficient heat to 
 emit light, a state of things which appears to exist permanently 
 in the case of the gaseous nebulae. 
 
 If the substance of the comet be taken to be pure carbon, it 
 would appear probable that the nucleus had been condensed from 
 the gaseous state in which it existed at some former period. It 
 would therefore probably consist of carbon in a state of ex- 
 cessively minute division, In such a form it would be able to 
 take in nearly the whole of the sun's energy, and thus acquire 
 more speedily a temperature high enough for its conversion into 
 vapour. In the liquid or gaseous state, or in a continuous solid 
 state, this substance appears, from Dr. Tyndall's researches, to 
 be diathermanous. Still, under the most favourable of known 
 
 1 The comet of 1843 "approached the luminous surface of the sun within about 
 a seventh part of the sun's radius. The heat to which the comet was subjected 
 (a glare as strong as. that of 47,000 suns, such as we experience the warmth of) 
 surpassed that in the focus of Parker's great lens in the proportion of 24 to 1 
 without, or 34 to 1 with, the concentrating lens. Yet that lens so used melted 
 cornelian, agate, and rock-crystal." SIR JOHN HERSCHEL, Outlines of A stronomy, 
 7th edit. p. 401. 
 
408 SPECTRUM ANALYSIS. [LECT. vi. 
 
 conditions, the solar heat, to which the majority of comets are 
 subjected, would seem to be inadequate to the production of 
 luminous vapour of carbon. 
 
 It should be stated that olefiant gas when burnt in air may 
 give a similar spectrum of shaded bands. If the gas be ignited 
 at the orifice of the tube from which it issues, the flame is 
 brilliantly white, and gives a continuous spectrum. When a jet 
 of air is directed through the flame, it becomes less luminous, and 
 of a greenish-blue colour. The spectrum is now no longer con- 
 tinuous, but exhibits the bands distinctive of carbon. Under 
 these circumstances, for obvious reasons, the bright lines of the 
 hydrogen spectrum are not seen. In this way a spectrum re- 
 sembling that of the comet may be obtained, with the difference 
 that the fourth more refrangible band, which was not seen in the 
 cometic spectrum, is stronger relatively to the other bands than 
 is the case when the spark is taken in olefiant gas. If we were 
 to conceive the comet to consist of a compound of carbon and 
 hydrogen, we should diminish in some degree the necessity for 
 the excessively high temperature w^hich pure carbon appears 
 to require for its conversion into luminous vapour : but other 
 difficulties would arise in connection with the decomposition we 
 must then suppose to take place ; for we have no evidence, I 
 believe, that oletiant gas or any other known compound of carbon 
 can furnish this peculiar spectrum of shaded bands without 
 undergoing decomposition. If, indeed, it were allowable to 
 suppose a state of combustion, with oxygen or some other 
 element, set up by the solar heat, we should have an explanation 
 of a possible source of a degree of heat sufficient to render the 
 cometary matter luminous, and which the sun's heat would be 
 directly inadequate to produce. 
 
 There is one observation made by Bun sen which appears to 
 stand as an exception to the rule that only bodies in the gaseous 
 state give, when luminous, discontinuous spectra. Bunsen dis- 
 covered that solid erbia, when heated to incandescence, gives a 
 spectrum containing bright bands. It is therefore conceivable, 
 though all the evidence we possess from experience is opposed to 
 the supposition, that carbon might exist in some form in which it 
 
APPEND. D.] HUGGINS ON COMETS. 409 
 
 would possess a similar power of giving a discontinuous spec- 
 trum without volatilization. There is the further objection to 
 this hypothesis, that the telescopic phenomena observed in 
 comets appear to show that vaporization does usually take place. 
 However this may be, a state of gas appears to accord with 
 the very small power of reflection which the matfy 
 
 coma of this comet possessed, as was shown by the 
 
 T 
 ness of the continuous spectrum. 
 
 A remarkable circumstance connected with comets is tJt^e'/', 
 great transparency of the bright cometary matter. The mos^ . ^ 
 remarkable instance is that of Miss Mitchell's comet in 1847, 
 which passed centrally over a star of the fifth magnitude. " The 
 star's light appeared in no way enfeebled : yet such a star would 
 be completely obliterated by a moderate fog extending a few 
 yards from the surface of the earth." 1 We do not know what 
 amount of transparency is possessed by the vapour of carbon, 
 but the absence of a continuous spectrum seems to show that, as 
 it existed in the comet, it was almost perfectly transparent. The 
 light of a star would suffer, therefore, only that kind and degree 
 of absorption which corresponds with its power of radiation, as 
 shown by its spectrum of bright lines. As these occur in the 
 brightest part of the spectrum, we should expect a noticeable 
 diminution of the star's light, if it were not for the luminous 
 condition of the gas, in consequence of which it would give back 
 to the beam light of precisely the same refrangibilities as it had 
 taken, and so enable the part of the field occupied by the image 
 of the star to appear of its original brightness, or nearly so. 
 This state of things would not prevent an apparent diminution 
 of the star's light from the effect upon the eye of the brightness 
 of the surrounding field. In the case of the tails of comets, the 
 great transparency observed is more probably to be referred to 
 the widely-scattered condition of the minute particles of the 
 cometary matter. 
 
 I may be permitted to repeat here a paragraph from my paper 
 on the Spectrum of Comet I. 1866. 2 
 
 1 Outlines of Astronomy, p. 373. 
 
 2 Proc. Roy. Soc. vol. xv. p. 5. 
 
410 SPECTR UM ANALYSIS. [LECT. vi . 
 
 "Terrestrial phenomena would suggest that the parts of a 
 comet which are bright by reflecting the sun's light are probably 
 in the condition of fog or cloud. 
 
 "We know from observation, that the comae and tails of 
 comets are formed from the matter contained in the nucleus. 1 
 
 "The usual order of the phenomena which attend the for- 
 mation of a tail appears to be that, as the comet approaches the 
 sun, material is thrown off, at intervals, from the nucleus in the 
 direction towards the sun. This material is not at once driven 
 into the tail, but usually forms in front of the nucleus a dense 
 luminous cloud, into which for a time the bright matter of the 
 nucleus continues to stream. In this way a succession of 
 envelopes may be formed, the material of which afterwards is 
 dissipated in a direction opposite to the sun, and forms the tail. 
 Between these envelopes dark spaces are usually seen. 
 
 " If the matter of the nucleus is capable of forming by con- 
 densation a cloudlike mass, there must be an intermediate state 
 in which the matter ceases to be self-luminous, but yet retains 
 its gaseous state, and reflects but little light. Such a non- 
 luminous and transparent condition of the cometary matter may 
 possibly be represented by some at least of the dark spaces 
 which, in some comets, separate the cloudlike envelopes from 
 the nucleus and from each other." 
 
 Now considerable differences of colour have been remarked in 
 the different parts of some comets. The spectrum of this comet 
 would show that its colour was bluish-green. Sir W. Herschel 
 described the head of the comet of 1811 to be of a greenish or 
 
 1 The head of Halley's comet in 1835 in a telescope of great power " exhibited 
 the appearance of jets as it were of flamej or rather of luminous smoke, like a gas 
 fan-light. ' These varied from day to day, as if wavering "backwards and forwards, 
 as if they were thrown out of particular parts of the iuternalnucleus or kernel, 
 which shifted round, or to and fro, by their recoil, like a squib not held fast. The 
 bright smoke of these jets, however, never seemed to be able to get far out towards 
 the sun, but always to be driven back and forced into the tail, as if by the action 
 of a violent wind setting against them (always from the sun), so as to make it clear 
 that the tail is neither more nor less than the accumulation of this sort of luminous 
 vapour darted off, in the first instance towards the sun, as it were something raised 
 up and, as it were, exploded by the sun's heat out of the kernel, and then imme- 
 diately and forcibly turned back and repelled from the sun. " SIR JOHN HERSCHEL, 
 Familiar Lectures un Scientific Subjects, p. 115. 
 
APPEND. D.] HUGGINS ON COMETS. 41 1 
 
 bluish-green colour, while the central point appeared to be of a 
 pale ruddy tint. The representations of Halley's comet at its 
 appearance in 1835, by the elder Struve, are coloured bluish- 
 green, and the nucleus on October 9 is coloured reddish-yellow. 
 He describes the nucleus on that day thus : " Der Kern zeigte 
 sich wie eine Ideine, etwas ins Gelbliche spielende, gluhende 
 Kohle von liinglicher Form." l Dr. Winnecke describes similar 
 colours in the bright Comet of 1862: "Die Farbe des Strahls 
 erscheint mir gelbrothlich ; die des umgebenclen Nebels (viel- 
 leicht aus Contrast) mattblaulich." " Die Farbe der Ausstromung 
 erscheint mir gelblich ; die Coma hat blauliches Licht." 2 
 
 Now carbon, if incandescent in the solid state, or reflecting, 
 when in a condition of minute division, the light of the sun, 
 would afford a light which, in comparison with that emitted by 
 the luminous vapour of carbon, would appear as yellowish or 
 approaching to red. 
 
 The views of comets presented in this paper do not, however, 
 afford any clue to the great mystery which surrounds the 
 enormous rapidity with which the tail is often projected to 
 immense distances. There are not any known properties peculiar 
 to carbon, even when in a condition of extremely minute division, 
 which would help to a solution of the enigma of the violent 
 repulsive power from the sun which appears to be exerted upon 
 cometary matter shortly after its expulsion from the nucleus, 
 and upon matter in this condition only. It may be that this 
 apparent repulsion takes place at the time of the condensation 
 of the gaseous matter of the coma into the excessively minute 
 solid particles of which the tail probably consists. There is a 
 phenomenon occasionally seen which must not be passed without 
 notice, namely, -the formation of faint narrow rays of light, or 
 secondary tails, which start off usually from the brightest side of 
 the principal tail, not far from the head. Sir John Herschel 3 
 considers that " they clearly indicate an analysis of the cometic 
 
 1 Beobachtungen des Halleyschen Cometsn, S. 41. 
 
 2 Memoires de I' Academic Imperials des Sciences de St. Petersbourg, tome vii. 
 No. 7. 
 
 3 Familiar Lectures on Scientific Subjects, p. 129. 
 
412 SPECTRUM ANALYSIS. [LECT. vi. 
 
 matter by the sun's repulsive action, the matter of the secondary 
 tails being darted off' with incomparably greater velocity (indi- 
 cating an incomparably greater intensity of repulsive energy) 
 than that which went to form the primary one." The important 
 differences which exist between the spectrum of Brorsen's comet 
 and that of Comet II. 1868 appear to show that comets may 
 vary in their constitution. If the phenomena of the secondary 
 tails were observed in a comet which, like Comet II. 1868, 
 appears to consist of carbon, the analytical action supposed by 
 Sir John Herschel might be to separate between particles of 
 carbon in different conditions, or possibly in a state of more or 
 less subdivision. The enormous extent of space, sometimes a 
 hundred millions of miles in length, over which a comparatively 
 minute portion of cometary matter is in this way diffused, would 
 suggest that we have in this phenomenon a remarkable instance 
 of the extreme division of matter. Perhaps it would be too 
 bold a speculation to suggest that, under the circumstances 
 which attend the condensation of the gaseous matter into 
 discrete solid particles, the division may be pushed to its utmost 
 limit, or nearly so. If we could conceive the separate atoms to 
 ba removed beyond the sphere of their mutual attraction of 
 cohesion, it might be that they would be affected by the sun's 
 energy in a way altogether different from that of which we have 
 been hitherto the witnesses upon the earth. 
 
 Though comets may differ in their constitution, reference may 
 be permitted to the periodical meteors, which have been shown 
 to move in orbits identical with those of some comets. If these 
 consist of carbon, we might have some explanation of the 
 appearances presented by these meteors, though their light is 
 doubtless greatly modified by that of the air rendered luminous 
 by their passage, as well as by the degree of temperature to 
 *which they are raised. Carbon is abundantly present in some 
 meteorites, but we have no certain evidence at present that the 
 periodical meteors belong to this class of celestial bodies. 
 
APPEND. E.] NEBULA IN ORION. 
 
 APPENDIX E. 
 
 ON THE SPECTRUM OF THE CHEAT NEBULA IN ORION, AND ON 
 THE MOTIONS OF SOME STARS TOWARDS OR FROM THE EARTH. 1 
 
 BY WILLIAM HUGGLNS, LL.D., D.C.L., F.R.S. 
 
 In ray early observations of the spectrum presented by the 
 gaseous nebulae, the spectroscope with which I determined the 
 coincidence of two of the bright lines respectively with a line of 
 nitrogen and a line of hydrogen, wa of insufficient dispersive 
 power to show whether the brightest nebular line was double, as 
 is the case with the corresponding line of nitrogen. 
 
 Subsequently I took some pains to determine this important 
 point by using a spectroscope of greater dispersive power. I 
 found, however, that the light furnished by the telescope of eight 
 inches aperture, to which the spectroscope was attached, was too 
 feeble, even in the case of the brightest nebulae, to give the line 
 with sufficient distinctness when a narrow slit was used. The 
 results of this later examination are given in a paper I had 
 the honour of presenting to the Eoyal Society in 1868. I 
 there say : 2 
 
 " I expected that I might discover a duplicity in the line in 
 the nebula corresponding to the two component lines of the line 
 of nitrogen, but I was not able, after long and careful scrutiny, to 
 see the line double. The line in the nebula was narrower than 
 the double line of nitrogen ; this latter line may have appeared 
 broader in consequence of irradiation, as it was much brighter 
 than the line in the nebula." When the spark was placed before 
 the object-glass of the telescope, the light was so much weakened 
 that one line only was visible in the spectroscope. " This line 
 was the one which agrees in position with the line in the nebula, 
 so that under these circumstances the spectrum of nitrogen 
 
 1 Paper read before the Royal Society, June ]3, 1872. 
 2 Phil. Trans. 1868, pp. 542, 5-13. 
 
414 SPECTRUM ANALYSIS. [LECT. vi. 
 
 appeared precisely similar to the spectra of these nebulae, of 
 which the light is apparently monochromatic. This resemblance 
 was made more complete by the faintness of the line ; from 
 which cause it appeared narrower, and the separate existence of 
 its two components could no longer be detected. When the line 
 was observed simultaneously with that in the nebula, it was 
 found to appear but a very little broader than that line." I also 
 remark : " The double line in the nitrogen-spectrum does not 
 consist of sharply defined lines, but each component is nebulous, 
 and remains of a greater width than the image of the slit. 1 The 
 breadth of these lines appears to be connected with the conditions 
 of tension and temperature of the gas. Pliicker states that when 
 an induction spark of great heating power is employed, the 
 lines expand so as to unite and form an undivided band. Even 
 when the duplicity exists, the eye ceases to have the power to 
 distinguish the component lines, if the intensity of the light be 
 greatly diminished." I state further : " I incline to the belief 
 that it [the line in the nebula] is not double." 
 
 One of the first investigations which I proposed to myself 
 when, by the kindness of the Eoyal Society, I had at my com- 
 mand a much more powerful telescope, was the determination of 
 the true character of the bright line in the spectrum of the 
 nebula, which is apparently coincident with that of nitrogen. 
 From various circumstances, chiefly connected with the altera- 
 tions and adjustments of new instruments, I was not able 
 to accomplish this task satisfactorily until within the last 
 few months. 
 
 Description of Apparatus. 
 
 It seems to me desirable to give a description of the spectro- 
 scopic apparatus with which the observations in this paper were 
 made. In the former paper, to which I have already referred, I 
 gave some reasons 2 to show that the ordinary method of com- 
 parison, by reflecting light into the spectroscope by means of a 
 small prism placed before one half of the slit, is not satisfactory 
 
 1 Phil. Trans. 1863, p. 13. 
 
 2 Ibid., 1868, pp. 537, 538. 
 
APPEND. E.] ARRANGEMENT OF SPECTROSCOPE. 415 
 
 for very delicate observations unless certain precautions are 
 taken. I then describe an arrangement for this purpose, which, 
 with one or two modifications, is adopted in the collirnator con- 
 structed for use with the Koyal Society's telescope. I give the 
 description from that paper : l 
 
 " The following arrangement for admitting the light from the 
 spark appeared to me to be free from the objections which have 
 been referred to, and to be in all respects adapted to meet the 
 requirements of the case. In place of the small prism, two 
 pieces of silvered glass were securely fixed before the slit at an 
 angle of 45. In a direction at right angles to that of the slit 
 an opening of about ^ inch was left between the pieces of glass 
 for the passage of the pencils from the object-glass. By means 
 of this arrangement, the spectrum of a star is seen accompanied 
 by two spectra of comparison, one appearing above and the 
 other below it. As the reflecting surfaces are about 0'5 inch 
 from the slit, and the rays from the spark are divergent, the 
 light reflected from the pieces of glass will have encroached 
 upon the pencils from the object-glass by the time they reach 
 the slit, and the upper and lower spectra of comparison will 
 appear to overlap to a small extent the spectrum formed by the 
 light from the object-glass. This condition of things is of great 
 assistance to the eye in forming a judgment as to the absolute 
 coincidence or otherwise of lines. For the purpose of avoiding 
 some inconveniences which would arise from glass of the ordi- 
 nary thickness, pieces of the thin glass used for the covers of 
 microscopic objects were carefully selected, and these were 
 silvered by floating them upon the surface of a silvering 
 solution. In order to ensure that the induction-spark should 
 always preserve the same position relatively to the mirror, a 
 piece of sheet gutta-percha was fixed above the silvered glass ; 
 in the plate of gutta-percha, at the proper place, a small hole 
 was made of about ?V inch in diameter. The ebonite clamp con- 
 taining the electrodes is so fixed as to permit the point of separa- 
 tion of these to be adjusted exactly over the small hole in the 
 gutta-percha. The adjustment of the parts of the apparatus 
 
 i Phil. Trans. 1868, p. 538. 
 
416 SPECTRUM ANALYSIS. [LECT. vi. 
 
 was made by closing the end of the adapting-tube, by which the 
 apparatus is attached to the telescope, with a diaphragm with a 
 small central hole, before which a spirit-lamp was placed. 
 When the lines from the induction spark in the two spectra of 
 comparison were seen to overlap exactly for a short distance the 
 lines of sodium from the light of the lamp, the adjustment was 
 considered perfect. The accuracy of adjustment has been con- 
 firmed by the exact coincidence of the three lines of magnesium 
 with the component lines of I in the spectrum of the moon." 
 
 The modifications of this plan consist in the substitution of a 
 thin silver plate polished on both surfaces for the pieces of 
 silvered glass. The opposite side of the silver plate to that from 
 which the terrestrial light is reflected to the slit reflects the 
 images formed by the object-glass to the side of the tube, where 
 a suitable eyepiece is fixed. This arrangement forms a very 
 convenient finder, for it is easy to cause the image of the star to 
 disappear in the hole in the silver plate. When this is the case 
 the line of light formed by the star falls on the slit, and its 
 spectrum is visible in the spectroscope. This collimator is so 
 constructed that, by means of a coupling screw, any one of three 
 spectroscopes can be conveniently attached to it. 
 
 This apparatus performs admirably; but it seemed to me 
 desirable, for observations of great delicacy, to be able to dis- 
 pense with reflection, and to place the source of the light for 
 comparison directly before the slit. Formerly I accomplished 
 this object by placing the spark or vacuum-tube before the 
 object-glass of the telescope. The great length of the present 
 telescope renders this method inconvenient ; but a more impor- 
 tant objection arises from the great diminution of the light when 
 the spark is removed to a distance of 1 5 ft. from the slit. I there- 
 fore resolved to place the spa,rk or vacuum-tube within the tele- 
 scope at a moderate distance from the slit. For this purpose holes 
 were drilled in the tube opposite to each other, at a distance of 
 2 ft. 6 in. within the principal focus. Before these holes short 
 tubes were fixed with screws ; in these tubes slide suitable 
 holders for carrying electrodes or vacuum-tubes. The spark is 
 thus brought at once nearly into the axis of the telescope. The 
 
APPEND. E.J NEBULA IN ORION. 417 
 
 final adjustment is made in the following manner : A bright 
 star is brought into the centre of the field of an ordinary eye- 
 piece ; the eyepiece is then pushed within the focus, when the 
 wires or vacuum-tube can be seen across the circle of light 
 formed by the star out of focus. The place of discharge between 
 the electrodes or the middle of the capillary part of the vacuum- 
 tube is then brought into the centre of the circle of light. The 
 vacuum-tubes are covered with black paper, with the exception 
 of a space about J inch long in the middle of the capillary 
 part ; through this small uncovered space alone can the light 
 escape to reach the slit. 
 
 The accuracy of both methods of comparison, that by reflection 
 and that by the spark within the tube, was tested by the com- 
 parison of the three bright lines of magnesium and the double 
 line of sodium with the Fraunhofer lines b and D in the spectrum 
 of the moon. I greatly prefer the latter method, because it is 
 free from several delicate adjustments which are necessary when 
 the light is reflected, and which are liable to be accidentally 
 displaced. 
 
 Spectroscope A is furnished with a single prism of dense glass 
 with a refracting angle 59 42', giving 5 6' from A to H. 
 
 Spectroscope B has two compound prisms of Mr. Grubb's con- 
 struction, which move automatically to positions of minimum 
 deviation for the different parts of the spectrum. Each prism 
 gives about 9 6' for minimum deviation from A to H. 
 
 Spectroscope c is furnished with four similar prisms. 
 
 The small telescopes of the three spectroscopes are of the 
 same size. Diameter of object-glass 1 J inch ; each is furnished 
 with three eyepieces magnifying 5 '5, 9*2, and 16*0 diameters. 
 
 Spectrum of the Nebula of Orion. 
 
 With spectroscopes A and B four lines are seen. 1 
 First line. With spectroscope B and eyepiece 1 and 2, the 
 slit being made very narrow, this line was seen to be very 
 narrow, of a width corresponding to the slit, and defined at both 
 
 i The fourth line was first seen in nebula 18 H. IV. (Phil. Trans. 1864, p. 441). 
 
 E E 
 
418 SPECTRUM ANALYSTS, [LKCT. vi. 
 
 edges, and undoubtedly not double. The line of nitrogen 
 when compared with it appeared double, and each component 
 nebulous, and broader than the line of the nebula. This latter 
 line was seen on several nights to be apparently coincident with 
 the middle of the less refrangible line of the double line of 
 nitrogen. This observation was on one night confirmed by 
 observation with the more powerful spectroscope c. 
 
 The question suggests itself whether, under any conditions of 
 pressure and temperature, the double line of the nitrogen- 
 spectrum becomes single ; and further, if this should be found 
 to be the case, whether the line becomes single by the fading out 
 of its more refrangible component, or in what other way the 
 single line comes to occupy the position in the spectrum, not of 
 the middle of the double line, but that of the less refrangible of 
 the lines. 
 
 I stated in my former paper that when for any reason the 
 light from the luminous nitrogen is greatly reduced in intensity, 
 the double line under consideration is the last to disappear, and 
 consequently a state of things may be found in which the light 
 of nitrogen is sensibly monochromatic when examined with a 
 narrow slit. 1 Under these circumstances the line of nitrogen 
 appears narrower, and the separate components can be detected 
 with difficulty, if at all. 
 
 I stated also that the breadth of the component lines appears 
 to be connected with the conditions of density and temperature 
 of the gas. As was to be expected from theoretical considera- 
 tions, the lines become narrower and less nebulous as the 
 pressure is diminished. My observations of this change seemed 
 to show that the diminution of the breadth of the lines takes 
 place chiefly at the outer sides of the lines, so that in the light 
 from very rarefied gas the double line is narrower, but the space 
 of separation between the components is not as much wider as 
 would be the case if the lines had equally decreased in width on 
 the sides towards each other. 
 
 3 Phil. Trans. 1868, pp. 540-546. Observations on this point were subse- 
 quently made by Frankland and Lockyer (Proc. Boy. Soc. vol. xvii. p. 453). It 
 should be stated that they make no reference to my observations, though they 
 refer to a purely hypothetical suggestion contained in the same paper. 
 
APPEND. E.j NEBULA IN ORION. 
 
 419 
 
 When the pressure of the gas is reduced to about 15 inches of 
 mercury, the line spectrum fades out to give place to Pliicker's 
 spectrum of the first order. During this process a state of 
 things occurs when, for reasons already stated, the spectrum 
 becomes sensibly monochromatic when viewed with a narrow 
 slit and a spectroscope of several prisms. The line is narrower, 
 and remains double, and has the characters described in the 
 preceding paragraph. 
 
 As the pressure is diminished, the double line fades out 
 entirely, and the spectrum of the second order gives place to the 
 spectrum of the first order. When, however, the pressure 
 becomes exceedingly small, from 01 inch to O'Oo inch, or less, of 
 mercury, there is a condition of the discharge in which the line 
 again appears, while the other lines remain very faint. Under 
 these conditions I have always been able, though with some 
 difficulty on account of the faint light when the necessary dis- 
 persive power (spectroscope B with second or third eyepiece) 
 and a narrow slit are used, to see the line to be double, but it is 
 narrower than when the gas is more dense, and may be easily 
 mistaken for a single line. I have not yet been able to find a 
 condition of luminous nitrogen in which the line has the same 
 characters as those presented by the line in the nebula, where it 
 is single and of the width of the slit. 
 
 Upon the whole I am still inclined to regard the line in the 
 nebula as probably due to nitrogen. 
 
 If this should be found to be the case, and that the nebular 
 line has originally the refrangibility of the middle of the double 
 line of nitrogen, then we should have evidence that the nebula 
 is moving from the earth. The amount of displacement of the 
 nebular line from the middle of the nitrogen double line corre- 
 sponds to a velocity of 55 miles per second from the earth. At 
 the time of observation the part of the earth's orbital motion, 
 which was from the nebula, was 14'9 miles per second. From 
 the remaining 40 miles per second would have to be deducted 
 the probable motion from the nebula due to the motion of the 
 solar system in space. This estimation of the possible motion of 
 the nebula can be regarded as only approximate. 
 
 E E 2 
 
420 SPECTRUM. ANALYSIS. [LEUT. vi. 
 
 If the want of accordance of the line in the nebula with the 
 middle of the double line of nitrogen be due to a recession of 
 the nebula in the line of sight, there should be a corresponding 
 displacement of the third line as compared with that of hydrogen. 
 For reasons which will be found in a subsequent paragraph, I 
 have not been able to make this comparison with the necessary 
 accuracy. 
 
 In my former paper 1 I gave reasons against supposing so large 
 a motion in the nebula ; these were based on the circumstance 
 that the nebular line falls upon the double nitrogen line, which 
 the present observations confirm. I was not then able to use a 
 slit sufficiently narrow to show that the nebular line is single and 
 not coincident with the middle of the double line of nitrogen. 
 
 I am still pursuing the investigation of the parts of this 
 inquiry which remain unsettled. 
 
 Second line. This line was found by my former comparison to 
 be a little less refrangible than a strong line in the spectrum of 
 barium. Three sets of measures give for this line a wave-length 
 of 4,957 on Angstrom's scale; this would show that the line 
 agrees nearly in position with a strong line of iron. At present 
 
 I am not able to suggest to what substance this line belongs. 
 This ]ine is also narrow and defined. I suspect that the 
 
 brightness of this line relatively to the first line varies in diffe- 
 rent nebulae. 
 
 Third and fourth lines. My former observations show that 
 these lines agree in position with two lines of the spectrum of 
 hydrogen, that at r and the line near G. 
 
 These lines are very narrow, and are defined ; the hydrogen, 
 therefore, must be at a low tension. 
 
 The brightness of these lines relatively to the first and second 
 lines varies considerably in different nebulae ; and I suspect they 
 may also vary in the same nebulas at different times, and even 
 in different parts of the same nebula, but at present I have not 
 sufficient evidence on these points. 2 I regret that, in conse- 
 
 1 Phil. Trans. 1868, pp. 542, 543. 
 
 2 Since writing this sentence I have seen a note by Prof. D'Arrest in the 
 
 II Astronomische Nachrichten," No. 1,885. Speaking of the nebula H. IV. 37. 
 
APPEND. E.] ON THE MOTIONS OF THE STARS. 421 
 
 quence of a continuance of bad weather, I have not yet been 
 able to obtain decisive observations as to the possible motion of 
 the nebula in the line of sight. With spectroscope B and eye- 
 piece 2, the lines appear to be coincident with those of hydrogen. 
 In consequence of the uncertainty of the character of the first 
 line, which is single, while that of nitrogen is double, this deter- 
 mination can now only be made by means of the comparison of 
 the third line with that of hydrogen. This third line becomes 
 very faint from great loss of light unavoidable in a spectro- 
 scope that gives a sufficient dispersive power, and the comparison 
 can only be attempted when the sky is very clear and the nebula 
 near the meridian. 
 
 On the Motions of some Stars towards or from the Earth. 
 
 In the early part of 1868 I had the honour of presenting to 
 the Eoyal Society some observations on a small change of re- 
 frangibility which I had observed in a line in the spectrum of 
 Sirius as compared with a line of hydrogen, from which it 
 appeared that the star was moving from the earth with a velocity 
 of about twenty-five miles per second, if the probable advance 
 of the sun in space be taken into account. 1 
 
 he says : "Seiii Spectrum 1st ausser von Huggins bisliev nur noch von Dr. H, 
 Vogel untersucht worden. In No. 1,864, Astron. Nadir, theilt Letzterer niit, 
 trotz er im Jahre 1871, im Widerspruch mit Huggins' Angabe, die Linie Neb. 
 (3) = (2), bisweilen sogar (2)<(3) gefunden haben. Audi Huggins war dagegen 
 im Jahre 1864 positiv (2) >(3). 1st Vogel's Beobachtuug, wie ichnicht bezweifle, 
 zuverlassig, so wird seine Vermuthung einer Verandening hier in der That be- 
 griindet sein, denn diesen "Winter, namentlich im Februar und Marz 1872, fand 
 ich wiederum, so wie es Huggins friiher gesehen hat, unzsveifelhaft (2) >(3). Die 
 relative Intensitat der drei Liehtarten habe ich mehrfach in Zahlen geschatzt und 
 erhielt, z. B. in den letzten Nachten : 
 
 Marz 6. Marz 13. 
 
 (1) 100 100 
 
 (2) 58 63 
 
 (3) 49 52 
 
 1 Phil. Trans. 1868, pp. 529-550. Asa curious instance in which later methods 
 of observations have been partially anticipated, a reference may be made to an 
 ingenious paper in the Philosophical Transactions for 1783, vol. Ixxiv., by the 
 Bev. John Mitchell, entitled "On the means of discovering the Distance, 
 Magnitude, &c., of the Fixed Stars, in consequence of the Diminution of the 
 
422 SPECTRUM ANALYSIS. [LECT. vi. 
 
 It is only within the last few months that I have found myself 
 in possession of the necessary instrumental means to resume 
 this inquiry, and since this time the prevalence of bad weather 
 has left but few nights sufficiently fine for these delicate 
 observations. 
 
 Some time was occupied in obtaining a perfectly trustworthy 
 method of comparison of the spectra of stars with those of 
 terrestrial substances, and it was not until I had arranged the 
 spark within the tube, as described at the beginning of this note, 
 that I felt confidence in the results of my observations. 
 
 It may be well to state some circumstances connected with 
 these comparisons which necessarily make the numerical estima- 
 tions given further on less accurate than I could wish. Even when 
 spectroscope c, containing four compound prisms, and a magni- 
 fying power of 16 diameters, are used, the amount of the change 
 of refrangibility to be observed appears very small. The probable 
 error of these estimations is therefore large, as a shift corre- 
 sponding to five miles per second (about TO of the distance of 
 D 1 to D 2 ), or even a somew r hat greater velocity, could not be 
 certainly observed. The difficulty arising from the apparent 
 smallness of the change of refrangibility is greatly increased by 
 some other circumstances. The star's light is faint when a 
 narrow slit is used, and the lines, except on very fine nights, 
 cannot be steadily seen, in consequence of the movements in our 
 atmosphere. Further, when the slit is narrow, the clock's motion 
 is not uniform enough to keep the spectrum steadily in view ; 
 for these reasons I found it necessary to adopt the method of 
 estimation by comparing the shift with a wire of known thick- 
 ness, or with the interval between a pair of close lines. I found 
 that, under the circumstances, the use of a micrometer would 
 
 Velocity of their Light." The author suggests that by the use of a prism "''we 
 might be able to discover diminutions in the velocity of light, as perhaps a 
 hundredth, a two hundredth, a five hundredth, or even a thousandth part of 
 the whole." But he then goes on to reason on the production of this diminished 
 velocity by the attraction produced on the material particles of light by the 
 matter of the stars, and that the diminutions stated above would be "occasioned 
 by spheres whose diameter should be to the sun, provided they were of the same 
 density, in the several proportions of 70, 50, 30, and 22 to 1 respectively." 
 
APPEND. E.] MOTION OF BETELGEUX. 403 
 
 have given the appearance only of greater accuracy. I wish it 
 therefore to be understood that I regard the following estimations 
 as provisional, as I hope, by means of apparatus now being 
 constructed, to be able to get more accurate determinations of 
 the velocity of the motions. 
 
 Sirius. The comparison of the line at F with the correspond- 
 ing line of hydrogen was made on several nights from January 
 18 to March 5. Spectroscope c and eyepieces 2 and 3 were 
 used. These observations confirm the conclusion arrived at in 
 my former paper, that the star is moving from the earth ; but 
 they ascribe to the star a velocity smaller than that which I then 
 obtained. 
 
 These observations on different days show a change of refran- 
 gibility corresponding to a velocity of from twenty-six miles to 
 thirty-six miles per second. The part of the earth's orbital 
 motion from the star varied on these days from ten miles to 
 fourteen miles per second. We may take, therefore, eighteen to 
 twenty-two miles per second as due to the star. 
 
 The difference of this estimate, which is probably below rather 
 than in excess of the true amount, from that which I formerly 
 made may be due in part or entirely to the less perfect instru- 
 ments then at my command. At the same time, if Sirius be 
 moving in an elliptic orbit, as suggested by Dr. Peters, that part 
 of the star's proper motion which is then in the direction of the 
 visual ray, would constantly vary. 1 
 
 Betdgeux (a Orionis). In the early observations of Dr. Miller 
 and myself on this star, we found that there are no strong lines 
 coincident with the hydrogen lines at C and F. The line H a 
 falls on the less refrangible side of a group of strong lines, and 
 
 1 H, Vogel at Bothkamp seems to have repeated my observations on Sirius with 
 the necessary care. He says (Astron. Nachr. No. 1,864): "Mit der eben be- 
 schriebenen Anordnung gelang es Herrn Dr. Lohse uud mir am 22 Marz (1871) bci 
 ganz vorziiglicher Luft die Nichtcoincidenz der drei Wasserstominieu H a, H ft, 
 und H 7, der Geissler'schen Rohre mit den entsprechenden Linien des Sirius- 
 spectrums zu sehen . . . mit Beriicksichtigung der Geschwindigkeit der 
 Erde zur Zeit der Beobachtung berechnet sich die Geschwindigkeit mit welcher 
 sich Sirius voii der Erde bewegt zu 10 '0 Meilen in der Secunde, wogegen Procyon 
 sich 13 '8 Meilen in der Secunde von unserer Erde eutfernen wiirde. 
 
424 SPECTRUM ANALYSIS. [LECT. vi. 
 
 H /3 occurs in the space between two groups of strong lines, 
 where the lines are faint. On one night of unusual steadiness in 
 the air, when the finer lines in the star's spectrum were seen 
 with more than ordinary distinctness, I was able with the more 
 powerful instruments now at my command to see a narrow 
 denned line in the red apparently coincident with H a, and a 
 similar line at the position of H ft. These lines are much less 
 intense than the lines c and F in the solar spectrum ; there are 
 certainly no bright lines in the star's spectrum at these places. 
 
 The most suitable lines in this star for comparison with terres- 
 trial substances for ascertaining the star's motion are the lines of 
 sodium and of magnesium. The double character of the one 
 line agreeing exactly with that of sodium, and the further cir- 
 cumstance that the more refrangible of the lines is the stronger 
 one, as is the case in the sodium spectrum and in the solar spec- 
 trum, and the relative distances from each other and comparative 
 brightness of the three lines, which correspond precisely to the 
 triple group of magnesium, can allow of no doubt that these lines 
 in the star are really produced by the vapours of these substances 
 existing there, and that we may therefore safely take any small 
 displacement of either set of lines to show a motion of the star 
 towards or from the earth. The lines due to sodium are perhaps 
 more intense, but are as narrow and defined as the lines D p D 2 in 
 the solar spectrum ; they fall, however, within a group of very fine 
 lines ; this circumstance may possibly account for the nebulous 
 character which has been assigned to them by some observers. 
 
 The bright lines of sodium were compared with spectroscope 
 B and eyepiece 3 ; they appeared to fall very slightly above the 
 pair in the star, showing that the stellar lines had been degraded 
 by the star's motion from the earth. The amount of displace- 
 ment was estimated at about one-fifth of the distance of D : from 
 D 2 , which is probably rather smaller than the true amount. This 
 estimation would give a velocity of separation of thirty-seven 
 miles per second. At the time of observation the earth was 
 moving from the star at about fifteen miles per second, leaving 
 twenty-two miles to be due to the star. 
 
 When magnesium was compared, a shift in the same direction, 
 
APPEND. E.] PROPER MOTIONS OF THE STARS. 425 
 
 and corresponding in extent to about the same velocity of re- 
 cession, was observed ; but in consequence of other lines in the 
 star at this place, the former estimation, based on the displacement 
 of the lines of sodium, was considered to be more satisfactory. 
 
 Rig el The lines of hydrogen are strong in the spectrum of 
 this star, and are suitable for comparison. 
 
 The line of H ^ is not so broad as it appears in the spectrum 
 of Sirius, but is stronger than F in the solar spectrum: this 
 line was compared by means of spectroscope c and eyepieces 2 
 and 3. The line of terrestrial hydrogen falls above the middle 
 of the line in the star ; the star is therefore receding from the 
 earth. The velocity of recession may be estimated as rather 
 smaller than Sirius, probably about thirty miles per second, the 
 earth at the time of observation moving from the star with a 
 velocity of fifteen miles, leaving about fifteen miles as due to the 
 star. This estimate is probably rather smaller than the true 
 velocity of the star. 
 
 Castor. The spectra of the two component stars of this double 
 star blend in the spectroscope into one spectrum. The line H ft is 
 rather broad, nearly as much so as the same line in the spectrum 
 of Sirius. 
 
 The narrow line of rarefied hydrogen was compared in spectro- 
 scope B with eyepiece 3 ; it appeared to fall on the more re- 
 frangible side of the middle of the line in the star, leaving more 
 of the dark line on the side towards the red. The shift seemed 
 to be rather greater than that in Sirius, and may probably be 
 taken at from forty to forty-five miles per second ; but the 
 earth's orbital motion was nearly seventeen from the star, thus 
 leaving about twenty-five miles for the apparent velocity of the 
 star. This result rests at present on observations on one night 
 only, but they seemed at the time to be satisfactory. 
 
 Eegulus. The line at F rather broad. The corresponding line 
 of hydrogen falls on the more refrangible side of the middle of 
 the dark line in the star. The air was unfavourable on all the 
 evenings of comparison ; a rough estimate gives a velocity of 
 from twelve to seventeen miles for the velocity of recession 
 between the star and the sun. 
 
426 SPECTRUM ANALYSIS. [LECT. vi. 
 
 /3 and 8 Leonis. These stars were compared with hydrogen ; 
 they appear to be moving from the earth, but want of steadiness 
 in the air prevented me from making a satisfactory estimate of 
 their velocity. I suspected their motion to be smaller than that 
 of Eegulus. 
 
 /3, 7, S, e, f Ursce Majoris. All these stars have similar spectra, 
 in which the line F is strong, though there are small differences 
 in the breadth of the line. They were compared with hydrogen, 
 and appear to be moving from our system with about the same 
 velocity. Probably their motion may be taken to be not far 
 from thirty miles per second. The earth's motion at the time 
 of observation was from nine to thirteen miles for these stars, 
 leaving a probable velocity of recession of seventeen to twenty 
 miles per second. In the case of the double star the spectrum 
 consisted of the light of both stars. 
 
 it] Ursce Majoris was also compared with hydrogen. I believe 
 it shows a motion from the earth, but the observations of this 
 star are at present less satisfactory. 
 
 a Virginis and a Coronce Borealis. These stars were coin- 
 pared with hydrogen. I suspect that they are receding, but I 
 have not had nights sufficiently fine to enable me to make satis- 
 factory observations of these stars. 
 
 In addition to these stars some observations (which are less 
 satisfactory on account of the unfavourable state of the weather 
 at the time) appear to show that the stars Procyori, Capella, and 
 possibly Aldebaran, are moving from the earth. 
 
 The stars which follow have a motion of approach. 
 
 Arcturus. In the spectrum of this star the lines of hydrogen, 
 of magnesium, and of sodium are sufficiently distinct for com- 
 parison. I found the comparison could be most satisfactorily 
 made with magnesium. 
 
 The bright lines of magnesium fall on the less refrangible side 
 of the corresponding dark lines in the star's spectrum, showing 
 that the star is approaching the earth. I estimated the shift at 
 about ~ to | of the interval between Mg 2 and Mg 3 ; this amount 
 of displacement would indicate a velocity of approach of fifty 
 miles per second. To this velocity must be added the earth's 
 
APPEND. E.] MOTION OF POLLUX. 427 
 
 orbital motion from the star of 5'25 miles per second, increasing 
 the star's motion to fifty-five miles per second. 
 
 When I can get favourable weather, I hope to obtain inde- 
 pendent estimations from the lines of sodium and of hydrogen. 
 
 a Lyrce. In the spectrum of Vega the line corresponding to 
 H/3 is strong and broad. Comparisons were made on several 
 nights, but on one evening only was the air favourable. The 
 observations are accordant in showing that the narrow bright 
 line from a Geissler's tube falls on the less refrangible side of the 
 middle of the line in the star, thus leaving more of the line on 
 the side towards the violet. The estimations give a motion of 
 approach between the earth and the star of from forty to fifty 
 miles per second, to which must be added 3*9 miles after the 
 earth's motion from the star. 
 
 a Gygni. The hydrogen line at F in the spectrum of this star 
 is narrower than in the spectrum of Sirius and of a Lyrse, though 
 probably rather broader than the same line in the solar spectrum. 
 I have at present observations made on two evenings only on 
 both of which the state of the air was unfavourable of the com- 
 parison of this line with that of terrestrial hydrogen. They give 
 to the star a motion of approach of about thirty miles per second, 
 which would have to be increased by nine miles, the velocity at 
 the time of the earth from the star. 
 
 Pollux. The lines of magnesium and those of sodium are very 
 distinct in the spectrum of this star. As the air was not very 
 steady at the time of my observations, I found it more satis- 
 factory to use for comparison the lines of magnesium, which are 
 rather stronger than those of sodium. The three lines of magne- 
 sium appeared to be less refrangible than the corresponding dark 
 lines in the spectrum of the star by about one-sixth of the 
 interval from Mg 2 Mg 3 . This estimation would represent a 
 velocity of approach equal to about thirty-two miles per second. 
 The earth's motion from the star was 17'5 miles, which increases 
 the apparent velocity of approach to forty-nine miles per second. 
 On one evening only was the air favourable enough for a numerical 
 estimate, but the observations were entered in my observatory- 
 book as satisfactory. 
 
428 SPECTRUM ANALYSIS. [LECT. vi. 
 
 a Ursce Majoris. This spectrum of the star is different 
 from the spectra of the other bright stars of this constellation. 
 The line at F is not so strong, while the lines at 6 are more dis- 
 tinct, and are sufficiently strong for comparison with the bright 
 lines of magnesium. The bright lines of this metal fall on the 
 less refrangible side of the dark lines, and show a motion of 
 approach of from thirty-five to fifty miles per second. The earth's 
 motion of 11*8 miles from the star must be added. 
 
 7 Leonis and e Bootis. In both these double stars the com- 
 pared spectrum due to the light of both component stars was 
 observed. Both stars are most conveniently compared with 
 magnesium. I do not consider my observations of these stars 
 as quite satisfactory, but they seem to show a movement 
 of approach ; but further observations are desirable. 
 
 The stars 7 Cygni, a Pegasi, 7 Pegasi, and a Anclromedce were 
 compared with hydrogen on one night only. It is probable that 
 these stars are approaching the earth, but I wish to re-observe 
 them before any numerical estimate is given of their motion. 
 
 7 Cassiopeia?. On two nights I compared the bright lines 
 which are present in its spectrum at c and F with the bright 
 lines of terrestrial hydrogen. The coincidence appeared nearly 
 perfect in spectroscope c with eyepieces 2 and 3 ; but on the 
 night of least definition I suspected a minute displacement of 
 the bright line towards the red when compared with H (3. As 
 the earth's orbital motion from the star at the time w r as very 
 small, about 3 '2 5 miles per second, which corresponds to a shift 
 that could not be detected in the spectroscope, it seems probable 
 that 7 Cassiopoeiae has a small motion of recession. 
 
 In the calculation of the estimated velocities the wave-lengths 
 employed are those given by Angstrom in his " Eecherches sur le 
 Spectre solaire," Upsal, 1868. The velocity of light was taken 
 at 185,000 miles per second. 
 
 The velocities of approach and of recession which have been 
 assigned to the stars in this paper represent the whole of the 
 motion in the line of sight which exists between them and the 
 sun. As we know that the sun is moving in space, a certain 
 part of these observed velocities must be due to the solar motion. 
 
APPEND. E.] PROPER MOTION OF THE STARS. 429 
 
 I have not attempted to make this correction, because, though 
 the direction of the sun's motion seems to be satisfactorily ascer- 
 tained, any estimate that can be made at present of the actual 
 velocity with which he is advancing must rest upon suppositions, 
 more or less arbitrary, of the average distance of stars of different 
 magnitudes. It seems not improbable that this part of the stars' 
 motions may be larger than would result from Otto Struve's 
 calculations, which give, on the supposition that the average 
 parallax of a star of the first magnitude is equal to 0"'209, a 
 velocity but little greater than one-fourth of the earth's annual 
 motion in its orbit. 
 
 It will be observed that, speaking generally, the stars which 
 the spectroscope shows to be moving from the earth (Sirius, 
 Betelgeux, Eigel, Procyon) are situated in a part of the heavens 
 opposite to Hercules, towards which the sun is advancing ; while 
 the stars in the neighbourhood of this region, as Arcturus, Vega, 
 a Cygni, show a motion of approach. There are in the stars already 
 observed exceptions to this general statement ; and there are 
 some other considerations which appear to show that the sun's 
 motion in space is not the only, or even in all cases, as it may be 
 found, the chief cause of the observed proper motions of the stars. 1 
 
 There can be little doubt but that in the observed stellar 
 movements we have to do with two other independent motions, 
 namely, a movement common to certain groups of stars, and also 
 a motion peculiar to each star. 
 
 Mr. Proctor has brought to light strong evidence in favour of 
 the drift of stars in groups having a community of motion, by his 
 graphical investigation of the proper motions of all the stars in 
 the catalogues of Mr. Main and Mr. Stone. 2 The probability of 
 the stars being collected into such systems was early suggested 
 
 1 As the velocities assigned to the stars are, for the reasons already stated, pro- 
 visional only, I feel some hesitation in drawing from them the obvious conclu- 
 sions which they would suggest. The velocities given in the Tables for those 
 stars which are moving in direction in accordance with the sun's motion towards 
 Hercules, do not bear to each other the relation which they should have if they 
 were mainly produced by the sun's motion. Even for these stars, therefore, we 
 must look elsewhere for the cause to which they are chiefly due. 
 
 2 See " Preliminary Paper on certain Drifting Motions of Stars," Proc. Roy. 
 Soc. vol. xviii. p. 169. 
 
430 
 
 SPECTRUM ANALYSIS. 
 
 LECT. VI. 
 
 by Mitchell and the elder Herschel. 1 One of the most remark- 
 able instances pointed out by Mr. Procter are the stars /:?, 7, S, e 
 of the Great Bear, which have a community of proper motions, 2 
 while a and TJ of the same constellation have a proper motion in 
 the opposite direction. Now, the spectroscopic observations show 
 that the stars /3, 7, S, e, f have also a common motion of reces- 
 sion while the star a is approaching the earth. The star rj 
 indeed appears to be moving from us, but it is too far from 
 a to be regarded as a companion to that star. 
 
 TABLE I. STARS MOVING FROM THE SUN. 
 
 Star. 
 
 Compared with 
 
 Apparent 
 motion. 
 
 Earth's motion. 
 
 Motion from 
 sun. 
 
 Sirius .... 
 
 H 
 
 26 to 36 
 
 -10 to 14 
 
 18 to 22 
 
 Betelgeux . . . 
 
 Na 
 
 37 
 
 -15 
 
 22 
 
 Rigel .... 
 
 H 
 
 30 
 
 -15 
 
 15 
 
 Castor .... 
 
 H 
 
 40 to 45 
 
 -17 
 
 23 to 28 
 
 Regulus .... 
 
 H 
 
 30 to 35 
 
 -18 
 
 12 to 17 
 
 )8 Ursse Maj. . . 
 
 H ) 
 
 
 
 
 7 
 
 H 
 
 
 
 
 5 ,, ,, . . . 
 
 K[ 
 
 30 
 
 - 9 to 13 
 
 17 to 21 
 
 < ,, ,, 
 
 H| 
 
 
 
 
 r - . . 
 
 HJ 
 
 
 
 
 ft Leonis . . . 
 
 H 
 
 
 
 
 5 ... 
 
 H 
 
 
 
 
 fl Ursse Maj. . . 
 
 H 
 
 
 
 
 a Virginis . 
 
 H 
 
 
 
 
 a Coronse B. . 
 
 H 
 
 
 
 
 Procyon . . . 
 
 H 
 
 
 
 
 Capella .... 
 Aldebaran ? 
 
 H 
 Mg 
 
 
 
 
 7 Cassiopeise . 
 
 H 
 
 
 
 
 1 Sir William Herschel writes: "Mr. Mitchell's admirable idea of the stars 
 being collected into systems appears to be extremely well founded, and is every 
 day more confirmed by observations, though this does not take away the proba- 
 bility of many stars being still as it were solitary, or, if I may use the expression, 
 intersystematical. ... A star, or sun such as ours, may have a proper 
 motion within its own system of stars ; while at the same time the whole starry 
 system to which it belongs may have another proper motion totally different in 
 quantity and direction." Herschel further says, "And should there be found in 
 any particular part of the heavens a concurrence of proper motions of quite 
 a different direction, we shall then begin to form some conjectures which stars 
 may possibly belong to ours and which to other systems.'* Phil. Trans. 1783. 
 pp. 276, 277. 
 
 2 Mr. Procter, speaking of these stars, says : "Their drift is, I think, most 
 significant. If, in truth, the parallelism and equality of motion are to be regarded 
 
APPEND. E.] PROPER MOTIOtf OF THE STARS. 
 
 431 
 
 TABLE II. STARS APPROACHING THE SUN. 
 
 Star. 
 
 Compared with 
 
 Apparent 
 motion. 
 
 Earth's motion. 
 
 Motion 
 towards sun. 
 
 Arctums 
 
 Mg 
 
 50 
 
 + 5 
 
 55 
 
 Vega . 
 
 H 
 
 40 to 50 
 
 + 39 
 
 44 to 54 
 
 a Cygni . 
 
 H 
 
 30 
 
 + 9 
 
 39 
 
 Pollux . 
 
 Mg 
 
 32 
 
 + 17 
 
 49 
 
 a Ursa? Ma] 
 
 Mg 
 
 35 to 50 
 
 + 11 
 
 46 to 60 
 
 7 Leonis 
 
 Mg 
 
 
 
 
 e Bootis 
 
 Mg 
 
 
 
 
 7 Cygni . 
 
 H 
 
 
 
 
 a Pegasi. 
 
 H 
 
 
 
 
 7 ? 
 
 H 
 
 
 
 
 a Andromeda} 
 
 H 
 
 
 
 
 Although it was not to be expected that a concurrence would 
 always be found between the proper motions which indicate the 
 apparent motions at right angles to the line of sight and the 
 radial motions as discovered by the spectroscope, still it is in- 
 teresting to remark that in the case of the stars Castor and Pollux, 
 one of which is approaching and the other receding, their proper 
 motions also are different in direction and in amount ; and further, 
 that 7 Leonis, which has an opposite radial motion to a and ft of 
 the same constellation, differs from these stars in the direction 
 of its proper motion. 
 
 It scarcely needs remark that the difference in breadth of the 
 line H /3 in different stars affords us information of the difference 
 of density of the gas by which the lines of absorption are pro- 
 duced. A discussion of the observations in reference to this 
 point and to other considerations on the physical condition of 
 the stars and nebulse, I prefer to reserve for the present. 
 
 as accidental, the coincidence is one of most remarkable character. But such an 
 interpretation can hardly be looked upon as admissible when we remember that 
 the peculiarity is only one of a series of instances, some of which are scarcely 
 less striking." 0th er Worlds than Ours, p. 269: and paper in Proc. Roy. 
 Soc. vol. xviii. p. 170. 
 
432 SPECTRUM ANALYSIS. [LECT. vi. 
 
 APPENDIX F. 
 
 PRELIMINARY NOTE OF RESEARCHES ON GASEOUS SPECTRA IN 
 RELATION TO THE PHYSICAL CONSTITUTION OF THE SUN. 1 
 
 BY E. FRANKLAND, F.R.S., AND J. NORMAN LOCKYER. 
 
 With reference to the orange line of the chromosphere, we 
 have failed to detect any line in the hydrogen spectrum in the 
 place indicated, i.e. near the line D. With regard to the thickening 
 of the F line, we may remark that we have convinced ourselves 
 that this widening out is due to pressure, and not appreciably, if 
 at all, to temperature per se. 
 
 Having determined that the phenomena presented by the F 
 line were phenomena depending on and indicating varying pres- 
 sures, we were in a position to determine the atmospheric pressure 
 operating in a prominence in which the red and green lines are 
 nearly of equal width, and in the chromosphere, through which 
 the green line gradually expands as the sun is approached. 
 With regard to the higher prominences, we have ample evidence 
 that the gaseous medium of which they are composed exists in 
 a condition of excessive tenuity, and that at the lower surface 
 of the chromosphere itself the pressure is very far below the 
 pressure of the earth's atmosphere 
 
 We believe that the determination of the above-mentioned 
 facts leads us necessarily to several important modifications of 
 the received theory of the physical condition of our central 
 luminary. According to KirchhofFs theory the photosphere 
 itself is either solid or liquid, and is surrounded by an atmo- 
 sphere composed of gases and the vapours of the substances 
 incandescent in the photosphere. We find, however, instead of 
 this compound atmosphere, one which gives us nearly, or at all 
 events mainly, the spectrum of hydrogen; and the tenuity of 
 this incandescent atmosphere is such that it is extremely im-, 
 probable that any considerable atmosphere such as the corona 
 
 1 Proc. Roy. Soc. Feb. 11, 1869. 
 
APPEND. F.] LOCKYER'S SOLAR RESEARCHES. 433 
 
 has been imagined to indicate, lies outside it : with regard to 
 the photosphere itself, so far from being either a solid surface or 
 a liquid ocean, that it is cloudy or gaseous follows both from our 
 observations and experiments. 
 
 1. The gaseous condition of the photosphere is quite con- 
 sistent with its continuous spectrum. 
 
 2. The spectrum of the photosphere contains bright lines 
 when the limb is observed, indicating probably an outer shell 
 of gaseous matter. 
 
 3. The sun-spot is a region of greater absorption. 
 
 4. Occasionally photospheric matter appears to be injected 
 into the chromosphere. 
 
 May not these facts indicate that the absorption to which the 
 reversal of the spectrum and Fraunhofer's lines is due takes 
 place in the photosphere itself, or extremely near to it, instead 
 of in an extensive outer absorbing atmosphere ? 
 
 ADDENDUM: LOCKYER'S SPECTEOSCOPIC OBSERVATIONS ON THE 
 
 SUN. 1 
 
 Since the date on which the foregoing paper was written I 
 have obtained additional evidence on the points referred to. I 
 beg theiefore to be permitted to make the following additions 
 to it. 
 
 The possibility of our being able to determine the velocity 
 of movements of uprush and downrush taking place in the 
 chromosphere depends upon the alterations of wave-length 
 observed. 
 
 It is clear, therefore, that a mere uprush or downrush at the 
 sun's limb will not affect the wave-length, but that if we have 
 at the limb cyclones, or backward and forward movements, the 
 wave-length will be altered ; so that we may have : 
 
 1. An alteration of wave-length near the centre of the . disc 
 caused by upward or downward movements. 
 
 2. An alteration of wave-length close to the limb, caused by 
 backward or forward movements 
 
 1 April 29, 1869. 
 F F 
 
434 SPECTR UM ANALYSIS. f LECT. vi. 
 
 On April 21st I was enabled to extend my former observa- 
 tions. The spot under observation was very near the limb, so 
 near that its spectrum and that of the chromosphere were both 
 visible in the field of view. 
 
 The spot-spectrum was very narrow, owing to the foreshort- 
 ening of the spot ; but the spectrum of the chromosphere showed 
 me that the whole adjacent limb was covered with prominences 
 of various heights all blended together. Further, the promi- 
 nences seemed fed, so to speak, from apparently the preceding 
 edge of the spot ; for both c, F, and the line near D, were magni- 
 ficently bright on the sun itself, the latter especially striking me 
 with its thickness and brilliancy. 
 
 In the prominences, c and F were observed to be strangely 
 gnarled, knotty, and irregular ; and I thought at once that some 
 "injection" must be taking place. I was not mistaken. On 
 turning to the magnesium lines, I saw them far above the spec- 
 trum of the limb, and unconnected with it. A portion of the 
 upper layer of the photosphere had in fact been lifted up beyond 
 the usual limits of the chromosphere, and was there floating 
 cloudlike. The vapour of sodium was also present in the chro- 
 mosphere, though not so high as the magnesium, or unconnected 
 with the spectrum of the limb : and, as I expected, with such a 
 tremendous uplifting force, I saw the iron lines (for the first 
 time) in the spectrum of the chromosphere. My observations 
 commenced at 7.30 A.M. ; by 8.30 there was comparative quiet; 
 at 9.30 the action had commenced afresh. There was now a 
 single prominence. 
 
 The changes in the F line are seen better than those 
 of any other line. On the 17th the following changes were 
 noted : 
 
 I. It often stopped short of one of the small spots, swelling 
 out prior to disappearance. 
 
 II. It was invisible in a facula between two small spots. 
 
 III. It was changed into a bright line, and widened out on loth 
 sides two or three times in the very small spots. 
 
 IV. Once I observed it to become bright near a spot, and to 
 expand over it on both sides 
 
APPEND, p.] LOCKYER'S SOLAR RESEARCHES. 435 
 
 I observed it in all gradations of darkness ; when the bright 
 and dark lines were alongside, the latter was always the least 
 refrangible. 
 
 RESEARCHES ON GASEOUS SPECTRA IN RELATION TO THE PHYSI- 
 CAL CONSTITUTION OF THE SUN, STARS, AND NEBULA. 
 
 BY E. FRANKLAND, F.R.S., AND J. N. LOCKYER. 1 
 
 I. The Fraunhofer line on the solar spectrum, named li by 
 'Angstrom, which is due to the absorption of hydrogen, is not 
 visible in the tubes we employ with low battery and Ley den jar 
 power: it may be looked upon therefore as an indication of 
 relatively high temperature. As the line in question has been 
 reversed by one of us in the spectrum of the chromosphere, it 
 follows that the chromosphere, when cool enough to absorb, is 
 still of a relatively high temperature. 
 
 II. Under certain conditions of temperature and pressure the 
 very complicated spectrum of hydrogen is reduced in our instru- 
 ment to one line in the green corresponding to F in the solar 
 spectrum. 
 
 III. The equally complicated spectrum of nitrogen is simi- 
 larly reducible to one bright line in the green, with traces of 
 other more refrangible faint lines. 
 
 By removing the tubes from the slit the combined spectra 
 (II. and III.) were reduced to two bright lines. 2 By reducing 
 the temperature all spectroscopic evidence of the nitrogen 
 vanished, arid by increasing it many new nitrogen lines made 
 their appearance ; the hydrogen lines always remaining visible. 
 
 These latter 'observations bear on the observations of the 
 nebulae, especially on the conclusions of Mr. Huggins. 
 
 1 Proc. Roy. Soc. xvii. p. 458 (June 10, 1869). 
 
 2 This observation had previously been made by Huggins [H.E.R.j. See 
 Appendix D. 
 
 F F 2 
 
436 SPECIE UM ANALYSIS. [LECT. VT. 
 
 RESEARCHES IN SPECTRUM ANALYSIS IN CONNECTION WITH THE 
 SPECTRUM OF THE SUN. No. 1. 
 
 BY J. N. LOCKYER, F.R.S. 1 
 
 (Abstract.) 
 
 The author, after referring to the researches in which he has 
 been engaged since January 1869, in conjunction with Dr. 
 Frankland, refers to the evidence obtained by them as to the 
 thickening and thinning of spectral lines by variations of pres- 
 sure, and to the disappearance of certain lines when the method 
 employed by them since 1869 is used. This method consists of 
 throwing an image of the light-source to be examined on to the 
 slit of the spectroscope. 
 
 It is pointed out that the phenomena observed are of the 
 same nature as those already described by Stokes, W. A. Miller, 
 Eobinson, and Thalen, but that the application of this method 
 enables them to be better studied, the metallic spectra being 
 clearly separated from that of the gaseous medium through 
 which the spark passes. Photographs of the spark, taken in 
 air between zinc and cadmium and zinc and tin, accompany the 
 paper, showing that when spectra of the vapours given off by 
 electrodes are studied in this manner, the vapours close to the 
 electrode give lines which disappear from the spectrum of the 
 vapour at a greater distance from the electrode, so that there 
 appear to be long and short lines in the spectrum. 
 
 The following elements have been mapped on this method : 
 Na, Li, Mg, Al, Mn, Co, Ni, Zn, Sr, Cd, Sn, Sb, Ba, and Pb, the 
 lines being laid down from Thalen's maps, and the various 
 characters and lengths of the lines shown. In some cases the 
 spectra of the metals, enclosed in tubes and subjected to a 
 continually decreasing pressure, have been observed. In all 
 these experiments the lines gradually disappear as the pressure 
 is reduced, the shortest lines disappearing first and the longest 
 lines remaining longest visible. 
 
 1 Proc. Roy. Soc. Dec. 12, 1872, vol. xxi. p. 83. 
 
APPEND. F.] LOCKYER'S SOLAR RESEARCHES. 437 
 
 Since it appeared that the purest and densest vapour alone 
 gave the greatest number of lines, it became of interest to 
 examine the spectra of compounds consisting of a metal com- 
 bined with a non-metallic element. Experiments with chlorides 
 are recorded. It was found in all cases that the difference 
 between the spectrum of the chloride and the spectrum of the 
 metal was that under the same spark-conditions all the short 
 lines were obliterated. Changing the spark-conditions, the final 
 result was that only the very longest lines in the spectrum 
 of the metallic vapour remained. It was observed that in the 
 case of elements with low atomic weights, combined with one 
 equivalent of chlorine, the numbers of lines which remain in 
 the chloride is large, 60 per cent., e.g. in the case of Li, and 
 40 per cent, in the case of Na, while in the case of elements 
 with greater atomic weights, combined with two equivalents of 
 chlorine, a much smaller number of lines remain 8 per cent, 
 in the case of Ba, and 3 per cent, in the case of Pb. The 
 application of these observations to the solar spectrum, to 
 elucidate which they were undertaken, is then given. 
 
 It is well known that all the known lines of the metallic 
 elements on the solar atmosphere are not reversed. Mr. Lockyer 
 states what Kirchhoff and Angstrom have written on this sub- 
 ject, and what substances, according to each, exist in the solar 
 atmosphere. He next announces the discovery that, with no 
 exception whatever, the lines which are reversed are the longest 
 lines. With this additional key he does not hesitate to add, on 
 the strength of a small number of lines reversed, zinc and 
 aluminium (and possibly strontium), to the last list of solar 
 elements given by Thalen, who rejected zinc from Kirchhoff 's 
 list, and agreed with him in rejecting aluminium. It need 
 scarcely be added that these lines are in each case the longest 
 lines in the spectrum of the metal. 
 
 The help which these determinations afford to the study 
 of the various cyclical changes in the solar spectra is then 
 referred to. 
 
438 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. vi. 
 
 APPENDIX G. 
 
 TABLES OF THE DARK LINES OF THE SOLAR SPECTRUM, SHOW- 
 ING THE COINCIDENCES WITH THE BRIGHT LINES OF THE 
 SPECTRA OF MANY METALS, AS GIVEN IN PROFESSOR KIRCH- 
 HOFF'S DRAWINGS.i 
 
 PLATE III. STRIP 1. 
 
 381.7 
 
 Ic 
 
 447.0 
 
 2a 
 
 483.3 
 
 U 
 
 509.9 
 
 26 
 
 565.0 
 
 2c 
 
 384.1 
 
 2c 
 
 448.4 
 
 16 
 
 484.1 
 
 2d 
 
 510.9 
 
 la 
 
 566.0 
 
 2c 
 
 385.9 
 
 2d 
 
 452.6 
 
 2c 
 
 485.1 
 
 3d 
 
 512.9 
 
 26 
 
 566.9 
 
 26 
 
 387.5 
 
 3d 
 
 453.0 
 
 16 
 
 486.2 
 
 6e 
 
 513.6 
 
 36 
 
 567.4 
 
 36 
 
 388.9 
 
 4d 
 
 454.4 
 
 16 
 
 486.8 
 
 2c 
 
 517.1 
 
 26 
 
 /56S.6 
 
 26 
 
 390.4 
 
 4e 
 
 460.0 
 
 Ic 
 
 from/488.2 
 
 1 
 
 519.3 
 
 26 
 
 V 
 
 1 
 
 392.1 
 
 5e 
 
 461.0 
 
 16 
 
 \488.8 
 
 5a 
 
 521.6 
 
 16 
 
 569.2 
 
 26 
 
 393.6 
 
 6e 
 
 462.2 
 
 26 
 
 489.6 
 
 6c 
 
 529.4 
 
 16 
 
 / 
 
 3c 
 
 395.0 
 
 6e 
 
 463.3 
 
 2a 
 
 /491.2 
 
 3e 
 
 530.4 
 
 Ic 
 
 \570.0 
 
 26 
 
 396.2 
 
 5e 
 
 466.0 
 
 16 
 
 \491.5 
 
 56 
 
 532.8 
 
 16 
 
 570.6 
 
 36 
 
 397.4 
 
 4:6 
 
 466.5 
 
 2c 
 
 491.9 
 
 4c 
 
 536.9 
 
 26 
 
 572.2 
 
 16 
 
 398.4 
 
 4-d 
 
 467.0 
 
 16 
 
 493.1 
 
 2c 
 
 537.3 
 
 16 
 
 572.9 
 
 3c 
 
 399.2 
 
 4o" 
 
 468.1 
 
 2e 
 
 494.1 
 
 36 
 
 540.6 
 
 36 
 
 573.6 
 
 16 
 
 399.8 
 
 4d 
 
 470.0 
 
 26 
 
 /495.4 
 
 le 
 
 541.1 
 
 2c 
 
 574.4 
 
 2d 
 
 400.4 
 
 3d 
 
 470.5 
 
 3c 
 
 \495.7 
 
 26 
 
 542.0 
 
 la 
 
 575.1 
 
 2d 
 
 401.9 
 
 }4c 
 
 470.9 
 
 26 
 
 497.2 
 
 16 
 
 543.6 
 
 46 
 
 576.6 
 
 3d 
 
 \402.4 
 
 4.09 8 
 
 } 3 
 4 
 
 7472.4 
 V472.7 
 
 2e 
 3c 
 
 497.5 
 498.4 
 
 2a 
 4c 
 
 544.6 
 547.0 
 
 3d 
 4c 
 
 578.1 
 579.6 
 
 3d 
 3e 
 
 t\j,<3 
 4.OQ o 
 
 5 
 
 /473.S 
 
 4d 
 
 499.0 
 
 56 
 
 547.9 
 
 26 
 
 581.1 
 
 3e 
 
 ^rV/cJ.^ 
 A(\K A 
 
 )6 
 
 ^ 
 
 1 
 
 499.9 
 
 5a- 
 
 549.6 
 
 3e 
 
 582.5 
 
 4e 
 
 4UO.U 
 
 \5 
 
 474.7 
 
 36 
 
 500.8 
 
 3a- 
 
 551.2 
 
 3c 
 
 583.8 
 
 4f 
 
 406.2 
 
 } 3 
 
 from (475.7 
 /476.4 
 
 2 
 16 
 
 /501.8 
 \502.0 
 
 2c 
 56 
 
 552.5 
 / 553.8 
 
 3c 
 Ic 
 
 585.0 
 586.2 
 
 3e 
 
 V406.8 
 
 >& 
 
 
 2 
 
 502.6 
 
 5c 
 
 \554.0 
 
 36 
 
 587.0 
 
 26 
 
 408.5 
 
 Id 
 
 477.0 
 
 56 
 
 503.8 
 
 60- 
 
 554.6 
 
 26 
 
 587.9 
 
 36 
 
 423.7 
 
 26 
 
 / 
 
 2 
 
 504.3 
 
 56 
 
 557.0 
 
 la 
 
 589.0 
 
 36 
 
 426.6 
 
 26 
 
 V 477.8 
 
 46 
 
 505.1 
 
 6c 
 
 557.7 
 
 26 
 
 589.4 
 
 36 
 
 433.8 
 
 2c 
 
 /479.1 
 
 2c 
 
 /506.2 
 
 26 
 
 558.1 
 
 16 
 
 589.9 
 
 36 
 
 437.0 
 
 26 
 
 V 
 
 1 
 
 \506.4 
 
 56 
 
 559.7 
 
 Ic 
 
 590.3 
 
 36 
 
 442.8 
 
 2d 
 
 /480.1 
 
 6c 
 
 /506.6 
 
 26 
 
 561.5 
 
 16 
 
 590.7 
 
 36 
 
 444.6 
 
 2c 
 
 V480.4 
 
 4a* 
 
 \507.4 
 
 5c 
 
 562.5 
 
 36 
 
 591.1 
 
 36 
 
 445.8 
 
 26 
 
 481.2 
 
 4c 
 
 508.2 
 
 36 
 
 563.0 
 
 2c 
 
 591.5 
 
 46 
 
 446.1 
 
 26 
 
 482.1 
 
 2d 
 
 509.1 
 
 36 
 
 564.1 
 
 4c 
 
 591.9 
 
 46 
 
 1 See Plates facing Lecture V. 
 
APPEND. Q.] KIRCHHOFF'S TABLES. 
 
 PLATE III. STRIP 1 (continued}. 
 
 439 
 
 592.3 
 
 36 
 
 602.8 
 
 la 1638.4 
 
 16 
 
 
 669.5 
 
 26 
 
 690.9 
 
 la 
 
 
 /592.7 
 
 6c 
 
 606.0 
 
 16 
 
 639.8 
 
 16 
 
 
 678.6 
 
 16 
 
 692.1 
 
 2a 
 
 
 V593.1 
 
 9 
 
 608.3 
 
 la 
 
 641.0 
 
 26 
 
 Co. 
 
 681.4 
 
 la 
 
 from / 693.4 
 
 1 
 
 
 595.0 
 
 la 
 
 612.4 
 
 16 
 
 645.3 
 
 16 
 
 
 682.8 
 
 16 
 
 (694.1 
 
 6e 
 
 
 596.6 
 
 la 
 
 613.4 
 
 la 
 
 648.1 
 
 16 
 
 
 683.1 
 
 2a 
 
 to V 694.1 
 
 1 
 
 Air. 
 
 597.4 
 
 16 
 
 623.4 
 
 16 
 
 654.3 
 
 26 
 
 
 685.3 
 
 16 
 
 698.1 
 
 2a 
 
 
 601.2 
 
 la 
 
 626.1 
 
 16 
 
 659.3 
 
 2a 
 
 
 689.8 
 
 26 
 
 700.0 
 
 2a 
 
 
 601.8 
 
 Ib 
 
 631.4 
 
 16 
 
 665.7 
 
 2a 
 
 
 
 
 
 
 
 PLATE III. STRIP 2. 
 
 690.9 
 
 la 
 
 
 729.0 
 
 26 
 
 Ca 
 
 798.1 
 
 3a 
 
 
 692.1 
 
 2a 
 
 
 731.7 
 
 56 
 
 Ca 
 
 798.5 
 
 4a 
 
 Fe, 
 
 fromx693.4 
 
 1 
 
 ) 
 
 734.0 
 
 Id 
 
 
 799.8 
 
 26 
 
 
 (694.1 
 
 6e 
 
 }Air 
 
 736.9 
 
 36 
 
 Ca 
 
 800.3 
 
 26 
 
 
 to V 694.8 
 
 I 
 
 } 
 
 740.9 
 
 56 
 
 Ca, Cd 
 
 801.2 
 
 la 
 
 
 698.1 
 
 2a 
 
 
 743.7 
 
 26 
 
 
 801.5 
 
 la 
 
 
 700.0 
 
 2a 
 
 
 744.3 
 
 46 
 
 
 802.7 
 
 16 
 
 
 701.1 
 
 26 
 
 
 748.1 
 
 46 
 
 
 803.5 
 
 2a 
 
 
 702.1 
 
 2a 
 
 
 748.7 
 
 36 
 
 
 805.8 
 
 16 
 
 
 702.6 
 
 16 
 
 
 750.1 
 
 la 
 
 
 807.4 
 
 26 
 
 
 705.5 
 
 2a 
 
 
 751.0 
 
 16 
 
 
 808.2 
 
 2c 
 
 
 705.9 
 
 2a 
 
 
 752.3 
 
 46 
 
 
 808.7 
 
 Ic 
 
 
 707.5 
 
 16 
 
 
 753.8 
 
 36 
 
 Sr 
 
 809.5 
 
 36 
 
 Au 
 
 708.6 
 
 26 
 
 
 756.9 
 
 56 
 
 Fe 
 
 809.9 
 
 2a- 
 
 
 710.5 
 
 2e 
 
 
 759.3 
 
 36 
 
 
 812.7 
 
 la 
 
 
 711.4 
 
 3c 
 
 
 764.2 
 
 la 
 
 
 813.1 
 
 2a 
 
 
 712.0 
 
 26 
 
 
 771.8 
 
 la 
 
 Zn 
 
 815.0 
 
 46 
 
 
 713.2 
 
 16 
 
 
 773.4 
 
 26 
 
 
 816.8 
 
 26 
 
 
 714.4 
 
 Ic 
 
 
 774.8 
 
 26 
 
 
 818.0 
 
 3c 
 
 
 717.8 
 
 26 
 
 Ca 
 
 778.3 
 
 16 
 
 (RuJr) 
 
 819.0 
 
 46 
 
 
 from/718.7 
 
 2 
 
 Ba 
 
 779.5 
 
 16 
 
 
 820.1 
 
 46 
 
 
 V719.6 
 
 3a 
 
 
 781.9 
 
 36 
 
 
 820.9 
 
 46 
 
 
 720.1 
 
 2e 
 
 Ca 
 
 783.1 
 
 46 
 
 
 823.5 
 
 la 
 
 
 721.1 
 
 26 
 
 Fe 
 
 783.8 
 
 36 
 
 
 824.0 
 
 46 
 
 
 823.7 
 
 2c 
 
 
 786.8 
 
 la 
 
 
 824.9 
 
 Id 
 
 
 724.2 
 
 16 
 
 
 788.9 
 
 36 
 
 
 826.4 
 
 2a 
 
 
 725.1 
 
 16 
 
 Air 
 
 791.0 
 
 Id 
 
 
 827.6 
 
 la 
 
 
 726.7 
 
 3c 
 
 
 791.4 
 
 36 
 
 
 828.0 
 
 2a 
 
 
 727.8 
 
 Id 
 
 
 792.9 
 
 2a- 
 
 
 830.2 
 
 36 
 
 
 728.0 
 
 2a 
 
 
 794.5 
 
 Id 
 
 
 831.0 
 
 4c 
 
 Fe 
 
440 
 
 SPECTRUM ANALYSIS. 
 PLATE TIL 'STRIP 2 (continued). 
 
 [LEOT. vi. 
 
 831.7 
 
 16 
 
 
 896.1 
 
 la 
 
 
 970.5 
 
 16 
 
 
 836.5 
 
 26 
 
 
 898.7 
 
 16 
 
 
 971.5 
 
 2c 
 
 
 838.2 
 
 16 
 
 
 898.9 
 
 la 
 
 
 972.1 
 
 16 
 
 
 838.6 
 
 26 
 
 
 899.1 
 
 la 
 
 
 973.1 
 
 3a 
 
 
 839.2 
 
 26 
 
 
 900.2 
 
 la 
 
 
 973.5 
 
 3a 
 
 
 845.7 
 
 26 
 
 
 901.4 
 
 la 
 
 
 974.3 
 
 2a 
 
 
 849.7 
 
 3c 
 
 Fe 
 
 901.6 
 
 la 
 
 
 975.0 
 
 2a 
 
 
 851.2 
 
 la 
 
 
 902.4 
 
 la 
 
 
 976.8 
 
 3a 
 
 
 851.8 
 
 la 
 
 
 903.1 
 
 la 
 
 
 977.4 
 
 2a 
 
 
 855.0 
 
 2a 
 
 
 903.6 
 
 la 
 
 
 977.7 
 
 2a 
 
 
 856.8 
 
 2a 
 
 
 904.6 
 
 la 
 
 
 979.1 
 
 16 
 
 
 857.5 
 
 2a 
 
 
 906.1 
 
 2c 
 
 
 980.8 
 
 la 
 
 
 858.3 
 
 2a 
 
 
 912.1 
 
 36 
 
 Fe 
 
 981.2 
 
 36 
 
 
 859.7 
 
 3a 
 
 
 916.3 
 
 26 
 
 
 982.0 
 
 la 
 
 
 860.2 
 
 3d 
 
 Ca 
 
 923.0 
 
 26 
 
 
 982.3 
 
 2a 
 
 
 861.6 
 
 2a 
 
 
 929.5 
 
 26 
 
 
 983.0 
 
 3c 
 
 
 862.2 
 
 la 
 
 
 931.3 
 
 46 
 
 Fe 
 
 984.5 
 
 Ic 
 
 
 863.2 
 
 2c 
 
 
 932.5 
 
 46 
 
 
 986.3 
 
 la 
 
 
 863.9 
 
 56 
 
 Ca 
 
 933.3 
 
 4c 
 
 
 986.7 
 
 2c 
 
 
 864.4 
 
 Id 
 
 
 935.1 
 
 46 
 
 
 987.4 
 
 16 
 
 
 866.2 
 
 26 
 
 
 936.7 
 
 46 
 
 
 988.9 
 
 2a 
 
 
 867.1 
 
 26 
 
 
 937.4 
 
 16 
 
 
 989.2 
 
 2a 
 
 
 867.6 
 
 la 
 
 
 940.1 
 
 36 
 
 
 989.6 
 
 2a 
 
 
 869.2 
 
 26 
 
 
 940.4 
 
 26 
 
 
 990.8 
 
 2a 
 
 
 870.9 
 
 16 
 
 
 943.4 
 
 36 
 
 
 991.2 
 
 la 
 
 
 871.4 
 
 26 
 
 
 946.6 
 
 36 
 
 
 991.9 
 
 36 
 
 Fe 
 
 872.5 
 
 16 
 
 
 947.0 
 
 la 
 
 
 992.4 
 
 la 
 
 
 874.0 
 
 16 
 
 
 949.4 
 
 16 
 
 
 993.9 
 
 16 
 
 
 874.3 
 
 46 
 
 Ba 
 
 949.8 
 
 16 
 
 
 994.3 
 
 16 
 
 
 876.5 
 
 4a 
 
 
 951.7 
 
 Ic 
 
 
 995.0 
 
 la 
 
 
 877.0 
 
 4c 
 
 Fe 
 
 952.9 
 
 36 
 
 
 997.2 
 
 26 
 
 
 879.8 
 
 16 
 
 
 954.3 
 
 36 
 
 
 998.1 
 
 la 
 
 
 880.9 
 
 la 
 
 
 954.8 
 
 36 
 
 
 998.9 
 
 la 
 
 
 881.6 
 
 2a 
 
 
 958,8 
 
 36 
 
 
 999.2 
 
 la 
 
 
 882.6 
 
 la 
 
 
 959.6 
 
 36 
 
 
 1000.0 
 
 la 
 
 
 883.2 
 
 16 
 
 
 961.9 
 
 la 
 
 
 1000.4 
 
 la 
 
 
 884.9 
 
 46 
 
 Ca, Co 
 
 963.7 
 
 Ic 
 
 
 1001.4 
 
 la 
 
 
 887.7 
 
 2a 
 
 Ni 
 
 964.4 
 
 Ic 
 
 
 1002.8 
 
 66 
 
 Na 
 
 890.2 
 
 16 
 
 Ba 
 
 968.7 
 
 2a 
 
 
 1005.0 
 
 26 
 
 Ni 
 
 891.7 
 
 2a 
 
 Ni 
 
 969.0 
 
 2a 
 
 
 1006.8 
 
 66 
 
 Na 
 
 894.9 
 
 2e 
 
 Ca, Li 
 
 969.6 
 
 3a 
 
 
 
 
 
AIVEND. G.] 
 
 KIRCHHOFF'S TABLES. 
 PLATE III. STRIP 3. 
 
 411 
 
 1000.0 
 
 la 
 
 
 1122.6 
 
 2a 
 
 
 1189.3 
 
 36 
 
 
 1000.4 
 
 la 
 
 
 1128.3 
 
 26 
 
 
 1190.1 
 
 26 
 
 
 1001.4 
 
 la 
 
 
 1130.9 
 
 26 
 
 
 1193.1 
 
 3a 
 
 
 1002.8 
 
 66 
 
 Na 
 
 1133.1 
 
 3c 
 
 
 1199.6 
 
 2d 
 
 
 1005.0 
 
 26 
 
 Ni 
 
 U33.9 
 
 3c 
 
 
 1200.6 
 
 46 
 
 Fe 
 
 1006.8 
 
 66 
 
 Na 
 
 1135.1 
 
 4d 
 
 
 1201.0 
 
 2a 
 
 
 1011.2 
 
 3a 
 
 
 1135.9 
 
 2c 
 
 
 1203.5 
 
 2c 
 
 
 1023.0 
 
 la 
 
 
 1137.0 
 
 26 
 
 
 1204.2 
 
 2c 
 
 
 1025.5 
 
 3a 
 
 
 1137.8 
 
 36 
 
 
 1204.9 
 
 2d 
 
 
 1027.7 
 
 2a 
 
 
 1141.3 
 
 2c 
 
 
 12061 
 
 Ic 
 
 
 1029.3 
 
 3c 
 
 Ca,Ni 
 
 1143.6 
 
 2c 
 
 
 1207.3 
 
 fy 
 
 Fe 
 
 1031.8 
 
 2a 
 
 Ba 
 
 1146.2 
 
 16 
 
 
 1217.8 
 
 5d 
 
 Fe,Ca 
 
 1032.8 
 
 la 
 
 
 1147.2 
 
 16 
 
 
 1219.2 
 
 3c 
 
 Ca 
 
 1035.3 
 
 la 
 
 
 1148.6 
 
 16 
 
 
 12201 
 
 2c 
 
 
 1058.0 
 
 26 
 
 
 1149.4 
 
 16 
 
 
 12216 
 
 5d 
 
 Ca 
 
 1063.0 
 
 26 
 
 
 1151.1 
 
 46 
 
 
 1224.7 
 
 5d 
 
 Ca 
 
 1065.0 
 
 26 
 
 
 1152.5 
 
 26 
 
 
 1225.3 
 
 16 
 
 
 1066.0 
 
 la 
 
 
 1154.2 
 
 26 
 
 
 , 1226.6 
 
 2d 
 
 
 1067.0 
 
 26 
 
 
 /1155.7 
 
 36 
 
 
 1228.3 
 
 2d 
 
 Ca 
 
 1070.5 
 
 26 
 
 
 U155.9 
 
 2c 
 
 
 1229.6 
 
 4c 
 
 Ca 
 
 1073.5 
 
 la 
 
 
 1158.3 
 
 2a 
 
 
 1230.5 
 
 2 
 
 
 1074.2 
 
 la 
 
 
 1160.9 
 
 2a 
 
 
 1231.3 
 
 5d 
 
 Fe 
 
 1075.5 
 
 3a 
 
 
 1165.2 
 
 la 
 
 
 1232.8 
 
 26 
 
 
 1077.5 
 
 la 
 
 
 1165.7 
 
 la 
 
 
 1235.0 
 
 3d 
 
 Ca 
 
 from 1078.9) 
 
 i 
 
 
 1167.0 
 
 Id 
 
 
 1237.8 
 
 2c 
 
 
 to 1079.7J 
 
 i 
 
 
 1168.3 
 
 la 
 
 
 1239.9 
 
 4a 
 
 Fe 
 
 1080.3 
 
 la 
 
 
 1169.4 
 
 la 
 
 
 1242.6 
 
 Qc 
 
 Fe 
 
 1080.9 
 
 la 
 
 
 1170.6 
 
 2c 
 
 
 1245.6 
 
 U 
 
 Fe 
 
 1081.8 
 
 26 
 
 Cu 
 
 1174.2 
 
 5d 
 
 
 1247.4 
 
 36 
 
 
 1083.0 
 
 2a 
 
 Ba 
 
 1175.0 
 
 2a 
 
 
 1248.6 
 
 3d 
 
 
 1087.5 
 
 2a 
 
 
 1176.6 
 
 3c 
 
 
 1250.4 
 
 3c 
 
 
 1089.6 
 
 2a 
 
 
 1177.0 
 
 2a 
 
 
 1251.1 
 
 26 
 
 
 1096.1 
 
 3c 
 
 Fe 
 
 1177.3 
 
 la 
 
 
 1253.3 
 
 26 
 
 
 10968 
 
 la 
 
 
 1177.6. 
 
 la 
 
 
 1255.2 
 
 26 
 
 
 10978 
 
 la 
 
 
 1178.6 
 
 la 
 
 
 1257.5 
 
 3c 
 
 
 11004 
 
 la 
 
 
 1179.0 
 
 la 
 
 
 1258.5 
 
 26 
 
 
 1102.1 
 
 36 
 
 
 1179.4 
 
 la 
 
 
 1264.4 
 
 la 
 
 
 1102.9 
 
 3a 
 
 
 11798 
 
 la 
 
 
 1264.9 
 
 2a 
 
 i 
 
 1103.3 
 
 26 
 
 
 1180.2 
 
 la 
 
 
 1267.3 
 
 3a 
 
 
 1104.1 
 
 26 
 
 
 1183.4 
 
 2a 
 
 
 1268.0 
 
 3a 
 
 
 1107.1 
 
 2c 
 
 
 1184.8 
 
 3a 
 
 
 1271.9 
 
 la 
 
 
 1111.4 
 
 la 
 
 
 1186.8 
 
 2a 
 
 
 1272.4 
 
 la 
 
 
 1119.0 
 
 2a 
 
 
 1187.1 
 
 2a 
 
 
 1274.2 
 
 36 
 
 Ba 
 
 
 
 
 
 
 
 
 
 
442 
 
 SPECTRUM ANALYSIS. 
 PLATE III. STRIP 3 (continued). 
 
 [LECT. vi. 
 
 1274.7 
 
 3a 
 
 Sr 
 
 1289.7 
 
 2c 
 
 
 1299.7 
 
 2c 
 
 
 1276.2 
 
 2a 
 
 
 1291.9 
 
 3c 
 
 
 1302.0 
 
 2c 
 
 
 1276.7 
 
 la 
 
 
 1293.8 
 
 3o 
 
 
 1303.5 
 
 5c 
 
 
 1280.0 
 
 Qd 
 
 
 1294.5 
 
 3c 
 
 
 1306.7 
 
 5c 
 
 
 1281.3 
 
 3c 
 
 
 1295.6 
 
 la 
 
 
 1315.0 
 
 4c 
 
 
 1282.6 
 
 2c 
 
 
 1296.3 
 
 2c 
 
 
 1315.7 
 
 26 
 
 
 1285.3 
 
 2c 
 
 
 1297.5 
 
 la 
 
 
 1319.0 
 
 3c 
 
 Co 
 
 1287.5 
 
 Ic 
 
 Ba 
 
 1298.9 
 
 5c 
 
 
 
 
 
 PLATE III. STRIP 4. 
 
 1315.0 
 
 4c 
 
 
 1372.6 
 
 56 
 
 Fe 
 
 1427.5 
 
 36 
 
 
 1315-7 
 
 26 
 
 
 1374.8 
 
 Ic 
 
 
 1428.2 
 
 56 
 
 Fe 
 
 1319.0 
 
 3c 
 
 Go 
 
 1375.8 
 
 2a 
 
 
 1430.1 
 
 56 
 
 
 1320.6 
 
 4c 
 
 Sr 
 
 1377.4 
 
 la 
 
 
 1431.2 
 
 16 
 
 
 1321.1 
 
 36 
 
 
 1379.0 
 
 la 
 
 
 1438.9 
 
 4c 
 
 Co 
 
 1323.3 
 
 26 
 
 
 1380.5 
 
 4c 
 
 Fe 
 
 1440.2 
 
 16 
 
 Co 
 
 1324.0 
 
 26 
 
 
 1384.7 
 
 4c 
 
 Fe 
 
 1443.1 
 
 26 
 
 
 1324.8 
 
 U 
 
 Ni 
 
 1385.7 
 
 56 
 
 Cr 
 
 1443.5 
 
 26 
 
 Ca 
 
 1325.3 
 
 2d 
 
 
 1386.3 
 
 26 
 
 
 1444.4 
 
 46 
 
 
 1327.7 
 
 46 
 
 
 1387.4 
 
 26 
 
 
 1446.7 
 
 4c 
 
 
 1328.7 
 
 26 
 
 
 1389.4 
 
 6c 
 
 Fe 
 
 1448.7 
 
 2a 
 
 Co 
 
 1330.4 
 
 36 
 
 
 1390.9 
 
 5d 
 
 Fe 
 
 1449.4 
 
 la 
 
 Co 
 
 1333.3 
 
 la 
 
 
 1394.2 
 
 4c 
 
 
 1450.8 
 
 5c 
 
 Fe 
 
 1334.0 
 
 46 
 
 
 1395.3 
 
 Ic 
 
 
 1451.8 
 
 56 
 
 Fe 
 
 1336.3 
 
 16 
 
 
 1396.4 
 
 2c 
 
 
 1453.7 
 
 la 
 
 
 1337.0 
 
 4d 
 
 Fe 
 
 1397.5 
 
 5c 
 
 Fe 
 
 1454.7 
 
 36 
 
 
 1337.8 
 
 16 
 
 
 1400.2 
 
 36 
 
 
 1456.6 
 
 la 
 
 
 1338.5 
 
 16 
 
 
 1401.6 
 
 4c 
 
 Fe 
 
 1458.6 
 
 3c 
 
 
 1343.5 
 
 6c 
 
 Fe 
 
 1403.1 
 
 3c 
 
 
 1461.5 
 
 2c 
 
 
 1351.1 
 
 5d 
 
 Fe 
 
 1404.1 
 
 16 
 
 
 1462.2 
 
 2c 
 
 
 1352.7 
 
 56 
 
 Fe 
 
 1405.2 
 
 36 
 
 
 1462.8 
 
 5c 
 
 Fe 
 
 1356.5 
 
 la 
 
 
 1410.5 
 
 4c 
 
 Fe 
 
 1463.3 
 
 5c 
 
 Fe 
 
 1360.9 
 
 la 
 
 
 1412.5 
 
 26 
 
 
 1464.8 
 
 la 
 
 
 1361.6 
 
 la 
 
 
 1414.0 
 
 26 
 
 
 1465.3 
 
 la 
 
 
 1362.9 
 
 56 
 
 Fe 
 
 1415.8 
 
 26 
 
 
 1466.8 
 
 5c 
 
 Fe 
 
 1364.3 
 
 la 
 
 
 1419.4 
 
 26 
 
 
 1468.8 
 
 26 
 
 
 1364.7 
 
 la 
 
 
 1421.5 
 
 6c 
 
 Fe 
 
 1469.6 
 
 16 
 
 
 1367.0 
 
 Qd 
 
 Fe 
 
 1423.0 
 
 56 
 
 Fe 
 
 1473.9 
 
 56 
 
 Fe 
 
 1371.4 
 
 16 
 
 Ba 
 
 1423.5 
 
 26 
 
 
 1475.3 
 
 la 
 
 
 1372.1 
 
 16 
 
 
 1425.4 
 
 56 
 
 Fe 
 
 1476.8 
 
 la 
 
 
APPEND. & .] KIR CHHOFF >S TABLES 
 
 PLATE III. STRIP 4 (continued). 
 
 443 
 
 1477.5 
 
 la 
 
 
 1527.7 
 
 5c 
 
 Fe, Co 
 
 1579.4 
 
 2a 
 
 
 1483.0 
 
 46 
 
 
 1528.7 
 
 5c 
 
 Ca 
 
 1580.1 
 
 2a 
 
 
 1487.7 
 
 56 
 
 Fe 
 
 1530.2 
 
 4c 
 
 
 1588.3 
 
 1.9 
 
 Cu 
 
 1489.2 
 
 2c 
 
 
 1531.2 
 
 4c 
 
 
 1589.1 
 
 36 
 
 
 1489.9 
 
 la 
 
 
 1532.5 
 
 46 
 
 Ca 
 
 1590.7 
 
 36 
 
 
 /1491.2 
 
 Ic 
 
 
 1533.1 
 
 46 
 
 Ca 
 
 1592.3 
 
 36 
 
 
 V1491.6 
 
 3c 
 
 
 /1541.4 
 
 1.9 
 
 
 1598.9 
 
 26 
 
 
 1492.4. 
 
 46 
 
 
 \1541.9 
 
 36 
 
 
 /1601.4 
 
 66 
 
 Cr 
 
 1493.1 
 
 46 
 
 
 1543.7 
 
 2a 
 
 
 V1601.7 
 
 3^ 
 
 
 1494.5 
 
 la 
 
 
 1545.5 
 
 2a 
 
 
 1604.4 
 
 56 
 
 Cr 
 
 1495.9 
 
 la 
 
 
 1547.2 
 
 3a 
 
 
 1606.4 
 
 56 
 
 Ct 
 
 1497.3 
 
 la 
 
 Cu 
 
 1547.7 
 
 2a 
 
 
 1609.2 
 
 56 
 
 
 1501.3 
 
 26 
 
 
 1551.0 
 
 2a 
 
 
 1611.3 
 
 Ic 
 
 
 1504.8 
 
 la 
 
 
 1551.6 
 
 2a 
 
 
 1613.9 
 
 36 
 
 
 1505.3 
 
 la 
 
 
 1555.6 
 
 2a 
 
 
 1615.6 
 
 26 
 
 
 1505.7 
 
 2a 
 
 
 1557.3 
 
 3a 
 
 
 1616.6 
 
 16 
 
 
 1506.3 
 
 5c 
 
 Fe 
 
 1561.0 
 
 la 
 
 
 1617.4 
 
 26 
 
 
 1508.6 
 
 56 
 
 Fe 
 
 1564.2 
 
 la 
 
 
 1618.2 
 
 36 
 
 
 1510.3 
 
 2c 
 
 Co 
 
 1566.5 
 
 26 
 
 Co 
 
 1618.9 
 
 46 
 
 
 1515.5 
 
 4d 
 
 
 1567.5 
 
 26 
 
 
 1621.5 
 
 16 
 
 
 1516.5 
 
 4c 
 
 
 1569.6 
 
 5c 
 
 Fe 
 
 1622.3 
 
 5c 
 
 Fe 
 
 1519.0 
 
 U 
 
 
 1573.5 
 
 5a 
 
 
 1623.4 
 
 56 
 
 Fe 
 
 1522.7 
 
 6c 
 
 Fe,Ca 
 
 1575.4 
 
 16 
 
 
 1627.2 
 
 56 
 
 Ca 
 
 1523.7 
 
 6c 
 
 Fe 
 
 (1577.2 
 
 5c 
 
 Fe 
 
 1628.2 
 
 16 
 
 
 1525.0 
 
 16 
 
 Co 
 
 V1577.6 
 
 3c 
 
 
 
 
 
 PLATE IV. STRIP 1. 
 
 1621.5 
 
 16 
 
 
 /1648.4 
 
 4, 
 
 
 1670.3 
 
 la 
 
 
 1622.3 
 
 
 Fe 
 
 V1648.8 
 
 6/ 
 
 Mg 
 
 1671.5 
 
 36 
 
 
 1623.4 
 
 56 
 
 Fe 
 
 /1649.2 
 
 
 
 1672.2 
 
 4a 
 
 Ni 
 
 1627.2 
 
 56 
 
 Ca 
 
 \1650.3 
 
 66 
 
 Fe 
 
 1673.7 
 
 4a 
 
 
 1628.2 
 
 16 
 
 
 1653.7 
 
 66 
 
 Fe Ni 
 
 1674.7 
 
 3c 
 
 Cu 
 
 /1631.5 
 \1633.5 
 
 16 
 
 
 1654.0 
 1655.6 
 
 4c 
 Qe 
 
 Fe^Mg 
 
 /1676.2 
 V1676.5 
 
 2d 
 46 
 
 
 /1634.1 
 V1634.7 
 1638.7 
 1642.1 
 
 4 
 16 
 16 
 
 Mg 
 
 1655.9 
 1657.1 
 / 1658.3 
 Uol659.4 
 
 56 
 26 
 1 
 
 
 1677.9 
 1681.6 
 1684.0 
 1684.4 
 
 16 
 
 Ni 
 
 1643.0 
 
 16 
 
 Ni 
 
 1662.8 
 
 56 
 
 Fe 
 
 1685.9 
 
 2a 
 
 
 1647.3 
 
 
 
 1667.4 
 
 3a 
 
 
 1686.3 
 
 2a 
 
 
444 
 
 SPECTRUM ANALYSIS. 
 PLATE IV. STRIP 1 (continued}. 
 
 [LECT. vi. 
 
 1639.5 
 
 5c 
 
 
 1784.4 
 
 16 
 
 
 1868.4 
 
 56 
 
 
 1690.0 
 
 56 
 
 m 
 
 1785.0 
 
 46 
 
 
 1869.5 
 
 Ic 
 
 ' Ni 
 
 1691.0 
 
 5b 
 
 
 1787.7 
 
 2c 
 
 
 1870.6 
 
 3a 
 
 
 1693.8 
 
 6e 
 
 Fe 
 
 1788.7 
 
 36. 
 
 
 1872.4 
 
 56 
 
 
 1696.5 
 
 3c 
 
 
 1793.8 
 
 46 
 
 
 1873.4 
 
 66 
 
 
 1697.0 
 
 3c 
 
 Ni 
 
 1795.4 
 
 la 
 
 
 1874.2 
 
 2a 
 
 
 1701.8 
 
 5c 
 
 Fe 
 
 1796.0 
 
 3a 
 
 
 1874.8 
 
 2a 
 
 -. 
 
 /1704.6 
 
 2c 
 
 
 1797.8 
 
 la 
 
 
 1875.8 
 
 2e 
 
 
 VI 704. 9 
 
 36 
 
 
 1799.0 
 
 4c 
 
 
 1876.5 
 
 66 
 
 
 /1707.6 
 
 2c 
 
 
 1799.6 
 
 36 
 
 
 1884.3 
 
 66 
 
 
 V.1707.9 
 
 36 
 
 
 1806.4 
 
 26 
 
 
 1885.8 
 
 66 
 
 
 1710.7 
 
 5a 
 
 
 1818.7 
 
 56 
 
 
 1886.4 
 
 66 
 
 
 1712.2 
 
 36 
 
 
 1821.4 
 
 56 
 
 
 1889.5 
 
 Iff 
 
 
 1713.4 
 
 56 
 
 
 1822.6 
 
 3a 
 
 
 1891.0 
 
 36 
 
 
 1715.2 
 
 46 
 
 
 1823.2 
 
 2 
 
 
 1892.5 
 
 56 
 
 
 1717.9 
 
 46 
 
 
 1823.6 
 
 2a 
 
 
 1893.8 
 
 16 
 
 
 1719.4 
 
 Ic 
 
 
 1828.6 
 
 16 
 
 
 1894.8 
 
 36 
 
 
 1726.9 
 
 la 
 
 
 1830.1 
 
 36 
 
 
 1896.2 
 
 46 
 
 
 1727.3 
 
 36 
 
 Ni 
 
 1832.8 
 
 2a 
 
 Ca 
 
 1897.9 
 
 Ic 
 
 
 1733.6 
 
 56 
 
 
 1833.4 
 
 6c 
 
 
 1900.0 
 
 Ic 
 
 
 1734.6 
 
 36 
 
 
 1834.3 
 
 6c 
 
 
 1904.5 
 
 46 
 
 
 1737.7 
 
 5d 
 
 
 1835.9 
 
 36 
 
 
 1905.1 
 
 2c 
 
 
 1741.0 
 
 46 
 
 Cu 
 
 1836.7 
 
 3c 
 
 
 1908.5 
 
 5d 
 
 
 1742.7 
 
 la 
 
 
 1837.5 
 
 3c 
 
 
 1911.9 
 
 3c 
 
 
 1743.1 
 
 la 
 
 
 1841.0 
 
 46 
 
 
 1916.2 
 
 Id 
 
 
 1744.6 
 
 2te 
 
 
 1841.6 
 
 46 
 
 
 1917.5 
 
 46 
 
 
 1748.9 
 
 3c 
 
 Ni 
 
 1842.2 
 
 46 
 
 Ni 
 
 1917.9 
 
 46 
 
 
 1749.6 
 
 2d 
 
 Ni 
 
 1848.9 
 
 2c 
 
 
 1919.8 
 
 46 
 
 
 1750.4 
 
 5c 
 
 
 1851.0 
 
 Ic 
 
 
 1920.2 
 
 46 
 
 
 1752.0 
 
 26 
 
 
 1853.2 
 
 36 
 
 
 1921.1 
 
 46 
 
 Ni 
 
 1752.8 
 
 4c 
 
 
 1854.0 
 
 26 
 
 
 1922.0 
 
 46 
 
 
 1762.0 
 
 3c 
 
 
 1854.9 
 
 4c 
 
 
 1922.4 
 
 46 
 
 
 1771.5 
 
 3c 
 
 
 1856.9 
 
 Ic 
 
 
 1923.5 
 
 46 
 
 
 1772.5 
 
 3c 
 
 
 1857.9 
 
 26 
 
 
 1925.8 
 
 46 
 
 Ni 
 
 1774.0 
 
 26 
 
 
 1860.4 
 
 26 
 
 
 1928.0 
 
 46 
 
 
 1775:8 
 
 36 
 
 Ni 
 
 1861.3 
 
 3c 
 
 
 1931.2 
 
 Ic 
 
 
 1776.5 
 
 3c 
 
 Ni 
 
 1862.3 
 
 26 
 
 
 1932.5 
 
 Ic 
 
 
 1777.5 
 
 3c 
 
 
 1864.9 
 
 36 
 
 
 1936.2 
 
 3c 
 
 
 1778.5 
 
 3e 
 
 
 1867.1 
 
 5d 
 
 Fe 
 
 1939.5 
 
 2c 
 
 
 1782.7 
 
 36 
 
 
 
 
 
 
 
 
APPEND. G.] 
 
 KIRCH HOFF'S TABLES. 
 PLATE IV. STRIP 2. 
 
 445 
 
 1931.2 
 
 Ic 
 
 
 2008.6 
 
 16 
 
 
 /2080.0 
 
 % 
 
 
 1932.5 
 
 Ic 
 
 
 2009.8 
 
 26 
 
 
 \2080.5 
 
 4e 
 
 
 1936.2 
 
 3c 
 
 
 2013.9 
 
 2a 
 
 
 2082,0 
 
 6a 
 
 Fe 
 
 1939.5 
 
 2c 
 
 
 2014.3 
 
 2a 
 
 
 2084.6 
 
 26 
 
 
 1940.6 
 
 2c 
 
 
 2015.7 to 16.9 
 
 1 
 
 
 2086.0 to 86.9 
 
 1 
 
 
 1941.5 
 
 36 
 
 
 /2017.7 
 
 26 
 
 
 2086.9 
 
 36 
 
 Ni 
 
 1943.5 
 
 2c 
 
 
 ( 
 
 1 
 
 
 2087.6 
 
 la 
 
 
 1944.5 
 
 36 
 
 
 2018.5 
 
 26 
 
 
 2089.7 
 
 la 
 
 
 1947.6 
 
 4c 
 
 
 2019.5 
 
 2a 
 
 
 2090.9 
 
 la 
 
 
 1949.4 
 
 Ic 
 
 
 2021.2 
 
 \9 
 
 
 2094.0 
 
 26 
 
 
 1953.6 
 
 26 
 
 
 2024.9 
 
 la 
 
 
 2096.8 
 
 16 
 
 
 1960.8 
 
 66 
 
 We 
 
 2025.7 
 
 4a 
 
 Ni 
 
 2098.8 
 
 la 
 
 
 / 
 
 4 
 
 JF G 
 
 2026.8 . 
 
 46 
 
 
 2099.8 
 
 2a 
 
 
 V1961.2 
 
 66 
 
 
 2031.1 
 
 2c 
 
 Ba 
 
 2100.4 
 
 la 
 
 
 1964.3 
 
 2c 
 
 
 2035.4 
 
 16 
 
 
 2102.6 
 
 4a 
 
 
 1966.2 
 
 26 
 
 
 2039.6 
 
 16 
 
 
 2103.3 
 
 46 
 
 
 1966.7 
 
 26 
 
 
 2041.3 
 
 6c 
 
 Fe 
 
 2104.0 
 
 4a 
 
 
 1970.1 
 
 36 
 
 
 2042.2 
 
 66 
 
 Fe 
 
 2105.1 
 
 46 
 
 
 1974.7 
 
 46 
 
 
 2044.5 
 
 56 
 
 
 2107.0 
 
 la 
 
 
 1975.7 
 
 2d 
 
 
 2045.0 
 
 56 
 
 
 2107.4 
 
 2a 
 
 
 1979.2 
 
 3c 
 
 
 2047.0 
 
 3d 
 
 
 2109.1 
 
 26 
 
 
 1982.8 
 
 5a 
 
 
 2047.8 
 
 36 
 
 
 2111.1 
 
 36 
 
 
 J 983.3 
 
 5a 
 
 
 2049.3 
 
 3a 
 
 
 2112.7 
 
 36 
 
 Ni 
 
 1983.8 
 
 5a 
 
 
 2049.7 
 
 3a 
 
 
 2115.0 
 
 3a 
 
 Ni 
 
 1984.5 
 
 46 
 
 
 2051.3 
 
 3c 
 
 
 2115.4 
 
 3a 
 
 
 1985.8 
 
 46 
 
 
 2053.0 
 
 46 
 
 
 2119.8 
 
 16 
 
 
 1986.9 
 
 2a 
 
 
 2053.7 
 
 4c 
 
 
 2121.2 
 
 46 
 
 
 1987.5 
 
 3a 
 
 Ni 
 
 2058.0 
 
 6c 
 
 Fe, Ca 
 
 2121.9 
 
 5c 
 
 
 1989.5 
 
 6c 
 
 Ba 
 
 2060.0 
 
 26 
 
 
 2124.3 
 
 16 
 
 
 1990.4 
 
 56 
 
 
 2060.6 
 
 5a 
 
 
 2125.1 
 
 26 
 
 
 1991.8 
 
 16 
 
 
 2061.0 
 
 la 
 
 
 2127.7 
 
 36 
 
 
 1994.1 
 
 56 
 
 
 2064.7 
 
 2c 
 
 Ni 
 
 2132.3 
 
 2a 
 
 Co 
 
 1996.9 
 
 2a 
 
 
 2066.2 
 
 5c 
 
 Fe 
 
 2132.7 
 
 la 
 
 
 1997.5 
 
 2a 
 
 
 2067.1 
 
 5c 
 
 Fe 
 
 2133.8 
 
 2a 
 
 
 1999.6 
 
 2c 
 
 
 2067.8 
 
 36 
 
 
 2134.3 
 
 la 
 
 
 2000.6 
 
 5a 
 
 
 2068.8 
 
 36 
 
 
 2136.0 
 
 5a 
 
 Zn 
 
 2001.6 
 
 5c 
 
 Fe 
 
 2070.6 
 
 16 
 
 
 /2138.0 
 
 2^ 
 
 
 2003.2 
 
 36 
 
 
 2071.3 
 
 16 
 
 Co 
 
 V2138.4 
 
 4a 
 
 
 2003.7 
 
 la 
 
 
 2073.5 
 
 36 
 
 Ni 
 
 2139.5 
 
 4a 
 
 
 /2004.9 
 
 2d 
 
 
 2074.6 
 
 26 
 
 
 2140.4 
 
 4a 
 
 
 V 200,5. 2 
 
 6d 
 
 Fe 
 
 2076.5 
 
 16 
 
 
 2141.9 
 
 2a 
 
 
 2007.2 
 
 6c 
 
 Fe 
 
 /2077.3 
 
 26 
 
 
 2142.4 
 
 5d 
 
 i 
 
 2008.1 
 
 16 
 
 Ni 
 
 (,2079.5 
 
 4* 
 
 
 2144.6 
 
 4a 
 
 
446 
 
 SPECTRUM ANALYSIS. 
 PLATE IV. STRIP 2 (continued). 
 
 [LECT. vi. 
 
 2146.9 
 
 3a 
 
 
 2187.9 
 
 5a 
 
 
 2219.8 
 
 36 
 
 
 2147.4 
 
 4a 
 
 
 2188.5 
 
 5a 
 
 
 2221.3 
 
 la 
 
 
 2148.5 
 
 4a 
 
 
 2190.1 
 
 56 
 
 
 2221.7 
 
 la 
 
 
 2146.9 
 
 3a 
 
 
 /2191.9 
 
 3e 
 
 
 2222!3 
 
 5c 
 
 
 2150.1 
 
 3a 
 
 
 V2192.3 
 
 56 
 
 
 2223.5 
 
 3c 
 
 
 2150.5 
 
 3a 
 
 
 2193.3 
 
 5a 
 
 
 2225.4 
 
 26 
 
 
 2157.0 
 
 3a 
 
 Co,Au 
 
 2195.7 
 
 26 
 
 
 2226.2 
 
 46 
 
 
 2157.4 
 
 5a 
 
 
 2197.1 
 
 26 
 
 
 2227.6 
 
 2a 
 
 
 2159.0 
 
 Ic 
 
 
 2197.7 
 
 26 
 
 
 2228.6 
 
 2a 
 
 
 2160.6 
 
 5a 
 
 
 2198.8 
 
 4a 
 
 
 2229.1 
 
 4a 
 
 
 2160.9 
 
 4:0, 
 
 
 2199.2 
 
 3a 
 
 2ft 
 
 2230.7 
 
 4a 
 
 
 2161.7 
 
 4a 
 
 
 2201.1 
 
 26 
 
 
 2231.2 
 
 2a 
 
 
 2162.6 
 
 3a 
 
 
 2201.9 
 
 5c 
 
 
 2232.3 
 
 4a 
 
 
 2163.7 
 
 4a 
 
 
 2203.3 
 
 2a 
 
 
 /2233.7 
 
 5c 
 
 
 2164.0 
 
 4a 
 
 Ni 
 
 2203.8 
 
 la 
 
 
 V2234.0 
 
 2c 
 
 
 2167.5 
 
 66 
 
 
 2205.1 
 
 16 
 
 
 2237.4 
 
 16 
 
 
 2171.5 
 
 36 
 
 Co 
 
 2206.4 
 
 la 
 
 Oo 
 
 2238.7 
 
 16 
 
 
 2172.2 
 
 2a 
 
 
 2206.7 
 
 la 
 
 
 2240.0 
 
 36 
 
 Zn 
 
 2175.7 
 
 26 
 
 
 2209.1 
 
 4c 
 
 
 2241.4 
 
 26 
 
 
 2176.4 
 
 16 
 
 
 2211.7 
 
 46 
 
 
 2245.1 
 
 36 
 
 
 2179.9 
 
 56 
 
 
 2213.4 
 
 46 
 
 
 2246.2 
 
 16 
 
 
 2181.2 
 
 3e 
 
 
 2215.1 
 
 16 
 
 
 2248.2 
 
 3c 
 
 
 2184.9 
 
 56 
 
 
 2216.7 
 
 36 
 
 
 /2249.7 
 
 6a 
 
 Ni 
 
 2186.5 
 
 36 
 
 
 2217.5 
 
 36 
 
 
 \2250.0 
 
 3^ 
 
 
 2187.1 
 
 5a 
 
 
 2218.3 
 
 3a 
 
 
 
 
 
 PLATE IV. STRIP 3. 
 
 2240.0 
 
 36 
 
 ^w 
 
 2259.4 
 
 4c 
 
 
 2278.4 
 
 4c 
 
 
 2241.4 
 
 26 
 
 
 2261.4 
 
 16 
 
 
 2279.8 
 
 2a 
 
 
 2245.1 
 
 36 
 
 
 2262.1 
 
 2a 
 
 
 2280.7 
 
 2a 
 
 
 2246,2 
 
 16 
 
 
 2263.4 
 
 2a 
 
 
 2282.0 
 
 la 
 
 
 2248.2 
 
 3c 
 
 
 2264.3 
 
 Qd 
 
 
 2282.3 
 
 16 
 
 
 2249.7 
 
 66 
 
 JW 
 
 2266.2 
 
 2a 
 
 
 2283.6 
 
 2a 
 
 
 /2250.0 
 
 3d 
 
 
 2266.6 
 
 2a 
 
 
 2284.9 
 
 26 
 
 
 V2255.4 
 
 46 
 
 
 2268.0 
 
 3a 
 
 
 2286.1 
 
 26 
 
 
 2256.2 
 2257.1 
 
 26 
 d 
 
 
 2269.1 
 2269.9 
 
 3a 
 3a 
 
 
 f /2288.1 
 from V2289.1 
 
 2a 
 1 
 
 
 2257.6 
 
 26 
 
 
 2270.2 
 
 3a 
 
 
 2289.9 
 
 26 
 
 
 2258.5 
 
 2c 
 
 
 2274.2 
 
 1^ 
 
 
 2290.4 
 
 16 
 
 
APPEND. G.J 
 
 KIRCHHOFF'S TABLES. 
 
 447 
 
 PLATE IV. STRIP 3 (continued}. 
 
 2291.8 
 
 2<7 
 
 Zn 
 
 2361.0 
 
 Id 
 
 (2416.0 
 
 3d 
 
 
 ,2293.1 
 
 2a 
 
 
 2362.2 
 
 Ic 
 
 V2416.3 
 
 56 
 
 
 ( 
 
 1 
 
 
 2362.6 
 
 46 
 
 2418.0 
 
 36 
 
 
 2293.6 
 
 36 
 
 
 2364.0 
 
 46 
 
 2419.3 
 
 56 
 
 Co 
 
 2294.5 
 
 26 
 
 Cd 
 
 2365.9 
 
 26 
 
 2420.6 
 
 26 
 
 
 2301.7 
 
 4c 
 
 
 2366.8 
 
 16 
 
 2422.3 
 
 6d 
 
 
 2302.9 
 
 36 
 
 
 2367.7 
 
 26 
 
 2423.8 
 
 3c 
 
 
 2305.3 
 
 3d 
 
 
 2369.7 
 
 26 
 
 2424.4 
 
 46 
 
 
 2306.8 
 
 4c 
 
 
 (2371.4 
 
 26 
 
 2426.5 
 
 46 
 
 
 2307.8 
 
 16 
 
 
 V2371.6 
 
 46 
 
 2428.4 
 
 la 
 
 
 2308.2 
 
 56 
 
 
 2372.4 
 
 46 
 
 2429.5 
 
 36 
 
 
 (2309.0 
 
 5c 
 
 
 2374.2 
 
 36 
 
 2431.9 
 
 26 
 
 
 to \2310.4 
 
 1 
 
 
 2375.0 
 
 26 
 
 2432.4 
 
 16 
 
 
 2310.9 
 
 2e 
 
 
 2375.6 
 
 46 
 
 (2435.3 
 
 26 
 
 
 2312.5 
 
 36 
 
 
 2376.1 
 
 16 
 
 V2435.5 
 
 5c 
 
 
 2313.7 
 
 36 
 
 
 2379.0 
 
 6c 
 
 (2435.7 
 
 26 
 
 
 2314.3 
 
 36 
 
 
 2381.6 
 
 6c 
 
 \2436.5 
 
 5a 
 
 
 2316.0 
 
 26 
 
 
 2386.1 
 
 36 
 
 2438.5 
 
 la 
 
 
 2316.6 
 
 16 
 
 
 2386.6 
 
 2a 
 
 2439.4 
 
 26 
 
 
 2322.0 
 
 26 
 
 
 2388.7 
 
 2c 
 
 2440.0 
 
 la 
 
 
 2323.0 
 
 26 
 
 
 2389.7 
 
 2c 
 
 2441.8 
 
 2a 
 
 
 2325.3 
 
 6(i 
 
 ' 2390.7 
 
 3a 
 
 2442.4 
 
 la 
 
 
 2328.3 
 
 56 
 
 
 2391.2 
 
 16 
 
 2443.9 
 
 5a 
 
 
 2329.5 
 
 56 
 
 Cu 
 
 2393.1 
 
 56 
 
 2444.2 
 
 5a 
 
 
 /2332.8 
 
 26 
 
 
 2394.4 
 
 4a 
 
 2445.3 
 
 Ic 
 
 
 V2333.0 
 
 56 
 
 
 (2395.8 
 
 I/ 
 
 2446.6 
 
 56 
 
 
 2334.1 
 
 2d 
 
 Ni 
 
 V2396.1 
 
 36 
 
 2452.1 
 
 2c 
 
 
 2335.0 
 
 56 
 
 
 ,2396.7 
 
 2a 
 
 2454.1 
 
 46 
 
 
 2336,2 
 
 2d 
 
 
 f 
 
 1 
 
 2457.5 
 
 46 
 
 
 2336.8 
 
 56 
 
 
 2397.4 
 
 2a 
 
 2457.9 
 
 46 
 
 
 2339.9 
 
 46 
 
 
 2399.6 
 
 3a 
 
 2458.6 
 
 3a 
 
 
 2342.5 
 
 Id 
 
 
 2399.9 
 
 3a 
 
 2459.5 
 
 26 
 
 
 from(2343.7 
 
 I 
 
 
 2402.2 
 
 36 
 
 2460.4 
 
 Ic 
 
 
 V2345.1 
 
 2d 
 
 
 2403.2 
 
 36 
 
 2461.2 
 
 66 
 
 Ba 
 
 2346.7 
 
 46 
 
 
 2404.9 
 
 26 
 
 2463.4 
 
 46 
 
 
 2347.3 
 
 46 
 
 
 2406.2 
 
 26 
 
 ,2466.0 
 
 3a 
 
 
 2349.4 
 
 16 
 
 
 2406.6 
 
 6c 
 
 }2467.3 
 
 3c 
 
 
 2349.9 
 
 26 
 
 
 2407.2 
 
 16 
 
 ^2467.6 
 
 5c 
 
 
 2351.4 
 
 Ic 
 
 
 2408.2 
 
 46 
 
 2467.9 
 
 3c 
 
 
 2352.2 
 
 26 
 
 
 2409.0 
 
 16 
 
 2468.7 
 
 3a 
 
 
 2354.1 
 
 6c 
 
 
 2410.2 
 
 46 
 
 2470.1 
 
 4a 
 
 
 2357.4 
 
 5a 
 
 
 2412.8 
 
 36 
 
 /2471.2 
 
 26 
 
 
 2358.4 
 
 56 
 
 
 2414.7 
 
 26 
 
 V2471.4 
 
 4a 
 
 
448 
 
 SPECTRUM ANALYSIS. 
 PLATE IV. STRIP 3 (continued). 
 
 2472.9 
 
 4a 
 
 
 2499.0 
 
 36 
 
 
 2537.1 
 
 5c 
 
 
 2473.8 
 
 2c 
 
 
 2499.8 
 
 36 
 
 
 2538.0 
 
 16 
 
 
 i 2474.6 
 
 46 
 
 
 2500.3 
 
 4c 
 
 
 2538.3 
 
 2a 
 
 
 2475,5 
 2477.4 
 
 Ic 
 
 2a 
 
 
 /2502.2 
 V2502.4 
 
 4c 
 16 
 
 1 Ba 
 
 2540.5 
 2543.5 
 
 2^ 
 4e 
 
 yv 
 
 2477.8 
 
 2a 
 
 
 2505.6 
 
 4^ 
 
 
 2544.5 
 
 2d 
 
 
 2478.7 
 
 2a 
 
 
 2509.4 
 
 2d 
 
 
 2545.4 
 
 Ic 
 
 
 2479.7 
 
 2a 
 
 
 2512.1 
 
 le 
 
 
 2547.2 
 
 6c 
 
 
 2480.,! 
 
 2a 
 
 
 2512.5 
 
 2a 
 
 
 2547.7 
 
 26 
 
 
 2481.1 
 
 la 
 
 
 2513.2 
 
 26 
 
 
 2548.4 
 
 Ic 
 
 
 2482.1 
 
 la 
 
 
 2513.5 
 
 16 
 
 
 2549.7 
 
 16 
 
 
 ; 2482.4 
 
 Ic 
 
 
 2517.0 
 
 36 
 
 
 2550.1 
 
 16 
 
 
 2486.6 
 2487.0 
 
 56 
 56 
 
 
 /2518.2 
 \2518.4 
 
 2c 
 3a 
 
 
 /2551.2 
 \2551.4 
 
 16 
 3a 
 
 
 . 2488.2 
 
 46 
 
 
 2520.9 
 
 3a 
 
 
 /2552.4 
 
 3a 
 
 
 2489.4 
 
 5d 
 
 
 2522.3 
 
 la 
 
 
 V2552.6 
 
 16 
 
 
 /2490.5 
 
 5a 
 
 
 2525.0 
 
 2a 
 
 
 2553.6 
 
 3a 
 
 
 A2490.8 
 
 3d 
 
 
 2525.4 
 
 16 
 
 
 2554.0 
 
 3a 
 
 
 2493.0 
 
 3a 
 
 
 2527.0 
 
 4a 
 
 
 /2554,9 
 
 3a 
 
 
 Y2493.6 
 
 5a 
 
 (7o 
 
 2532.0 
 
 26 
 
 
 \2555.1 
 
 2c 
 
 
 \2493.9 
 
 3/ 
 
 
 2535.5 
 
 26 
 
 
 2556.3 
 
 2c 
 
 
 2495.8 
 
 56 
 
 
 2535.9 
 
 26 
 
 
 2559.9 
 
 36 
 
 
 2497.2 
 
 6d 
 
 
 2536.6 
 
 16 
 
 
 
 
 
 PLATE IV. STRIP 4. 
 
 2550.1 
 
 16 
 
 2565.0 
 
 6c 
 
 2585.4 
 
 56 
 
 2597.7 
 
 36 
 
 /2551.2 
 
 16 
 
 2565.9 
 
 26 
 
 2587.9 
 
 3a 
 
 2598.5 
 
 16 
 
 V2551.4 
 
 3a 
 
 2566.3 
 
 3d 
 
 2588.5 
 
 56 
 
 /2S99.4 
 
 3c 
 
 /2552.4 
 
 3a 
 
 2567.8 
 
 36 
 
 2589.7 
 
 16 
 
 V2599.7 
 
 56 
 
 V2552.6 
 
 16 
 
 2568.4 
 
 26 
 
 2591.3 
 
 4a 
 
 2600.6 
 
 2a 
 
 2553.6 
 
 3a 
 
 2574.4 
 
 5c 
 
 2591.7 
 
 2c 
 
 2601.0 
 
 2c 
 
 2554.0 
 
 3a 
 
 2579.3 
 
 3d 
 
 2593.0 
 
 Ic 
 
 2602.1 
 
 46 
 
 2554.9 
 
 3a 
 
 2581.0 
 
 la 
 
 /2594.9 
 
 26 
 
 2602.9 
 
 la 
 
 2555.1 
 
 2c 
 
 2581.5 
 
 la 
 
 V 
 
 1 
 
 2603.6 
 
 26 
 
 2556.3 
 
 2c 
 
 2582.0 
 
 2a 
 
 2595.4 
 
 4a 
 
 2604.0 
 
 la 
 
 2559.9 
 
 36 
 
 2582.4 
 
 2a 
 
 2595.9 
 
 4a 
 
 2604.8 
 
 46 
 
 2562.1 
 
 46 
 
 2582.8 
 
 la 
 
 ( 
 
 1 
 
 
 
 2564.0 
 
 36 
 
 2584.0 
 
 3e 
 
 V 2596.4 
 
 2c 
 
 
 
APPEND. G.] 
 
 KIRCHHOFF'S TABLES. 
 
 449 
 
 PLATE IV. STRIP 4 (continued). 
 
 
 
 
 
 
 
 . 
 
 
 ,2605.8 
 
 IV 
 
 36 
 2 
 
 u 
 
 /26S2.9 
 \2653.2 
 
 Id 
 
 56 
 
 \ C 1 
 
 /2707.4 
 \2707.7 
 
 I/ 
 
 
 S 2606.6 
 
 5c 
 
 , L- a 
 
 from (2656.7 
 
 1 
 
 } Ca 
 
 2708.9 
 
 46 
 
 
 2607.1 
 
 3c 
 
 J 
 
 V2657.9 
 
 36 
 
 
 2709.6 
 
 26 
 
 
 2608.2 
 
 Ic 
 
 
 2658.6 
 
 16 
 
 
 /2710.6 
 
 3a 
 
 
 2608.6 
 
 16 
 
 
 2664.9 
 
 3a 
 
 
 \2710.9 
 
 If/ 
 
 
 2608.9 
 
 la 
 
 
 2665.9 
 
 36 
 
 
 2711.9 
 
 la 
 
 
 2610.2 
 
 la 
 
 
 2666.7 
 
 16 
 
 
 2712.8 
 
 2a 
 
 
 2612.3 
 
 36 
 
 
 2667.6 
 
 3a 
 
 
 2713.3 
 
 3a 
 
 
 2613.6 
 
 2c 
 
 
 2668.0 
 
 16 
 
 
 2714.3 
 
 2a 
 
 
 2614.1 
 
 3c 
 
 
 2669.4 
 
 36 
 
 
 2715.2 
 
 26 
 
 
 2616.5 
 
 26 
 
 
 2670.0 
 
 Qe 
 
 
 2716.1 
 
 Id 
 
 
 2619.1 
 
 56 
 
 
 2673.8 
 
 la 
 
 Fe 
 
 2718.5 
 
 3^7 
 
 
 2619.9 
 
 3a 
 
 
 2674.5 
 
 2a 
 
 
 ,2719.0 
 
 4c 
 
 
 2620.3 
 
 3a 
 
 
 2675.6 
 
 2c 
 
 
 ( 
 
 ,1 
 
 1 
 I 
 
 2622.3 
 
 16 
 
 
 2676.5 
 
 2a 
 
 
 2720.2 
 
 2 
 
 i 
 
 2624.1 
 
 16 
 
 
 2677.2 
 
 la 
 
 
 2720.8 
 
 
 
 2625.2 
 
 5a 
 
 
 2678.4 
 
 la 
 
 
 2721.6 
 
 |6 
 
 Fe 
 
 2625.9 
 
 4a 
 
 
 2679.0 
 
 2a 
 
 
 2722.8 
 
 3 
 
 
 2626.3 
 2627.0 
 
 2a 
 56 
 
 
 /2680.0 
 V2680.2 
 
 56 
 36 
 
 
 /2725.5 
 
 V2725.8 
 
 3a 
 
 
 2627.9 
 
 2a 
 
 
 2681.2 
 
 5a 
 
 
 2726.8 
 
 2a 
 
 
 2628.9 
 
 Ic 
 
 
 2683.1 
 
 46 
 
 
 2728.0 
 
 46 
 
 
 2629.7 
 
 16 
 
 
 ,2686.0 
 
 3c 
 
 
 2728.4 
 
 16 
 
 
 2630.5 
 
 la 
 
 
 J2686.4 
 
 6/ 
 
 
 2729.8 
 
 2c 
 
 
 2633.6 
 
 2c 
 
 
 1 2686.8 
 
 
 Fe 
 
 2730.7 
 
 16 
 
 
 2634.4 
 
 Id 
 
 
 2688.4 
 
 2e 
 
 
 2731.6 
 
 3c 
 
 
 2635.5 
 
 36 
 
 
 2690.8 
 
 56 
 
 
 2732.4 
 
 Ic 
 
 
 2636.4 
 
 2c 
 
 
 2691.1 
 
 3e 
 
 
 2733.7 
 
 56 
 
 
 2637.4 
 
 46 
 
 
 2692.3 
 
 3c 
 
 
 2734.1 
 
 36 
 
 
 /26S8.5 
 
 V2638.8 
 
 5a 
 
 } Ca 
 
 2693.5 
 from 2695.2 
 
 4c 
 
 
 ^2735.7 
 
 1 
 36 
 
 
 2639.6 
 
 Ic 
 
 
 to 2696.8 
 
 
 
 2736.5 
 
 36 
 
 
 2640.6 
 
 2c 
 
 
 2698.2 
 
 
 
 2736.9 
 
 36 
 
 
 2641.6 
 
 3c 
 
 
 from/2699.8 
 
 1 
 
 
 2737.4 
 
 la 
 
 
 2642.5 
 
 2a 
 
 
 V2700.7 
 
 2a 
 
 
 2737.8 
 
 2a 
 
 
 2643.2 
 
 la 
 
 
 ,2702.1 
 
 36 
 
 
 2739.2 
 
 2c? 
 
 
 2643.5 
 2645.6 
 
 la 
 46 
 
 
 J2702.3 
 <2702.5 
 
 36 
 
 
 2739.9 
 2741.3 
 
 16 
 3d 
 
 
 2646.2 
 
 2? 
 
 
 2703.5 
 
 3a 
 
 
 2741.7 
 
 36 
 
 
 /2650.5 
 
 56 
 
 (La, Di) 
 
 from 2703.8 
 
 L 
 
 
 2743.8 
 
 I/ 
 
 
 V2650.7 
 
 3c 
 
 
 to 2704.9 
 
 1 
 
 
 }2 744.1 
 
 4c 
 
 
 
 
 
 
 ) 
 
 
 ( 2744.3 
 
 1 
 
 
 G G 
 
450 
 
 SPECTRUM ANALYSIS. 
 
 [LKCT. vi. 
 
 PLATE IV. STRIP 4 (continued). 
 
 2746.8 
 
 
 
 2796.7 } 
 
 
 2828.9 
 
 36 
 
 /2747.2 
 V2747.6 
 
 3a 
 
 
 V2797.6 
 / 
 
 z 
 36 
 
 
 2830 7 
 2834.2 
 
 5c 
 
 2748.0 
 2749.8 
 2750.6 
 2754.5 
 2755.4 
 2755.8 
 
 4c 
 3c 
 
 2c 
 16 
 26 
 
 
 ^2798.0 
 /279S.9 
 /2T99.5 
 
 2 
 36 
 1 
 2c 
 1 
 2c 
 
 
 2837.7 
 /2841.4 
 \2841. 7 
 /2843.0 
 V2843.3 
 2844.0 
 
 56 
 
 4a 
 36 
 
 2756.5 
 
 2757.2 
 
 Ic 
 Ic 
 
 
 /2800.1 
 
 36 
 i 
 
 
 /284S.3 
 
 
 
 2 
 
 2759.4 
 2760.1 
 
 la 
 
 
 /2800.7 
 
 36 
 
 
 /2846.1 
 
 3c 
 2 
 
 2760.6 
 2762.0 
 2763.8 
 2767.2 
 2768.2 
 2768.5 
 
 V 
 
 Id 
 
 la 
 
 
 2801.4 
 2804.5 
 2805.4 
 2806.9 
 2807.2 
 
 16 
 16 
 Ic 
 
 2a 
 
 1 7, 
 
 
 /2S46.9 
 /2847.7 
 /2848.0 
 
 4c 
 1 
 4a 
 2 
 4a 
 2 
 
 2770.0 
 2770.8 
 2774.0 
 ,2775.4 
 
 26 
 26 
 5c 
 4c 
 
 
 (.2808.8 
 (2809 
 2810.8 
 
 Lo 
 
 16 
 26 
 
 
 /2S48.4 
 /2S48.9 
 
 36 
 2 
 
 36 
 2 
 
 2775.7 
 (2776.0 
 2777.3 
 
 6c 
 4c 
 3a 
 
 \ 
 
 
 2811.7 
 2812.0 
 /2812.5 
 V2812.8 
 
 le 
 
 
 .^2849.3 
 
 /2849.S 
 
 36 
 2 
 36 
 
 V2777.8 
 
 I" 
 
 \ 
 
 
 2814.1 
 2817.7 
 
 16 
 3c 
 
 
 \ 
 
 /2850.2 
 
 36 
 
 2 
 
 2778.5 
 2781.2 
 2782.2 
 2782.9 
 2783.9 
 /2784.8 
 V2785.1 
 /2788.S 
 V2789.1 
 
 I 1 
 
 26 
 16 
 36 
 16 
 Ic 
 2c 
 16 
 3c 
 
 
 2819.2 
 2819.6 
 2820.6 
 2821.0 
 2821.6 
 2822.3 
 
 \2823.4 
 
 2824.2 
 
 36 
 26 
 
 }3 
 
 3 
 
 3a 
 o 
 
 * 
 
 /2S50.7 
 /2851.1 
 /2851.6 
 /2852.0 
 /2S52.3 
 
 36 
 2 
 36 
 
 2 
 
 36 
 2 
 
 4a 
 
 2 
 4a 
 
 2790.5 
 2791.1 
 2793.0 
 2794.0 
 
 Ic 
 
 36 
 
 I 1 
 
 
 V2825 
 V2825.9 
 
 ( 
 
 3 
 
 46 
 
 
 2853.1 
 2853.6 
 2854.1 
 
 1 
 }3 
 
 2795.7 
 
 } 2 
 
 
 2826.5 
 
 4e 
 
 
 2854.7 
 
 L 6 _ 
 
APPEND 
 
 KIRCHHOFF'S TABLES. 
 PLATE IV. STRIP 4 (continued}. 
 
 2855.2 
 
 4 
 
 
 (2863.1 
 
 36 
 
 
 /2S69.7 
 
 5c 
 
 2855.7 
 
 3 
 
 
 /2863.G 
 
 
 
 y 
 
 4 
 
 2856.9 
 
 4:d 
 
 
 ( 
 
 4 
 
 
 2871.2 
 
 
 from /2S57.9 
 
 \2858.5 
 
 3 
 
 >Sr 
 
 /2S64.2 
 
 56 
 2 
 
 
 /2S72.2 
 
 1 
 
 x 
 
 V2858.9 
 
 9 
 I 
 
 
 /2S64.7 
 
 46 
 2 
 
 Ca 
 
 /2S73.4 
 
 26 
 
 1 
 
 
 |3 
 
 \ 
 
 
 /2S65.3 
 
 4c 
 
 
 /2S73.9 
 
 26 
 
 
 | 
 
 
 I 
 
 1 
 
 
 ( 
 
 1 
 
 2859.4 
 
 j 1 
 
 
 /2866.3 
 
 56 
 
 
 ,2874.3 
 
 36 
 
 2860.2 
 
 1 
 
 
 \ 
 
 3 
 
 
 ( 
 
 1 
 
 ,2860.9 
 
 '2 
 
 
 /2867.1 
 
 2 
 
 
 2874.7 
 
 26 
 1 
 
 (2861.7 
 
 46 
 
 
 /2868.1 
 
 4c 
 
 
 ^2875.2 
 
 4c 
 
 ,2861.9 
 
 36 
 
 
 V 
 
 3 
 
 
 
 
 v 
 
 1 
 
 
 
 
 
 
 
 j 
 
 
 
 i 
 
 
 
 
 451 
 
 Ca 
 
452 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. vi. 
 
 POSITIONS OF THE LINES OF CERIUM, LANTHANUM, DIDYMIUM, 
 PALLADIUM, PLATINUM, IRIDIUM, AND RUTHENIUM, ON 
 PLATES III. & IV. (KIRCHHOFF). 
 
 (The lines marked with an asterisk appear to coincide with dark lines in the Solar Spectrum.) 
 
 
 
 
 
 1 
 
 1 
 
 . Oe 
 
 
 from 1364. 5 
 
 \ l 
 
 1303.4 
 
 
 
 2 
 
 1279.1 
 
 1 
 
 1190.1 
 
 1 
 
 to 1365.2 
 
 r 
 
 1317.6 
 
 1 
 
 from 1400.0 
 
 I 9 
 
 1249.9 
 
 1 
 
 1431.9 
 
 i 
 
 1345.4 
 
 1 
 
 *to 1400.7 
 
 J " 
 
 1256.7 
 
 1 
 
 147-1.1 
 
 i 
 
 from 1486. 8 
 
 I 9 
 
 1430.1 
 
 1 
 
 1329.1 
 
 2 
 
 from 1518.6 
 
 ) , 
 
 to 1489.2 
 
 r 
 
 1447.0 
 
 1 
 
 1332.4 
 
 2 
 
 *to 1519.4 
 
 I 1 
 
 *1622.3 
 
 
 1477.0 
 
 1 
 
 1336.2 
 
 1 
 
 1536.0 
 
 i 
 
 *1623.3 
 
 i 
 
 1495.2 
 
 3 
 
 1385.0 
 
 2 
 
 1541.4 
 
 i 
 
 1716.6 
 
 2 
 
 1540.0 
 
 1 
 
 1401.7 
 
 2 
 
 1548.9 
 
 2 
 
 1728.8 
 
 2 
 
 from 1566.5 
 
 U 
 
 1438.9 
 
 3 
 
 1567.5 
 
 1 
 
 from 1894.5 
 
 1 9 
 
 to 1567.1 
 
 } 2 
 
 1460.9 
 
 1 
 
 1709.2 
 
 2 
 
 to 1895.2 
 
 ) ^ 
 
 1601.4 
 
 1 
 
 1517.9 
 
 3 
 
 
 
 1903.0 
 
 1 
 
 from 1660.0 
 
 u 
 
 froml571.0 
 
 U 
 
 La 
 
 
 1940.2 
 
 1 
 
 to 1660.7 
 
 } 3 
 
 t. 1572.4 
 
 r 
 
 from 141 1.6 
 
 1 9 
 
 from 198& 6 
 
 I , 
 
 1732.9 
 
 2 
 
 1573.0 
 
 2 
 
 *to 1412.8 
 
 J " 
 
 to 1989.5 
 
 J 
 
 1801.9 
 
 1 
 
 1623.1 
 
 1 
 
 1416.8 
 
 2 
 
 2003.8 
 
 2 
 
 2062.0 
 
 2 
 
 from 1629.2 
 
 I 9 
 
 1451.0 
 
 1 
 
 2004.7 
 
 2 
 
 2123.6 
 
 2 
 
 to 1630.4 
 
 
 1606.8 
 
 2 
 
 2031.0 
 
 2 
 
 2162.0 
 
 2 
 
 1683.1 
 
 1 
 
 162-7.9 
 
 2 
 
 2081.0 
 
 2 
 
 
 
 1725.5 
 
 1 
 
 1634.8 
 
 2 
 
 2121.4 
 
 1 
 
 Pt 
 
 
 *1777.5 
 
 2 
 
 2136.8 
 
 1 
 
 2208.2 
 
 2 
 
 1325.7 
 
 1 
 
 from 1782.4 
 
 
 
 
 2214.5 
 
 2 
 
 from 1488. 2 
 
 1 ^ 
 
 to 1784.5 
 
 
 (La, Di} 
 
 
 2217.8 
 
 2 
 
 to 1489.0 
 
 J 
 
 1938.8 
 
 2 1025.0 
 
 1 
 
 
 
 1576.8 
 
 1 
 
 2052.3 
 
 1 i! 1064.5 
 
 1 
 
 Pd 
 
 
 from 1806.1 
 
 I 9 
 
 2221.5 
 
 1 
 
 1066.1 
 
 1 
 
 1114.7 
 
 1 
 
 *to 1806.9 
 
 J "* 
 
 
 
 1071.1 
 
 1 
 
 -1146.2 
 
 2 
 
 2057.0 
 
 1 
 
 
 
 1075.6 
 
 1 
 
 1164.9 
 
 2 
 
 
 
 Di. 
 
 
 1077.0 
 
 1 
 
 1185.6 
 
 1 
 
 (Ru, Ir) 
 
 
 1225.0 
 
 2 
 
 1092.1 
 
 2 
 
 1264.6 
 
 2 
 
 1348.3 
 
 2 
 
 1230.0 
 
 1 
 
 *1302.0 
 
 1 
 
 1269.0 
 
 2 
 
 *1489.9 
 
 1 
 
 
 
 
 
 
 
 
 
 ATMOSPHERIC LINES. 
 
 711.4 
 
 954.2 
 
 964.4 
 
 970.5 
 
 976.1 
 
 988.9 
 
 998.1 
 
 1008.3 
 
 1015.1 
 
 948.0 
 
 958.8 
 
 965.7 
 
 972.1 
 
 977.4 
 
 989.2 
 
 999.2 
 
 1009.2 
 
 1016.4 
 
 949.4 
 
 959.6 
 
 968.7 
 
 974.3 
 
 977.7 
 
 989.6 
 
 1000.0 
 
 1010.5 
 
 1017.7 
 
 949.8 
 
 961.9 
 
 969.0 
 
 975.0 
 
 982.0 
 
 993.1 
 
 1001.4 
 
 1013.9 
 
 1018.2 
 
 951.7 
 
 963.7 
 
 969.6 
 
 975.7 
 
 982.3 
 
 993.4 
 
 1005.8 
 
 
 
APPEND, a.] ANGSTROM A^D THALEN'S TABLES. 
 
 453 
 
 EXPLANATION OF ANGSTROM AND THALEN'S TABLES. 1 
 
 In the following Tables we have registered the principal of the 
 iron lines and of the new coincidences which we over and above 
 those observed by Kirchhoft' have discovered between A and a. 
 Their position is given in the first column according to the 
 measuring scale adopted in KirchhofF s and Hofmann's tables, 
 Plates III. and IV. The second column gives the relative strength 
 of the lines, according to the gradation employed in the same 
 tables, where 6 indicates the strongest and 1 the weakest lines. 
 The third column contains the name of the metal, and the fourth 
 the lines already identified by Kirchhoff with corresponding 
 sun lines. The letter K indicates that Kirchhoff has observed 
 the coincidence for the same metal as we, but the other signs, as 
 for example K. Sr, that he found the coincidence belong to a 
 strontium line, whereas we have found it belong moreover to 
 the metal stated in the third column. 
 
 PLATE III. STRIP 1. 
 
 
 
 
 
 
 
 
 
 468-1 
 
 2 
 
 Ca 
 
 
 509-1 
 
 8 
 
 Fe 
 
 
 65') '3 
 
 2 
 
 Fe 
 
 
 498-4 
 
 4 
 
 Fe 
 
 
 513-6 
 
 8 
 
 Ca 
 
 
 683-1 
 
 2 
 
 Fe 
 
 
 499-9 
 
 5 
 
 Ca 
 
 
 638'4 
 
 
 Ca 
 
 
 689-8 
 
 2 
 
 Fe 
 
 
 603-8 
 
 6 
 
 Fe 
 
 
 654-3 
 
 2 
 
 Fe 
 
 
 
 
 
 
 PLATE III. STRIP 2. 
 
 C 694-1 6 
 
 H 
 
 
 7f29 
 
 
 
 Fe 
 
 
 932-5 
 
 4 
 
 Mn 
 
 
 719-6 
 
 A 
 
 Fe 
 
 
 798-5 
 
 4 
 
 Fe 
 
 K 
 
 933-3 
 
 4 
 
 Fe 
 
 
 721-1 
 
 2 
 
 Fe 
 
 K 
 
 820-9 
 
 4 
 
 / Fe 
 
 
 935-1 
 
 4 
 
 Mn 
 
 
 744-3 
 
 4 
 
 Fe 
 
 
 824-0 
 
 4 
 
 Fe 
 
 
 9367 
 
 1 
 
 Mn 
 
 
 748-1 
 
 4 
 
 Fe 
 
 
 831-0 
 
 4 
 
 Fe 
 
 K 
 
 940-1 
 
 a 
 
 Fe 
 
 
 752-3 
 
 4 
 
 Fe 
 
 
 849-7 
 
 3 
 
 Fe 
 
 K 
 
 943-4 3 
 
 Fe 
 
 
 7538 
 
 8 
 
 Fe 
 
 K. Sr 
 
 864-4 
 
 1 
 
 Na 
 
 
 952-9 
 
 8 
 
 F 
 
 
 756-9 
 
 fi 
 
 Fe 
 
 K 
 
 867-6 
 
 1 
 
 Na 
 
 
 954-3 
 
 8 
 
 Fe 
 
 
 759-3 
 
 8 
 
 Fe 
 
 
 S77'0 
 
 4 
 
 Fe 
 
 K 
 
 954-8 
 
 8 
 
 Fe 
 
 
 7S3-1 
 
 4 
 
 Fe 
 
 
 906-1 
 
 2 
 
 Fe 
 
 
 958-8 
 
 S 
 
 Fe 
 
 
 783-8 
 788-9 
 
 8 
 
 3 
 
 Fe 
 Fe 
 
 
 912-1 
 916-3 
 
 :; 
 2 
 
 Fe 
 
 Fe 
 
 K 
 
 959-6 
 991 9 
 
 ;>, 
 3 
 
 Fe 
 Fe 
 
 K 
 
 7914 
 
 3 
 
 Fe 
 
 
 931-3 
 
 4 
 
 Fe 
 
 R 
 
 
 
 
 , 
 
 Abhandl. d. K. Akad. d. Wiss. zn Berlin 1861 u. 1862. 
 
454 
 
 SPECTRUM ANALYSIS. 
 
 [LECT. vi. 
 
 PLATE IIT. STRIP 3. 
 
 1011-2 
 
 3 
 
 Fe 
 
 
 1151-1 
 
 4 
 
 Na 
 
 
 1239-9 
 
 4 
 
 Fa K 
 
 1025-5 
 
 3 
 
 Fa 
 
 
 1152-5 
 
 2 
 
 Fe 
 
 
 1242 6 
 
 6 
 
 Fe 
 
 K 
 
 10277 
 
 2 
 
 Fe 
 
 
 1155-8 
 
 3 
 
 Na 
 
 
 1245-6 
 
 4 
 
 Fe 
 
 K 
 
 1058-0 
 
 2 
 
 Fe 
 
 
 1158-3 
 
 z 
 
 Fe 
 
 
 12486 
 
 3 
 
 Fe 
 
 
 1075-5 
 
 8 
 
 Fe 
 
 
 1170-6 
 
 2 
 
 Fe 
 
 
 1250-4 
 
 3 
 
 Fe 
 
 
 1087-5 
 
 2 
 
 Fe, 
 
 
 1174-2 
 
 5 
 
 Fe 
 
 
 1257-5 
 
 3 
 
 Fe 
 
 
 1096-1 
 
 8 
 
 Fe 
 
 K 
 
 11766 
 
 3 
 
 Fe 
 
 
 1264-9 
 
 2 
 
 Fe 
 
 
 1102-9 
 
 3 
 
 Fe 
 
 
 1190-1 
 
 2 
 
 Fe 
 
 
 1263-0 
 
 8 
 
 Fe 
 
 
 1103-3 
 
 2 
 
 Mn 
 
 
 11931 
 
 3 
 
 Fe 
 
 
 12742 
 
 8 
 
 Fe 
 
 K. Ba 
 
 1119-0 
 
 2 
 
 Fe 
 
 
 1200-6 
 
 4 
 
 Fe 
 
 K 
 
 1276-2 
 
 2 
 
 Fe 
 
 
 1128-3 
 
 2 
 
 Fe 
 
 
 1207-3 
 
 5 
 
 Fe 
 
 K 
 
 1280'Q 
 
 6 
 
 Mg 
 
 
 1130-9 
 
 2 
 
 Fe 
 
 
 1217-8 
 
 5 
 
 Fe 
 
 K 
 
 1282-6 
 
 2 
 
 Fe 
 
 
 1133-9 
 
 8 
 
 Fe 
 
 
 1221-6 
 
 5 
 
 Fe 
 
 K. Ca 
 
 1298-9 
 
 6 
 
 Fe 
 
 
 1135-1 
 
 4 
 
 Fe 
 
 
 1224-7 
 
 5 
 
 Fe 
 
 K. Ca 
 
 1303-5 
 
 B 
 
 Fe 
 
 
 1137-8 
 
 a 
 
 Fo 
 
 
 1226-6 
 
 2 
 
 Fe 
 
 
 13067 
 
 6 
 
 Fe 
 
 
 1141-3 
 
 2 
 
 Fe. 
 
 
 1231-3 
 
 5 
 
 Fe 
 
 K 
 
 1315-0 
 
 4 
 
 Fe 
 
 
 PLATE III. STRIP 4. 
 
 
 
 
 
 
 
 
 
 
 
 
 13150 
 
 4 
 
 Fe 
 
 
 1414-0 
 
 2 
 
 Fe 
 
 1531-2 
 
 4 
 
 Fe 
 
 
 13200 
 
 4 
 
 Fe 
 
 K. Sr 
 
 14158 
 
 2 
 
 Mu 
 
 
 1541-9 
 
 3 
 
 Fe 
 
 
 1324-8 
 
 4 
 
 Fe 
 
 K. Ni 
 
 1421-5 
 
 6 
 
 Fe 
 
 K 
 
 1543-7 
 
 2 
 
 Fe 
 
 
 1327? 
 
 4 
 
 Fe 
 
 
 1423-0 
 
 5 
 
 Fo 
 
 K 
 
 1545-5 
 
 2 
 
 Fe 
 
 
 1384-0 
 
 4 
 
 Fe 
 
 
 1425-4 
 
 5 
 
 Fe 
 
 K 
 
 1547-2 
 
 3 
 
 Fe 
 
 
 1337-0 
 
 4 
 
 Fe 
 
 K 
 
 1428-2 
 
 5 
 
 Fe 
 
 K 
 
 1551-6 
 
 2 
 
 Fe 
 
 
 1343-3 
 
 6 
 
 Fe 
 
 K 
 
 1438-9 
 
 4 
 
 Fe, 
 
 K. Co 
 
 1555-6 
 
 2 
 
 Fe 
 
 
 1351-1 
 
 5 
 
 Fe 
 
 K 
 
 1443-1 
 
 '_' 
 
 Fe 
 
 
 1557-3 
 
 3 
 
 Fe 
 
 
 13527 
 
 5 
 
 Fe 
 
 K 
 
 1450-8 
 
 5 
 
 Fe. Mn 
 
 K. Fe 
 
 1569-6 
 
 5 
 
 Fe 
 
 K 
 
 13629 
 
 5 
 
 Fe 
 
 K 
 
 1451-8 
 
 5 
 
 Fe 
 
 K 
 
 1573-5 
 
 5 
 
 Fe 
 
 
 1367-0 
 
 6 
 
 Fe 
 
 K 
 
 14586 
 
 H 
 
 Fe 
 
 
 1577-2 
 
 5 
 
 Fe 
 
 K 
 
 1372-6 
 
 5 
 
 Fe 
 
 K 
 
 1462-8 
 
 f, 
 
 Fe 
 
 K 
 
 1589-1 
 
 3 
 
 Fe 
 
 
 1377-4 
 
 1 
 
 Mn 
 
 
 1463-3 
 
 r, 
 
 Fe 
 
 K 
 
 1590-7 
 
 3 
 
 Fe 
 
 
 13805 
 
 4 
 
 Fe 
 
 K 
 
 1466-8 
 
 6 
 
 Fe 
 
 K 
 
 1592-3 
 
 3 
 
 Fe 
 
 
 1384 7 
 
 4 
 
 Fe 
 
 K 
 
 1473-9 
 
 5 
 
 Fe 
 
 K 
 
 1601-7 
 
 3 
 
 Fe 
 
 
 1389-4 
 
 6 
 
 Fe 
 
 K 
 
 1483-0 
 
 4 
 
 Fe 
 
 
 1606-4 
 
 5 
 
 Fe 
 
 K. Cr 
 
 1390-9 
 
 5 
 
 Fe 
 
 K 
 
 1487-7 
 
 5 
 
 Fe 
 
 K 
 
 1609-2 
 
 5 
 
 F 
 
 
 13942 
 
 4 
 
 Mn 
 
 
 1501-3 
 
 2 
 
 Fe 
 
 
 1613-9 
 
 3 
 
 Fe 
 
 
 1397-5 
 
 5 
 
 Fe 
 
 K 
 
 1506-3 
 
 5 
 
 Fe 
 
 K 
 
 1618-9 
 
 4 
 
 Fe 
 
 
 1400-2 
 
 8 
 
 Mn 
 
 
 1508-6 
 
 , r ) 
 
 Fe 
 
 K 
 
 1622-3 
 
 5 
 
 Fe 
 
 K 
 
 14016 
 
 4 
 
 Fe 
 
 K 
 
 1519-0 
 
 4 
 
 Fe 
 
 
 1623-4 
 
 5 
 
 Fe 
 
 K 
 
 1403-1 
 
 3 
 
 Fe 
 
 
 15227 
 
 6 
 
 Fe 
 
 K 
 
 1627-2 
 
 5 
 
 Fe 
 
 K. Ca 
 
 1405-2 
 
 8 
 
 Fe 
 
 
 E 1523 7 
 
 6 
 
 Fe 
 
 K 
 
 
 
 
 
 1410-5 
 
 4 
 
 Fe K 
 
 15277 
 
 5 
 
 Fe 
 
 K 
 
 
 
 
 
 PLATE IV. STRIP 1. 
 
 1622-3 
 
 6 
 
 Fe 
 
 K 
 
 17377 
 
 5 
 
 Fe 
 
 1 1857-9 
 
 2 
 
 Ca 
 
 
 1623-4 
 
 5 
 
 Fe 
 
 K 
 
 1750-4 
 
 5 
 
 Fe 
 
 1 1860-4 
 
 2 
 
 Ca 
 
 
 1627-2 
 
 5 
 
 Fe 
 
 K. Ca 
 
 1752-8 
 
 4 
 
 Fe 
 
 1861-3 
 
 3 
 
 Fe 
 
 
 1633-5 
 
 4 
 
 Fe 
 
 
 1762-0 
 
 3 
 
 Fe 
 
 1864-9 
 
 3 
 
 Ca 
 
 
 b 16387 
 
 1 
 
 Fe 
 
 
 1772-5 
 
 8 
 
 Fe 
 
 
 1867-1 
 
 5 
 
 Fe 
 
 K 
 
 1650-3 
 
 6 
 
 Fe 
 
 K 
 
 1777-5 
 
 3 
 
 Fe 
 
 
 1868-4- 
 
 B 
 
 Fe 
 
 K. Ni 
 
 1053-7 
 
 6 
 
 Fe 
 
 K 
 
 1778-5 
 
 3 
 
 Fe 
 
 
 1872-4 
 
 5 
 
 Fe 
 
 
 1655-6 
 
 6 
 
 Fe 
 
 K 
 
 17827 
 
 3 
 
 Fe 
 
 
 1873-4 
 
 6 
 
 Ca 
 
 
 1662-8 
 
 5 
 
 Fe 
 
 K 
 
 1785-0 
 
 4 
 
 Fe 
 
 
 1876-5 
 
 6 
 
 Fe 
 
 
 1671'S 
 
 3 
 
 Na 
 
 
 1787-7 
 
 2 
 
 Fe 
 
 
 1884-3 
 
 6 
 
 FeCa 
 
 
 1674-7 
 
 8 
 
 Na 
 
 K. Cu 
 
 1793-8 
 
 4 
 
 Fe 
 
 
 1886-4 
 
 6 
 
 Fe 
 
 
 1676-5 
 
 4 
 
 Fe 
 
 
 1796-0 
 
 3 
 
 Fe 
 
 
 1892-5 
 
 5 
 
 Fe 
 
 
 1677-9 
 
 4 
 
 Fe, 
 
 
 1799'0 
 
 4 
 
 Fe 
 
 
 1894-8 
 
 3 
 
 Fe 
 
 
 1681-6 
 
 4 
 
 Fe 
 
 
 1799-6 
 
 8 
 
 Ca 
 
 
 1896-2 
 
 4 
 
 Ca 
 
 
 1690-0 
 
 5 
 
 Fe 
 
 K. Ni 
 
 1818-7 
 
 6 
 
 Fe 
 
 
 1904-5 
 
 4 
 
 Fe 
 
 
 1691-0 
 
 5 
 
 Fe 
 
 
 1821-4 
 
 5 
 
 Fe 
 
 
 1908-5 
 
 5 
 
 FeCa 
 
 
 1693-8 
 
 (3 
 
 Fe 
 
 K 
 
 1830-1 
 
 8 
 
 Fe 
 
 
 1911-9 
 
 8 
 
 Fe 
 
 
 1696-5 
 
 8 
 
 Fo 
 
 
 1833-4 
 
 6 
 
 Fe 
 
 
 19175 
 
 4 
 
 Fe 
 
 
 1701-8 
 
 5 
 
 Fe 
 
 K 
 
 1834-3 
 
 6 
 
 Fe 
 
 
 1919-8 
 
 4 
 
 Fe} 
 
 
 1704-9 
 
 3 
 
 Fe 
 
 
 1835-9 
 
 3 
 
 Fo.Ca 
 
 
 1921-1 
 
 4 
 
 Fe Na 
 
 
 17107 
 
 5 
 
 Fe 
 
 
 1837-5 
 
 3 
 
 Ca 
 
 
 1922-4 
 
 4 
 
 Fel 
 
 
 1713-4 
 
 5 
 
 Fe 
 
 
 1841-0 
 
 4 
 
 Ca 
 
 
 192G -u 
 
 i 
 
 Cu 
 
 
 1T15-2 
 
 4 
 
 Fe 
 
 
 1841-6 
 
 4 
 
 Ca 
 
 
 1928 
 
 4 
 
 Fe 
 
 
 1717'9 
 
 4 
 
 Fe 
 
 
 1853-2 
 
 3 
 
 Fe 
 
 
 1936-2 
 
 3 
 
 Fe 
 
 
 1733-6 
 
 5 
 
 Fe 
 
 
 1854-9 
 
 4 
 
 Fe 
 
 
 19395 
 
 2 
 
 Fe 
 
 
APPEND. G.] ANGSTROM AND THALEN'S TABLES. 
 PLATE IV. STRIP 2. 
 
 455 
 
 1936"2 
 
 3 
 
 Fe 
 
 
 2018-5 
 
 2 
 
 Fe 
 
 
 2150-5 
 
 3 
 
 Fe 
 
 
 1939-5 
 
 2 
 
 Fe 
 
 
 2021-2 
 
 1 
 
 Fe 
 
 
 2160-6 
 
 5 
 
 Fe 
 
 
 1944-5 
 
 3 
 
 Fe 
 
 
 2026-8 
 
 4 
 
 Fe 
 
 
 2163-7 
 
 4 
 
 Fe 
 
 
 1947-6 
 
 4 
 
 Fe 
 
 
 2041-3 
 
 6 
 
 Fe 
 
 K 
 
 2167-5 
 
 6 
 
 Mn 
 
 
 1961-0 
 
 4 
 
 Fe 
 
 K 
 
 2042 -2 
 
 6 
 
 Fe 
 
 K 
 
 2179-9 
 
 5 
 
 Fe 
 
 
 1974-7 
 
 4 
 
 Fe 
 
 
 2047'0 
 
 3 
 
 Fe 
 
 
 2184-9 
 
 5 
 
 Fe 
 
 
 1979-2 
 
 3 
 
 Fe 
 
 
 2047-8 
 
 3 
 
 Fe 
 
 
 2187-9 
 
 5 
 
 Mn 
 
 
 1983-3 
 
 5 
 
 Fe 
 
 
 2053-0 
 
 4 
 
 Fe 
 
 
 2192-3 
 
 5 
 
 Mn 
 
 
 1983-8 
 
 6 
 
 Fe 
 
 
 2058-0 
 
 6 
 
 Fe 
 
 K 
 
 2201-9 
 
 5 
 
 Mn 
 
 
 1990-4 
 
 5 
 
 Fe 
 
 
 2066-2 
 
 5 
 
 Fe 
 
 K 
 
 2211-7 
 
 4 
 
 Fe 
 
 
 1994-1 
 
 5 
 
 Fe 
 
 
 2067-1 
 
 6 
 
 Fe 
 
 K 
 
 2216-7 
 
 3 
 
 Fe 
 
 
 1996'9 
 
 2 
 
 Fe 
 
 
 2077-3 
 
 2 
 
 Fe 
 
 
 2219-8 
 
 3 
 
 Mn 
 
 
 1997-5 
 
 2 
 
 Fe 
 
 
 F 2080-0 
 
 t) 
 
 H 
 
 
 2222-3 
 
 5 
 
 Fe 
 
 
 2001 '6 
 
 5 
 
 Fe 
 
 K 
 
 2082-0 
 
 6 
 
 Fe 
 
 K 
 
 2226-2 
 
 1 
 
 Fe 
 
 
 2005-2 
 
 6 
 
 Fe 
 
 K 
 
 2086-5 
 
 1 
 
 Fe 
 
 
 2227-6 
 
 2 
 
 Fe 
 
 
 2007-2 
 
 6 
 
 Fe 
 
 K 
 
 2121-9 
 
 5 
 
 Mn 
 
 
 2230-7 
 
 4 
 
 Fe 
 
 
 2008-6 
 
 1 
 
 Fe 
 
 
 2147-4 
 
 4 
 
 Fe 
 
 
 22323 
 
 4 
 
 Fe 
 
 
 2017-7 
 
 2 
 
 Fe 
 
 
 2148-9 
 
 8 
 
 Fe 
 
 
 2233-7 
 
 5 
 
 Mn 
 
 
 
 
 
 
 
 
 
 
 
 
 1 
 
 PLATE IV. STRIP 3. 
 
 2255-4 
 
 4 
 
 Fe 
 
 
 2335-0 
 
 5 
 
 Fe 
 
 
 2416-3 
 
 5 
 
 Ca 
 
 
 2257-1 
 
 4 
 
 Mn 
 
 
 23.,9'9 
 
 4 
 
 Fe 
 
 
 24223 
 
 6 
 
 Ca 
 
 K. ( 
 
 2259-4 
 
 4 
 
 Fe 
 
 
 2346-7 
 
 4 
 
 Fe 
 
 
 2426-5 
 
 4 
 
 v'a. 
 
 
 2-261-4 
 
 1 
 
 Fe 
 
 
 2347-3 
 
 4 
 
 Fe 
 
 
 2457-5 
 
 4 
 
 Fe 
 
 
 2264-3 
 
 6 
 
 Mg? 
 
 
 2354-1 
 
 6 
 
 Fe 
 
 
 24579 
 
 4 
 
 Fe 
 
 
 2266-6 
 
 2 
 
 Fe 
 
 
 2358-4 
 
 5 
 
 Fe 
 
 
 2470-1 
 
 4 
 
 Fe 
 
 
 2268-0 
 
 3 
 
 Mn 
 
 
 2364-0 
 
 4 
 
 Fe 
 
 
 2487-0 
 
 5 
 
 Ca 
 
 
 2278-4 
 
 4 
 
 Fe 
 
 
 2371-6 
 
 4 
 
 Fe 
 
 
 2490-5 
 
 5 
 
 Ca 
 
 
 2291-8 
 
 
 Mn 
 
 K. Zn 
 
 2379-0 
 
 6 
 
 Fe 
 
 
 2493 '6 
 
 5 
 
 Fe 
 
 K. ( 
 
 2293-6 
 
 8 
 
 Fe 
 
 
 2381 "6 
 
 6 
 
 Fe 
 
 
 2497-2 
 
 6 
 
 Fe 
 
 
 2306-8 
 
 4 
 
 Fe 
 
 
 2386-1 
 
 3 
 
 Fe.Ca. 
 
 
 2502-2 
 
 4 
 
 Fe 
 
 
 2308-2 ! 5 
 
 Fe 
 
 
 2393-1 
 
 5 
 
 Fe 
 
 
 2547-2 
 
 6 
 
 Fe 
 
 
 2309-0 : 5 
 
 Fe.Ca 
 
 
 2402-2 
 
 3 
 
 Fe 
 
 
 
 
 
 
 2325-3 | 6 
 
 Fe 
 
 
 2406-6 
 
 6 i Fe 
 
 
 
 
 
 
 PLATE IV. STRIP 4. 
 
 2553-6 3 
 
 Fe 
 
 li 2641-6 
 
 3 
 
 Fe 
 
 
 2744-1 
 
 4 
 
 Fe 
 
 
 2562-1 
 
 4 
 
 Fe 
 
 
 2645-6 
 
 4 
 
 Fe 
 
 
 2748-0 
 
 4 
 
 Fe 
 
 
 2565-0 
 
 6 
 
 Fe 
 
 
 2650-5 
 
 5 
 
 Fe.Ca 
 
 
 2762-0 
 
 4 
 
 Fe 
 
 
 2574-4 
 
 5 
 
 Fe 
 
 
 2657-9 
 
 3 
 
 Fe 
 
 
 2774-0 
 
 5 
 
 Fe 
 
 
 2584-0 
 
 8 
 
 Fe 
 
 
 2670-0 
 
 6 
 
 Fe.Mn 
 
 K. Fe 
 
 2796-7 
 
 6 
 
 H 
 
 
 2588-5 
 
 5 
 
 Fe 
 
 
 2680-0 
 
 5 
 
 Fe 
 
 
 2801-4 
 
 4 
 
 Fe 
 
 
 2595-4 
 
 4 
 
 Fe 
 
 
 2681-2 
 
 5 
 
 Fe 
 
 
 2822-3 
 
 
 
 Fe 
 
 K 
 
 2599-4 
 
 9 
 
 Fe 
 
 
 2686-4 
 
 6 
 
 Fe 
 
 K 
 
 2841 '4 
 
 5 
 
 Fe 
 
 
 2604'8 
 
 4 
 
 Ca 
 
 
 2692 -3 
 
 3 
 
 Fe 
 
 
 2852-3 
 
 4 
 
 Fe 
 
 
 2606-6 
 
 5 
 
 Fe 
 
 K. Ca 
 
 2708-9 
 
 4 
 
 Fe 
 
 
 G 2854 -4 
 
 
 
 Fe 
 
 K 
 
 2619-1 
 
 6 
 
 Fe 
 
 
 2713-3 
 
 3 
 
 Fe 
 
 
 2858-5 
 
 4 
 
 Fe 
 
 
 2625-9 
 
 4 
 
 Fe 
 
 
 2714 3 
 
 2 
 
 Fe 
 
 
 2869-7 
 
 
 
 Fe 
 
 K. Ca 
 
 2627 -0 
 
 5 
 
 Fe 
 
 
 2721-2 
 
 6 
 
 Fe 
 
 
 
 
 
 
 2637-4 
 
 4 
 
 Ca 
 
 
 2733-7 
 
 5 
 
 Fe 
 
 K 
 
 
 
 
 
4 5 6 SPECTR UM ANAL YSIS. [ LECT . v i . 
 
 DESCRIPTION OF BROWNING'S NEW AUTOMATIC 
 SPECTROSCOPE. 
 
 This instrument is furnished with a battery of six equilateral 
 prisms of dense flint glass. All the prisms are linked together 
 like a chain by their respective corners ; the bases being in this 
 manner linked together. This chain of prisms is then bent 
 round, so as to form a circle with the apices outwards. The 
 centre of the base of each prism is attached to a radial rod. All 
 these rods pass through a common centre. The prism nearest 
 the collimator, that is, the first prism of the train, is a fixture. 
 The movement of the other prisms is then in the proportion of 
 1, 2, 3, 4, 5, the last, or 6th prism, moving five times the amount 
 of the 2nd. All these motions are communicated by the simple 
 revolution of the micrometer screw, which is used for measuring 
 the position of the lines in the spectrum, and the amount of 
 motion of each and of the telescope is so arranged, that the 
 prisms are automatically adjusted to the minimum angle of 
 deviation for the ray under examination. It is easy to test the 
 efficiency of the instrument in this respect. On taking the lenses 
 out from the eyepiece of the telescope, the whole field of view is 
 found to be filled with light of the colour of that portion of the 
 spectrum which the observer wishes to examine ; while in a 
 spectroscope of the usual construction, at the extreme ends of 
 the spectrum, just where the light is most. required, only a lens- 
 shaped line of light would be found in the field of view. As a 
 consequence of this peculiarity, the violet and deep-red ends of 
 the spectrum are greatly elongated, or, rather, much more of them 
 can be seen than in an ordinary spectroscope, and the H lines, 
 which are generally seen only with difficulty, come out in a 
 marked manner. 
 
LIST OF THE PEINCIPAL 
 
 MEMOIRS, ETC. ON SPECTRUM ANALYSIS. 
 
LIST OF THE PRINCIPAL 
 
 MEMOIRS, ETC, ON SPECTRUM ANALYSIS, 
 
 i. 
 
 LECTURES OR MEMOIRS RELATING TO THE 
 SUBJECT OF SPECTRUM ANALYSIS GENERALLY. 
 
 BREWSTER, SIR I). : 
 
 Data towards a History of Spectrum Analysis. Compt. Rend. 
 Ixii. 17. 
 
 DEL A UN AY : 
 
 Notice bur la Constitution de 1'Univers. Premiere Partie : Analyse 
 Spectrale. Aunuaire (1869) public par le Bureau des Longi- 
 tudes. Paris: Gauthier-Villars. 
 A most masterly and complete essay on the subject. 
 
 DIBBITS, H. C.: 
 
 De Spectral- Analyse. Academiscli Proefschrift. Rotterdam : Tus- 
 selmeyer. 1863. 
 
 A complete treatise on Spectrum Analysis, giving an historical 
 sketch of the discoveries, with chromolitha of the Carbon and other 
 Spectra. 
 
 GRANDEAU, L. : 
 
 Instruction pratique sur 1' Analyse Spectrale. Paris : AJallet- 
 Bachelier. 1863. I. De.-ci iption des Appareils. II. Leur 
 Application aux Recherches chiraiques. III. Leur Appli- 
 cation aux Observations physiques. IV. La Projection des 
 Spectres. Avoc 2 planches sur cuivre et 1 planche chromo- 
 lithographiec. 
 
460 LIST OF MEMOIRS, ETC. 
 
 HERSOHEL, ALEX. S. : 
 
 On the Methods and recent Progress of Spectrum Analysis. Chem. 
 News, xix. 157. 
 
 HOPPE-SEYLER : 
 
 Die Spectralanalyse. Ein Vortrag, Berlin, 1869. Luderitz'scher 
 Verlag. 
 
 HUGGINS, WILLIAM : 
 
 Lecture on the Physical and Chemical Constitution of the Fixed 
 
 Stars and Nebula3. Royal Institution of Great Britain, 
 
 May 19, 1865. Chemical News, xi. 270. 
 On some further Results of Spectrum Analysis as applied to the 
 
 Heavenly Bodies. Printed in extenso in Report of British 
 
 Association, 1868, p. 152. 
 On tlie Results of Spectrum Analysis as applied to the Heavenly 
 
 Bodies. A Lecture delivered before the British Association at 
 
 the Nottingham Meeting, August 24, 1866. Published, with 
 
 photographs of the Stellar Spectra, by William Ladd, Beak 
 
 Street, London. Chemical News, xiv. 173, 199, 209, 235. 
 On some Recent Spectroscopic Researches. Quarterly Journa. 
 
 Science, No. xxii. April 1869. 
 JAMIN : 
 
 Lectures on Spectrum Analysis. Journ. Pharm. Third Series, 
 
 xlii. 9, 1862. 
 
 KlRCHHOFF, G. : 
 
 On the Solar Spectrum and the Spectra of the Chemical Elements 
 
 Parts I. and II. MacmiLan. 1861-62; 
 
 These Memoirs are translations of the original communications to 
 the Academy of Sciences of Berlin. They contain KirchhofPs theory 
 of the chemical and physical constitution of the Sun, and are accom- 
 panied by four plates of the fixed dark lines in the Solar Spectrum 
 from A to G, and the bright lines of the Metals, showing the coin- 
 cidences. Reduced copies of these plates are given facing Lecture V. 
 and copies of the Tables at the end of this volume. 
 LIELEGG, A. : 
 
 Die Spectralanalyse. Weimar, 1867. Fried. Voigt. 
 
 LOCKYER, J. N. : 
 
 On Recent Discoveries in Solar Physics made by means of the 
 Spectroscope. Royal Institution Proceedings, May 28, 1869. 
 Phil. Mag. [4], xxxviii. 142. 
 Giving an abstract of Lockyer's own researches on Solar Physics. 
 
si 
 
 MOUSSON, A. : 
 
 ON SPECTRUM ANALYSIS. 4 6 1 
 
 LOCKYER, J. N. : 
 
 On Spectrum Analysis. Lectures delivered before the Society of 
 Arts. Journal of the Society of Arts, 1870. 
 
 LORSCHEID, J. : 
 
 Die Spectralanalyse. Munster : Aschendorff. 1870. 
 
 MILLER, W. A. : 
 
 Lectures on Spectrum Analysis (1862). Pharmaceutical Journal, 
 Second Series, iii. 399. Chemical News, v. 201 214. 
 
 A Course of Four Lectures on Spectrum Analysis, with its Applica- 
 tions to Astronomy. Delivered at the Royal Institution of 
 Great Britain. Miy June 1867. Chemical News, xv. 259, 
 276; xvi. 8,20, 47,71. 
 
 Exeter Lecture, 1869. Popular Science Review, Oct. 1S69. 
 
 MOIGNO, FR. : 
 
 Sur r Analyse Spectrale. Cosmos, xxii. 23, 52, 75. 
 
 Resume de nos Connaissances actuelles sur le Spectre. Archives des 
 Sciences Naturelles de Geneve, tome x. mars 1861. 
 
 PROCTOR, R. A. : 
 
 The Sun : Ruler, Fire, Light, and Life of the Planetary System. 
 With ten lithographic plates and numerous illustrations. 
 Longmans. 1871. 
 
 ROSCOE, H. E. : 
 
 Lectures on Spectrum Analysis. Delivered at the Royal Institution 
 
 of Great Britain (1861). Chemical News, iv. 118. 
 Lectures on Spectrum Analysis. Ditto (1862). Chemical News, 
 v. 218, 261, 287. 
 
 SCHELLEN, A. : 
 
 Die Spectralanalyse in ihrer Anwendung auf die Stoffe der Erde 
 und die Natur der Hiinmelskorper. Braunschweig: Wester- 
 mann, 1870. 
 
 A valuable and luminous account of the recent discoveries in 
 Celestial Chemistry and Physics, fully and accurately illustrated by 
 engravings and chromoliths. 
 
 Spectrum Analysis (the same work), translated by J. and C. Lassall, 
 edited, with Notes, by Dr. Huggins, F.R.S. Longmans. 1872. 
 
4()2 LIST OF MEMOIRS, ETC. 
 
 SECCHI : 
 
 Resume* of the Results of Spectrum Analysis applied to Astronomy. 
 
 N. Arch. Ph. Nat. xxiii. 145. 
 Le Soleil. Paris: Gauthier-Villars, 1870. 
 Die Sonue. German translation by Sehellen of the above \vork. A 
 
 complete and splendidly illustrated work on the Sun. Wester- 
 
 mann, 1872. 
 
 STEWART, BALFOUR : 
 
 On the Sun as a Variable Star. Lecture at Royal Institution, April 
 12, 1867. 
 
 THAL^N, R. : 
 
 Spektralanalya expose oeh Hi.storik, med en Spektralkarta. Upsala, 
 1866. 
 
 TYNDALL, J. : 
 
 On the Basis of Solar Chemistry. June 7, 1861. Phil. Mag. Fourth 
 Series, xxii. 147. 
 
 WATTS, W. MARSHALL : 
 
 Index of Spectra. London : Gillman. 1872. 
 
 A most valuable work of reference, in which all the chief lines of 
 the elementary bodies arc mapped according to their wave-lengths. 
 
 II. 
 
 MEMOIRS RELATING TO THE APPLICATION OF 
 SPECTRUM ANALYSIS TO TERRESTRIAL CHEMISTRY. 
 
 ALLEN, O. D. : 
 
 Observations on Cfesium and Rubidium. Silliman's Journal, 
 
 November 1862. Phil. Mag. xxv. 189. 
 The new alkalies shown to be contained in lepidolite from Hebron. 
 
 ALLEN, O. D., <k JOHNSON, S. W. : 
 
 On the Equivalent and Spectrum of Caesium : showed that the Equi- 
 valent of Cfesium is 133. Silliman's Journal, January 1863. 
 Phil. Mag. xxv. 196. 
 
ON SPECTli UM ANALYSIS. 4 (j 3 
 
 ANGSTROM, A. J. : 
 
 Optical Researches. Fogg. Ann. xciv. 141. Phil. Mag. Fourth 
 
 Series, ix. 327. 
 
 In this he shows that a twofold spectrum is always seen when we 
 examine the Electric Spark ; one set of lines being due to the ignition 
 of the particles of air or gas through which the sparks pass, whilst 
 the second set is caused by the incandescence of the metallic particles 
 themselves. 
 
 ATTFIELD : 
 
 On the Carbon Spectrum. Phil. Trans. 1862, p. 221. 
 
 He obtained results similar to those of Swan, but noticed a larger 
 number of lines, and attributes the lines to the glowing vapour of 
 Carbon. 
 
 BABINET : 
 
 Sur la Paragenie. Cosmos, xxv. 393 et seq. 
 
 BECQUEREL : 
 
 On the Spectra of Phosphorescent Bodies. La Lumiere, vol. i. 
 p. 207. (See Lecture V.) 
 
 BRASSAGE: : 
 
 On the Electric Spectra of the Metals. Zeitschr. f. d. ges. Xaturw. 
 ix. 185. 
 
 BREWSTER, SIR D. : 
 
 On the Action of various Coloured Bodies on the Spectrum. Phil- 
 
 Mag. Fourth Series, xxiv. 441. 
 
 On the Monochromatic Lump. Eilin. Royal Soc. Trans. 1822. 
 On Paragenic Spectra. Phil. Mag. January 1866. 
 
 BUNSEN : 
 
 Discoveries of the New Alkaline Metals." Berlin Acad. Ber., 10th 
 
 May, 1860, p. 221. Chem. News, iii. 132. 
 On Cesium. Phil. Mag. xxvi. 241. 
 
 Confirms the atomic weight of Caesium to be 133. 
 On the Presence of Lithium in Meteorites. Phil. Mng. Fourth 
 
 Series, xxiii. 474. 
 On the Preparation of the Rubidium Compounds. Phil. Mng. 
 
 Fourth Series, xxiv. 46. 
 On the Inversion of the Bands in the Didymium Absorption Spectra. 
 
 Phil. Mag. Fourth Series, xxviii. 246; xxxii. 177. (See 
 
 Lecture IV. Appendix F.) 
 
4G4 LIST OF MEMOIRS, ETC. 
 
 BUNSEN & BAHR : 
 
 On the Erbium Spectrum. Ann. Ch. Pharm. cxxxvii. 1. 
 
 CHAUTABD : 
 
 Spectra of Karefied Gases. Phil. Mag. Nov. 1864. 
 
 CHRISTOFLE & BEILSTEIN : 
 
 On the Phosphorus Spectrum. With a Chromolith. of the Spectrum. 
 Ann. Chem. Phys. Fourth Series, iii. 280. 
 
 COOKE, J. P. : 
 
 On the Construction of Spectroscopes. Am. Journ. Sc. and Arts, 
 
 vol. xl. Nov. 1865. 
 
 On the Projection of the Spectra of the Metals. Sill. Journ. [2] 
 xl. 243. 
 
 CROOKES, W. : 
 
 On the Means of increasing the Intensity of Metallic Spectra. 
 
 Chemical News, v. 234 (1862). 
 Thallium, Discovery of. Chemical News, iii. 193. 
 On Thallium and its Compounds. Chem. Soc. Journ. xvii. 112. 
 
 DANIEL : 
 
 On the Spectra of the Induction Spark. Compt. Eend. Ivii. 98. 
 
 DEBRAY, M. H. : 
 
 Sur la Projection des Raies brillantes des Flames colorees par les 
 Metaux. Ann. Chim. Phys. Troisieme Serie, Ixv. 331. 
 
 DELAFONTAINE : 
 
 Note on the Absorption Spectra of Erbium, Didymium, and Terbiara. 
 Ann. Ch. Pharm. cxxxv. 194. Chemical News, xi. 253. 
 
 DIACON, M. E. : 
 
 Recherches sur Hn'fluence des Elements electronggatifs sur le 
 
 Spectre des Metaux. Ann. Chim. Phys. Quatrieme Serie, vi. 1. 
 
 With Drawings of the Spectra of Copper Chloride and Bromide, &c. 
 
 DIACON & WOLF : 
 
 Sur les Spectres des Metaux Alkalins. Mem. de TAcad. de Mont- 
 pellier. 1863. 
 
 DIBBITS : 
 
 Pogg. Ann. 1864, cxxii. 497. 
 
 Observed continuous Spectra by combustion of hydrogen in oxygen 
 and chlorine. 
 
ON SPECTRUM ANALYSIS. 455 
 
 FEUSSNER : 
 
 On the Absorption of Light at different Temperatures. Phil. Mag. 
 Fourth Series, xxix. 471. 
 
 FIZEATJ : 
 
 On the Spectrum of Burning Sodium. Compt. Rend. liv. 493. 
 A figure of the phenomena here observed is given in Fig. 62. 
 
 FOUCAULT : 
 
 Institut, 1849, p. 45. 
 
 Observed the dark double line D in the Spectrum from the electric 
 arc. 
 
 FRANKLAND : 
 
 On the Combustion of Hydrogen and Carbonic Oxide in Oxygen 
 
 under great Pressure. Proc. Roy. Soc. xvi. p. 419. (See 
 
 Lecture IV., Appendix D.) 
 On the Blue Band in the Lithium Spectrum. Phil. Mag. [4], 
 
 xxii. 472. 
 
 FRASER, W. : 
 
 On the Spectrum of Osmium. Chemical News, viii. 34. 
 
 GAMGE, ARTHUR : 
 
 On the Action of Nitrites on the Blood. Phil. Trans. 1868 r p. 589. 
 
 The author shows that the Colour as well as the Absorption 
 Spectrum of Blood undergoes change when acted on by nitrites. 
 The two sharply-defined absorption bands of the oxidized colouring 
 matter become very faint, and an additional though faint band 
 appears in the red. Jf the blood thus altered be acted upon by 
 ammonia, the colour changes from chocolate-brown to blood-red 
 again, and the absorption band in the red disappears, and the two 
 bands between D and E again become visible. 
 
 GASSIOT : 
 
 Description of a large Spectroscope. Proc. Roy. Soc. 1863, xii. 536. 
 Spectroscope with Eleven Prisms. Phil. Mag. Fourth Series, 
 xxviii. 69. 
 
 GIBBS, WOLCOTT : 
 
 Description of Large Spectroscope. Silliman's Journal, Second 
 
 Series, xxv. 110. 
 
 On the Measurement of Wave-lengths by means of Indices of 
 Refraction. Phil. Mag. [4], xl. 177. 1870. 
 H H 
 
466 LIST OF MEMOIRS, ETC. 
 
 GLADSTONE, J. H. : 
 
 On an Optical Test for Didymium. Chem. Soc. Journ. 1858, 
 x. 219. 
 
 In this paper the existence of the Didymium Absorption Lines 
 was first pointed out. 
 
 On the Use of the Prism in Qualitative Analysis. Chem. Soc. 
 Journ. 1858, x. 79. 
 
 In this paper the Absorption Spectra of many coloured 
 metallic salts are given. 
 
 On the Violet Flame of many Chlorides. Phil. Mag. Fourth Series, 
 xxiv. 417. 
 
 GRANDEAU, L. : 
 
 Recherches sur la Presence de Rubidium et Caesium dans les Eaux 
 naturelles, les Mineraux et les Vegetaux. Ann. de Chim. et de 
 Phys., Troisieme Serie, 
 
 HEINRICKS : 
 
 On the Distribution of Lines in Spectra. Silliman's Journal, July 
 1864. 
 
 HEREPATH, W. BIRD : 
 
 On the Use of the Micro-Spectroscope in the Discovery of Blood- 
 stains. Chem. News, xvii. 113, 123. 
 
 HOPPE, F. : 
 
 On the Absorption Lines in the Blood Spectrum. Schmidt's Jahr- 
 buch d. ges. Med. cxiv. 3 (1862). 
 
 HUGGINS, WILLIAM : 
 
 On the Spectra of some of the Chemical Elements. Phil. Trans. 
 
 1864, p. 139, and PoggendorfPs Ann. 
 Giving exact measurement of the lines of twenty-four metals, 
 
 with maps. For reduced copy of these maps see Plates I. and 
 
 II., end of Lecture III. 
 On the Prismatic Examination of Microscopic Objects. Transactions 
 
 of the Royal Microscopic Society. Quarterly Journal of 
 
 Microscopical Science, July 1865. 
 Description of a Hand Spectrum- Telescope. Proc. Roy. Soc. xvi. 241. 
 
 JONES, H. BENCE : 
 
 On the Rate of Passage of Crystalloids in and out of the Body. 
 
 Proc. Roy. Soc. vol. xiv. p. 400. 
 On the Chemical Circulation in the Body. Proc. Roy. List, May 
 
 26, 1865 
 
ON SPECTR UM ANAL YSIS. 4 G 7 
 
 KETTELEB : 
 
 Wave-length Measurement of Metallic Lines. Monatsbericht d. K. 
 Pr. Akad. d. Wiss. zu Berlin, 1864, p. 632. 
 
 KlRCHHOFF & BUNSEN : 
 
 Chemical Analysis by Spectrum Observations. First Memoir. Pogg. 
 
 Ann. ex. 161. Phil. Mag. Fourth Series, xx. 89. (See 
 
 Lecture II. Appendix A.) 
 
 This Memoir contains the exposition of the method of experi- 
 ment, and a description of the Spectra of the metals of the 
 
 alkalies and the alkaline earths. 
 Description of the Properties of the new Metals Caesium and Kubi- 
 
 dium. Second Memoir. Pogg. Ann. cxiii. 337. Phil. Mag. 
 
 Fourth Series, xxii. , 498. (See Lecture III. Appendix A.) 
 KUNBT : 
 
 Spectrum of Phosphorescent Light, with Dark Lines. Phil. Mag. 
 
 Dec. 1867. 
 LAMY, A. : 
 
 De 1'Existence d'un nouveau M6tal, le Thallium. Ann. de Chim. 
 
 et de Phys. Troisieme Serie, Ixvii. 385. 
 LIELEGG, A. : 
 
 On the Spectrum of the Bessemer Flame. Phil. Mag. Fourth 
 
 Series, xxxiv. 302. 
 Contributions to our Knowledge of the Spectra of the Flames of 
 
 Gases containing Carbon. Phil. Mag. Fourth Series, xxxvii. 208. 
 
 MASCABT : 
 
 On the Wave-length of the Lines of certain Metals, directly deter- 
 mined by a Diffraction Grating. Annales Scientifiques de 
 1'Ecole Normale Superieure, tome iv. Paris, 1866. 
 MASSON : 
 
 On the Nature of the Electric Spark. Giving Drawings of the 
 Electric Spectra of several Metals. Ann. de Chim. et de Phys. 
 Troisieme Serie, xxxi. 295. 
 
 MELDE, F. : 
 
 On the Absorption of Light by Coloured Liquids. Pogg. Ann. 
 
 cxxiv. 91 ; cxxvi. 264. 
 MELVILL, THOMAS : 
 
 On the Examination of Coloured Flames by the Prism. Edinburgh 
 
 Phys. and Lit. Essays, ii. 12 (1752). 
 
 To the writer of this paper the remarkable phenomena exhibited 
 by coloured lights when examined by the prism were well known. 
 H H 2 
 
468 LIST OF MEMOIRS, ETC. 
 
 MILLER, WILLIAM ALLEN : 
 
 Experiments and Observations on some cases of Lines in the Pris- 
 matic Spectrum produced by the Passage of Light through 
 coloured Vapours and Gases, and from certain coloured Flames. 
 Kead June 21, 1845, at British Association. Printed in 
 Phil. Mag. Third Series, xxvii. 81. 
 
 On the Photographic Transparency of various Bodies, and on the 
 Photographic Effects on Metallic and other Spectra obtained by 
 means of the Electric Spark. Phil. Trans. 1862, p. 861. 
 
 Note on the Spectrum of Thallium. Proc. Roy. Soc. xii. 407. 
 Heated in the Electric Spark, Thallium exhibits five lines in 
 
 addition to the green line Tl a. 
 
 MILLER, W. HALLOWS : 
 
 On the Absorption Bands of Nitrous Acid Gas, &c. Phil. Mag. 
 Third Series, ii. 381. 
 
 MlTSCHERLICH, ALEXANDER : 
 
 On the Spectra of Compounds and Simple Substances. With Two 
 
 Plates. Phil. Mag. xxviii. 169. 
 
 He concludes that compounds whose vapours can be heated up to 
 incandescence without undergoing decomposition yield spectra dif- 
 ferent from those of their elementary constituents. He adds some 
 singular speculations concerning a supposed relation between the 
 atomic weights of the haloid compounds of Barium and the distance, 
 on an arbitrary scale, read off between the chief lines of their spectra. 
 
 MORREN, M. A. : 
 
 De la Flamme de quelquea Gaz Carbures, et en particulier de celle 
 de P Acetylene et du Cyanogen. Ann. Chem. Phys. [4], iv. 
 305. With figure of the Carbon Spectrum. 
 
 On the Spectrum of the Non-luminous Gas-flame. Chemical News, 
 ix. 135. 
 
 MULDER, E. : 
 
 On the Spectra of Phosphorus, Sulphur, and Selenium. Journ. Pr. 
 Chem. xci. III. 
 
 MULLER, J. : 
 
 Determination of the Wave-length of certain Bright Lines in the 
 
 Spectrum. Phil. Mag. Fourth Series, xxvi. 259. 
 Wave-lengths of the Metallic Lines. Fortsch. d. Physik. Jahr^. 
 
 1863, p. 191; 1865, p. 229. 
 On the Wave-length of the Blue Indium Line. Phil. Mag. [4], 
 
 xxx. 76. 
 
ON SPECTR UM ANAL YSIS. 4 (J 9 
 
 PASTEUR : 
 
 On the Spectrum of the Phosphorescent Light emitted by certain 
 
 Animals. Corapt. Rend. lix. 509. 
 
 He found that the light from a Mexican Fyrophorus gave a con- 
 tinuous spectrum. 
 
 PICKERING : 
 
 Comparative Efficiency of different Forms of Spectroscopes. Silli- 
 man's Journal, May 1868. 
 
 Pis AN I : 
 
 On Pollux, a Silicate of Caesium. Compt. Rend. Iviii. 714. 
 
 PLUCKER : 
 
 On the Measurements of the Wave-lengths of the Metallic Lines. 
 
 Quoted in Wiedemann, Lehre von Galvanismus, ii. 875, Taf. i. 
 On the Nature of the Electric Discharge in vacua. Pogg. Ann. civ. 
 
 March August, 1858; cv. May 1859; cvii. 497638. 
 
 PLUCKER & HITTORF : 
 
 On the Spectra of Ignited Gases and Vapours, with especial regard 
 to the different Spectra of the same Elementary Gaseous Sub- 
 stance. Phil. Trans. 1865, p. 1. 
 
 These important experiments show that by varying the physical 
 conditions certain of the elementary bodies yield two distinct spectra. 
 Pliicker explains this by the assumption of several allotropic con- 
 ditions of the element existing at various temperatures. 
 
 ROBINSON, DR. : 
 
 On Electric Spectra. Phil. Trans. 1863. 
 
 ROOD, O. N. : 
 
 On the Didymhim Absorption Spectrum. Silliman's Journal, Second 
 Series, xxxiv. 129. 
 
 ROSCOE, H. E. : 
 
 On the Spectrum produced by the Flame evolved in the Manufacture 
 of Steel by the Bessemer Process. Proc. Lit. Phil. Soc. 
 Manchester, Feb. 24, 1863; Phil. Mag. Fourth Series, xxv. 
 318 ; Journ. Iron and Steel Institute, vol. ii. p. 38. 
 
 ROSCOE & CLIFTON : 
 
 On the Effect of Increased Temperature upon the Nature of the Light 
 emitted by the Vapour of certain Metals or Metallic Compounds. 
 Chemical News, v. 233 (1862). 
 
470 LIST OF MEMOIRS, ETC. 
 
 RUTHERFURD, L. M. : 
 
 On the Construction of the Spectroscope, Am. Journ. Sc. Arts, 
 vol. xxxix. 1869, p. 129. 
 
 SEGUIX, J. M. : 
 
 On the Spectrum of Fluoride of Silicium. Compt. Rend. liv. 993 ; 
 
 Chemical News, vi. 282. 
 
 On the Spectra of Phosphorus and Sulphur. Phil. Mag. Fourth 
 Series, xxiii. 416. 
 
 SORBY, H. C. : 
 
 On the Application of Spectrum Analysis to Microscopical Investi- 
 gations, and especially to the Detection of Bloodstains. Chemi- 
 cal News, xi. 186, 194, 232, 256. 
 
 On a Definite Method of Qualitative Analysis of Animal and Vege- 
 table Colouring Matters hy means of the Spectrum-Microscope. 
 Proc. Roy. Soc. xv. 433. 
 
 On a New Micro-Spectroscope, and on a New Method of printing a 
 Description of the Spectra seen with the Spectrum-Microscope. 
 Chem. News, xv. 220. 
 
 On Jargonium, a new Element accompanying Zirconium. Chemical 
 News, xix. 121. Proc. Roy. Soc. xvii. 511. 
 
 On some remarkable Spectra Compounds of Zircouia and the Oxides 
 of Uranium. Proc. Roy. Soc. xviii. 197. 
 
 STOKES, G. G. : 
 
 On the Long Spectrum of the Electric Light. Phil. Trans. 1862, 
 p. 599. 
 
 He shows that rays exist in the ultra-violet portion at a dis- 
 tance from the last visible rays equal to six times the length of 
 the whole visible spectrum. Each metal possesses a peculiar 
 series of these bands, which may be rendered visible by allowing 
 the rays to fall on a fluorescent body. 
 
 On the Discrimination of Organic Bodies by their Optical Properties. 
 Roy. Inst. March 4, 1864. Phil. Mag. Fourth Series, xxvii. 
 388. 
 
 On the Reduction and Oxidation of the Colouring Matter of the 
 Blood. Proc. Roy. Soc. xiii. 353. 
 
 SWAN : 
 
 On the Prismatic Spectra of the Flames of Compounds of Carbon 
 
 and Hydrogen. Ed. Phil. Trans, xxi. 411. 
 
 These lines remained unaffected by alteration in composition of 
 the burning body in hydrogen or oxygen. Swan carefully measured 
 
ON SPECTRUM ANALYSIS. 471 
 
 the position of these lines, and he first explained the delicacy of 
 the Sodium reaction, and first described the use of a collimator for 
 epeetroscopic research, rendering the rajs thus parallel as if the slit 
 were placed at an infinite distance (1856). 
 
 TALBOT, H. Fox : 
 
 Some Experiments on Coloured Flames. Brewster's Journal of 
 
 Science, v. 1826. 
 On a Method of obtaining Homogeneous Light of Great Intensity. 
 
 Phil. Mag. Third Series, 1833, iii. 35. 
 
 On the Flame of Lithia. Phil. Mag. Third Series, 1834, iv. 11. 
 On Prismatic Spectra. Phil. Mag. 1836, ix. 3. 
 
 THALEN, E. : 
 
 On the Determination of the Wave-lengths of the Lines of the 
 
 Metals. Nova Acta Keg. Soc. Sc. Upsal., Third Series, vi. 
 
 Upsala, 1868. 
 
 Taking as his starting-point the determination of wave-lengths of 
 the principal Fraunhofer's Lines by Angstrom (Eecherches sur le 
 Spectre Solaire, par A. J, Angstrom. I. Spectre Normal du Soleil. 
 Upsal, 1868), the author, by graphical interpolation, obtains, from 
 KirchhofFs and Angstrom's Tables, the wave-lengths of the bright 
 metallic lines. A large Plate accompanies the Memoir, giving the 
 lines and their wave-lengths of forty-five metals. The following 
 twenty-three were examined in the metallic state : K, Na, Mg, Al, 
 Fe, Co, Ni, Zn, Cd, Pb, Tl, Bi, Cu, Hg, Ag, Au, Sn, Pt, Pd, Os, 
 Sb, Te, In. The remaining twenty-two were examined as chlorides : 
 Li, Cs, Kb, Ba, Sr, Ca, Gl, Zr, Er, Y, Th, Mn, Cr, Ce, D, L, U, 
 Ti, Wo, Mo, V, As. 
 
 TYNDALL & FEANKLAND : 
 
 On the Blue Band of the Lithium Spectrum. Phil. Mag. Fourth 
 Series, xxii. 151, 472. 
 
 VAN DEB WILLIGEN : 
 
 On the Spark of the Induction Coil. Pogg. Ann. cvi. 615. 
 
 VlERORDT, K. : 
 
 Die Anwendung des Spectral Apparates zur Vergleichung und 
 Messung der Starke des farbigen Lichtes. Tubingen, 1871. 
 
 WALTENHOFEN, A. VON : 
 
 Spectra of Electric Spark in rarefied Gases. Dingl. Pol. J. 
 clxxvii. 38. 
 
4 72 LIST OF MEMOIRS, ETC. 
 
 WATTS, W. M. : 
 
 On the Spectrum of the Bessemer Flame. Phil. Mag. Fourth 
 
 Series, xxxiv. 437. 
 
 On the Spectra of Carbon. Phil. Mag. Fourth Series, xxxviii. 249. 
 On Double Spectra. Quart. Journ. Science, Jan. 1871. 
 On the Spectrum of the Bessemer-flame. Phil. Mag. vol. 45, p. 81. 
 
 WHEATSTONE, C. : 
 
 On the Prismatic Decomposition of the Electric, Voltaic, and Electro- 
 magnetic Sparks. Read August 12, 1835. British Assoc. 
 Dublin. Chemical News, iii. 198. 
 
 WULLNER : 
 
 On the Spectra of the Gases under different Pressures. Phil. Mag. 
 Fourth Series, xxxvii. p. 405 ; xxxix. p. 365. 
 
 YOUNG, C. A. : 
 
 Spectroscopic Notes. Journ. Franklin Institute. 
 
 III. 
 
 MEMOIRS RELATING TO THE APPLICATION OF 
 SPECTRUM ANALYSIS TO CELESTIAL CHEMISTRY. 
 
 AIRY, G. B., Astronomer Royal : 
 
 Measurements of Stellar Lines. Monthly Notices of the Roy. Astron. 
 
 Soc. xxiii. 190. 
 Wave-lengths of Lines in Kirchhoff's Maps. Phil. Trans. 1868, 
 
 p. 29. 
 
 ANGSTROM, A. J. : 
 
 Wave-length Measurements. Aus Oefversigt af K. Vetensk. Acad. 
 
 Forh. No. 2. Pogg. Ann. cxxiii. 489. 
 
 On the Fraunhofer Lines visible in the Solar Spectrum, and on the 
 Coincidence of these Lines with the Bright Lines of certain 
 Metals. Phil. Mag. Fourth Series, xxiv. 1. 
 
 Optical Researches. Vetensk. Acad. February 1853. Phil. Mag. 
 Fourth Series, ix. 327. 
 
 The nature of the Electric Spectrum pointed out. 
 
ON SPECTR UM ANALYSIS. 473 
 
 ANGSTBOM, A, J. : 
 
 Observations on certain Lines of the Solar Spectrum. Phil. Mag. 
 Fourth Series, xxiii. 76. 
 
 Angstrom believes that the groups A and B, as well as a group 
 lying between B and c, are due to absorption in the earth's 
 atmosphere, caused by the presence of some compound gas 
 perhaps carbonic acid but not due to aqueous vapour. 
 Recherches sur le Spectre normal du Soleil, avec Atlas de six planches. 
 Upsal. : W. Schultz, 1868. 
 
 The Solar Lines from A to H mapped according to their 
 wave-lengths. A most valuable and interesting memoir. See 
 Lecture V. Appendix A. 
 
 AGNELLO ANGELO : 
 
 Ecclisse Totale del 22 Dec. 1870. Palermo, 1870. 
 
 BLASEBNA, P. : 
 
 Sulla Polarizzazione della Corona Solare. Palermo, 1871. 
 
 BREWSTEB, SIB D. : 
 
 Observations of the Lines of the Solar Spectrum, and on those pro- 
 duced by the Earth's Atmosphere, and by the Action of Nitrous 
 Acid Gas. Phil. Mag. Third Series, viii. 384. 
 
 BBEWSTEB & GLADSTONE : 
 
 On the Lines of the Solar Spectrum. Map of the Solar Spectrum, 
 giving the Absorption Lines of the Earth's Atmosphere. Phil. 
 Trans. 1860, p. 149. 
 
 BBOWNING, J. : 
 
 On the Spectra of the Meteors of Novemher 13-14, 1866. Phil. 
 Mag. Fourth Series, xxxiii. 234. 
 
 CHACOBNAC : 
 
 Physical Constitution of the Sun. Compt. Rend. Ix. 170. 
 
 COOKE, J. P. : 
 
 On the Aqueous Lines of the Solar Spectrum. Phil. Mag. Fourth 
 
 Series, xxxi. 337. 
 
 When the air was damp Cooke saw seven lines and a nebulous 
 band, besides the Nickel line, between the D lines. These seven 
 lines disappeared when the air was dry. 
 
 DlTSCHEINEB, L. ! 
 
 Wave-length of Fraunhofer's Lines measured. Wien. Acad. 1 
 2 Abthl. 1. 296. 
 
474 LIST OF MEMOIRS, ETC. 
 
 DONATI : 
 
 Intorno alle Strie degli Stellari. II Nuovo Cimento, xv. 292. 
 
 DRAPER, WILLIAM : 
 
 On the Variation in Intensity of the Fixed Lines of the Solar 
 
 Spectrum. Phil. Mag. [4], xxv. 342. 
 FAYE : 
 
 On the Physical Constitution of the Sun. Compt. Rend. Ix. 89, 
 
 138, 468. 
 FRANKLAND & LOCKYER : 
 
 Preliminary Note of Researches on Gaseous Spectra in relation to 
 the Physical Constitution of the Sun. Proc. Roy. Soc. xvii. 288. 
 Researches on Gaseous Spectra in relation to the Physical Constitu- 
 tion of the Sun, Stars, and Nebulae. Proc. Roy. Soc. xvii. 453 ; 
 xviii. 79. 
 FRAUNHOFER : 
 
 Denkschriften der Miinchener Academie. 1814 and 1815. Giving 
 exact measurement of the dark Solar Lines. 
 
 For fac-simile of Fraunhofer's map see p. 27. 
 GIBBS, WOLCOTT : 
 
 On the Normal Solar Spectrum. Silliman's Journal, Jan. 1867. 
 
 This paper gives the wave-lengths of the principal lines of the 
 Solar Spectrum. 
 On Wave-lengths. Silliman's Journal, March 1869. 
 
 GLADSTONE, J. H. : 
 
 Notes on the Atmospheric Lines of the Solar Spectrum, and on certain 
 
 Spectra of Gases. Proc. Roy. Soc. xi. 305. 
 GRANDEATT, L. : 
 
 On the Spectrum of Lightning. Chemical News, ix. 66. 
 HERSCHEL, ALEX. : 
 
 On the Spectra of Meteors. Intellectual Observer, Oct. 1866. 
 
 On the Total Eclipse of the Sun of 18th August, 1868. Proc. Roy. 
 
 Inst. 1868-9. 
 HERSCHEL, LIEUT. JOHN : 
 
 On Spectra of Southern Nebulae, and Spectrum of Lightning. Proc. 
 
 Roy. Soc. xvi. 416, 451 ; xvii. pp. 5861. 
 Additional Observations of Southern Nebulae. Proc. Roy. Soc. 
 
 xvii. 303. 
 
 On the Solar Eclipse of 1868 seen at Jamkandi. 
 Spectroscopic Observations of the Solar Prominences. Proc. Roy. 
 Soc. xviii. 62. 
 
ON SPECTR UM ANALTSIS. 475 
 
 HUGGINS, WILLIAM : 
 
 On the Disappearance of the Spectrum of e Pisciura at its Occulta- 
 tion of January 4, 1865. With Conclusions as to the Non-exist- 
 ence of a Lunar Atmosphere. Monthly Notices, Roy. Aatron. 
 Soc. xxv. 60. Ohem. News, xi. 175. 
 
 On the Spectra of the Nebulae Phil. Trans. 1864, p. 437. Phil. 
 Mag. June 1866. 
 
 On the Nebula in the Sword-handle of Orion. Proc. Roy. Soc. 
 1865, p. 39. 
 
 Further Observations on the Spectra of some of the Nebulae, with a 
 
 Mode of determining the Brightness of these Bodies. Phil. 
 
 Trans. 1866, pp. 381397. 
 
 On the Spectrum of Comet I. 1866. Proc. Roy. Soc. xv. 5. 
 On the Spectrum of Comet II. 1867. Monthly Notices, Roy. Astron. 
 
 Soc. xvii. 288. 
 On the Spectrum of Brorsen's Comet, 1868. Proc. Roy. Soc. 
 
 xvi. 386. 
 Further Observations on the Spectra of some of the Stars and 
 
 Nebulae, with an Attempt to determine therefrom whether these 
 
 bodies are moving towards or from the Earth ; also Observations 
 
 of the Spectra of the Sun and of Comet II. 1868. Phil. Trans. 
 
 1868, p. 529. 
 On the Spectrum of Mars. Monthly Notices, Royal Astron. Soc. 
 
 xxvii. 178. 
 
 Description of a Hand Spectrum-Telescope. Proc. Roy. Soc. xvi. 241. 
 This instrument is suitable for an observation of Meteors, and 
 
 was successfully used at the Solar Eclipse of 1868. 
 Note on a Method of viewing the Solar Prominences without an 
 
 Eclipse. Proc. Roy. Soc. xvii. 302. 
 
 Note on the Heat of the Stars. Proc. Roy. Soc. xvii. 309. 
 On some further Results of Spectrum Analysis as applied to the 
 
 Heavenly Bodies. Lecture at Roy. lust. Reported in Chem. 
 
 News, .xix. 187. 
 On the Spectrum of the Great Nebula in Orion and on the Motions 
 
 of some Stars towards or from the Earth. Proc. Roy. Soc. 
 
 vol. xx. 379. 
 
 HUGGINS, WILLIAM, & MILLER, W. A. : 
 
 On the Lines of the Spectra of some of the Fixed Stars. Proc. 
 Roy. Soc. xii. 444. 
 
476 LIST OF MEMOIRS, ETC. 
 
 HUGGINS, WILLIAM, & MILLER, W. A. : 
 
 On the Spectra of some of the Fixed Stars. Phil. Trans. 1864, 
 
 p. 413 ; Phil. Mag. June 1866. 
 
 The first complete and accurate investigation of the Stellar 
 
 Spectra. 
 On the Spectrum of the Variable Star a Orionis. Monthly Notices, 
 
 xxvi. p. 215. 
 On the Spectrum of a New Star in Corona Borealis. Proc. Roy. 
 
 Soc. xv. 146, May 17, 1866. 
 JANSSEN : 
 
 On the Terrestrial Rays of the Solar Spectrum. Phil. Mag. Fourth 
 
 Series, xxx. 78. 
 Reply to Angstrom's Observations on the Solar Lines. Phil. Mag. 
 
 Fourth Series, xxiii. 78. 
 On the Spectrum of Aqueous Vapour. Phil. Mag. Fourth Series, 
 
 xxxii. 315. 
 
 According to Janssen the line A, a great part of B, c, and two 
 
 lines between c and D, are caused by aqueous vapour. See Fig. 66. 
 Absorption Spectra of Aqueous Vapour. Compt. Rend. Ivi. 538 ; 
 
 Ix. 213. 
 On the Terrestrial Atmospheric Absorption Lines. Compt. Rend. liv. 
 
 1280. 
 
 On the Solar Protuberances. Proc. Roy. Soc. xvii. 276. 
 Report on the Solar Eclipse of 1868 as seen at Guntoor. Annuaire 
 
 du Bureau des Longitudes, 1869, p. 584. 
 KIRCHHOFF, G. : 
 
 On the Relation between the Radiating and Absorbing Powers of 
 
 different Bodies for Light and Heat. Phil. Mag. [4], xx. 1. 
 This paper contains a discussion of the Mathematical Theory 
 
 of the Law of Exchanges. It is followed by a Postscript by 
 
 the author, on the history of the subject. 
 Ueber den Zusammenhang zwischen Emission und Absorption von 
 
 Licht und Warme. Monatsberichte d. Berliner Acad. 27th Oct. 
 
 1859. Phil. Mag. [4], xix. 163. 
 
 This contains the statement of the Law of Exchanges, and 
 
 the first announcement of the discovery of the cause of Fraun- 
 
 hofer's lines. 
 
 On the History of Spectrum Analysis. Phil. Mag. [4], xxv. 250. 
 An interesting historical survey of the early researches on 
 
 Spectrum Analysis, and remarks on the history of the chemical 
 
 analysis of the Solar Atmosphere. 
 
ON SPECTR UM ANALYSIS. 477 
 
 LE SUEUB, : 
 
 On the Nebulae of Argo and Orion, and on the Spectrum of Jupiter. 
 Proc. Roy. Soc. xviii. 
 
 On Spectroscopic Observations with the -245 Great Melbourne 
 Telescope, xviii. 242. 
 
 LOCKYEB, J. N. : 
 
 Spectroscopic Observations of the Sun. No. I. Proc. Roy. Soc. xvii. 
 
 91 ; No. IT. xvii. 128131 ; No. III. xvii. 350 ; No. IV. 
 
 xvii. 415 ; No. V. xviii. 74. (See also Lecture V. Appendix C.) 
 Notice of an Observation of the Spectrum of a Solar Prominence. 
 
 Proc. Roy. Soc. xvii. pp. 91, 104. 
 Supplementary Note on a Spectrum of a Solar Prominence, xvii. 
 
 p. 128. 
 Remarks on the recent Eclipse of the Sun as observed in the United 
 
 States. Proc. Roy. Soc. xviii. 179. 
 
 Reply to some Remarks of Father Secchi on the recent Solar Dis- 
 coveries. Phil. Mag. Jan. 1870. 
 Solar Eclipse 1869. American Observations, Report on. Nature, 
 
 vol. i. p. 14. 
 Spectroscopic Observations of the Sun, No. II. Phil. Trans. 1869. 
 
 Part I. p. 425. 
 Researches in Spectrum Analysis in connection with the Spectrum 
 
 of the Sun. No. I. Proc. Roy. Soc. xxi. 83. Dec. 12, 1872. 
 
 MASCABT : 
 
 On the Rays of the Ultra-violet Solar Spectrum. Compt. Rend. 
 
 Nov. 1863. Phil. Mag. Fourth Series, xxvii. 159. 
 Sur 1' Application du Spectroscope & 1'Observation des Phenomenes 
 
 d'Interfe'rence. Journal de Physique, No. 1, p. 17, 1872. 
 
 MERZ, S. : 
 
 On the Dark Lines in the Spectra of Stars. Pogg. Ann. cxvii. 654. 
 
 RAYET : 
 
 On the Solar Eclipse of 1868. Roy. Astron. Soc. Report, 1868-9, 
 
 p. 152. 
 On the Refrangibility of the Brilliant Yellow Ray of the Solar 
 
 Atmosphere. Chem. News, xix. 158. 
 
478 LIST OF MEMOIRS, ETC. 
 
 RESPIGHI, L. : 
 
 Oaservazioni spettroscopiche del Bordo e delle Protuberanze Solari. 
 Roma, 1871. 
 
 With lithographic plate of prominences. 
 Sulla Constituzione fisica del Sole. R. Accad. dei Lincei, 10 April, 
 
 1871. 
 
 RICCA, V. S. : 
 
 La Corona Solare 1' ecclisse. 22 Dec. 1870. Palermo, 1871. 
 ROSCOE, H. E. : 
 
 On the Opalescence of the Atmosphere for the Chemically Active 
 Rays. Roy. Inst. June 1, 1866. Chem. News, xiv. 28. 
 
 RUTHERFURD, L. M. : 
 
 Measurement of Stella Spectra. Silliman's Journ. xxxv. 71. 
 
 SEC CHI : 
 
 On the Spectrum of the Great Nebula in Orion. Chem. News, xi. 
 
 136. Read before the French Academy, March 5, 1865. 
 On the Spectral Rays of the Planet Saturn. Phil. Mag. Fourth 
 
 Series, xxx. 73. 
 
 Measurement of a few Stellar Lines. Astron. Nachr., 3 Marz, 1863. 
 Spectrum Observations, made at the Roman Observatory. Volumi 
 
 dell' Accademia de Roma, xl. 
 
 On a Continuous Solar Spectrum. Compt. Rend. Mars. 1869. 
 On Stellar Spectrometry. Chem. News, xviii. 167. 
 On the Spectrum of the Planet Neptune. Compt. Rend. Nov. 22, 
 
 1869. 
 
 Spectrum of a Orionis. Monthly Notices, xxvi. 214. 
 Spettri prismatici delle Stelle fisse. Atti della Soc. Ital. Roma, 1868. 
 Catalogo delle Stelle, &c. Parigi : Gauthier-Villars, 1867. 
 Memoria Seconda, 1868. 
 
 STEWART, BALFOUR : 
 
 Report on the Theory of Exchanges. British Assoc. Reports, 1861. 
 On the Nature of Light emitted by heated Tourmaline. Phil. Mag. 
 
 Fourth Series, xxi. 391. 
 Reply to Kirchhoff on the History of Spectrum Analysis. Phil. 
 
 Mag. Fourth Series, xxv. 354. 
 On the Theory of Exchanges. Trans. Roy. Soc. Edin. 1858. 
 
 Enunciated this principle completely for the heating rays pre- 
 viously proposed by Prevostaye and Dessains. In Feb. 1860, 
 Stewart applied this theory to the luminous rays, subsequently to, 
 but independently of, KirchhofF. 
 
ON SPECTRUM ANALYSIS. 479 
 
 STOKES, G. G. : 
 
 Ori the Change of Refrangibility of Light. Phil. Trans. 1 1852, 
 Part II. p. 463. With drawing of the fixed lines in Solar 
 Spectrum in the extreme violet, and in the invisible region 
 beyond. 
 
 STONEY : 
 
 On the Physical Constitution of the Sun and Stars. Proc. Roy. 
 
 Soc. xvi. 25 ; xvii. 1. 
 
 On the Bearing of recent Observations upon Solar Physics. Phil. 
 Mag. Fourth Series, xxxvi. 447. 
 
 STRUVE, OTTO VON : 
 
 Beobachtung eines Nordlichtspectrum (Aurora Borealis). Bull, de 
 1'Acad. Imp. des Sciences de St. Petersbourg, tome xiii. 49, 50. 
 
 TENNANT, MAJOR : 
 
 Report of the Indian Eclipse, 1868. Roy. Astron. Society. Memoirs, 
 vol. vii. Nature, vol. i. 536. 
 
 TYNDALL, J. : 
 
 On Cometary Theory. Phil. Mag. Fourth Series, xxxvii. 241. 
 
 WEISS, A. : 
 
 On the Changes produced in the Position of the Fixed Lines in the 
 
 Spectrum of Hyponitric Acid by Changes in Density. Phil. 
 
 Mag. Fourth Series, xxii. 80. 
 On Fraunhofer's Lines seen in Sunlight at Low Altitudes. Phil. 
 
 Mag. Fourth Series, xxiv. 407. 
 
 WOLF & RAYET : 
 
 On Three Small Stars with Bright Lines. Compt. Rend. August 
 
 1867. 
 
 WOLLASTON, W. H. : 
 
 A Method of examining Refractive and Dispersive Powers by Pris- 
 matic Reflexion. Containing the first discovery of the dark 
 Solar Lines. Phil. Trans. 1802, p. 365. 
 
 YOUNG, C. A. : 
 
 Spectroscopic Notes on the Sun. Chem. News, xx. 271. 
 On the Solar Corona. Amer. Journ. Sci. and Arts, May 1871. 
 Spectroscopic Notes. Spot Spectra. Journ. Franklin Institute, 
 vol. Ix. 
 
480 LIST OF MEMOIRS, ETC. 
 
 ZOLLNEB, F. : 
 
 On a New Spectroscope, with Contributions to the Spectral Analysis 
 of the Stars. Phil. Mag. Fourth Series, xxxviii. 360. 
 
 On the Spectrum of the Aurora. Phil. Mag. xli. 122. 
 
 On the Influence of Density and Temperature. 
 
 On the Spectra of Incandescent Gases. Phil. Mag. xli. 190. 
 
 On the Spectroscopic Eeversion Telescope. Phil. Mag. xliii. 47 ; 
 xliv. 417. 
 
INDEX. 
 
 A. 
 
 Absorption and Radiation, 309. 
 
 Absorption spectra, changes in, 177. 
 
 Air spectrum, the, 191. 
 
 Aldebaran, spectrum of. 328. 
 
 Alizarine, artificial spectrum of, 180. 
 
 Alkalies and alkaline earths, spectra of, 
 shown, 63. 
 
 Analysis of mineral waters, 106. 
 
 Angstrom on the normal solar spec- 
 trum, 272; on the spectra of com- 
 
 pounds, 274. 
 
 Angstrom's maps of the metal lines, 
 Plate V. facing Lecture V. ; tables of 
 solar lines, 453. 
 
 Apparatus used for star spectra, 324. 
 
 Aquarius, nebula in, 338. 
 
 Aqueous vapour in the planetary atmo- 
 spheres, 321. 
 
 Atmospheric absorption bands, 251. 
 
 Aurora borealis, spectrum of, 270, 275. 
 
 B, 
 
 Barium, spectrum reactions of, 90. 
 
 Basis of solar chemistry, 223. 
 
 Becquerel, phosphorescence, 188. 
 
 Bessemer flame, spectrum of, 175, 215. 
 
 Betelgeux, spectrum of, 330. 
 
 Blood, absorption lines in, 181. 
 
 Blood-stains, discrimination of, 185. 
 
 Brewster and Gladstone, absorption 
 lines, 250. 
 
 Brewster on coloured flames, 103. 
 
 Brewster's monochromatic lamp, 101; 
 absorption bands, 177. 
 
 Brorsen's comet, 344. 
 
 Browning, new spark holder, 326 ; 
 automatic spectroscope, 456. 
 
 Bunsen and Kirchhoff, first Memoir on 
 spectrum analysis, 77; on the mode 
 of using a spectroscope, 94. 
 
 Bunsen, burner flame of, 55. 
 
 Buiisen on spectrum analysis, 77; dis- 
 covery of the new alkaline metals, 
 104 ; on a method of mapping spectra, 
 97 ; on erbium and didymium, 217. 
 
 C, 
 
 Cjesium and rubidium, discovery of,104; 
 
 reactions of, 106 ; spectra of, 107. 
 Calcium compounds, spectra of, 165. 
 Calcium, spectrum reactions of, de- 
 scribed, 85. 
 Calorescence, 13. 
 Carbon in comets, 344 404. 
 Carbon spectra, Plate facing Lect. VI, 
 
 Nos. 10, 11 ; figures of the, 174. 
 Carbon, spectrum of, 169, 210. 
 Chemical action of the constituent parts 
 
 of solar light, 43 ; chemical rays, 
 
 varying intensity of, 19. 
 Chemically active rays, 17, 229. 
 Chlorine and hydrogen exploded, 17. 
 Chromosphere, discovery of the, 258; 
 
 lines in the, 304. 
 Coincidence of bright iron and dark 
 
 solar lines, 239 ; of metallic lines, 
 
 122. 
 Coloured flames, early observations of, 
 
 101 ; spectra of, 55. 
 Coloured stars, 330. 
 Comet II. 1868, spectrum of, 345, 399. 
 Comets, spectra of, 344. 
 Complementary colours, 7. 
 Composition of white light, 7. 
 Compound bodies, spectra of, 165. 
 Compounds, spectra of, 207. 
 Continuous spectra from ignited gases, 
 
 164. 
 
 Corona, spectrum of the, 267. 
 Crookes' discovery of thallium, 110. 
 Cruorine, bands of, 182. 
 Cyclones in the sun, 263, 353. 
 
 D. 
 Dark lines in solar spectrum, discovery 
 
 of, 26. 
 
 Dark sodium flame explained, 235. 
 Daylight, chemical action of, 22. 
 Delicacy of spectrum-analytical method, 
 
 69. 
 Deville on luminosity of gases under 
 
 pressure, 210. 
 
 I I 
 
482 
 
 INDEX. 
 
 Didymium, absorption bands of, 177 ; 
 
 compounds, spectra of, 217. 
 Double spectra of the elements, 193. 
 Double stars, 331. 
 Draper's law, 51. 
 
 E. 
 
 Eclipse, total solar, 254, 267, 276, 285. 
 
 Electric discharge, light of, 115 ; lamp, 
 arrangement of, 52 ; spark in hydro- 
 gen, 158. 
 
 Erbium, spectrum of, 217. 
 
 Exchanges, law of, 239, 309. 
 
 Explanation of dark solar lines, 231. 
 
 Extracts from "Newton's Opticks," 
 31. 
 
 F. 
 
 Faculse on the sun's surface, 263. 
 
 Faraday on the nature of the electric 
 spark, 114. 
 
 Fixed stars, constitution of, 328. 
 
 Fluorescence, 189. 
 
 Foucault's experiment, 231. 
 
 Fox-Talbot on spectra of coloured 
 flames, 102 ; on metal spectra, 118. 
 
 Frankland and Lockyer on spectra of 
 glowing gases, 208 ; on the atmo- 
 spheric pressure operating in a pro- 
 minence, 432. 
 
 Fraunhofer's discovery and map, 28 ; 
 conclusion as to cause of dark lines, 
 30 ; observations on planet light, 
 223 ; lines produced artificially, 233. 
 
 Gases, spectra of incandescent, 53, 191. 
 Geissler's tubes, spectra of, 158. 
 
 H. 
 
 Hsematin, bands of, 182. 
 
 Heat, action of increased, 204. 
 
 Heating rays of the spectrum, 11. 
 
 Heavy metals, spectra of, 113. 
 
 Helmholtz on vision, 7. 
 
 Herschel, Lieut., on the solar eclipse, 
 
 281. 
 
 Herschel, Sir J. ,on coloured flames, 101. 
 Historical sketch, 101. 
 History of spectrum analysis, Kirchhoff 
 
 on the, 132. 
 
 Huggins and Miller, extract from Me- 
 moir by, 359. 
 
 Huggins' maps of the metallic lines, 
 Tlates I. and II. following Lecture 
 III.; description of, 125. 
 
 Huggius on the spectra of the elements, 
 140 ; on the red solar prominences, 
 301 ; on the motion of stars, 349 
 et seq. ; on the spectra of stars and 
 nebulae, 349 et seq.; on comets, 374 
 et seq. 
 
 Hydrogen compared with nebular spec- 
 trum, 344; lines, broadening of, 163 ; 
 spectrum, description of, 192 ; spec- 
 trum of, Plate facing Lecture VI. 
 No. 8. 
 
 I. 
 
 Ignited gases sometimes give continuous 
 
 spectra, 164. 
 
 Incandescent solids, spectrum of, 51. 
 Increase of heat, effect of, on gases, 
 
 208 ; on solids, effect of, 51. 
 Indium, discovery of, 112. 
 Intensity of heating, luminous, and 
 
 chemical rays, 12. 
 Iron in the solar atmosphere, 241. 
 
 .1. 
 
 Janssen, lines of terrestrial absorption, 
 251 ; on the red prominences, 261. 
 
 Jupiter, absorption lines in spectrum 
 of, 322. 
 
 K. 
 
 Ktrchhoff and Bunsen on the spectra of 
 
 the new alkalies, 104. 
 Kirchhoff on the history of spectrum 
 
 analysis, 132 ; extracts from Memoir 
 
 by, 207 ; discovery of metals in the 
 
 sun, 243. 
 KirchhofTs maps of the metal lines, 
 
 Plates III. and IV. facing Lecture 
 
 V. ; most delicate spectroscope, 62 ; 
 
 description of, 94 ; discovery, 230 ; 
 
 tables of position of the solar lines, 
 
 438 et seq. 
 
 L. 
 
 Lamy, preparation of thallium, 111. 
 Light, decomposition of white, 5. 
 Lightning, spectrum of, 191. 
 
INDEX. 
 
 483 
 
 Limits of vision, 10. 
 
 Lines of the metals, 121. 
 
 List of Memoirs, &c., on spectrum 
 
 analysis, 457. 
 .List of metals seen in the sun, 245 ; by 
 
 Angstrom, 272 ; by Young, 304. 
 
 Lithium, wide distribution of, 79 ; blue 
 line seen, 72 ;' spectrum reactions 
 of, described, 79. 
 
 Lockyer and Janssen on the solar 
 eclipse, 293. 
 
 Lockyer, observations of the sun, 255 ; 
 discovery of nature of solar protuber- 
 ances, 256 ; velocity of motion on the 
 sim, 355. 
 
 Lunar atmosphere, question of a, 320. 
 
 M. 
 
 Magnesium wire, light from burning, 41. 
 
 Mapping the spectra, 97. 
 
 Maps of the metallic lines, Huggins, fol- 
 lowing Lect. IV.; of stellar spectra, 
 328 ; of the metallic lines, Kirchhoff, 
 facing Lecture V. 
 
 Mars, spectrum of, 322 ; on the spec- 
 trum of, 368. 
 
 Measurement of the chemical action in 
 solar spectrum, 43. 
 
 Measurement of the lines, 227. 
 
 Melville on the yellow soda flame, 101. 
 
 Memoirs on spectrum analysis, list of, 
 457. 
 
 Metallic lines mapped by Kirchhoff, 
 
 Huggins, and Angstrom, 121; by 
 
 Thalen, 123. 
 
 Metallic lines shown on screen, 117. 
 Microscopic objects, prismatic examina- 
 tion of, 219. 
 Micro-spectroscope, description of the, 
 
 183 ; construction of the, 219. 
 Miller, W. Allen, 'on coloured flames, 
 
 104. 
 Mineral water containing the new 
 
 alkalies, 106. 
 Minerals examined spectroscopically, 
 
 93. 
 
 Moon has no atmosphere, 320. 
 Motion of hydrogen storms in the sun, 
 
 355. 
 Motion of the stars ascertained, 349, 
 
 351. 
 
 N. 
 
 Nebulae, examination of light of, 336 ; 
 luminosity of, 336 ; spectra of the, 
 338 ; Huggins' latest observations of, 
 413. 
 
 Newton's discovery of the composition 
 
 of white light, 5 ; "Opticks," extracts 
 
 from, 31. 
 Nitrogen lines, see Huggins' maps, 
 
 Plates I. and II., after Lecture 111. 
 Nitrogen spectrum, description of, 198. 
 Nitrogen, spectrum of, Plate facing 
 
 Lecture VI. No. 9. 
 Non-metals, spectra of the, 195. 
 Normal solar spectrum, on the, by 
 
 Angstrom, 273. 
 
 0. 
 
 Occurrence of the new alkalies, 104. 
 Orion, nebula in sword -handle of, 341. 
 Oxygen spectrum, description of, 194. 
 
 P. 
 
 Phosphorescence, phenomena of, 187. 
 
 Phosphorus spectrum, description of, 
 195. 
 
 Photographs of the spectrum, 229. 
 
 Photography in the blue rays, 20 ; mag- 
 nesium light, 41. 
 
 Physical constitution of the sun, 255. 
 
 Planets, atmospheres of the, 322. 
 
 Pliicker's experiments on gases, 158. 
 
 Potassium, spectrum reactions of, 82. 
 
 Pressure in chromosphere ascertained, 
 432. 
 
 Principles of spectrum analysis, 59. 
 
 Prominences in the sun, 253. 
 
 Rare metals mapped by Thalen, 123. 
 
 lied solar prominences, 253. 
 
 Reich and Richter, discovery of indium, 
 112. 
 
 Reversal of sodium spectrum, 233. 
 
 Roscoe and Clifton, effect of increased 
 temperature, 204. 
 
 Rubidium and caesium, discovery of, 
 104. 
 
 Rubidium, spectrum of, detailed de- 
 scription, 128. 
 
 Rutherfurd's photographs of the spec- 
 trum, 230. 
 
 8. 
 
 Saturn, absorption lines in spectrum 
 
 of, 322. 
 Screen, spectra thrown on, 53. 
 
484 
 
 INDEX. 
 
 Secchi, classification of stars, 332. 
 Selective absorption, 177. 
 Sirius, proper motion of, 397. 
 Sirius' spectrum accurately examined, 
 
 393. 
 
 Sodium and iron in the sun's atmo- 
 sphere, 233. 
 
 Sodium, general diffusion of, 70. 
 Sodium, spectrum reactions of, 72, 77. 
 Solar and stellar chemistry, foundation 
 
 of, 223. 
 Solar atmosphere, metals seen in the, 
 
 245. 
 Solar eclipse of 1860, 254 ; of 1868, 
 
 account of, 276; of 3870, 267; of 
 
 1871, 285. 
 Solar spectrum, intensity in various 
 
 parts of, 12. 
 Solid substance yielding bright lines, 
 
 217. 
 
 Spark spectrum, examination of, 121. 
 Spectra of the alkalies and alkaline 
 
 earths, see Frontispiece ; thrown on 
 
 screen, 75 ; mode of mapping, 67 ; 
 
 description of a mode of mapping, 97; 
 
 of gases, 156 ; of nitrogen, 168; of 
 
 gases and solids, 208 ; of the first and 
 
 second order, Pluck er, 191. 
 Spectroscope for star observations, 378, 
 
 414 ; on mode of using a, 94. 
 Spectroscopes, description of various, 
 
 58 ; of large size, 225. 
 Spectroscopic observations of the sun, 
 
 293. 
 Spectrum analysis, delicacy of method, 
 
 69 ; advantages of, 93 ; application 
 
 of, to steel-making, 170. 
 Spectrum reactions of the alkalies and 
 
 alkaline earths, 77 ; of burning 
 
 sodium, 233 ; of nebulae, 338. 
 Star clusters and nebulas, 337; spectro- 
 scope, 324; outburst in T Coronae, 
 
 335. 
 Stellar chemistry, 322; methods of 
 
 investigation, 324; spectra, see Chro- 
 
 molith.- facing Lecture VI. 
 Stokes' blood bands, 181. 
 Stokes on the long spectrum of the 
 
 electric arc, 126, 229. 
 
 Strontium, spectrum reactions of, 83. 
 Sulphur spectrum, description of, 105. 
 Sun, physical constitution of, 243. 
 Sun spots, nature of, 263. 
 
 T. 
 
 Tables of the metal lines, Huggins, 
 148155 ; of solar Hues, Kirchhotf, 
 
 438 et seq. ; of Angstrom's lines, 
 
 453. 
 
 Telluric lines, map of Janssen's, 251. 
 Temperature, effect of increased, 163, 
 
 208. 
 
 Temporary stars, 335. 
 Thallium, spectrum of, 110. 
 Theory of vision, 9. 
 Toxicology, aid of spectrum analysis in, 
 
 185. 
 Tyndall's experiments on caloresceuce, 
 
 U. 
 
 Ultra-violet rays, lines in, 229. 
 
 V. 
 
 Variable stars, 333 ; spectra of, 373. 
 Venus, spectrum of, 322. 
 
 W. 
 
 Wheatstone's metal lines, 116. 
 White light, composition of, 7. 
 Wollastou's discovery of dark solar 
 lines, 26. 
 
 Y. 
 
 Young, lines in chromosphere, 304. 
 
 Z. 
 
 Zodiacal light, spectrum of, 275. 
 Zollner, pictures of solar prominences, 
 261 ; reversing spectroscope, 351. 
 
 LONDON: R. CLAY, SONS, AND TAYLOR, FRINTKRS. 
 

THIS BOOK IS DUE ON THE LAST DATE 
 
 STAMPED BELOW 
 AN INITIAL FimToF 25 PFMTC 
 
 REC'D LD 
 
 KAY 2 3 ; 
 
HU.C. BERKELEY LIBRARIES ff