^SP^ 
 
 'TVT?. P ?T1 
 
 REPORTS OF OBSERVATIONS 
 
 OF THE 
 
 TOTAL ECLIPSE OF THE SUN. 
 
 A. UaiJ SIT 7, 11869, 
 
 MADE BY PARTIES UNDER THE GENERAL DIRECTION OP 
 
 PROFESSOR J. H. C. COFFIN, U. S. N., 
 
 SUPERINTENDENT OF THE AMERICAN EPHEMEBIS ANDJ NAUTICAL ALMANAC. 
 
 
 
 
 PUBLISHED BY AUTHORITY OF THE SECRETARY OF THE NAVY. 
 

 I 
 
 u 
 
TABLE OF CONTENTS. 
 
 Page. 
 
 REPORT OF PROFESSOR COFFIN' TO THE SECRETARY OF TUB NAVY 
 
 GENERAL REPORT OF PROFESSOR COFFIN -- 
 
 Latitude and longitude <if Coast Survey Station, Burlington, Iowa 
 
 Local times: Chronometers; chronometer corrections 
 
 REPORT OF PHOFF.SSOR COFFIN, BURLINGTON, IOWA: 
 
 Position of eclipse station. Burlington 
 
 Preparations for the eclipse 
 
 Arrangement of the party "" 
 
 Meteorological oliservations ^ 
 
 Observations of the eelipse - 
 
 First contaet; notes of the eelipse; total obscuration ; the C'trona ; prominenees; last contact 22-2f> 
 
 Collected results of the several observers at P.iirlington (loeal mean ti i es at the stations occupied) 2<i 
 
 RKPORT OF l)i!. Gori.n, HUUI.INGTON 
 
 First, con tar I : the corona and prominences 30 
 
 Last contact 
 
 Supplementary report "*6 
 
 REPORT OF PROFESS. >u You.vo, BURLINGTON 
 
 Instruments 41 
 
 Preliminary operations , 
 
 Lunar prominence; first contact determined by the spectroscope 43 
 
 Lunar atmosphere 
 
 Spectrum lines observed during totality 
 
 Polarization ; general impressions 
 
 Last contact . . 
 
 Comparison of the spectra of the corona and the aurora borealis 
 
 Results - so 
 
 Observation of the eclipse at Hanover, N. H., by Lewis Boss ' r >l 
 
 REPORT OF Miss MITCHELL AND'IIEU ASSISTANTS, BURLINGTON 
 
 REPORT OF MR. STOCKWELL 
 
 REPORT OF PROFESSOR EATON 
 
 REPORT OF MR. WIESSNER 
 
 Geographical positions of Mount Pleasant, Iowa; Kewanee, 111. ; and Monroe, Mo (>9-71 
 
 Observations of the eclipse at Monroe 
 
 REPORT OF Mu. AUSTIN, KEWANEE, ILL 7:< 
 
 REPORT OF PROFESSOR WATSON, MOUNT PLEASANT, IOWA 79 
 
 Chronometer corrections 
 
 Observations of the eclipse ; collected results 
 
 REPORT OF PROFESSOR VAN VLKCK, MOUNT PLEASANT, IOWA 
 
 Contacts 
 
 Spectroscopic observations 
 
 REPORT OF PROFESSOR PICKERING, MOUNT PLEASANT, IOWA 
 
 The total phase; observations with the spectroscope and polariscopc 
 
 Note on the supposed polarization of the corona 
 
 REPORT OF PROFESSOR ALEXANDER, OTTCMWA, IOWA 
 
 Observations of the eclipse 
 
 The corona and its appendages 10o 
 
 Other observations 
 
 Thermometer and barometer observations . 
 
 Observations for latitude 
 
 Supplementary report of Professor Cofiin; latitude and longitude of Ottumwa Ill 
 
 i 
 
ii TABLE OF CONTEXTS. 
 
 1{KI>ORTS OK THE PHILADELPHIA I'lIOTOCiHArillC Kxi'EIMTIl >X 11") 
 
 liKi-oRT OK PUOKKSSOR MOHTO.V 11"' 
 
 * Distribution of parlies Ht> 
 
 Arrangement (if i list rii iiic-iits f.ir photographic work Ill) 
 
 Preparations 117 
 
 Partial phase pictures 1-1 
 
 Totality pictures - !-> 
 
 The corona 125 
 
 b KBPORT o* PROFKSSOU MAYHR, BCRIINGTOS I'-i'J 
 
 Preparatory work 12i) 
 
 Position ami ill-script ion of the si at inn 1 '>(.) 
 
 The equatorial anil irs adjustments; prcliminai-y adjust men t without the aid of stars 1H1 
 
 The camera and chronograph 132 
 
 Work during the eclipse 135 
 
 Description of the photographs K!7 
 
 Results U4 
 
 Position-angles, and heights of the prominences 14") 
 
 Measurements on I he solar spot iu the southwest quadrant 14S 
 
 Oti the application of photography to observations of the transits of Venus in 1>74 and lf^ 14-< 
 
 c RKPOKT OF PKOKKSSOK HIMKS, OTTUMWA 151 
 
 Instruments and station 151 
 
 Times and exposure of the photograph ie plates 154 
 
 NOTE ON PHOTOllUAl'lIIXli THE COIJOXA. BY PUOKK.SSOH PlCKEKlXti 15(i 
 
 SUPPI.KMKXTAUY NoTK MY PROFESSOR L'ol I IX ON TIIK lifHLIXOTOX PlH)TO(iUAl>lIS 157 
 
.DESCIUPTIOX OF THE PLATES. 
 
 PLATK I. Fig. 1. Corona and prominences, as seen in field of the telescope, by Professor Coffin. 
 
 Fig. 2. C'onma iind prominences, liy Professor Watson. 
 
 Figs. :! and -I. Daily's beads, liy Professor'Watson. 
 PLATE II. Three views of the Orona and prominences, by Dr. Gould (the position-angles of the prominences are 
 
 taken from Professor Mayer's description and diagram). 
 PLATE III. Fig. 1. Solar spectrum, by Professor Young. 
 
 Fig. -2. Spectrum (if lines at first contact, by Professor Young. 
 
 PLATE IV. From photograph plate 24. Burlington, 18 s after beginning of totality. 
 PLATK V. From photograph plate is, Ottutmva, 44" after beginning of totality. 
 PLATE VI. From photograph plate I'.l. Ottnnnva, l m 31" after beginning of totality. 
 PLATE VII. From photograph plate 27, .Burlington, I" 1 57" after beginning of totality. 
 PLATE VIII. From pholngraph plate '20, Ottnmwa, 28" before end of totality. 
 PLATE IX. Enlarged photograph of solar crescent, plate 21, Burlington. 
 PLATE X. Fig. 1. Diagram ofihe prominences, by Professor Mayer. 
 
 Fig. 2. Lunar mountain, from photograph plate Ifi, Burlington, by Professor Mayer. 
 
 Fig. 3. Solar spot, from photograph plate 4, Burlington, by Professor Mayer. 
 
 Fig. 4. Solar spot, from photograph plate 44, Burlington, by Professor Mayer. 
 
 Hi 
 
NAUTICAL ALMANAC OFFICE, 
 
 Washington, March 31, 1870. 
 
 SIR : In response to recommendations in my annual report in October, 1 868, and 
 the representations of the American Academy of Arts and Sciences in Boston, the 
 American Philosophical Society and the Franklin Institute in Philadelphia, and of 
 others interested in the promotion of science, Congress appropriated $5,000 "for 
 observations of the eclipse of the sun in August, 1869, under the direction of the 
 superintendent of the Nautical Almanac." 
 
 The appropriation was desired " for defraying expenses of observers, of moving 
 instruments of sufficient power to the line of central eclipse, and of preparing for abun- 
 dant photographic records and spectroscopic observations." 
 
 I have the honor to present the accompanying reports of the observations of the 
 several parties organized, or aided, under this authority. 
 
 After ascertaining how other important positions were provided for, and the dis- 
 tribution of observers, and on consulting with the committee of the National Academy 
 of Sciences, of which Prof. Stephen Alexander, of the College of New Jersey, was 
 chairman, I selected Burlington, Iowa, as the principal station. The determination 
 of its geographical position was provided for by Prof. Benjamin Peirce, Superintendent 
 of the United States Coast Survey. 
 
 Appreciating the importance of photographs of this eclipse " taken with all the 
 sharpness of definition which the art admits of," and " with a precision which will 
 admit of microscopic measurement," I requested Prof. Henry Morton, Ph. D., secre- 
 tary of the Franklin Institute in Philadelphia, to undertake the organization and direc- 
 tion of a party for the purpose. Entering into it with characteristic zeal, he soon 
 enlisted as volunteers in this work, from among the best photographers in Philadel- 
 phia, a sufficient number to form three parties. 
 
 Col. Thomas A. Scott, vice-president of the Pennsylvania Central Railroad, fur- 
 nished a special car, and with the cordial co-operation of Mr. Robert Harris, general 
 superintendent of the Chicago, Burlington and Quincy, and Mr. C. E. Perkins, of the 
 Burlington and Missouri Railroad, provided free transportation for these parties, with 
 all their instruments and apparatus, to and from the places of observation. Free 
 passes to ten or twelve others, over these same routes, were also granted ; and return- 
 tickets to several from Chicago to Buffalo, over the Michigan Southern and Lake 
 Shore Roads, and from Chicago to Pittsburgh by the Pan-Handle Route. Such liber- 
 ality, in aid of a scientific work, needs but to be mentioned to insure for it a cordial 
 appreciation. 
 
 The trustees of the Philadelphia Central High School, of Pennsylvania College 
 in Gettysburg)!, and of the University of Pennsylvania in Philadelphia, kindly granted, 
 at my request, the use of their telescopes. Those of the two former institutions were 
 
4 EOLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 each of 6.4 inches aperture, and furnished with clock-motion, and thus were well 
 adapted for photographing the total phase of the eclipse. 
 
 I am indebted to Commodore B. F. Sands, U. S. N., Superintendent of the Naval 
 Observatory, Washington, for a supply of chronometers, and to him and Vice-Admiral 
 D. D. Porter, U. S. N., Superintendent of the United States Naval Academy, for such 
 other needed instruments as those institutions could supply. 
 
 My acknowledgments are also due to Mr. J. J. S. Wilson, superintendent of the 
 Western Union Telegraph Company, at Chicago, and to the operators at the several 
 stations, for the free use of their lines for comparison of chronometers, and such com- 
 munications as our work required. 
 
 With these aids, I was enabled to provide for three stations near the central line, 
 instead of one, as originally contemplated, and I thought it best thus to divide the 
 parties and diminish the chance of failure from clouds or other unfavorable circum- 
 stances. 
 
 Associated with me at Burlington, Iowa, were 
 
 Dr. B. A. Gould, of Cambridge, Mass., chiefly for observation and measurement 
 of the corona, and search for intra-Mercurial planets ; 
 
 Prof. Charles A. Young, of Dartmouth College, New Hampshire, for spectroscopic 
 observations ; and 
 
 Prof. Alfred M. Mayer, Ph. D., of the Lehigh University, Bethlehem, Pa., in 
 charge of the photographic party, with 
 
 Mr. O. H. Willard, of Philadelphia, as photographer. 
 
 Miss Maria Mitchell, professor of astronomy in Vassar College, Poughkeepsie, 
 N. Y., was also at Burlington for astronomical observations, but occupied a station in 
 a different part of the city. 
 
 At Mount Pleasant, Iowa, 28 miles to the westward, on the Burlington and Mis- 
 souri Railway, were stationed 
 
 Prof. James C. Watson, director of Ann Arbor Observatory, University of Michi- 
 gan, for astronomical observations ; 
 
 Prof. J. M. Van Vleck, of the Wesleyan University, Middletown, Conn., for spec- 
 troscopic observations ; 
 
 Prof. Henry Morton, Ph. D., of the Franklin Institute, in Philadelphia, in charge 
 of the photographic party, with 
 
 Mr. Edward L. Wilson, of Philadelphia, as photographer. 
 
 Prof. Edward C. Pickering, Ph. D., of the Massachusetts Institute of Technology, 
 Boston, was also associated with this party for physical observations. 
 
 At Ottumwa, Iowa, 75 miles from Burlington, Iowa, on the same railroad, were 
 
 Prof. Stephen Alexander, of the College of New Jersey, Princeton, for astronomi- 
 cal and physical observations ; and 
 
 Prof. Charles F. Himes, Ph. D., of Dickinson College, Carlisle, Pa., in charge of 
 the photographic party, with 
 
 Mr. J. Zentmayer, of Philadelphia, as chief photographer. 
 
 The names of the assistants connected with these several parties will be found in 
 the separate reports of each. 
 
REPORT OF PROFESSOR COFFIN. 5 
 
 Prof. James McClure, of the Philadelphia Central High School, and 
 
 Prof. S. G. Gummere, of Haverford College, Pennsylvania, also accompanied the 
 expedition, and went forward to Oscaloosa, 25 miles beyond Ottumwa. 
 
 Mr. E. P. Austin and Mr. John Weissner, assistants in this office, were dispatched, 
 respectively, to Kewanee, in Illinois, and Monroe, in Missouri, near the limits of the 
 shadow, for observing specially the duration of totality. 
 
 The reports of these several parties are all replete with interest ; they show how 
 abundantly" successful all have been, and how faithfully and earnestly each one. per- 
 formed his allotted part. The kind feeling and cordial co-operation of all in a work 
 of common, yet varied, interest, is gratefully remembered. 
 
 The rich materials contributed in general observations and notes on the corona, 
 by Dr. Gould ; in spectral analysis, by Professor Young ; and in photography, by the 
 " Philadelphia Photographic Expedition," organized by Professor Morton, are espe- 
 cially valuable. 
 
 Professor Young's novel method of observing contacts in an eclipse, by means 
 of a spectroscope, has attracted much attention. 
 
 The collection of photographs is invaluable. Those taken during the totality are 
 described in this volume, and engravings of several of them given. The others are 
 yet to be subjects of measurement and study. 
 
 It is regretted that the means at command allow only a limited distribution of 
 photographs. 
 
 I have added reports from several others, besides those who were formally con- 
 nected with these parties, and extracts from communications made to me of observa- 
 tions in other places. 
 
 I have the honor to be, sir, very respectfully, your obedient servant, 
 
 J. H. C. COFFIN, 
 Professor of Mathematics, U. S. N., 
 
 Superintendent of Nautical Almanac. 
 Hon. GEORGE M. ROBESON, 
 
 Secretary of the Navy. 
 
 NOTE. Failing health, culminating in a severe illness in the early part of 1871 and subse- 
 quent nervous prostration, led me to lay aside these reports and the requisite computations. 
 Those who have similarly suffered know how hard it is, amid other occupations, to resume work 
 
 long deferred. 
 
 J. H. 0. C. 
 
 AUGUST, 1877. 
 
REPORT 
 
 OF 
 
 PROFESSOR JOHN H. C. COFFIN, U. S. N. f 
 
 BTJRLIISI 
 
REPORT OF PROF. JOHN H. C. COFFIN, U. S. 
 
 THE 
 
 BURLINGTON, IOWA. W ' V E R * 
 
 LOCATION AND GEOGRAPHICAL POSITION. 
 
 Burlington is on the west side of the Mississippi River, about 1,540 miles from its 
 mouth. It is situated chiefly on the top and sloping sides of bluffs, which rise in some 
 places abruptly from the river and are divided by a rugged ravine. 
 
 Its geographical position was determined at my request by parties of the United 
 States Coast Survey under the direction of Assistant K. Goodfellow. The observa- 
 tions at Burlington were made by Mr. K. P. Austin. The instruments which he used 
 were Wtirdemann's portable transit-instrument No. 6, belonging to the Naval Acad- 
 emy, sidereal chronometer Hutton 202, and for latitude a zenith telescope furnished 
 by the Coast Survey. The same transit instrument and chronometer were used sub- 
 sequently at the same station during the period of the eclipse. 
 
 The station occupied was in a public reservation on South Hill, in the southern - 
 part of the city, and about 200 feet south of Saint John's (Roman Catholic) Church. 
 The stone pier of the transit-instrument remains to mark the spot. 
 
 The longitudes from Burlington and the Burlington times in the following reports 
 refer to this point. 
 
 The latitude of this station, obtained from observations with the zenith telescope 
 of 20 pairs of stars on 5 different nights, was found to be 
 
 + 40 48' 2 3 ".o 9 o".2i; 
 
 its longitude, by comparison of chronometers by means of the electric telegraph, 
 
 1869, June 17, 19 20". 10 
 
 21, 20 .28 
 
 22, 20.31 
 
 19 20.23 
 
 east of the Coast Survey station at Omaha in Nebraska. The chronometer-corrections 
 at the two stations were determined by observations with portable transit-instruments 
 on the same nights. 
 
 From previous determinations under the Coast Survey, by means of the electric 
 telegraph, we have 
 
 Omaha, i h 39 I5".O7* west of Cambridge, Mass. 
 Cambridge, o 23 41.11 east of Washington ; 
 
 whence Burlington, o 56 13 .73 = 14 3' 26"o. west of Washington; 
 or, 6 4 25 .8-2 91 6 27 .3 west of Greenwich. 
 
 * Report of United States Coast Survey, 1870, pp. 100, 104. 
 2 E S 
 
10 
 
 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 LOCAL TIMES CHRONOMETERS. 
 
 Subsequently, the same transit-instrument was remounted by Mr. Austin in the 
 same position, and the following corrections found for sidereal chronometer Hutton 
 202, with which the other chronometers of the expedition were compared directly or 
 by telegraph. 
 
 The transit-instrument was reversed and stars observed in both positions on 
 each night, except that of August 6, astronomical day, when the unfavorable circum- 
 stances of clouds, rapidly-approaching daylight, and the necessity of other prepara- 
 tions for the eclipse prevented the completion of the intended series of observations. 
 The collimation-correction was found to be nearly constant ; but the instrument lacked 
 stability in level and azimuth, so that adjustments were usually necessary at the com- 
 mencement of each night's work. The changes of level, determined by the spirit-level, 
 were not very great during any night ; but those of azimuth were decidedly manifest. 
 Prof. Reuel Keith, formerly of the Washington Observatory, who reduced these obser- 
 vations, has carefully discussed these changes, and deduced for each night the most 
 probable result Inequality of pivots has been taken into account. 
 
 Corrections of sidereal chronometer Hutton 202. 
 
 Referred to sidereal time of Burlington C. S. station. 
 
 
 
 
 
 
 No. of stars for 
 
 
 Burlington 
 mean time. 
 
 Chron. 
 time. 
 
 Chron. 
 correction. 
 
 Daily change. 
 
 Irregularity. 
 
 
 Observer. 
 
 
 
 
 , .. 
 
 
 
 
 Time. 
 
 Az. 
 
 
 1869. h. 
 
 h. 
 
 m. s. 
 
 s. 
 
 s. 
 
 
 
 
 July 29 9.7 
 
 18 
 
 + ii 9-3 
 
 + 5-1 
 
 + 0.3 
 
 4 
 
 3 
 
 Mr. Austin. 
 
 30 9.6 
 
 18 
 
 ii M-4 
 
 5-5 
 
 + 0.6 
 
 4 
 
 2. 
 
 Do. 
 
 3i 9-5 
 
 18 
 
 ii 19.9 
 
 
 + 0.6 
 
 4 
 
 3 
 
 Do. 
 
 Aug. 2 9.4 
 
 18 
 
 ii 31.2 
 
 '6.6 
 
 + 0.3 
 
 6 
 
 4 
 
 Do. 
 
 3 9-4 
 
 18 
 
 ii 37-8 
 
 6.0 
 
 - 0.9 
 
 6 
 
 3 
 
 Do. 
 
 4 9-3 
 
 18 
 
 II 43-8 
 
 5.3] 
 
 1-5 
 
 5 
 
 2 
 
 Do. 
 
 6 14.7 
 
 24 
 
 ii 55-7 
 
 4.7 1+4.85 
 
 i.i 
 
 3 
 
 I 
 
 Dr. Gould. 
 
 7 ii. 7 
 
 21 
 
 n 59-8 
 
 4.0J 
 
 - 0.6 
 
 6 
 
 I 
 
 Prof. Young. 
 
 8 9.0 
 
 18 
 
 12 3-3 
 
 -1- 5-05 
 
 + 0.7 
 
 7 
 
 5 
 
 Mr. Austin. 
 
 to 8.9 
 
 18 
 
 + 12 13.3 
 
 
 + 1.6 
 
 8 
 
 3 
 
 Do. 
 
 
 
 
 + 5-44 
 
 
 
 
 
 The column headed " irregularity " gives the deviations from a supposed uniform 
 rate of 5 8 44, or the additional correction required by such a supposition. These are 
 mainly due to transportation of the chronometer to and from the observatory. How 
 far they may involve errors of observation will be partially tested by comparisons 
 with other chronometers. 
 
 The separate results for each star observed on the 6th and 7th of August are 
 given in the following table : 
 
REPORT OP PROFESSOR COFFIN. 
 
 11 
 
 Meridian transits, Burlington, Iowa. 
 
 Sidereal chronometer Hutton 202. 
 
 Date. 
 
 Star. 
 
 No. of 
 
 wires. 
 
 Chron. 
 time. 
 
 Chron. correction. 
 
 Position and 
 azimuth. 
 
 Observer. 
 
 1869. 
 
 
 
 h. 
 
 m. s. 
 
 
 
 Aug. 6 
 
 a Andromedx . 
 
 7 
 
 24 
 
 + 11 55-77- -24A<J 
 
 ] 1 
 
 
 
 y Pegasi .... 
 
 5 
 
 24 
 
 55.74- .45Aa 
 
 Clamp E. 
 
 
 
 
 c Piscium 
 
 9 
 
 24 
 
 55.42- .55Aa 
 
 f a = + i'. 3 o f 
 
 Dr. Gould. 
 
 
 n Ursae Minoris. 
 
 5 
 
 24 
 
 54.9 +30.9 Aa 
 
 J J 
 
 
 7 
 
 o 5 Capricorn!. 
 K Capricorn!. 
 
 4 
 
 5 
 
 21 
 21 
 
 + 11 59.93 .83Aa 
 59.69 .goAa 
 
 } Clamp E. 
 
 
 
 
 
 
 
 
 a = I 8 .2o 
 
 
 
 
 e Delphini 
 
 5 
 
 21 
 
 59-95 -49Aa 
 
 
 
 
 
 f Aquarii 
 
 5 
 
 21 
 
 59.83- .77Aa 
 
 1 
 
 
 
 
 XII Y. Cat., 1879. 
 
 2 
 
 21 
 
 59.92+ 3.67AO 
 
 >a = - 2'.88 
 
 
 Prof. Young. 
 
 
 XII Y. Cat., 1879. 
 6i'Cygni .... 
 
 2 
 2 
 
 21 
 21 
 
 59.80+ 3.67A* 
 59.90 .o6A0 
 
 ) Clamp W. 
 
 
 
 
 
 
 
 
 \ a = 2'. 15 
 
 
 
 
 C Cygni .... 
 
 3 
 
 21 
 
 59.72- .22Aa 
 
 J J 
 
 
 
 
 
 
 1 
 
 
 
 The observations of the first three stars on the 7th are of little value. 
 
 Comparisons of the other chronometers with Hutton 202 were made by coinci- 
 dence of beats before, and of most of them after, the eclipse, and on the nights of 
 August 6 and 7, when they were at distant stations, by means of the electric telegraph. 
 For this purpose, the chronometers were taken to the nearest telegraph-offices, and 
 signals passed at Burlington at each 10" of Hutton 202 through an entire minute, and 
 the times recorded by the chronometer at one of the other places. Similar signals were 
 then made at this other station and the times recorded by Hutton 202 at Burlington- 
 Four or more sets of such comparisons, each set comprising seven signals, were thus 
 made for each chronometer. 
 
 The times at Burlington were noted by Dr. Gould and myself, and on August 
 7 also by Professor Young. The personal differences in estimating these times were 
 
 C = G o 8 . 1 2 = Y o 9 . 1 6. 
 
 The results from each set of seven comparisons were remarkably uniform. 
 
 CHRONOMETER CORRECTIONS. 
 The corrections found for the several chronometers are given in the following tables : 
 
12 
 
 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 Corrections of chronometer Negus i 293. 
 
 Referred to mean time of Burlington C. S. station. 
 
 Burlington 
 mean time. 
 
 Chronometer 
 correction. 
 
 Daily 
 change. 
 
 Irregu- 
 larity. 
 
 Compared with Hutton 202 
 
 1869. h. 
 
 h. m. s. 
 
 s. 
 
 s. 
 
 
 July 29 21 
 
 + 5 48 57.7 
 
 O-7 
 
 - 0.7 
 
 By coincidence of beats. 
 
 30 21 
 
 57-0 
 
 
 O. I 
 
 Do. 
 
 Aug. I 21 
 
 54-4 
 
 1.3 
 
 0.8 
 
 + 0.5 
 
 Do. 
 
 2 21 
 
 53-6 
 
 
 + 0.5 
 
 Do. 
 
 
 
 0.6 
 
 
 
 3 21 
 
 53-0 
 
 
 + 0.3 
 
 Do. 
 
 
 
 I . I 
 
 
 
 4 21 
 
 51.9 
 
 
 + 0.8 
 
 Do. 
 
 
 
 0.5 
 
 
 
 5 21 
 
 51-4 
 
 
 + 0.5 
 
 Do. 
 
 
 
 0.05 
 
 
 
 7 21 
 
 51-3 
 
 
 - 0.9 
 
 Do. 
 
 8 21 
 
 50.0 
 
 - 1-3 
 
 - 0.4 
 
 Do. 
 
 
 
 - 0.75 
 
 
 
 This chronometer was stationary except on the 7th, when it was carried to Miss 
 Mitchell's station, half a mile distant. 
 
 Corrections of chronometer Negus 1311. 
 
 Referred to mean time of Burlington C. S. station. 
 
 Burlington 
 mean time. 
 
 Chronometer 
 correction. 
 
 Daily change. 
 
 Irregu- 
 larity. 
 
 Compared with Hutton 202 
 
 1869. h. 
 
 h. m. s. 
 
 s. 
 
 s. 
 
 
 July 29 21 
 
 + 5 48 52.4 
 
 
 0.4 
 
 By coincidence of beats. 
 
 30 21 
 
 49-7 
 
 2.7 
 
 - 0.3 
 
 Do. 
 
 Aug. I 21 
 
 43-5 
 
 3-1 * 
 
 + 0.6 
 
 Do. 
 
 2 21 
 
 41.2 
 
 2-3 
 
 + 0.2 
 
 Do. 
 
 3 21 
 
 38.9 
 
 2.3 
 
 O.I 
 
 Do. 
 
 4 21 
 
 35-6 
 
 3-3 
 
 + 0.6 
 
 Do. 
 
 6 9 
 
 32.1 
 
 ..! 
 
 + O.I 
 
 By telegraph. 
 
 
 
 2.1 [ 2.33 
 
 
 
 7 9 
 
 30.0 
 
 o 1 
 
 0.4 
 
 Do. 
 
 7 21 
 
 28.6 
 
 2.8J 
 
 - 0.3 
 
 By coincidence of beats. 
 
 8 21 
 
 25.6 
 
 3.0 
 
 + O.I 
 
 Do. 
 
 
 
 - 2.6 3 
 
 
 
 August 6 and 7 taken by Mr. Austin to Kewanee, 111. ; on other days, stationary 
 in Burlington. 
 
REPORT OF PROFESSOR COFFIN. 
 
 Comparisons by telegraph. 
 
 13 
 
 Burlington 
 mean time. 
 
 Chronometer 
 correction. 
 
 No. of 
 sets. 
 
 Signals made at 
 
 Received at 
 
 Compared with 
 
 1869. h. 
 
 h. m. s. 
 
 
 
 
 
 A A 
 
 
 
 
 
 Hutton 202 at Burlington. 
 
 
 
 * 
 
 
 
 
 
 
 
 
 
 Do. 
 
 
 31-93 
 
 2 
 
 Monroe 
 
 Burlington and Kewanee . 
 
 Do. 
 
 
 32.07 
 
 I 
 
 Burlington 
 
 Monroe and Kewanee . 
 
 Negus 1304 at Monroe. 
 
 
 
 
 
 
 Do. 
 
 
 
 
 
 
 Negus 1074 at Monroe. 
 
 
 31.92 
 
 I 
 
 Burlington 
 
 Monroe and Kewanee . 
 
 Do. 
 
 
 
 
 
 Kewanee 
 
 Hutton 202 at Burlington. 
 
 
 
 
 
 
 
 
 
 
 
 
 Do. 
 
 
 29.82 
 
 2 
 
 Monroe 
 
 Burlington and Kewanee . 
 
 Do. 
 
 
 29.78 
 
 3 
 
 Burlington 
 
 Monroe and Kewanee . 
 
 Negus 1304 at Monroe. 
 
 
 29.88 
 
 2 
 
 Monroe 
 
 Kewanee . ... 
 
 Negus 1074 at Monroe. 
 
 Kewanee is 75 miles from Burlington, on the telegraph-line from Burlington to 
 Chicago, and 162 miles from Monroe, Mo., on the line from Chicago through Quincy. 
 The latter line intersects the former at Galesburgh, 44 miles from Burlington. 
 
 Corrections of chronometer Negus 1304. 
 
 Referred to mean time of Burlington C. S. station. 
 
 Burlington 
 mean time. 
 
 Chronometer 
 correction. 
 
 Daily change. 
 
 Irregu- 
 larity. 
 
 Compared with Hutton 202 
 
 1869. h. 
 
 h. m. s. 
 
 s. 
 
 s. 
 
 
 July 29 21 
 
 + 5 55 42.2 
 
 o.o 
 
 i.i 
 
 By coincidence of beats. 
 
 30 9 
 
 42.2 
 
 o.o 
 
 - 0.9 
 
 Do. 
 
 30 21 
 
 42.2 
 
 o. 16 
 
 - 0.7 
 
 Do. 
 
 Aug. 2 9 
 
 41.8 
 
 + O.2 
 
 -1- I.O 
 
 Do. 
 
 2 21 
 
 41.9 
 
 0.6 
 
 + 1.2 
 
 By eye and ear.* 
 
 3 9 
 
 42.2 
 
 O.2 
 
 + I.O 
 
 By coincidence of beats. 
 
 3 21 
 
 42.3 
 
 
 + 1.2 
 
 Do. 
 
 6 9 
 
 44-9 
 
 1.04") 
 
 o.i l+o.8c 
 
 0.2 
 
 By telegraph. 
 
 7 9 
 
 45-0 
 
 o 84 
 
 + 0.3 
 
 Do. 
 
 9 21 
 
 47-1 
 
 . Wlf J 
 
 - 0.6 
 
 By coincidence of beats. 
 
 to 9 
 
 47-3 
 
 ' 1+0.65 
 
 - 0.5 
 
 By telegraph. 
 
 ii 6 
 
 48.0 
 
 
 - 0.8 
 
 By coincidence of beats. 
 
 
 
 + 0.50 
 
 
 
 Taken by Mr. Wiessner to Kewanee between July 30 and August 2 ; to Monroe 
 between August 4 and 9 ; and to Mount Pleasant, Iowa, between August 9 and 1 1. 
 
 * Chronometers 1304 and 1074 were compared by Mr. Wiessner with 202 by noting an exact io of 202, and with 
 each other by noting an exact 10' of 1074, and estimating the corresponding second and tenths of the other. Compar- 
 ing the results with those obtained from coincidence of beats, I find from 
 
 6 comparisons of 1304 with 202 + o*.35 ) 
 
 5 comparisons of 1074 with 202 o*.22 > + o.3o 
 
 9 comparisons of 1304 with 1074 '-3i ) 
 
 to be added to Mr. W.'s estimate of the seconds and tenths, or subtracted from his estimated 10"; and accordingly 
 
14 
 
 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 Comparisons ly telegraph. 
 
 Burlington 
 mean time. 
 
 Chronometer 
 correction. 
 
 No. of 
 sets. 
 
 Signals made at 
 
 Received at 
 
 Compared with 
 
 1869. h. 
 
 h. m. s. 
 
 + e ce 14 oe 
 
 i 
 
 
 
 
 
 
 
 
 Burlington 
 
 Do 
 
 7 9 
 
 45.14 
 
 45-01 
 
 + 5 55 45-iS 
 
 dd 8? 
 
 i 
 i 
 
 3 
 
 Monroe 
 Burlington 
 
 Burlington 
 
 Kewanee 
 Monroe and Kewanee . 
 
 Monroe 
 Burlington .... 
 
 Negus 1311 at Kewanee. 
 Do. 
 
 Hutton 202 at Burlington. 
 Do 
 
 10 9 
 
 45-24 
 
 + 5 55 47-20 
 4744 
 
 3 
 3 
 
 3 
 
 Burlington 
 
 Burlington 
 'Mount Pleasant 
 
 Monroe and Kewanee . 
 
 Mount Pleasant .... 
 Burlington 
 
 Negus 1311 at Kewanee. 
 
 Hutton 202 at Burlington. 
 Do 
 
 
 
 
 
 
 
 Corrections of clironometer Negus 1074. 
 
 Referred to mean time of Burlington C. S. station. 
 
 Burlington 
 mean time. 
 
 Chronometer 
 correction. 
 
 Daily change. . 
 
 Irregu- 
 larity. 
 
 Compared with Hutton 202 
 
 1869. h. 
 
 h. m. s. 
 
 s. 
 
 s. 
 
 
 July 29 9 
 
 + 5 56 16.6 
 
 4- 0.70 
 
 O.I 
 
 By eye and ear.* 
 
 30 9 
 
 17-3 
 
 + 0.40 
 
 - -5 
 
 By coincidence of beats. 
 
 3O 21 
 
 17-5 
 
 - 0.04 
 
 - 0.6 
 
 Do. 
 
 Aug. 2 9 
 
 '7-4 
 
 0.2O) 
 
 + 0.3 
 
 Do. 
 
 2 21 
 
 17-3 
 
 o oo( --7 
 
 + 0.5 
 
 By eye and ear.* 
 
 3 21 
 
 17.3 
 
 + 0.44 1 
 
 + 0.8 
 
 By coincidence of beats. 
 
 6 9 
 
 18.4 
 
 + 0.50 1+0.62 
 
 + 0.5 
 
 By telegraph. 
 
 7 9 
 
 18.9 
 
 + 0.84 j 
 
 + 0.3 
 
 Do. 
 
 9 21 
 
 21.0 
 
 0.07 
 
 I.O 
 
 By coincidence of beats. 
 
 ii 6 
 
 20.9 
 
 
 - 0.5 
 
 Do. 
 
 
 
 + 0.31 
 
 . 
 
 
 Taken by Mr. Wiessner to Kewanee between July 30 and August 2 ; to Monroe 
 between August 4 and 9 ; and to Mount Pleasant between August 9 and 1 1 . 
 
 been subtracted from the chronometer-corrections derived from these comparisons. The accordance of the several com- 
 parisons indicates uniformity in this personal peculiarity. 
 
 If the error is solely in estimating the seconds and tenths, o'.3o should be subtracted from the corrections of 1304 
 and 1704 and added to the corrections of 1311, obtained by telegraph-signals received by Mr. Wiessner at Monroe on the 
 6th and 7th and Mount Pleasant on the loth. If, however, the error is solely in estimating an exact 10', o".3o should be 
 added to the corrections of 130) and 1374, obtained from telegraph-signals made by him, and subtracted from the correc- 
 tions of 1311 when compared with 1304 or 1374, provided he made the signals exactly at the instant of his estimated 10*. 
 The correction of the telegraph comparisons is therefore uncertain. 
 
 *See note on pp. 13 and 14. 
 
REPORT OF PROFESSOR (JOFFIN. 
 
 15 
 
 Comparisons by telegraph. 
 
 Burlington 
 mean time. 
 
 Chronometer 
 correction. 
 
 No. of 
 sets. 
 
 Signals made at 
 
 Received at 
 
 Compared with 
 
 1869. h. 
 
 h. m. s. 
 
 
 
 
 Hutton 202 at Burlington. 
 
 Aug. 6 9 
 
 
 
 
 
 Do 
 
 
 T Q oQ 
 
 
 
 
 
 
 18.69 
 
 i 
 
 Burlington 
 
 Monroe and Kewance . 
 
 Do. 
 Hutton 202 at Burlington. 
 
 Aug. 7 9 
 
 19.01 
 
 2 
 
 Monroe 
 
 Kewanee 
 
 Negus 1311 at Kewanee. 
 
 Corrections of chronometer Negus 1233. 
 
 Referred to mean time of Burlington C. S. station. 
 
 Burlington 
 mean time. 
 
 Chronometer 
 correction. 
 
 Daily change. 
 
 Irregu- 
 larity. 
 
 Compared with 
 
 1869. h. 
 
 s 
 
 s. 
 
 s. 
 
 
 July 29 o 
 
 +62 42.9 
 
 I.O) 
 
 + 0.3 
 
 1293, 1304, 1311 by eye and ear. 
 
 29 21 
 
 42.0* 
 
 > + 0.90 
 4- 2.6$ 
 
 + 1.6 
 
 Hutton 202 by coincidence of beats. 
 
 30 21 
 
 44.6 
 
 o.o 
 
 0.4 
 
 Do. 
 
 Aug. i 21 
 
 44.6 
 
 0.4 
 
 + 0.6 
 
 Do. 
 
 2 21 
 
 46.2 
 
 + 1.5 
 
 - 0.3 
 
 Do. 
 
 3 21 
 
 47-7 
 
 + 0.3 1 
 
 i-5 
 
 Do. 
 
 6 9 
 
 48.4 
 
 i.o I 0.07 
 
 0.8 
 
 Hutton 202 by telegraph. 
 
 7 9 
 
 47-4 
 
 o.o J 
 
 + 0.7 
 
 Do. 
 
 7 21 
 
 47-4 
 
 
 + I.O 
 
 Hutton 202 by coincidence of beats. 
 
 8 21 
 
 49.1 
 
 
 0.2 
 
 Do. 
 
 
 
 + 0.53. 
 
 
 
 
 
 
 
 
 Taken by Professor Watson to Mount Pleasant August 4 and returned August 7. 
 
 Comparisons by telegraph. 
 
 Burlington 
 mean time. 
 
 Chronometer 
 correction. 
 
 No. of 
 sets. 
 
 Signals made at 
 
 Received at 
 
 Compared with 
 
 1869. h. 
 Aug. 6 9 
 
 h. m. s. 
 + 6 2 48.63 
 
 i 
 
 i 
 
 Burlfngton . 
 
 Mount Pleasant .... 
 
 Hutton 202 at Burlington. 
 Do. 
 
 
 48.26 
 48.51 
 
 i 
 i 
 
 Ottumwa 
 Burlington . 
 
 Burlington and Mt. Pleasant 
 Mt. Pleasant and Ottumwa. 
 
 Do. 
 Daniels -- at Ottumwa. 
 Do 8 ' 5 
 
 Aug. 7 9 
 
 48.65 
 +62 47.51 
 
 i 
 
 3 
 2 
 
 Ottumwa 
 Burlington . 
 
 Mount Pleasant . . 
 Mount Pleasant .... 
 
 Do. 
 
 Hutton 202 at Burlington. 
 Do, 
 
 
 47.28 
 47-40 
 47.38 
 
 2 
 
 3 
 
 2 
 
 Ottumwa 
 Burlington . 
 Ottumwa . 
 
 Burlington and Mt. Pleasant 
 Mt. Pleasant and Ottumwa. 
 Mount Pleasant .... 
 
 Do. 
 Daniels -5- at Ottumw'a. 
 Do" 5 
 
 * Probably an error of I" in the comparison, one only having been made. 
 
16 
 
 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 Mount Pleasant is on the telegraph-line of the Burlington and Missouri River 
 Railway, 28 miles from Burlington ; Ottumwa is on the same line, 75 miles from Bur- 
 lington. 
 
 Corrections of sidereal chronometer Negus 578. 
 
 Referred to sidereal time of Burlington C. S. station. 
 
 Burlington 
 mean time. 
 
 Chron. 
 time. 
 
 Chronometer 
 correction. 
 
 Daily 
 change. 
 
 Irregu- 
 larity. 
 
 Compared with 
 
 1869. h. 
 
 h. 
 
 m. s. 
 
 s. 
 
 s. 
 
 
 Aug. 3 21.8 
 
 7 
 
 - 31 24.4 
 
 - 3.76 
 
 O.2 
 
 Negus 1293 by coincidence of beats. 
 
 6 9.9 
 
 !9 
 
 33.8 
 
 4-33 
 
 + 0.4 
 
 Hutton 202 by telegraph. 
 
 7 21.9 
 
 7 
 
 40.3 
 
 
 O.2 
 
 Negus 1311 by coincidence of beats. 
 
 - 3-98 
 
 Taken by Professor Watson to Mount Pleasant August 4 and returned August 7. 
 
 Comparisons by telegraph. 
 
 Burlington 
 mean time. 
 
 Chron. 
 
 time. 
 
 Chronometer 
 correction. 
 
 No. of 
 sets. 
 
 Signals made at 
 
 Received at 
 
 Compared with 
 
 1869. h. 
 Aug. 6 9 
 
 h. 
 19 
 
 m. s. 
 - 31 33-57 
 34.02 
 
 I 
 
 2 
 
 Burlington 
 Mount Pleasant 
 
 Mount Pleasant .... 
 Burlington 
 
 Hutton 202, Burlington. 
 Do. 
 
 
 
 33-74 
 
 2 
 
 Ottumwa . 
 
 Burlington and Mt. Pleasant 
 
 Do. 
 
 
 
 33.48 
 
 I 3. f l Q7 
 
 I 
 
 2 
 
 Burlington 
 
 Ottumwa and Mt. Pleasant. 
 
 Daniels ^-, at Ottumwa. 
 815' 
 
 Do 
 
 
 
 33-55 
 
 2 
 
 Ottumwa . 
 
 Mount Pleasant .... 
 
 Do. 
 
 Corrections of chronometer Daniels gy> 
 
 Referred to mean time of Burlington C. S. station. 
 
 Burlington 
 mean time. 
 
 Chronometer 
 correction. 
 
 Daily 
 change. 
 
 Irregu- 
 larity. 
 
 Obtained from 
 
 1869. h. 
 
 h. m. s. 
 
 s. 
 
 s. 
 
 
 Aug. I 21 
 
 + 5 57 1-2 
 
 0.4 
 
 + 0.2 
 
 Comparison with Hutton 2O2*by coincidence of beats. 
 
 3 
 
 0.9 
 
 
 + 1.8 
 
 A. M. and P. M. observations of sun at Ottumwa. 
 
 
 
 + 3-4 
 
 
 
 4 
 
 4-2 
 
 
 - 0.6 
 
 Do. 
 
 
 
 + i .0 
 
 
 
 6 o 
 
 6.5 
 
 + 1.9 
 
 - 0.6 
 
 Comparison with Hutton'2O2 by telegraph. 
 
 6 22 
 
 7-5 
 
 
 - 1-5 
 
 A. M. observations of sun at Ottumwa. 
 
 
 
 2.2 
 
 
 
 7 9 
 
 6.4 
 
 + 1.2 
 
 + 0.5 
 
 Comparison withi Hutton 202 by telegraph. 
 
 9 o 
 
 8.3 
 
 
 + 0.3 
 
 A. M. andT.'M. observations'ofjsun at Ottumwa. 
 
 
 
 + 0.98 
 
 
 
 Taken by Professor Alexander, August 2, to Ottumwa, on the line of the Bur- 
 lington and Missouri River Railway, 75 miles from Burlington. Professor Alexan- 
 
BEPORT OF PROFESSOR COFFIN. 
 
 17 
 
 der's observations for time at Ottumwa are described at the end of his report. They 
 were reduced to Burlington time by adding the assumed difference of longitude, 5 
 6\ 7 . 
 
 Comparisons by telegraph. 
 
 Burlington 
 mean time. 
 
 Chronometer 
 correction. 
 
 No. of 
 sets. 
 
 Signals made at 
 
 Received at 
 
 Compared with 
 
 1869. h. 
 
 h. m. s. 
 
 _l_ -c CT 6 cfi 
 
 
 
 
 Hutton 202 at Burlington. 
 
 
 .26 
 
 ^ 
 
 Ottumwa 
 
 Burlington 
 
 Do. 
 
 
 .70 
 
 43 
 .27 
 
 3 
 I 
 I 
 
 Mount Pleasant 
 Burlington 
 Ottumwa . 
 
 Burlington and Ottumwa . 
 Mount Pleasant and Ottumwa 
 Mount Pleasant .... 
 
 Do. 
 Negus 1233, at Mount Pleasant. 
 Do. 
 
 
 .85 
 
 I 
 
 Mount Pleasant 
 
 
 Do. 
 
 
 .21 
 .26 
 
 2 
 2 
 
 Burlington 
 Ottumwa . 
 
 Mount Pleasant and Ottumwa 
 Mount Pleasant 
 
 Negus 578, at Mount Pleasant. 
 Do 
 
 
 .70 
 -1- c <;7 6. =;"* 
 
 I 
 
 3 
 
 Mount Pleasant 
 
 Ottumwa 
 Ottumwa 
 
 Do. 
 Hutton 202, at Burlington. 
 
 
 31 
 
 2 
 
 
 
 Do 
 
 
 .41 
 
 3 
 
 2 
 
 Burlington 
 
 Mount Pleasant and Ottumwa 
 
 Negus 1233, at Mount Pleasant. 
 Do 
 
 
 
 
 
 
 
 Corrections of chronometer Negus 2335. 
 
 Referred to mean time of Burlington C. S/ station. 
 
 Burlington 
 mean time. 
 
 Chronometer 
 correction. 
 
 Daily 
 change. 
 
 c-o 
 
 Compared with 
 
 1869. h. 
 
 h. m. s. 
 
 s. 
 
 s. 
 
 
 Aug. I 21 
 
 -H 5 55 56.8 
 
 0.2 
 
 Hutton 202 by coincidence of beats. 
 
 
 i -H 1.9 
 
 
 
 4 12 
 
 56 1.8 : 6 
 
 + 0.4 
 
 Daniels - by eye and ear. 
 
 5 12? 
 
 3.4 
 
 . +0.5 
 4.0 
 
 Do. 
 
 6 o? 
 
 5-7 
 
 I.O 
 
 Do. 
 
 
 O.O I 
 
 
 7 9 
 
 6.8 
 
 0.0 
 
 Hutton 202 by telegraph. 
 
 
 O.7 
 
 
 
 9 o 
 
 7-9 
 
 0.8 
 
 + 0.4 
 
 Daniels /- by eye and ear. 
 
 015 
 
 10 
 
 8-7 
 
 
 0.0 
 
 Do. 
 
 
 
 [+ 1.47 - o.24(/-6")] 
 
 Taken to Ottumwa August 2, by Professor Alexander. The times when the 
 comparisons were made, on August 5 and 6, are doubtful. 
 
 Comparisons by telegraph 
 
 Burlington 
 mean time. 
 
 Chronometer 
 correction. 
 
 No. of 
 sets. 
 
 Signals 
 made at 
 
 Received at 
 
 Compared with 
 
 1869. h. 
 
 h. m. s. 
 
 
 
 
 
 Aug. 7 9 
 
 + 5 56 7-n 
 
 2 
 
 Burlington . 
 
 Ottumwa 
 
 Hutton 202, at Burlington. 
 
 
 6.51 
 
 2 
 
 Ottumwa 
 
 Burlington . 
 
 Do. 
 
 3 E S 
 
18 
 
 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 The last column in the table for each chronometer gives the corrections which 
 would be required by the supposition that its rate was uniform and that these irreg- 
 ularities arose from errors in the determination of the chronometer-corrections. When 
 they are collected, however, as in the following table, we see that the mean, on each 
 date, for several chronometers is small, and hence indicative that those for Hutton 202, 
 on which the others depend, are mainly irregularities in its motion, and but little due 
 to errors of observation. 
 
 Burlington 
 mean time. 
 
 Hutton 202. 
 
 C1 
 
 O* 
 
 
 M 
 
 
 i 
 
 
 
 z 
 
 en 
 
 -i 
 
 OB 
 
 M 
 
 <u 
 
 Z 
 
 o 
 
 en 
 
 (/) 
 
 3 
 
 em 
 
 o> 
 
 Z 
 
 -r 
 r^ 
 
 o 
 
 V) 
 
 EC 
 
 O 
 
 Z 
 
 en 
 m 
 n 
 
 M 
 3 
 
 Eg 
 
 V 
 
 Z 
 
 CO 
 
 r^ 
 in 
 
 BO 
 
 3 
 
 bo 
 
 V 
 
 Z 
 
 ui 
 
 C*) 
 
 m 
 w 
 c/] 
 
 3 
 
 C>0 
 
 y 
 
 Z 
 
 Daniels . 
 
 c 
 
 o 
 
 s 
 
 No. of chro- 
 nometers. 
 
 1869. h. 
 July 29 21 
 
 s. 
 + 0.6 
 
 s. 
 - 0.6 
 
 s. 
 
 0.4 
 
 s. 
 i.i 
 
 s. 
 
 O.I 
 
 s. 
 + 1.6 
 
 s. 
 
 s. 
 
 s. 
 
 s. 
 o.o 
 
 6 
 
 30 9 
 
 + 0.6 
 
 . . 
 
 . . 
 
 - 0.9 
 
 - 0.5 
 
 
 
 
 . . 
 
 - 0.3 
 
 3 
 
 21 
 
 -1- 0.6 
 
 - 0.6 
 
 - 0.3 
 
 - 0.7 
 
 - 0.6 
 
 - 0.4 
 
 
 
 
 
 
 - 0.3 
 
 6 
 
 Aug. I 21 
 
 + 0.4 
 
 + 0.5 
 
 -t- 0.6 
 
 
 
 -t- 0.6 
 
 . . 
 
 O.2 
 
 + 0.2 
 
 + 0.3 
 
 6 
 
 2 9 
 
 + 0.3 
 
 
 
 H- 1.0 
 
 + 0.3 
 
 
 . . 
 
 . . 
 
 . . 
 
 + 0.5 
 
 3 
 
 21 
 
 - 0.3 
 
 + 0.5 
 
 + O.2 
 
 + 1.2 
 
 + 0.5 
 
 - 0.3 
 
 ." . 
 
 . . 
 
 
 + 0.3 
 
 6 
 
 3 9 
 
 - 0.9 
 
 
 
 + 1.0 
 
 . . 
 
 . . 
 
 
 
 . . 
 
 o.o 
 
 2 
 
 21 
 
 - 1-3 
 
 + 0.3 
 
 O.I 
 
 + 1.2 
 
 + 0.8 
 
 - 1-5 
 
 0.2 
 
 . . 
 
 
 O.I 
 
 7 
 
 4 21 
 
 i-4 
 
 + 0.8 
 
 + 0.6 
 
 . . 
 
 . . 
 
 
 . . 
 
 
 
 o.o 
 
 3 
 
 5 21 
 
 1.2 
 
 + 0.5 
 
 
 
 . . 
 
 
 
 
 
 - 0.8 
 
 2 
 
 6 9 
 
 I.I 
 
 
 
 + O.I 
 
 + 0.2 
 
 + 0.5 
 
 - 0.8 
 
 + 0.4 
 
 . . 
 
 1-5 
 
 - 0.3 
 
 8 
 
 7 9 
 
 - 0.7 
 
 
 
 - 0.4 
 
 + 0.3 
 
 + 0.3 
 
 + 0.7 
 
 
 o.o 
 
 + 0.5 
 
 o.o 
 
 7 
 
 21 
 
 O.I 
 
 - 0.9 
 
 - 0.3 
 
 
 
 + I.O 
 
 O.2 
 
 . . 
 
 
 O.I 
 
 5 
 
 8 21 
 
 + 0.9 
 
 - 0.4 
 
 + O.I 
 
 . . 
 
 
 O.2 
 
 
 
 . . 
 
 4 o.l 
 
 6 
 
 9 21 
 
 + 1.2 
 
 . . 
 
 . . 
 
 - 0.6 
 
 I.O 
 
 
 
 
 
 O.I 
 
 3 
 
 IO 9 
 
 + 1.6 
 
 
 
 - 0.5 
 
 - 0.5 
 
 
 
 
 
 
 -t- 0.2 
 
 3 
 
 THE ECLIPSE-STATION, BURLINGTON. 
 
 A vacant square, between 7th and 8th streets on the east and west, and Elm and 
 Maple streets on the north and south, was selected as a suitable place for observations 
 of the eclipse. It is in the vicinity of the Coast Survey station and on the summit of 
 the same hill, in a quiet location, surrounded by a hedge, and free from dust. My 
 request for its use was cordially granted by its proprietor, H. W. Storr, Esq. 
 
 It is elevated 1 56 feet above high-water mark of the Mississippi River at Bur- 
 lington, and about 630 feet above the ocean. Beyond its limits, the ground slopes 
 abruptly to the river on the east and a ravine on the north, but more gently to the 
 west and south. 
 
 A temporary observatory was erected near the middle of this lot, 16 feet 
 square, with a small addition 5 feet square at the northeast corner. It contained two 
 suitable dark rooms for the photographers, and afforded shelter for other instruments 
 as well as the equatorial of the Philadelphia High School, for which it was specially 
 designed. 
 
 The roof, sloping east and west, was mainly of roofing-paper on light sliding 
 
REPORT OF PROFESSOR COFFIN. \&* ify^ 
 
 
 T 4, 
 
 frames. Though exposed to a severe storm, it was uninjured by the heavy wi 
 proved impervious to the rain. 
 
 A cross of 8-inch timber was laid to support the equatorial, and a meridian line 
 transferred from the meridian line of the Coast Survey station, which had been pre- 
 viously marked, was traced on it by Mr. Austin- and the city surveyor, Mr. Ham. 
 From their measurements, the position of the equatorial was found to be S. 25 
 22' W., 296 feet, or 2". 6 south and o a . 11 west, from the Coast Survey station, or in 
 latitude 40 48' 20". 5 north, and longitude o h 56 i3".84 zr 14 3' 2 7". 6 west of 
 Washington; 
 
 Previous to my arrival, the city council of Burlington appointed the mayor, Hon. 
 William Bell, and Aldermen G. W. E. Edwards, B. Y. Overtoil, and Charles O'Brien 
 a committee " with full power to extend all needed facilities to those who should visit 
 the city to take observations of the eclipse." Besides other considerate attentions, 
 they provided a special police officer, to giiard the observatory at night ; and their 
 presence, with several city officers, at the time of the eclipse, was sufficient to prevent 
 the pressure of a crowd, and to secure for us the quiet and freedom from interruption 
 or distraction which were essential to the success of our observations. 
 
 PREPARATIONS FOR THE ECLIPSE. 
 
 At noon of Wednesday, the 4th of August, all the parties and instruments had 
 arrived ; but little, however, could be done toward mounting the large telescope until 
 the next day, when it was successfully accomplished. It was adjusted nearly in posi- 
 tion by Professor Mayer, by the method described in his report, without stars, and 
 with the aid only of a plumb-line and the meridian-line, which had been previously 
 traced. The subsequent work of completing the adjustment more closely by stars 
 was very slight. 
 
 The weather for several days had been pleasant, but the atmosphere had now 
 become thick and smoky, with appearances of an approaching storm ; and the night 
 of the th set in cloudy, with our preparations incomplete, and instruments only par- 
 tially adjusted. The 6th, the day before the eclipse, was rainy, with a blustering 
 northeast wind, and indications of a long continuance of bad weather. 
 
 But notwithstanding such unpromising prospects, preparations were continued 
 so far as was practicable ; and at night, the chronometers at the several stations were 
 compared by telegraph, as had been previously arranged. Soon after midnight, how- 
 ever, the clouds began to break ; and at 2 a. m. of the ;th, Dr. Gould and Professor 
 Mayer accompanied me to South Hill to obtain more observations for time, and 
 complete the adjustments of their instruments. Clouds still interfered, and the work 
 was barely accomplished when daylight interrupted it. 
 
 By 10 a. m. of the /th, clouds had entirely disappeared, the wind was moderate 
 from southeast, and the atmosphere remarkably clear. It continued thus bright and 
 pleasant through the day. Preparations were completed, though in some respects 
 hurriedly and not altogether satisfactorily. 
 
20 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 ARRANGEMENT OF THE PARTY. 
 
 Professor Young, Professor Mayer, and the photographic party were stationed 
 within the observatory ; Dr. Gould and myself outside, about twenty feet to the west. 
 Near the southwest corner, outside, was placed a Dolland telescope of i\ inches aper- 
 ture, which Professor Young had provided. His assistant, Mr. Emmerson, fitted it 
 with a screen of white Bristol-board, on which was thrown an image of the sun, 
 enlarged by the eye-piece to a diamete v of about six inches. Dr. Gould, Professor 
 Eaton, of Brooklyn, N. Y., Mr. Stockwell, of Ohio, and others, observed the contacts 
 with it. 
 
 Rev. J. Freeman Clarke, of Boston, with a party of friends and a Clark telescope 
 of 4 inches aperture, was a little farther '-emoved to the west. 
 
 Miss Mitchell's party was in another part of this city, in the grounds of the Bur- 
 lington Collegiate Institute, north and west from the Coast Survey station. 
 
 The sidereal chronometer Hutton 202 was placed just outside of the door, on 
 the west side of the observatory. The seconds were counted audibly, in a clear voice, 
 by Mr. Miles Rock, C. E., of Bethlehem, Pa., and tapped with an observing-key for 
 record on the Morse register-chronograph of the Washington Observatory, within the 
 building. Mr. Otis Kendall, of Philadelphia, was stationed at the chronograph, to call 
 the minutes and note them, and, occasionally, the seconds on the fillet. They were 
 relieved in these labors several times, respectively, by Mr. J. Bonsai and Mr. Charles 
 Stoddard, of Burlington. This work was performed with commendable fidelity. 
 
 From the table, page 10, we have for the correction of this chronometer during 
 the period of the eclipse, 
 
 + II m 58 8 .05+0 8 .20 (t I2 h ) 
 
 to local sidereal time of the Coast Survey station ; and 
 
 + i 5 h 6 m i6 9 . 7 o-9 8 .63 (-i2 h ) 
 as the reduction to local mean time, t being the time by chronometer in hours. 
 
 # 
 
 METEOROLOGICAL OBSERVATIONS. 
 
 The observatory on South Hill was provided with only a pair of Fahrenheit 
 thermometers, made by Mr. James Green, of New York, one of them arranged for a 
 wet bulb, and an aneroid barometer, which was compared by Mr. Green with his 
 standard in New York before and after the eclipse, and found to be correct. These 
 were supplied by Mr. Green, as also a standard mercurial barometer, which, however, 
 was deranged in transportation, and rendered useless. Other desirable instruments I 
 was unable to obtain. 
 
 The aneroid and thermometers were exposed to a free circulation of air on the 
 east side of the observatory near the northeast corner, but sheltered from the wind 
 and sun. 
 
 Mr. H. Thielson, engineer of the Burlington and Missouri Railway, was provided 
 with similar instruments and kept a record of thqm during the afternoon of the eclipse 
 at his house about half a mile N.NE. from the observatory, and 70 feet lower. His 
 readings of the aneroid barometer have been diminished by 0.46 inch, the correc- 
 tion obtained by comparisons with the other instrument on several different lays. 
 
KEPOET OF PBOFESSOB COFFIN. 
 
 Burlington, August 7, 1869. 
 
 21 
 
 Burlington 
 mean time. 
 
 On South Hill. 
 
 At Mr. Thielson's 
 
 Remarks. 
 
 Aneroid 
 barom. 
 
 Thermom's 
 
 Wind. 
 
 \neroid 
 barom. 
 
 Thermometers 
 
 Dry. 
 
 Wet 
 bulb. 
 
 At. 
 
 Dry. 
 
 Wet 
 
 bulb. 
 
 h, m. 
 
 in. 
 
 
 
 
 
 Southeas erly ; light 
 
 in. 
 29.68 
 29.68 
 29.68 
 29.67 
 29.66 
 29.66 
 
 29.65 
 29.64 
 29.63 
 29.63 
 
 77-9 
 79.0 
 79.0 
 79.8 
 
 79-9 
 80.0 
 
 79-9 
 79-4 
 76.7 
 75-0 
 
 74-4 
 
 74-4 
 75-5 
 74.8 
 75-2 
 74-5 
 
 74-2 
 74.0 
 70.0 
 69.2 
 68.0 
 
 65.2 
 65.2 
 66.5 
 
 65.3 
 66.3 
 66.0 
 
 65.0 
 65.0 
 62.0 
 62.0 
 62.0 
 
 Eclipse began. 
 Eclipse total. 
 
 Eclipse ended. 
 
 I 30 
 
 2 O 
 
 2 30 
 3 o 
 3 30 
 3 40 
 4 o 
 4 20 
 4 40 
 4 5 
 4 55 
 5 o 
 5 2 
 5 10 
 5 20 
 5 30 
 5 40 
 6 o 
 6 20 
 
 
 
 
 
 
 
 
 
 
 
 
 29.70 
 
 71.2 
 
 
 
 
 
 29.66 
 29.64 
 29.62 
 29.63 
 29.61 
 
 70.8 
 71.2 
 70.0 
 69.2 
 67.5 
 
 60.0 
 61.2 
 60.0 
 60.0 
 
 58.3 
 
 Southeasterly ; light 
 
 
 
 
 
 
 66.0 
 
 
 
 
 
 
 
 
 
 29.62 
 29.61 
 29.61 
 29.61 
 29.61 
 29.61 
 
 74.0 
 
 72.5 
 72.0 
 71.0- 
 71.2 
 71.6 
 
 67.0 
 67.2 
 
 67.7 
 68.8 
 69.0 
 68.0 
 
 62.0 
 62.0 
 62.8 
 63.0 
 63.0 
 63.0 
 
 
 
 
 
 29.59 
 
 66.2 
 
 59.0 
 
 Southeasterly; very light 
 
 29.58 
 29.58 
 29.58 
 
 66.8 
 67.0 
 
 65.8 
 
 60.0 
 
 59-7 
 59-5 
 
 
 
 Southeasterly; light 
 
 
 
 
 
 The sky generally appeared perfectly clear ; but at 4* 34 m p. m., Mr. Rock noted 
 a "low bank of clouds in western horizon." Mr. Gr. C. Morton, of Burlington, who, 
 with others, was watching the eclipse on an eminence in the northern part of the city 
 of Burlington, states that none of the party "had noticed a cloud in the sky before 
 the eclipse; we all spoke of the perfectly clear atmosphere, there being, seemingly, 
 absolutely nothing to prevent full, unobstructed view in every direction. Yet when 
 the totality came, clouds extending along the horizon to the north were very plainly 
 to be seen. Some one called my attention to the beautiful appearance of a bank of 
 clouds near the horizon at a particularly fortunate moment. At the instant I turned, the 
 moon's shadow was very clearly denned on the top of the bank, giving a remarkably 
 happy effect with the bright sunlight on that side farthest from me, and the dark 
 shadow on the other." Clouds invisible in full sunlight, appear to have been noticed 
 by others several minutes before the total obscuration. 
 
 OBSERVATIONS OF THE ECLIPSE. 
 
 I used for observing the eclipse a telescope made by Alvan Clark & Sons, 
 adjustable for latitude, with 3 inches aperture, 48 inches focal length, and magnifying 
 power of 3 1 ; a diagonal eye-piece adapted especially for observations of the sun, the 
 reflector being simply a plate of glass, inclined 45 to the optical axis of the telescope, 
 
22 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 and reflecting only about one-half of the rays to the eye ; it was, therefore, equivalent 
 to a diminution of the aperture to 2.1 inches. The telescope was furnished with three 
 shade-glasses, of one, two, three thicknesses, respectively, of glass of that peculiar 
 neutral tint called London smoke. The deepest of these presented a pleasant, softened 
 image of the full sun, and was used at the beginning and end of the eclipse; the 
 lightest was used at the commencement and during the first part of the total obscura- 
 tion. The field of view was 62' in diameter, or double the apparent diameter of the 
 sun, and was divided into octants by four spider-lines in the focus of the eye-lens. 
 There was nothing, however, to distinguish the lines, or to measure the rotation of the 
 diaphragm; and its connection with a diagonal eye-piece, which presents neither a 
 direct nor inverted, but a reversed image, and coidd be rotated -about the axis of 
 either the telescope or the eye-tube, added to the difficulty of estimating angles of 
 position with any precision or certainty. 
 
 FIRST CONTACT. 
 
 I noted the first contact at 1 2 h 50 4" by the chronometer, or 3'' 56 1 2". 5 mean time 
 of the Eclipse Station. There was nothing to indicate the approach of the moon 
 before actual indentation of the sun's limb. This time, therefore, may be too late by 
 2 s or 3", but would not be too early. 
 
 NOTES OF THE ECLIPSE. 
 
 
 
 The definition of the telescope was excellent; and during the eclipse, the limb of 
 the sun appeared smooth and well defined. The moon's limb, however, appeared in 
 some portions slightly serrated. This was especially noticeable in the eastern limb 
 soon after the beginning of the eclipse: but the magnifying power was insufficient for 
 the detection of any particular prominences or depressions. This irregular, serrated 
 appearance was specially noted near the southern cusp at 4 h i local mean time, and 
 about one-third the distance from the southern to the northern cusp at 4 h 36'". The 
 cusps, during the greater portion of the eclipse, were very sharply defined. Irregu- 
 larities were occasionally noticed, and the following noted : At 4'' 53, the southern 
 cusp appeared blunted and irregular, but soon after resumed its sharp appearance. 
 After the total obscuration, at 5 h i m 40", the southern cusp was terminated by a 
 detached luminoiis point. At 5'' 3^" and 5 b 2i m , the northern cusp appeared blunted 
 and irregular. 
 
 About 7'" after the total obscuration, a narrow band sensibly brighter than the 
 rest of the solar crescent, seemed to skirt the moon's limb. This was the only time 
 that I noticed this appearance. The lightest shade-glass was on at the time. 
 
 The largest and most fully developed solar spot was in the southwest quadrant 
 of the sun's disk. The first contact of the moon's limb with the edge of its nucleus 
 was noted at i3 b I4 m 52" by chronometer, or 4'' 20 56".6 local mean time; the entire 
 disappearance of the nucleus at i3 h i6 m 27", or 4'' 2 2'" 31 ".3 local mean time (probably 
 i m too great,) and its completed re-appearance at 14'' 9'" 20", or 5 h 15'" i6 8 local mean 
 time. The "outlines, both of the penumbra and nucleus, of this spot were very 
 
REPORT OF PROFESSOR COFFIN. 23 
 
 
 
 irregular. Other spots were visible; but, excep" a large one near the sun's eastern 
 limb, they were quite small and hardly distinguishable when close to the moon's limb. 
 
 THE TOTAL OBSCURATION. 
 
 For two minutes before the total disappearance of the sun, the lightest shade 
 glass was sufficient to protect the eye. The visible portion of the sun was reduced to 
 a very narrow crescent, sharply and beautifully denned, with hardly perceptible 
 irregularities, and sensibly diminishing in breadth and extent. When reduced to a 
 slender thread of light about 30 or 40 of the sun's limb in extent, it seemed 
 suddenly to break into distinct portions, to elongate in both directions, and then shorten 
 and run together with great rapidity changing so quickly that any distinction of 
 portions or of separating lines could not be noted; and then rapidly, but not instan- 
 taneously, to disappear. Except the illusory appearance of elongation, the phenomena 
 were simply such as would result from the serrt.ted irregularities of the moon's limb. 
 
 The time of total disappearance was noted at 13'' 51'" 46" by chronometer, or 
 4 h 57 44"- 6 local mean time. 
 
 THE CORONA. 
 
 At the instant of the sun's disappearance, the corona flashed out with unexpected 
 brightness, shining with a soft, nebulous, silvery-white light, with, perhaps, a slightly 
 bluish tinge as seen through the shade-glass. It was more brilliant, seemingly of 
 greater density close to the moon, fading away to indistinctness in all directions. It 
 was unequally distributed, and could be traced in some directions to a greater distance 
 than in others. Its structure was radial, but not distinctly striated. 
 
 In the direction 20 south of the place of the sun's disappearance, as estimated at 
 the time, or about 117, reckoned from the north point of the moon's disk, toward the 
 east, the corona was cut off by the limit of the field of view, the moon being a little out 
 of the center in that direction. In nearly the opposite direction, it could be distinctly 
 traced to the limit of the field. Thus its entire extent as far as visible, was 
 fully 64'. It could be traced nearly to the limit of the field towards the south-south- 
 east and southwest ; but its extent in other directions was more limited, and, at right 
 angles to the greatest elongation, was only two-thirds the breadth of the field, or 41'. 
 
 Plate I, Figure i, represents nearly its appaient outline in the field of the tele- 
 scope. The two radial points in the south-southeast and southwest directions were, 
 however, more distinctly marked, and the small portion of visible sky darker than is 
 represented. 
 
 The greatest elongation was also estimated to be in the direction 5 north of the 
 prominence hereafter described as the first which was noticed. This direction will be 
 92 or 105, reckoned from the north point of the disk, as we regard this prominence 
 as identical with No. 4 of Professor Mayer's diagram, Plate X, figure 1, as seems most 
 probable, or with No. 5. Neither differs greatly from 107. 2, the position of the 
 ecliptic, or 103. 7, the intersection of the plane of the sun's equator with that of the 
 sun's disk. The position of the sun's axis at the time of the eclipse was 13. 7, the 
 
24 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 north pole being 6.4 of a meridian circle of the sun within the disk, or the sun's 
 equator passing 6. 4 south of the center. 
 
 The elongation of the corona in the direction of the equator is manifest in Dr. 
 Gould's diagrams, Plate II ; but it is equally so in the direction of the axis ; while in 
 mine the minimum breadth is in that direction. 
 
 In comparing such representations, it should be considered that here the view was 
 with a telescope of diminished aperture and through a light shade-glass, and that dif- 
 ferent persons will estimate differently the distance to which they may be able to trace 
 a fading light until it becomes invisible ; and even the same person may estimate such 
 distance differently in different directions or in different planes through the axis of 
 the eye. In the present case, this last point could have been readily tested by simply 
 rotating the diagonal eye-piece, and thus changing the position of the image in the 
 field of view with reference to the eye of the observer. 
 
 The light of the corona reminded me at the time of colorless streamers of the 
 aurora borealis, as sometimes seen, and subsequently of the nebula of Orion, as seen 
 through a large telescope; and the tail of the great comet of 1843, as seen with the 
 naked eye. Indeed, a similarity in composition with the tails of comets is not improb- 
 able. 
 
 THE PROMINENCES. 
 
 Simultaneously with the sun's disappearance, a large prominence appeared sud- 
 denly to shoot up from the eastern limb of the moon, pyramidal in shape, but rounded 
 at the top, and its outline broken and irregular. It appeared to me of a beautiful rose- 
 color, very soft and delicate, more deeply tinted at the top than at the base, and to 
 stand out in bold relief from the white corona, which apparently formed the back- 
 ground. Its altitude was estimated to be 2l' or 3', its base 10 of the moon's limb, 
 and its position 20 to 30 south of the place of the sun's disappearance, or 117 
 to 127 from the north point of the disk. It is probably identical with No. 4 of Pro 
 fessor Mayer's description of the photographs, whoso position is 96, but may be No. 
 5, in position 110. The "eagle-wings" of No. 4, which appears to have attracted 
 the attention of most observers, as other prominences on the eastern limb, may have 
 been obscured by the colored glass until they were too faint to be noticed. 
 
 Another prominence, similar in shape and color, but larger, appeared as suddenly 
 and almost simultaneously on the southwest limb, extending about 13 along the 
 moon's limb, and rising to an altitude of 3'. Its estimated distance from the one first 
 described was 120, and its position 237 to 247, which identifies it with No. 8 of 
 Professor Mayer's description, whose position on the photographs is 238. This is the 
 large prominence on the moon's lower limb which, more than any other, attracted the 
 notice of spectators. 
 
 It was followed soon after by two others of the northwest limb, one similar in 
 shape and color to the two already described, but smaller, and estimated about 95 or 
 1 00 from the last. It is probably No. 1 1 of Professor Mayer's diagram, in position 
 318. The other, about 25 west of it, appeared in shape like a large mushroom, the 
 stem of a pale light, surmounted by a large head of the same beautiful rose color as 
 
 See Professor Mayer's report, and Plate X, figure 1. 
 
REPORT OF PROFESSOR COFFIN. 25 
 
 the other prominences, extending about 5 of the moon's limb. It is designated as 
 No. 10, in position 288. The altitude of each of these two was estimated at i' to i'. 
 
 Connecting them, and extending westward beyond the last about 20 or 25 
 toward the large prominence, was a band of rose-colored light, closely skirting the 
 moon's limb, and not more than i' in altitude. This, as well as the prominences, 
 appeared to stand out in bold relief from the corona. 
 
 On removing the shade-glass, about one minute after the sun's disappearance, the 
 whole scene greatly increased in brilliancy. The corona near the moon's limb now 
 shone with a glistening light, like the glow from a surface of molten metal in a fur- 
 nace, and extended throughout the field, so that no outline could be distinguished. 
 
 The prominences presented the same beautiful hue, but brighter and more intense. 
 That on the eastern limb appeared smaller, and gradually faded away. The large 
 one on the southwest limb appeared the same in size and shape. Those in the north- 
 west appeared larger, and the corona in that direction seemed to brighten as the total- 
 ity approached its termination. 
 
 The prominences seemed constantly to occupy the same relative positions, though 
 accurate estimates of positions were not attempted. They did not appear to me to 
 project on the limb of the moon, as described by observers with the naked eye, and 
 by some who had the aid of telescopes, and is so conspicuous in the photographs, espe- 
 cially where the exposure was prolonged. This lapping on the edge of the moon was 
 especially noticed in the large prominence on the southwest or lower limb.* But my 
 impression the day after the eclipse remained distinct that the moon's limb, under this 
 as the other prominences, appeared smooth and unbroken, although no note was made 
 of it at the time. 
 
 The darkness during the totality was not as great as I anticipated, as I was able, 
 with but little difficulty, to write in my note-book. 
 
 Mr. Rock 7iotes that "during totality, fire-flies were seen, as at night ; katydids com- 
 menced to chirp ; the landscape continued visible ; a bright orange-purple light encir- 
 cled the horizon, fading into the dull, ashen hue of the zenith." 
 
 THE SUN'S RE-APPEARANCE LAST CONTACT. 
 
 Straggling points of bright light, rapidly spreading and uniting, soon formed 
 a slender, brilliant line, regular and unbroken, as just before the sun's disappearance. 
 It seemed the work of an instant, and corona and prominences vanished from view. 
 The whole was a shifting scene of superb magnificence, occupying what seemed to 
 be a very brief moment of time. 
 
 The time of the re-appearance of the sun was noted at I3 h 54 32" by chronom- 
 eter, or 5 h o m 30". 2 local mean time. This may have been too soon, although I 
 thought myself sufficiently guarded against mistaking the increasing glow for the 
 actual re-appearance of sunlight. 
 
 The last contact was noted at i4 b 50 41" by chronometer, or 5 h 56 30'. 2 local 
 mean time. 
 
 * It was spokeo of by by-etanders as a bole cut in the edge of the moon. 
 4 E S 
 
26 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 COLLECTED RESULTS. 
 
 The following are the collected mean times at the eclipse stations in Burlington 
 of the several phases of the eclipse. They are l s .51 less than the Burlington mean 
 time for Miss Mitchell's observations, OM1 less for the rest 
 
 First contact. 
 
 Predicted from American Ephemeris 3'' 56 2". 5 
 
 Observed by Professor Coffin - 1 2 8 .5 
 
 ( suspected n 8 .5 
 
 Observed by Dr. Gould, on screen, < . 
 
 J ' ( certain 14 . .5 
 
 Observed by Professor Young, with spectroscope. ...... 7". 2 
 
 Observed by Mr. Stockwell, on screen 1 7 S .6 
 
 Observed by Professor Eaton, on screen 2 3 8 -5 
 
 Observed by Miss Mitchell 1 3 9 .8 
 
 Beginning of totality. 
 
 Predicted from American Ephemeris 4 h 57'" 27 s . i 
 
 Observed by Professor Coffin 44 s -6 
 
 Observed by Dr. Gould, (supposed 3 s too late) 43 8 -7 
 
 Observed by Mr. Stockwell, on screen 4O 8 -7 
 
 Observed by Professor Eaton, on screen 3 9 s - 7 
 
 Observed by Miss Mitchell 37 8 -7 
 
 End of totality. 
 
 Predicted from American Ephemeris 5 h o m i8 8 .7 
 
 Observed by Professor Coffin 30". 2 
 
 Observed by Dr. Gould 34". 2 
 
 Observed by Mr. Stockwell, on screen 28 s . 2 
 
 Observed by Professor Eaton, on screen 3 i s .2 
 
 Observed by Miss Mitchell 25 8 .6 
 
 Last contact. 
 
 Predicted from American Ephemeris 5 h 56 25".3 
 
 Observed by Professor Coffin 3O 8 .2 
 
 Observed by Dr. Gould, on screen 34 8 - 2 
 
 Observed by Mr. Stockwell, on screen 3 1 8 .2 
 
 Observed by Professor Eaton, on screen 3 i s .2 
 
 Observed by Miss Mitchell 29 B .8 
 
 METEORS. 
 
 A paragraph in the newspapers, a few days afterward, reminded me that just 
 before totality several bright flakes swept over the field from east to west, or more 
 nearly east-northeast to west-southwest, appearing like thistle-blows floating in the 
 sunlight. Similar appearances were noticed elsewhere, but their meteoric character is 
 very questionable. 
 
 Meteors, however, appear to have been noticed during the eclipse at several 
 places. Mr. Charles G. Boerner, of Vevay, Ind., reports that during the total phase 
 several meteors were seen with the naked eye, by some of their most reliable citizens, 
 about 45 above the horizon, their path being in a westerly direction. One counted 
 three, another five, quite brilliant. 
 
 J. H. C. COFFIN. 
 
REPORT 
 
 OF 
 
 DR. BENJAMIN APTHORP GOULD 
 
 , IOWA.. 
 
 27 
 
REPORT OF DR. B. A. GOULD. 
 
 BURLINGTON, IOWA. 
 
 CAMBRIDGE, August 14, 1869. 
 
 DEAR SIR : Having availed myself of your kind invitation to join your party for 
 observation of the total eclipse, at Burlington, Iowa, on August 7, I lose no time in 
 transmitting the results which I obtained. 
 
 The objects to which I proposed to give special attention, beside noting the times 
 of the contacts, were, in the first place, a determination of the form and dimensions 
 of the corona ; and, secondly, a sweep along the ecliptic during the total phase, in 
 order to learn whether any planet might be visible within the orbit of Mercury. 
 
 For these purposes, it seemed desirable to unite width of field with as much light 
 as possible, and I brought an equatorially-mounted comet-seeker, having a clear aper- 
 ture of 5 and a focal length of 35 English inches. This somewhat peculiar telescope 
 was constructed for me, a few years since, by Tolles, ithen of Canastota, N. Y., and 
 now superintendent of the Boston Optical Works. With its small focal length, it com- 
 bines great sharpness of definition ; and for this occasion, Mr. Tolles provided it with 
 an eye-piece of very low power, which affords a field somewhat exceeding i 45' in 
 diameter, and is traversed by a glass slide bearing three dark circles, of the diameters 
 4 1 '.6, 5 1 '.2, and 64'. o, respectively. These were intended for the double purpose of 
 affording an approximate estimate of the dimensions of the corona, and also of occult- 
 ing its light, to allow a better perception of any minute or faint objects in the vicinity 
 of the sun. 
 
 A contrivance for measuring the diameter of the corona, as seen by the naked 
 eye, was attached to the telescope-tube. It consisted of a firm steel rod, made of a 
 form adapted to resist flexure, and traversed by a metal carriage, bearing a blackened 
 disk of 0.25 inch diameter. This rod was graduated throughout its whole length, and 
 nicely adjusted parallel to the optical axis of the telescope, and at the end nearest the 
 eye it carried a circular screen, perforated with a sight-hole. Preliminary trials upon 
 the sun gave the diameter with a probable error not exceeding the quarter of a minute. 
 
 The shade-glasses available for observation of first contact with this instrument, 
 using a sufficiently high power, proved inadequate, even when the aperture was much 
 diminished ; and I availed myself of the kindness of the Rev. James F. Clarke, of 
 Boston, who was near me and offered the use of his 4-inch telescope. But, scarcely 
 half a minute before the computed time of first contact, the shade-glass of this tele- 
 scope suddenly cracked, and I hastened to another instrument near by, a 23-inch 
 telescope of 45 inches focal length, by Alvan Clark, which had been brought by 
 Prof. C. A. Young, of Dartmouth College, and was provided with a screen of white 
 card-board, on which the solar image was projected with a diameter of perhaps 6 
 
 inches, or a little more. < 
 
 29 
 
30 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 At i2 h 50 3 s chronometer-time, 3 h 56 i i s .5 local mean time, I suspected a con- 
 tact, and at 1 2 b 5o m 6* all doubt was removed by a well-marked indentation at this 
 point, This observation, however, is superseded by the successful execution of the 
 beautiful idea of Professor Young, who observed upon the spectroscope the gradual 
 extinction of the brightest line of the chromosphere, thus obtaining a sharp deter- 
 mination of the time of first contact, (corresponding to the complete disappearance of 
 this bright line,) and an excellent measure of the thickness of the luminous chromo- 
 sphere itself; and introduced a method of observing first contacts which can scarcely 
 fail to receive general adoption hereafter. 
 
 The sky was almost cloudless, and the atmosphere much more transparent and 
 clear than usual had been clarified by the heavy thunder-storms of the preceding 
 day. As the moon passed gradually over the sun's disk, the well-known phenomena 
 occurred, so often described. The light grew cold and weird, the heavens assumed a 
 grayish and, finally, an almost leaden hue, and the outlines of shadows became pre- 
 tematurally sharp and distinct. I examined the cusps carefully with two different 
 telescopes, by direct vision with powers of from 5<7 to 80, and also on the screen, btit 
 could discover no blunting or marked rounding of the extremities at 1 3 h 43, 1 3 h 45, 
 or i3 h 50. The sky at i h 50 m was of a cold gray color, shading off into blue at the 
 horizon. A glance through a field-glass at the landscape along the broad expanse of 
 the Mississippi, which was visible between wooded shores for some 1 2 or 1 5 miles to 
 the northward, showed the coloring of all objects reduced to an almost uniform tint, 
 not unlike that imparted under ordinary circumstances by the use of a light-shade 
 glass of " London smoke." 
 
 At i3 h 51 1 5 s , a plate of purple glass of not much deeper tint than I have seen 
 used for the windows of photographic establishments, sufficed to render vision 
 agreeable with the full aperture of my telescope. Through this, the corona was 
 distinctly visible on the preceding side, as well as above and below. It had 
 already been visible for some time through the field-glass, and General Wild, 
 who was using a binocular glass of about 2 inches aperture, with a light shade, had 
 seen it at i3 h 50 19". 
 
 For the moment of total obscuration, I consider my observation as uncertain by 
 two seconds. Anticipating a sudden and strongly-marked phenomenon, which would 
 permit no doubt as to the instant of its occurrence, the great brilliancy of the pho- 
 tosphere, or perhaps of the corona at the last point of occupation, led me to suppose 
 the totality still incomplete, when the simultaneous ejaculutions of the crowd assem- 
 bled around our place of observation, and which till that instant had maintained abso- 
 lute silence, convinced me that it had already taken place. I have recorded the 
 moment of totality as i3 h 51 45", 4 h 57 m 43". 7 local mean time; but this estimate 
 was made certainly three seconds later. Previous to this, the thread of solar light had 
 appeared broken into several fragments not beads, but patches many heliocentric 
 degrees in length. These had disappeared, and only at the point of last occupation 
 was the brilliancy maintained, which I erroneously supposed to belong to the body of 
 the sun. 
 
REPORT OF DR. GOULD. 31 
 
 Analogous remarks will apply almost equally well to my observation of the end 
 of totality, which took place a few seconds before I expected, and while my attention 
 was directed to a part of the limb at some little distance from the point of appearance 
 of the first ray. I recorded it as 13'' 54 36", 5 b o ul 34".2 local mean time, which 
 is not improbably too late, although in this case the involuntary buzz of the crowd was 
 subsequently heard. 
 
 Indeed, I now entertain serious doubts whether, with a power so low as that which 
 I was using, (amounting to riot more than five diameters,) and with an amount of light 
 relatively so large, the beginning or end of totality can be well determined without an 
 error to be apprehended not less than two seconds. The brilliant light of the luminous 
 envelope at the point of disappearance and re-appearance of the sun's limb, when con- 
 centrated by a lens collecting more than 3.000 times the light normally admitted to 
 the pupil, yet witli so slight an enlargement of the image, exhibits an intensity scarcely, 
 if any, less than 125 times that recognized by the unassisted eye; but had a power 
 of 55 or 60 been employed, the increase of intensity afforded by the object-glass 
 would have been counterbalanced by the magnifying power of the eye-piece, and the 
 intensity of the light at these points would not have differed essentially from that per- 
 ceived by an observer without a telescope. The beginning and end of totality usually 
 described as occurring with such extreme suddenness as to admit of determination 
 within a small fraction of a second, would seem nevertheless not to be instantaneous 
 phenomena, absolutely speaking, but in some degree subjective, although giving the 
 impression of instantaneousness, being, in fact, dependent upon the occultation of a pho- 
 tosphere, the brilliancy of which diminishes with the distance from the hidden surface 
 of the sun. If this view be correct, the appearance and disappearance of the totality 
 riiust depend in some degree upon a limit of perception in the observer, and its dura- 
 tion being lessened by an increase of the relation of light to magnifying power in the 
 telescope. And the correctness of the opinion may be tested in a future eclipse by 
 applying the spectroscopic method of Professor Young to the determination of the 
 second and third as well as of the first contact. Then, with a telescope of large aper- 
 ture the bright spectral lines of the photosphere ought to be distinctly seen for a short 
 interval after the solar spectrum has vanished, and again before its re-appearance; and 
 the length of this interval would afford a measure of the limits, between which the 
 time of total obscuration would be dependent upon the optical implements employed. 
 
 My friends, Messrs. A. C. Baldwin, of Boston, and John N. Stockwell, of Brecks- 
 ville, Ohio, and General Edward A. Wild, of Austin, Nevada, were near me, the first 
 being prepared to read the indications upon the graduated rod, and the second being 
 near the declination circle to read this off in case of need, while the last named mapped 
 for me at sundry different moments the form of the corona, and the position of the 
 protuberances. Each of them also noted sundry points to which I had asked their 
 special attention in advance, as also did my friend, Mr. Samuel S. Greeley, city sur- 
 veyor of Chicago. 
 
 The brilliancy of the corona, its extent, and the great irregularity of its form, 
 were sources of surprise to me. Throughout the period of totality the daylight was 
 amply sufficient for making and reading pencil-memoranda without conscious effort; 
 
32 ECLIPSE OF THE SUN, AUGUST 7, 18(59. 
 
 but Mr. Baldwin was obliged to use a lantern for reading the graduations of the steel 
 rod, which were in a very unfavorable position. 
 
 A rapid survey with the opera-glass, immediately after the occurrence of 
 totality, showed nothing essentially different from what was visible to the telescope or 
 the naked eye. The corona, as seen through the telescope, seemed a little larger, and 
 less jagged and irregular in outline. Venus and Mercury were very prominent objects, 
 the latter shining with a light as ruddy as Mars ; and Regulus was easily seen, midway 
 between Venus and the Sun. A moment's glance toward the zenith showed Arcturus, 
 then nearly on the meridian ; and my companions had no difficulty in recognizing 
 Mars and Saturn, as well as sundry fixed stars. 
 
 Just to the left of the lowest point of the moon, a large protuberance was con- 
 spicuous to the unaided eye. This I estimated as not less than ten heliocentric degrees 
 wide, and on the average nearly two minutes high ; but this estimate was hastily and 
 roughly made. In general, I had no time and made no effort to fix the position 
 either of this or of any of the other protuberances, but General Wild entered them 
 approximately on his charts. This largest one was to the naked eye brilliantly white; 
 through the opera-glass, it was tinted with rose-color, so as to contrast with the yet 
 whiter light at the base of the corona; but through the telescope it appeared strongly 
 tinged with red, especially along the summit, and some forked tongues protruded 
 nearly from the middle by nearly a minute in addition, so that the total height appeared 
 not far from one-tenth of the lunar diameter. An unmistakable peculiarity of this 
 protuberance was that it appeared strongly projected upon the dark limb of the moon. 
 This was the case whether seen with the unaided eye, the opera-glass, or the telescope, 
 and is supported by the concurrent testimony of all the observers. Casual spectators, 
 unfamiliar with astronomy, insisted vehemently that a piece had been missing from 
 the moon's limb, allowing the sunlight to pass through. One quite intelligent man 
 compared the moon to a cheese from the rim of which a small notch had been cut. 
 Mr. Stockwell describes it as presenting the form generally of a deep gorge or chasm, 
 through which the light issued, but sometimes actually resembling an orifice in the 
 body of the moon, being completely projected upon the disk. This observation seems 
 to explain the well-known and often-ridiculed assertion that the sunlight has been 
 jen in former eclipses through an aperture in the moon. 
 
 At about I3 h 52 1 5 s , I set the sliding disk cup on the rod, to occult the corona from 
 the naked eye. The very irregular form of the corona rendered this more difficult 
 and time-consuming than I had anticipated. My endeavor was to gauge the average 
 size of the corona, irrespective of the specially -projecting rays, and without regard to 
 the position of the moon, as concentric with it, or otherwise. After the brightest part 
 had been screened off, fainter portions at the circumference became distinctly visible, 
 and required a new setting of the disk, after which yet a third similarly became 
 needful. The best setting which 1 succeeded in making gave at i3 h 52 i6 8 an average 
 diameter of 63'. 6, biit left five large beams projecting beyond the rim of the screen; 
 thus indicating a general height of about 16' above the surface of the sun, or an 
 altitude equal to its whole semi-diameter even when we disregard the prominent beams 
 or streamers of which one at least extended to nearly or quite twice this distance. 
 
REPORT OP DR. GOULD. 33 
 
 This height of 16' is above the true average for the corona in general, inasmuch as 
 there were depressions which were likewise disregarded; and it may, moreover, have 
 been apparently exaggerated by diffraction, although no pains were spared to avoid 
 this source of error. But the luminous envelope must certainly have extended to as 
 rmich as 15' beyond the sun's limb, through three-fourths of the circumference, and 
 in several parts it exceeded this limit considerably. Still a measurement similarly 
 made for so much of the corona as was conspicuous to the eye without screening off 
 the most brilliant central portion would hardly have exceeded 54', corresponding to a 
 height of about 1 i'. 
 
 The five prominent beams which projected beyond the general outline were care- 
 fully mapped for three special moments by General Wild; and his sketches have 
 given much assistance to me in connection with my own far more hurried ones, in the 
 subsequent endeavors to delineate the form, and in recalling the outlines to my 
 memory. Messrs. Baldwin and Greeley also noted the position of the projecting beams; 
 and I was thus'able at the first convenient opportunity to construct drawings of the 
 form and dimensions of the corona, for the beginning, middle, and end of the totality. 
 My drawings have been reproduced in a more artistic form by an accomplished friend, 
 who has faithfully represented the general effect in the delineations herewith inclosed. 
 (Plate II, Figs, i, 2, 3.) They represent the positions as seen by direct vision, the ver- 
 tex being at the top of the drawing and the north point of the limb about 53 to the 
 right, or preceding, side. It will be remarked that the directions of the most promi- 
 nent beams corresponded approximately to the vertex, and the four cardinal points"; 
 also, that the aspect of the whole corona varied materially from minute to minute, though 
 hardly in such a way as to indicate that the irregularities of form were affected by the 
 position or contour of the moon. Nor do they seem to stand in any manifest relation 
 to the sun's equator, the position of which is show.n upon the drawings. 
 
 The largest beam pointed south, having at this time a base of about 50 and a 
 vertex perhaps 10 or 12 wide, as measured from the center. Its extent beyond the 
 screen I estimated as not less than 10' or 12' of a great circle, making its total height 
 not far from 43' from the center, or 27' from the surface of the sun. Another, nearly 
 as large, and of the same general form, projected similarly toward the preceding side 
 nearly in a parallel of declination. Two smaller ones were a little above the north 
 point, and nearly at the vertex respectively ; and a fifth, the smallest and obtusest of 
 all, pointed a little southward on the following side, and nearly toward Regulus, 
 extending less than two minutes beyond the screen. 
 
 My telescope was in such a position (circle preceding) that the graduated outer 
 face of the steel rest was inclined downward by more than 45, and was hardly more 
 than a meter from the ground. The graduation is in strong black lines, about one 
 millimeter in breadth ; but, as has been already stated, these lines were not distinct 
 enough against the gray steel for Mr. Baldwin to see them without a lantern. 
 
 I next introduced the glass slide into the telescope, and, disregarding as before 
 the long streamers, of which the two on the following side had become considerably 
 nearer to each other during the interval, the middle circle 51' in diameter was found 
 5 E s 
 
34 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 to hide more than half the general outline of the corona; although when the circle of 
 40' was tried, the luminosity appeared to extend beyond it in all directions by decid- 
 edly more than a quarter part its diameter. This measurement was at I3 h 52 m 4o", and 
 we may therefore consider the general diameter of the corona at that time, as seen 
 through my seeker with a power of 5, to have been a little more than 56', correspond- 
 ing to a general altitude of not quite 10'. How far the difference between this 
 measurement and the former may be owing to the use of the telescope, or how far it 
 may be due to actual change of apparent dimension, are questions upon which I am 
 unable to form an opinion, since no time was available for repeating the measure with 
 the naked eye. 
 
 The largest occulting circle, 64' in diameter, was then pushed over the sun, hiding 
 all the streamers except the extremity of the southern one, which would thus appear 
 to have been at least if or 18' in height, inasmuch as the opposite one was shorter, 
 and the center of the circle probably south of the sun's center. 
 
 With my eye thus protected from the light of the corona, I devoted some 25 
 seconds to a careful scrutiny of the immediate vicinity of the sun, in order to ascer- 
 tain whether any other luminous body might be visible there. My field gave a range 
 of fully 20' on all sides beyond this circle, but I could discover nothing upon the 
 nearly uniform background of bluish-gray, which was illuminated unmistakably by 
 au undefined radiance from behind the circle. Removing the slide, a slight motion of 
 the undamped telescope sufficed to throw n Cancri into the field. This I succeeded 
 in detecting, although with difficulty, thus fixing an outer limit for the magnitude of 
 any planetary body within my sweep at a greater distance from the sun. The mag- 
 nitude of this star is given as 5 M .8 by Argelander in his Durclimusterung, and was also 
 fixed as 5 M .8 in my Uranometrical Determinations at Albany in 1858. Had I not in 
 advance made myself familiar with its position, and with the motion necessary to bring 
 it into the center of the field, I do not think I should have detected it; but it seems 
 highly improbable that any star surpassing it in brightness by one magnitude could 
 have failed to arrest my attention, even in that close proximity to the sun's limb, 
 which was not 50' distant, although out of the field. 
 
 The position of the ecliptic was well marked by Mercury and Venus. Between 
 Mercury and the sun, no star was visible. This distance was about five degrees, and 
 was swept through in about 30 seconds, particular attention being given to the region 
 nearest the sun. Had any planet as bright as the 5th magnitude been within 40' of 
 the ecliptic, it could hardly have failed to be visible; indeed, I think that any object 
 of the 6th magnitude would have been seen if not within 2 of the sun. The same 
 process was then repeated on the other side in the direction of Venus, which required 
 somewhat more care and time, lasting from about i3 h 53 45" till i3 h 54 m 20". The 
 limit of the sweep was given by Leonis, (5 H .6,) which I found without difficulty by 
 means of a stop previously attached to my declination circle. Starting from a posi- 
 tion about one degree south, and one degree following this star, I moved cautiously 
 toward the sun, but saw no star whatever on the way, though very thoroughly scruti- 
 nizing a belt at least i in width. This sweep occupied a longer time than I had 
 supposed, and on reaching the sun, the increased brilliancy near the point where the 
 
REPORT OF DR. GOULD. 35 
 
 light was to re-appear warned me that the end of totality was close at hand. It did, 
 indeed, follow within five seconds. 
 
 Meanwhile, a range of protuberances had appeared on the north-preceding quad- 
 rant. These were four or five in number, and their variation in magnitude was evident 
 from the order of their appearance, which was not that of their distance from the point 
 of third contact. Their positions, and the order of their appearance, were rioted by 
 General Wild, from whose memorandum sketch I have roughly entered them upon 
 the drawing.* Two other protuberances visible from the beginning in the south fol- 
 lowing quadrant were occulted toward the close of the totality. 
 
 I had asked of the friends I have named attention tp the tints of the moon and 
 the corona, to the relative distribution of light in the corona, and to some other points, 
 all of which I myself bore in mind. Concerning these, the testimony of all is accordant. 
 
 The form of the corona does not appear to have been essentially modified by any 
 subjective influences. Seen with either eye alone, it presented the same aspect, nor 
 did the striations or projecting beams turn in the least when the observer changed the 
 posture of his head. 
 
 Its color was of a clear brilliant white without any tinge. Once it seemed to me 
 to have a very slight tinge of straw-color, but my present memory, corroborated by 
 my companions, is of a pure white, intensely brilliant at the base, and shading rapidly 
 by imperceptible gradations to its outer limit, which was entirely undefined and gray, 
 fading off into invisibility, and becoming perceptible, when the brighter portions were 
 screened from the eye, to a much greater distance than it could otherwise be seen. 
 There were no concentric strata of light visible to me, though these are mentioned by 
 others. The projecting beams were entirely radial, and the background between 
 them seemed filled with a faint diffuse light. The basis of these beams or streamers 
 were no brighter than the other parts of the corona at the same distance from the sun. 
 They stood in no apparent relation to the flame-like protuberances, or to the sun's 
 equator, and although they changed their positions to some extent, and also their 
 dimensions during the period of totality, the corona did not appear to grow constantly 
 smaller on the side toward which the moon was moving, or constantly larger on the 
 other side. That no such change as this took place I am not prepared to say, but if 
 there was any it was only to a small extent. The projecting beams were jagged in 
 their outline and at their extremities, and when two approached each other, as in the 
 north-following and also in the north-preceding quadrant at the middle of the eclipse, 
 these seemed like streaming remnants of some pale, tattered banner. A radiating 
 filamentous aspect was strongly marked. 
 
 The body of the moon was not of the intense blackness commonly represented; 
 this impression being manifestly due solely to the vivid contrast with the brilliant 
 corona; but it was of a deep slate-color, a very dark bluish-gray. There was nothing 
 of olive in the tint, which exhibited no apparent admixture of yellow or green, in 
 however small degree. 
 
 Of the protuberances I took no special note other than their color, and, in the 
 case of the large one, its cellular or honeycombed aspect and the projection of its 
 
 * Their positions in Plate II are from the diagram in the Report of Professor Mayer, Plate X, Figure 1. 
 
36 ECLIPSE OF THE SUN, AUGUST 7, 18G9. 
 
 base upon the moon's disk. This last very striking phenomenon seems due to an 
 actual reflection of the intense light froift the surface of the moon. The positions of 
 the protuberances upon the accompanying drawings are taken from measurements by 
 others. 
 
 Upon the reappearance of sunlight, the corona faded away as gradually as it had 
 appeared, remaining visible on the opposite side of the moon for nearly a minute. 
 Up to i4 h 5 m the cusps showed no sign of blunting or rounding at their extremities. 
 
 The last contact, like the first, I observed upon a screen; and the recorded time, 
 14'' 50 m 45 s , or 5 h 56"' 34 8 .2 local mean time, is, I think, a good determination. 
 I am, my dear sir, with much respect, very truly yours, 
 
 R A. GOULD. 
 Prof. JOHN H. C. COFFIN, 
 
 Superintendent American Ephemeris and Nautical Almanac. 
 
 SUPPLEMENTARY REPORT BY DR. B. A. GOULD. 
 
 CAMBRIDGE, October 25, 
 
 DEAR SIR: A careful study of the photographic records of the total phase of the 
 eclipse has led me to some inferences which, although not properly belonging within 
 the province of a report upon the results of personal observation at the time, may yet 
 fairly be regarded as deductions from your expedition. J therefore avail myself of 
 your invitation to communicate them, as an appendix to my report. 
 
 Almost the first impression given me by an inspection of the photographs, made 
 during the total obscuration at Burlington and Ottumwa, had reference to the very 
 limited extent of the photographic record of the corona, and to the remarkable defi- 
 ciency even of this record at two nearly opposite points of the limb, where no such 
 phenomenon had been recognizable by the eye. A comparison with my sketches, made 
 near the beginning, the middle, and the end of the totality, not only confirms this 
 impression, but shows that coronal beams had been especially conspicuous at these 
 parts of the limb, which coincide approximately with the extremities of the solar axis. 
 
 Soon afterward, I had an opportunity of examining the photograph taken by Mr. 
 Whipple, during the total obscuration at Shelbyville, Ky. In this, which was 
 obtained by an exposure in the principal focus of the telescope for 40 seconds, one 
 of the coronal beams (from 35 to 45 west of north, as nearly as I can estimate) is 
 depicted to the height of at least 7', and the radiance visible about the polar regions 
 of the sun is here also decidedly less than at other parts of the limb. None of the 
 finer details of the protuberances are exhibited in this photograph, although the pro- 
 tuberances themselves are recognizable to some extent from their superior brilliancy 
 to that of the surrounding radiance. 
 
 These facts, taken in connection with sundry others, and especially with the addi- 
 tional one that the coronal beams visible to the eye exhibited no relation whatsoever 
 to the protuberances, whereas the aureole shown upon the photographs, and especially 
 
KEPOET OF DR. GOULD. 37 
 
 upon those of short exposure, is most conspicuous in their immediate vicinity, have 
 suggested what I cannot but believe to be the true explanation of the phenomena. 
 
 Last year's eclipse led, as is well known, to the discovery that the protuberances 
 are but local aggregations of a brightly-glowing, gaseous medium, which surrounds 
 the solar photosphere, and is perceptible by the spectroscope at any part of the sun's 
 limb, although, like the protuberances themselves, it is less abundant near the poles. 
 This bright envelope has received from Lockyerthe name "chromosphere"; its outline 
 has been found to be quite irregular, jagged, and variable; in the neighborhood of a 
 protuberance it is very uneven and billowy, while at other parts of the limb it is, in 
 general, tolerably uniform in height. The observations of both Janesen and Lockyer, 
 corroborated by other investigators, have shown that the light of this chromosphere is 
 principally due to incandescent hydrogen gas, with which are intermingled the vapors 
 of sundry other metals. 
 
 The large quantity of photolytic rays, in the light of glowing hydrogen, would 
 naturally produce a prompt and distinct record upon the photographs, and the facts 
 observed have led me to the conviction that those taken at Burlington and Ottumwa 
 exhibit merely a representation of this chromosphere, wider and more irregular in its 
 chemical record than in its optical image, under the ordinary circumstances of spec- 
 troscopic observation. The Shelbyville photograph, which, as I have said, exhibits a 
 diminution of radiance at the poles, and a general outline altogether unlike that of the 
 visible corona, manifests, on the other hand, a width of the photographic corona singu- 
 larly contrasting with the slight aureole upon the much larger pictures of the Nautical 
 Almanac parties, who gave a short exposure in the field of the magnified image. If 
 we suppose the impression there, in which the radiance around the eclipsed sun is, on 
 the average, not less than 3' or 3 ' broad, to represent anything else than the brightest 
 portions of the visible corona, we encounter serious difficulties, and apparent improb- 
 abilities, it is true. Yet the essential diversity of its form from that of the visible 
 corona is a very important consideration, and the fact that the source of the radiance 
 exhibited upon the photographs is materially connected with the body of the sun is 
 established by its manifest relation to the solar axis, while the rapid variations of form 
 in the visible corona would suggest the reverse. 
 
 Therefore it is that, notwithstanding the apparent improbability of the idea, I 
 incline to the opinion that the glory seen around the sun's image, even upon these pho- 
 tographs of longest and intensest exposure, is something distinct from what was seen 
 by the spectators of the eclipse, and that the corona proper, or that whose outlines are 
 depicted in the drawings, is an independent phenomenon, the light from which, 
 although poor in photolytic rays, conceals from sight that chromospheric radiance to 
 which the photographs bear witness. If this be so, it would seem natural to infer that 
 the visible corona at least so much of it as attracts the observer's attention may not 
 be physically connected with the body of the sun, but may even have its origin within 
 our own atmosphere; an inference which the observed fluctuations in its form would 
 tend to corroborate. 
 
 These suggestions are offered with some diffidence, but they appear to me 
 quite in conformity with established or highly probable physical facts. They accord 
 extremely well with the observations of Lockyer and Miller, and with the solar theory 
 
38 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 of Faye. They lead, moreover, to the supposition that the chromosphere is simply 
 the atmosphere of the sun, where it is rendered luminous by the formation and pre- 
 cipitation of the photospheric material, whose vehement ejection from the sun's inte- 
 rior forms the protuberances, and which is dissipated according to the laws of gaseous 
 diffusion, while its constituent elements are condensed in the order of their tempera- 
 tures of vaporization. The abundance of violet and ultra-violet rays in the spectrum of 
 hydrogen, and the levity and low temperature of vaporization of this element, seem to 
 afford a full explanation of the photographic phenomena, when considered in connec- 
 tion with the higher radiant capacity of the condensed, though diffuse, chromospheric 
 matter, which has recorded itself on the plates of short exposure, although it was not 
 perceptible by the observer. 
 
 This last-mentioned fact was manifested by De La Rue's results in 1860, and is 
 still more fully illustrated by our present experience; for a considerable number of 
 the fleecy aggregations and nebulosities, shown upon the photographs of short expos- 
 ure almost as distinctly and conspicuously as the protuberances themselves, were 
 unseen by the observers, no matter what the telescopic powers employed. 
 
 These views apparently imply also an essential identity in the material of the 
 chromosphere, the faculse, and the photosphere, and they explain the small amount of 
 atmospheric refraction at the sun. It is probably needless to add, that while the chro- 
 mosphere should theoretically manifest the same lines as ordinary sunlight, although 
 reversed, still, its inferior brightness, and the different heights of condensation for dif- 
 ferent elements, would render it impossible that they should be exhibited. At the 
 same time the intense heat and the comparative faintness of the sources of chromos- 
 pheric light would essentially modify the relative intensity of the lines. The various 
 phenomena of the spots, the darker centers observed in their nuclei, and similar 
 unquestioned facts, seem to me strongly corroborative of this explanation. 
 
 Hoping to be excused, if I have transcended, the proper limits of a report, by 
 trespassing too far upon the domain of theory, 
 I am, very sincerely, yours, 
 
 B. A. GOULD. 
 
 Prof. J. H. C. COFFIN, 
 
 Superintendent American Ephemeris and Nautical Almanac. 
 
REPORT 
 
 OF 
 
 PROFESSOR CHARLES A. YOUNG. 
 
 39 
 
REPORT OF PROF. C. A. YOUNG. 
 
 BURLINGTON, IOWA. 
 
 HANOVER, N. H., November 8, 1869. 
 
 DEAR SIR : I have the honor to submit the following report of my observations 
 upon the eclipse of August 7, as a member of the party under your direction : 
 
 INSTRUMENTS. 
 
 The spectroscopic combination employed was made up of various instruments 
 belonging to the apparatus of Dartmouth College, arranged for the occasion in a man- 
 ner somewhat different from anything heretofore used, but which proved efficient. 
 
 The spectroscope proper had five prisms of dense flint-glass, (French,) with 
 refracting angles of 45, and faces i\ by 3 inches Its telescope and collimator (by 
 Alvan Clark) had each an aperture of 2\ inches, with a focal length of about 17. 
 The telescope was provided with a wire micrometer, and magnified fourteen times. 
 The prism-box was so connected with the arm which carried the telescope that any 
 motion of the latter by the tangent-screw, which brought the different portions of the 
 spectrum into the field of view, would give it an angular motion just half as great, 
 and thus keep the prisms in the position of least deviation and best definition. The 
 instrument gave a deviation of about 165 and a dispersion of 18 betw'een A and H, 
 and showed all the lines on Kirchhoff's and Angstrom's maps. The position of a line 
 could be determined by it by one observation, under favorable circumstances, within 
 one division of Kirchhoff's scale, which I shall employ throughout this report in describ- 
 ing the lines observed in the spectrum. The slit of the spectroscope was J of an inch 
 long, and of adjustable width. During the eclipse, it was kept open about soo of an 
 inch, as nearly as could be estimated. 
 
 A small camera-lucida prism was arranged in such a manner that it could be 
 turned up in front of the slit, covering half its length, and thus permitting direct com- 
 parison between any spectrum under observation and the air-spectrum formed between 
 platinum electrodes by the spark from a small induction-coil and Leyden jar. It was 
 not, however, found necessary to use this arrangement, as the six known lines of the 
 chromosphere spectrum furnished the needed points of reference, and the faint, con- 
 tinuous spectrum of the corona enabled the micrometer-wires to be easily seen with- 
 out the necessity of any further illumination. 
 
 The telescope, which formed the image of the sun upon the slit, was a so-called 
 comet-seeker, (by Merz & Sons,) of 4 inches aperture and 30^ focal length. An eye- 
 piece was employed which made the image upon the slit about 2\ inches in diameter." 
 I think the eye-piece important, because it gives an easy means of securing an exact 
 6 E s 
 
42 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 focus of the sun's limb upon the slit for any part of the spectrum under observation ; 
 and in even the most perfect achromatics this focus varies so greatly for the different 
 colors that it requires constant attention. 
 
 Upon the collimator was fastened a brass disk, to which was glued a circle of 
 white paper about 2 inches in diameter, with an orifice at its center, graduated by radi- 
 ating lines into angles of ro, and so placed that its center coincided with the center 
 of the slit. The image formed upon this paper disk furnished the means of directing 
 the instrument upon any portion of the sun, and answered every purpose of a finder. 
 During the totality, the whole circumference of the moon was visible upon this screen, 
 with the red prominences, and something even of the corona itself. The radiating lines 
 also enabled me to fix with sufficient accuracy the position of any object under obser- 
 vation on the sun's limb, or to bring any desired point to the slit, as, for instance, to 
 obtain the spectroscopic observation of a contact. 
 
 Of course this arrangement would not answer for the observation of any but 
 bright objects, like the sun and rnoon, whose images are easily visible upon a screen. 
 
 The comet-seeker and spectroscope were attached to a wooden frame-work, and 
 the whole was mounted equatorially, with tangent-screws for slow motion, both in right 
 
 ascension and declination. 
 
 The instrument is represented in 
 the accompanying figure. 
 
 Besides the spectroscope, I also took 
 with me a small telescope -of 2| inches 
 aperture and 45 inches focal length, 
 mounted upon a pillar and claw-stand. 
 This was fitted with screens by my as- 
 sistant, Mr. Emerson, in such a manner 
 as to cast an image of the sun about 6 
 indies in diameter upon a piece of Bristol 
 board carefully shaded from all sunlight 
 except what came through the instrument. This image was observed upon by Dr. 
 B. A. Gould, of Cambridge ; Professor Eaton, of the Packer Institute, and others, 
 who, I presume, will report to you directly. 
 
 I had, also, a spy-glass of 2\ inches aperture, which was loaned to Rev. W. Salter. 
 In addition, I took with me a small induction-coil, capable of giving a spark f 
 of an inch long ; a small Leyden jar, and three cups of Bunsen's battery, two-quart 
 jars ; also, a pair of Nicol's prisms, and an excellent plate of tourmaline. 
 
 PRELIMINARY OPERATIONS. 
 
 I arrived in Burlington Tuesday evening, and the next morning (August 4) the 
 instrument was mounted in the southwest corner of the building provided for the pho- 
 tographic operations. The same afternoon a few micrometrical measurements were 
 taken on the principal lines of the spectrum to ascertain whether the value of a revolu- 
 tion of the micrometer-screw had changed by any displacement of the prisms during 
 transportation. The results appeared satisfactory. I intended to make a thorough 
 
REPORT OF PROFESSOR YOUNG. 43 
 
 examination of the whole length of the spectrum before the eclipse, such as I had 
 made at Hanover previous to packing up ; but the instrument was so situated in the 
 building that the morning sun could not be used, and the afternoons of Thursday and 
 Friday were botli most discouragingly overcast and rainy. I think, however, from 
 the measurements made on Wednesday, we may safely assume the scale of the instru- 
 ment to have undergone no material alteration. 
 
 The unfavorable weather prevented any further operations until Saturday. The 
 forenoon of this day was mainly occupied by myself and assistant in setting up the 
 batteries, making the telegraphic connections, and giving what other aid we could to 
 the members of our party in the arrangement and adjustment of their instruments. 
 
 SOLAR PROMINENCES. 
 
 In the afternoon, before the commencement of the eclipse, I examined the whole 
 circumference of the sun, and noted protuberances in the following positions : (The 
 position-angles are reckoned from, the north toward the east.) 
 
 1. + 70 to 4- 90; a diffuse mass with many detached clouds. 
 
 2. 4- 146; very bright, but not large. 
 
 3 130; an enormous and very bright protuberance the principal one. 
 4. -- 7o-75; a long, low, but pretty bright mass. 
 
 Besides these, several smaller ones were seen whose positions were not noted 
 owing to the near approach of the eclipse. 
 
 FIRST CONTACT. 
 
 I had not intended to make any observation upon the time of contact, considering 
 the spectroscope an unsuitable instrument for the purpose; but about half an hour 
 before the event was to take place it occurred to me that, on the contrary, th'e spectro- 
 scope could be made to give results superior in value to any that could possibly be 
 obtained by other methods, excepting, perhaps, the data deduced by calculation from 
 measurement upon photographs. Accordingly, I connected myself with the chrono- 
 graph. 
 
 When the telescopes and collimator of the instrument are properly focused, and 
 the limb of the sun is made to bisect the slit nearly at right angles, the spectrum in 
 the neighborhood of the C line presents the appearance I have indicated in Plate III, 
 Figure 2. Half of the spectrum will be brilliant, and the other half, formed mainly 
 by the illuminated air just beyond the edge of the sun, comparatively obscure. Most 
 of the dark lines on the bright portion of the spectrum will continue directly across 
 the dusky portion. Not so the C line, however, which terminates at the edge of the 
 brilliant part, to be replaced in the dusky spectrum by a scarlet line running up like 
 a needle of light to a height depending upon the thickness of the chromosphere at the 
 point observed. (The chromosphere being the stratum mainly of incandescent hydrogen 
 which overlies the photosphere, and was first so named by Mr. Lockyer.) 
 
 In my instrument, the apparent breadth of the spectrum, referred to the limit of 
 distinct vision at a distance of 10 ; nches, is almost exactly i^ inches, and, with the 
 eye-piece used on the comet-seeker during the eclipse, corresponds to a width of 2' 54" 
 
44 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 on the sun's disk, determined by the time occupied by the sun's limb in traversing 
 the slit, which was, by repeated observations, i2 8 .62 on the gth of June. This very 
 conveniently gives a scale of almost precisely TOO of an inch to the second of arc. 
 
 The apparent length of this brilliant needle of the chromosphere spectrum usually 
 ranges from 6 to 1 2 hundredths of an inch, but when a prominence is on the slit it 
 may be of any length, depending, of course, upon the height of the protuberance. 
 
 Now, if we bring to the slit of the spectroscope that portion of the sun's limb where 
 the contact is to occur, it is obvious that before the edge of the moon reaches the sun 
 itself, it must first occult the chromosphere; and this will be evident to the observer 
 with the spectroscope by the gradual shortening and final extinction of the brilliant 
 needle in the C line; or, indeed, in any other line of the chromosphere spectrum, as 
 for instance F, or the line near 1) at 1017.5, now usually known as D 3 ; the C line is, 
 however, by far the best adapted to observat'on. 
 
 At the beginning of the eclipse, I had thus the pleasure of witnessing the gradual 
 approach of the moon, visible for more than 40 seconds before it reached the sun, 
 because there happened to be a prominence of considerable brightness, though small 
 elevation, exactly at the point of contact, ( 71,) which made the needle of light 
 nearly J of an inch in apparent length. The moon's arrival was first signaled by the 
 square truncation of the point of the needle, which before was somewhat acute; then 
 it grew perceptibly shorter (not fainter) second by second, until, at i2 h 49 58 8 .6 by 
 the chronometer, (3 h 56 7". 3 Burlington mean time,) its last spark was covered, and I 
 recorded the contact. I think the observation was as easy and as accurate as a star- 
 transit, (the star being about 20 from the pole,) and that the recorded time cannot 
 possibly be more than a second in error. 
 
 The gentlemen who observed in the usual methods, first noted the contact (as 
 might be, of course, expected, since they could only perceive the event after it had 
 actually occurred) from 5 to 20 seconds later; but I am informed by Professor Mayer, 
 who had charge of the photographic party, that the time deduced by a computation 
 based upon a preliminary measurement of two of the photographs taken within the 
 first minute after the contact was announced, agrees with my observation within A 
 of a second. 
 
 I am fully persuaded that hereafter Lie spectroscope ought to be considered 
 indispensable to the accurate observation of the first contact of any opaque body with 
 the sun's limb, and properly used will make such observations as easy and accurate 
 as those of any other appulsive phenomena. 
 
 [NOTE. Since writing this report, I have received volume 68 of the Comptes Rendus of 
 tlie French Academy of Sciences, and find that I have been anticipated in respect to this 
 application of the spectroscope by M. Faye. 
 
 At the session of Monday, January 1 1, 1869, in a discussion relating to the observa- 
 tion of Uie approaching transit of Venus, he proposed essentially the same method of observ- 
 ing the contact which I employed in this eclipse. I regret that I was not earlier aware of 
 this fact. Hanover, November 16, 1869.] 
 
 In the observation of the approaching transit of Venus it will, I believe, prove 
 of special value. Of course it is not yet possible to say precisely how much this 
 method may be affected by the planet's atmosphere and by irradiation; but it is diffi- 
 
REPORT OF PROFESSOR YOUNG. 45 
 
 cult to see why it should suffer more from any of these circumstances than the""older 
 modes of observing; and the astronomer armed with the spectroscope will have this 
 incalculable advantage over all his compeers, that, some time before the contact 
 actually takes place, he will be apprised of the planet's advent, will witness her gradual 
 approach, and thus be able to concentrate his attention on the one important moment 
 instead of being kept upon the strain for minutes. By opening the slit a little, as is 
 customary in making drawings of the prominences, he can even see the curved out- 
 line of the planet's disk, black upon the scarlet ground of the chromosphere, and can 
 select the precise point of impact. If his instrument has sufficient dispersive power, 
 (at least twice as great as that of the one I employed on this occasion,) and is provided 
 with an accurate clock-work, he can place the slit tangential to the limb, and opening 
 it somewhat widely, can command the chromosphere for several degrees on each side 
 of the computed point of contact, and thus avoid the anxious cruising that would 
 otherwise be necessary on account of the uncertainty of this important datum. 
 
 It would seem also that the internal contacts might be observed with the spectro- 
 scope at least as accurately as in any other method; for the phenomenon to be 
 observed, instead of being merely the breaking of a small black ligament, will be the 
 sudden formation of a line of brilliant light running the whole length of the spectrum 
 unless, indeed, the planet's atmosphei'e introduces some unforeseen complications. 
 
 LUNAR ATMOSPHERE. 
 
 As the eclipse proceeded, special attention was paid to the action of the moon's 
 limb upon the spectrum, in hopes of obtaining some evidence of a lu-nar atmosphere, 
 however rare. The results were wholly negative ; there was not the slightest trace 
 of absorption-bands, nor did the ordinary atmospheric lines, so abundant in the neigh- 
 borhood of D, acquire any new strength. There was not the slightest bending or 
 distortion of any of the lines at the moon's limb, but whether the slit were radial or 
 nearly tangential, they came up squarely and sharply to the edge, so that the line of 
 demarkation between the bright and dusky portions of the spectrum was perfectly 
 hard and definite. Just before the commencement of the totality, when the visible cres- 
 cent of the sun's image was narrower than the slit, the contrast between the effect of 
 the moon's limb and that of the sun was beautifully marked. The former, as I have 
 said, gives a perfectly defined boundary ; but the latter, whatever care may be taken 
 with the focus, is always somewhat indefinite and hazy, and there is no abrupt termi- 
 nation of the dark lines. Still, I have never seen any trace of the continuous spec- 
 trum described by Secchi, and am sure that if there is a layer on the sun's limb, giv- 
 ing such a spectrum, its thickness, instead of being 4" or 5", must be much less. 
 
 I at first supposed that the above-described negative evidence would be almost 
 decisive against a lunar atmosphere, but further reflection has convinced me that the 
 facts mentioned are not in the least inconsistent with the existence of an atmosphere 
 two or three thousand times rarer than our own, and yet sufficient to produce a refrac- 
 tion of 4" or 5", and thus to explain the crepuscle of light around the moon's limb, so 
 beautifully evident upon the photographs of the partial phases of the eclipse. Possi- 
 bly, however, this crepuscle may yet find an explanation, as a special case of diffraction, 
 upon purely optical principles, without the necessity of assuming a lunar atmosphere. 
 
46 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 SPECTRUM LINES OBSERVED DURING TOTALITY. 
 
 At the commencement of the totality, my instrument was directed upon the 
 prominence at 146, upon the southeast border of the sun, and just before the dark- 
 ness began I ran back my instrument to the neighborhood of the B line, in order to 
 examine whether any bright lines existed of a refrangibility lo wer than C. The last 
 ray of sunlight disappeared almost instantaneously, and I now greatly regret that I 
 did not record the moment upon the chronograph ; for it seems that to the observers 
 with the telescope, some of them at least, it was a gradual event occupying two or 
 three seconds. But I supposed it could be far better observed with the other instru- 
 ments, and accordingly confined my attention strictly to the spectrum. As soon as 
 the last sunlight vanished, the C line, before bright and conspicuous, blazed out with 
 brilliancy fairly dazzling, though it reached only partly across the spectrum, because 
 the protuberance upon which the slit was directed was of small extent. No line 
 appeared below it. 
 
 While my assistant, Mr. Emerson, with an accuracy of hand which answered 
 almost every purpose of a clock-work, kept the limb of the sun exactly on the center 
 of the slit by means of the right-ascension tangent-screw, I swept rapidly over the 
 spectrum. Between C and D, nothing was found. Just above D, shone out the well- 
 known but hitherto mysterious golden D 3 at 1017.5. It was very bright, but did not 
 equal C. Then came two very faint lines, of nearly equal brightness, situated about 
 1250 and 1350 of KirchhofFs scale, as nearly as I could estimate from their relation to 
 D 3 , and the 1474 line, which came next. Their exact position is, so far as my observa- 
 tion was concerned, doubtful to the extent of twenty or thirty scale-divisions. 
 
 Next above them, a little below E, appeared the line which I had before seen with 
 so much difficulty at 1474. I first discovered it on the gth of July ; but, as I have 
 since learned, it was before observed by Mr. Lockyer on the 6th of June. It was 
 also, undoubtedly, seen by Rayet at the eclipse of August, 1 868, thou gh by him mis- 
 taken for E. 
 
 It was sufficiently bright to be conspicuous, though far inferior to D 3 , and imme- 
 diately attracted my attention by the fact that it extended entirely across the spectrum, 
 which was not the case with C or D 3 . Concluding at once that this line belonged to 
 the spectrum of the corona, and not to that of the protuberance, I tested my idea by 
 simply touching the declination tangent-screw, and so throwing the slit off from the 
 prominence. The D 3 line, which was visible in the edge of the field at the same time, 
 immediately disappeared, but 1474 was, if anything, brighter than before. The same 
 was true, if my recollection serves me, of the two fainter lines between it and D 3 ; but 
 of this I am not positive. 
 
 The question has been raised whether these lines may not pertain neither to the 
 spectrum of the prominences nor to that of 'he corona proper, but to the spectrum of 
 the diffuse nebulosity which is shown upon the photographs as surrounding the pro- 
 tuberances. I dare not assert positively that this may not be the case, for I do not 
 know precisely how far I removed the slit from the prominence, though I think as 
 much as 5' or 6'. But my present, though hardly very confident, belief is that this nebu- 
 
REPORT OF PROFESSOR YOUNG. 47 
 
 lo.sity is the corona, and in no way to be distinguished from the rest of the diffuse 
 light around the sun. The longer the exposure of the plate, the more nearly, I think, 
 the outline of the photographic corona agrees with that seen by the eye, as, for instance, 
 in the beautiful photograph of Mr. Whipple produced by an exposure of forty sec- 
 onds. I am aware that some most eminent observers think differently, and maintain 
 that the actinic corona presents entirely a different outline from the visible, and is less 
 extensive ; and for that reason, as I said, I do not feel certain as to the correctness 
 of my view ; but I am rather confirmed in it by the observation of Professor Picker- 
 ing. He used a spectroscope with a single prism of 60, having no lens or telescope 
 to throw an image of the sun upon the slit, and thus obtained a spectrum produced by 
 all the light that came from a region 7 or 8 in diameter around the sun. In this 
 case, of course, the brightness of any particular portion or line of the spectrum depends 
 upon the absolute quantity of light of that special refrangibility -which comes to the 
 instrument from the whole space included by the cone, whose base is the object glass 
 of the collimator, and whose vertex is the center of the slit, An extensive faint lumi- 
 nosity may in this case have as powerful an effect as a light far more intense, but con- 
 centrated into a smaller angular area. Now, in my instrument, there was absolutely 
 no comparison between the dazzling blaze of the C, F, and D 3 lines and the subdued 
 light of 1474 ; but in the spectrum seen by Professor Pickering, the " line near E " 
 was much the brightest their relations were reversed. I think this shows conclusively 
 that the light, to which is due the 1474 line, must be diffused over a far more extensive 
 angular surface than that which produces the other rays. It does not, however, show 
 that there may not be in the corona other light besides this. Probably there is. 
 
 To return from this digression. By the time I had carefully examined 1474 the 
 moon had advanced so far that it became necessary to transfer the slit to the other 
 edge of the solar image. While my assistant was doing this by the tangent-screws, I 
 suppose that inadvertently I continued to move the spectrum across the field of view, 
 thus passing the region of the b line while there was no protuberance upon the slit. I 
 have no distinct recollection .in regard to this, but it is the only way in which I can 
 account for not seeing this line, which was easily seen by others, as I have since learned. 
 The next line I saw was the F line, exceedingly brilliant, very nearly equal to D 3 , perhaps 
 a little brighter. It was broad at the base and tapered to a fine line at an elevation of 30" 
 or 40" above the limb. On account of the great size of the prominence upon which the 
 instrument was now directed, and the oblique position of the slit, it reached nearly, if 
 not quite, across the spectrum; but it disappeared as soon as the slit was moved away. 
 Passing on, a new line about as bright as 1474 made its appearance above F; but 
 without stopping to measure its exact position then, I pushed along. Next came the 
 2796 line (hydrogen 7) just below G, and soon the h line (hydrogen ) appeared in 
 the edge of the field clear and bright, though less so than 2796. My impression, but 
 I cannot give it with any confidence, is that I saw three other faint lines in addition 
 to the nine I have named, one not far above F and two between Gf and h. I failed to 
 note them, however. Finding nothing above h, I at once turned back to determine 
 the position of the. new line* between F arid Gr. I obtained a satisfactory measure- 
 
 * This is undoubtedly the line referred to l>y Lieutenant Hersoliel in a letter to Mr. Hnggins from India, dated last 
 July, and quoted in a recent number of tlie Chemical News. 
 
48 ECLIPSE OF THE SUN, AUGUST 7, 1809. 
 
 merit upon it, as I supposed, which fixed its position i i r 38 dlv of my micrometer screw 
 below 2796 ; that is, at 2602 of Kirchhoff's scale, with a probable error of 2 or 3 divis- 
 ions. 
 
 A brilliant protuberance observed by me on October 7, however, gave a line, 
 very distinct, though short, at 2581.5; and from this circumstance I am led to suspect 
 an error of a whole revolution in my measurement. If there be such an error, the 
 result of this measurement, using i2 r 38 div instead of n r 38 div , as recorded, would be 
 2584, which accords perhaps as well as could be expected from a single measurement 
 under so exciting circumstances. Just as I was finishing this reading, and before I 
 could examine any of the fainter lines, the sun burst out. They disappeared almost 
 instantaneously, but 2 796 remained visible for several seconds, so that I could be sure 
 I had made no mistake in its identification. 
 
 Plate III, figure 1, represents the spectrum as seen by me. I cannot describe the 
 sensation of surprise and mortification, of personal imbecility and wasted opportunity, 
 that overwhelmed me when the sunlight flashed out. I think it was shared by other 
 observers to a greater or less degree. 
 
 POLARIZATION. 
 
 While I was upon the 1474 line, I examined carefully the faint, continuous 
 spectrum which formed the background for the bright lines. It was strong enough 
 to have its edges well defined, but showed not the slightest trace of any dark line, 
 though my instrument shows the stronger lines plainly in spectra, which I should 
 judge to be no brighter, formed by clouds or diffuse daylight. Testing it with a tour- 
 maline held in the hand between the eye and the eye-piece of the spectroscope, I found 
 that when the axis of the crystal was parallel to the slit, which at this point was nearly 
 perpendicular to the sun's limb, the light seemed to be unaffected; but on placing the 
 axis perpendicular to the slit, the faint continuous spectrum nearly vanished while the 
 bright lines remained unchanged. It is perhaps not impossible that the polarization 
 thus manifested may, as suggested by Professor Pickering, have originated in the suc- 
 cessive refractions through the ten surfaces of the prisms. If not, the absence of the 
 dark lines in the faint spectrum is certainly a very puzzling fact; and yet the ordinary 
 solar spectrum, tested in the same way, shows no sensible polarization. 
 
 GENERAL IMPRESSIONS. 
 
 During the totality, the darkness became such that I could not read the micrometer- 
 head without artificial light; and while Mr. Emerson, at my request, was handing me 
 a lantern which hung in readiness, I turned my head, and for perhaps loor 15 seconds 
 beheld the spectacle, the most beautiful and wonderful upon which the human eye 
 can ever rest. The impression was overwhelming, and so nearly blotted from my 
 memory all that I had observed before that I can now recall it with certainty only 
 from the written notes kept by my assistant; where they are wanting, I can only speak 
 doubtfully. Of course, from so short a view I could obtain but little worth mention- 
 ing in an official report, I saw Venus, Mercury, Saturn, and Regulus. The great 
 
REPORT OF PROFESSOR YOUtfG. 49 
 
 protuberance on the lower edge appeared exactly like the planet Mars, and for an 
 instant it was my impression that it actually was that planet. I mention this as show- 
 ing its color viewed by the naked eye. The corona seemed to me nearly white, with 
 the slightly bluish or greenish tinge of silver. As to its form, my recollection is not 
 very distinct, but I remember my surprise at the definiteness and irregularity of its 
 boundary, for I had expected an insensible gradation from the center to the edges, 
 like that of the zodiacal light, for instance, and that it would be nearly circular. It 
 was much brighter, also, than I had looked for, and was distinctly visible on the screen 
 of my spectroscope. Could extraneous light have been excluded, it would have been 
 possible to draw its outline. Perhaps a good method to secure accurate delineation 
 of its form at some future eclipse would be to attach to the eye-piece of a large tele- 
 scope with low magnifying power a screen properly shaded, forming a sort of camera 
 obscura. Upon this screen, with a pencil made visible in the darkness by rubbing it 
 over with phosphoric oil or by some similar contrivance, the observer could sketch the 
 outlines with accuracy. Outlines thus drawn and compared with photographs would 
 settle decisively the question whether there is really the great difference supposed 
 between the actinic and the visible corona 
 
 LAST CONTACT. 
 
 A few minutes before the end of the eclipse, I exchanged the eye-piece before 
 used in the comet-seeker for a solar eye-piece, magnifying about 25 times, and 
 observed the last contact in the ordinary method. By some means, however, my con- 
 nection with the chronograph had been disarranged, and the observation failed to be 
 recorded. 
 
 COINCIDENCES "BETWEEN THE SPECTRUM OF THE CORONA AND THAT OF THE AURORA 
 
 BOREALIS. 
 
 On returning from Burlington, I found awaiting me the July number of Silliman'e 
 Journal, in which are given the places of five bright lines, observed by Professor Win- 
 Jock, in the spectrum of the aurora borealis, as follows, in numbers of Huggins's scales : 
 " 1 280 brightest, 1 400, 1 5 50, 1 680, and 2640." Reduced to KirchhofFs scale, the three first 
 would stand 1247, 1351, and 1475, using, for the comparison of the scales, the data 
 given by Professor Gibbs, in his paper, upon "Wave lengths by the method of com- 
 parison." If these measures are correct, and I know no reason to doubt them, though, 
 on account of the faintness and evanescence of the lines, except the first, I have not 
 been able to verify them in the auroras of the past season, and have even seen them 
 but three times, and then only for a few moments, we have the following remarkable 
 coincidence: I found in the corona spectrum, 1250^= 20, 1350 20, and 1474; in 
 the aurora, we have 1247, 1351, and 1475. On the first two coincidences but little 
 stress should be laid, as the positions of the corona lines are mere estimations ; but 1474 
 is perfectly well known, being the reversal of a dark line of the solar spectrum, which 
 is given by both Kirchhoff and Thalen as belonging to Iron, (not by Huggins, who, 
 however, omits many faint lines ;) and its coincidence, though but with one of the 
 
 7 E S 
 
50 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 fainter lines of our aurora borealis, gives, I think, considerable probability to the con- 
 jecture that the aurora borealis and the solar corona are closely related, if not identical 
 phenomena. The fact that Angstrom has detected the principal aurora line (1280 
 Huggins) in the spectrum of the zodiacal lig'ht, points, to my mind, in the same direc- 
 tion, as showing that the principal seat of the auroral light is in a gas which has cos- 
 mical relations, and is not solely terrestrial , an atmosphere above our air of oxygen 
 and nitrogen, and indefinitely more rare. 
 
 Upon Plate III, figure 1, which exhibits the bright lines observed by me, I have 
 written the numbers of certain of the dark lines according to Huggins's scale, while 
 the scale of construction is that of Kirchhoff. This renders the comparison of the two 
 scales very easy to the eye. 
 
 RESULTS. 
 
 To recapitulate : The results of my observations were briefly these : 
 
 FIRST, positively and certainly 
 
 a) The determination of the instant of contact by a new method. 
 
 6) The observation of the following nine bright lines in the spectrum, viz, C, D 3 , 
 1250 20, 1350 20, 1474, F, 2602 i 3, (2585 i 3 1) 2796 and h, of which two are 
 entirely new. 
 
 SECOND, more or less probably but not certainly 
 
 a) The determination that 1474, and probably, also, the two fainter lines between 
 it and D 3 , belong to the spectrum of the corona. 
 
 6) The identification of these lines with certain lines in the spectrum of the aurora 
 borealis. 
 
 c) The polarization of the light of the faint, continuous spectrum in a plane pass- 
 ing through the sun's center. (This is very doubtful.) 
 
 THIRD, negatively 
 
 a) There was no evidence obtained of a lunar atmosphere. 
 
 6) No differences were observed between the spectra of the different prominences. 
 Very little weight should be given to this, however, as, from the construction of my 
 instrument and the shoiiness of the time at command, only different portions of the 
 spectrum were observed with the different prominences. 
 
 c) I saw nothing of the "layer giving a continuous spectrum," reported by 
 Secchi, and am confident that if it exists it must be exceedingly thin. 
 
 d) I saw no trace of dark lines in the faint, continuous spectrum from the corona. 
 I ought not to conclude this report without putting on record my obligations to 
 
 my assistant, Mr. Emerson, whose presence of mind, fidelity, good judgment, and 
 steady hand were invaluable to me. Allow me to mention, also, Mr. Lewis Boss, of 
 the present senior class in Dartmouth College, who. during the summer, was my 
 enthusiastic and indefatigable assistant in the preliminary measurements which were 
 necessary to determine the relations between the scale of my spectroscope and that 
 of Kirchhoff, and the other observations by which I became accustomed to the man- 
 agement of the instrument. 
 
REPORT OF PROFESSOR YOUNG. 51 
 
 Left at Hanover, in charge of the Shattuck Observatory, he made the observa- 
 tions upon the eclipse which I take the liberty to append as a supplement to this 
 report, and for whose accuracy I will vouch. 
 
 Very respectfully, yours, 
 
 C. A. YOUNG. 
 Prof. J. H. C. COFFIN, 
 
 Super intendi'iit of the American Nautical Almanac. 
 
 NOTE. Although the progress of science siuce this report was prepared, while confirming 
 most of the results above stated, has invalidated others, and notably the speculation as to the 
 identity of the spectra of the Corona, the Aurora Borealis, and the Zodiacal Light, it is thought 
 only right that it should stand as written. Accordingly, in revising the proofs for printing, no 
 alterations have been made, except a few verbal corrections of no importance to the sense. 
 
 0. A. Y. 
 
 PEINCETON, September, 1877. 
 
 SUPPLEMENT. 
 
 Observations on the eclipse of August 7, 1869. made at the Shattuck Observatory, Hanover 
 
 N. H. By Lewis Boss, assistant. 
 
 The instrument used was the equatorial, 6.4 inches aperture, 8 feet 8 inches focal 
 length. Aperture reduced to 2 inches ; power, 127. 
 
 The "numbers" of the spots were determined by the order of their occultation. 
 The accompanying diagram, roughly mapped from memory, will assist in their iden- 
 tification. 
 
 First contact, Hanover mean time (all corrections applied), 5'' 14"' 57". 
 
 Spot No. i. 
 
 (North 12 west .58 of sun's diameter from center of disc.) 
 
 h. m. s. 
 
 Contact with penumbra S3 2 6.5 
 
 Contact with nucleus 5 3 2 H-5 
 
 Nucleus eclipsed 5 3 2 2 5- 
 
 Re-appearance of nucleus - 6 27 49.0 
 
 Re-appearance of penumbra . . 
 
52 ECLIPSE OF THE SUN, AUGUST 7, 18G9. 
 
 Small spot No. 2. 
 (South 40 west .40 of sun's diameter from center of disc.) 
 
 h. m. s. 
 Eclipsed . 5 52 35.5 
 
 No. 3, (first in group.) 
 (North .09 of sun's diameter from center of disc.) 
 
 First contact ...................................... 5 56 1 9.0 
 
 Eclipsed '. ...................................... ___ 5 56 29.0 
 
 Re-appearance ............... ..................... 642 21.5 
 
 Entirely clear of moon's limb. 
 
 Spot No. 4, (last in group.) 
 (East .09 of sun's diameter from center of disc.) 
 
 Eclipsed . 5 59 10.5 
 
 Re-appearance .................................... 6 44 33.0 
 
 Entirely clear of moon's limb. 
 
 Spot No. 5. 
 (South 40 east from center, distant from limb .1 of sun's diameter.) 
 
 First contact ....................................... 6 13 50.2 
 
 Eclipsed .......................................... 6 14 o.o 
 
 First re-appearance ................................. 6 54 15.5 
 
 Complete emersion .................................. 6 54 26.5 
 
 Sun set eclipsed, apparently, about 2\ minutes before last contact. Sky mainly 
 clear. Flying clouds. Wind northwest. 
 
 C. A. Y, 
 
EEPOET 
 
 OF 
 
 Miss MARIA MITCHELL 
 
 , IOWA.. 
 
 53 
 
REPORT OF MISS MITCHELL 
 
 BURLINGTON, IOWA. 
 
 Observations of solar eclipse of August 7, 1869, at Burlington, loiva. 
 
 Station: The grounds of the Burlington Collegiate Institute, 1514 feetzz 14". 95 
 north, and 1596 feet= I 8 .52 west, of the Coast Survey Station. 
 
 Instrument: Telescope by Dollond. Aperture, 4 inches, reduced to \y 2 inches by 
 paper cover; equatorially mounted; moved by tangent screw, which worked imper- 
 fectly. The power used was about 56.* Colored glass, orange-yellow. 
 
 Chronometer: (Negus, 1293) slow of Burlington (Coast Survey) mean time, 
 
 5 h 4 8 m 5i 8 .3 (P- 12). 
 
 The time was counted aloud by Miss Starke. 
 
 BY CHRONOMETER 
 
 Eclipse began io h 7 m 24 s . 
 
 Totality began , 1 1 8 47 .9. 
 
 Totality ended 1 1 1 1 35 .8. 
 
 Eclipse ended . -. 12 7 40 . 
 
 Moon's limb seemed to touch small spot 10 30 48 .5. 
 
 Moon's limb seemed to touch penumbra of large spot 1031 38 .5. 
 
 Moon's limb seemed to touch edge of nucleus 1032 4. 
 
 Moon's limb seemed to touch second edge of nucleus 10 32 38. 
 
 Spot disappeared 10 32 44 .5. 
 
 The times of passing off were lost. 
 
 The moon's limb was plainly uneven, and there was a deeper indentation a little 
 below this spot. 
 
 The penumbra of this spot became paler as the moon's limb approached it, while 
 the nucleus of the spot seemed to grow darker, but did not become as dark as the moon. 
 
 The penumbra at the right of the spot was lost by paling out. 
 
 Near the limb of the moon was a narrow bordering of light, and the extremities 
 of the cusps seemed still brighter. I changed the color of the glass to red, but still 
 saw this. 
 
 I changed back again to the yellow-orange glass before totality. 
 
 * I liad intended to use a lower power, but did not find it in the box. 
 
56 ECLIPSE OP THE SUN, AUGUST 7, 1869. 
 
 As totality approached, perhaps two or three seconds before the time recorded, 
 the limb of the sun seemed to break up into lines and points. 
 
 I have no reason to think the glass out of focus, and I was not expecting any 
 such appearance. 
 
 I had intended to revolve the circle of differently colored glasses as totality came 
 on, but finding it slide with some difficulty, I removed the colored glasses entirely 
 While doing this, I glanced at the corona. It was of a dull, smoky white, not uniform 
 around the sun. There were long rays. 
 
 On looking through the glass, I perceived two rosy protuberances* on the right, 
 spirally-shaped. They resembled the whorl of a half-blown morning glory. They 
 were not of one color, but mingled white and pink. I had no means of measuring 
 size, but estimated them as three times that of the spot. As I turned my glance from 
 them, I saw on the left of the vertex (inverting telescope) another, f much larger, hive- 
 shaped, irregular in outline, undulated, much like heaped-up cumulus clouds. The 
 color of this was also a mingling of rose-color and white. In my rough notes I use 
 the word "mottled." As I looked at this, I thought I saw changes in itself which 
 were not the result of the moon's motion. Upon reflection, I am doubtful about it; 
 but I received an impression of the motion of sea-waves. 
 
 Two other rosy prominences J sprang up on the left, sharply pointed and spread- 
 ing at the base. These were rose-colored (pink and not red rose), white, and violet. 
 
 A sixth protuberance began on the left, which I called "arrow-shaped" in my 
 first notes, and near this the sun burst forth. 
 
 While watching these rosy points, I was twice disturbed by what seemed to be a 
 flickering of light on the moon's surface near its center. 
 
 Just before the total phase, mists seemed to rise, and it seemed to grow hazy 
 around the sun. 
 
 The darkness was at no time so great that print could not be read. My assistant 
 used a candle for the chronometer, but is not sure that it was necessary. 
 
 In passing off, the moon's limb was less rugged, and I did not see the bordering 
 of brighter light until near the end of the eclipse. 
 
 MARIA MITCHELL. 
 
 Miss Whitney's notes. 
 
 Sun's cusps definitely cut. 
 
 Upon instant of totality the corona seemed to burst forth, irregular and cloud-like, 
 with a soft light. 
 
 Protuberance at vertex brilliant and rounded, immediately followed by two others 
 45 to the east, rapidly increasing in size; then another, not so rounded in appearance, 
 about 90 from first, and along this arc, almost immediately, the sun appeared. 
 
 "Probably 6 and 7 of Mayer's diagram, Plate X, Fig. I. 
 
 t Probably 8 of Mayer's diagram. 
 
 t Probably 9 and 10 of Mayer's diagram. 
 
 $ Probably n of Mayor's diagram, C. 
 
EEPORT OF MISS MITCHELL. 57 
 
 The corona was prolonged in different directions, not evenly distributed. 
 Moon's edge in passing off not so rough as the other. 
 Telescope by Alvan Clark ; 3 inches aperture. 
 
 Eclipse began, 3'' 56"' 2O 8 .5; known to be late. 
 Eclipse ended, 5 56 28 . 
 
 Time by watch compared immediately before eclipse with chronometer, and set 
 to Burlington time. 
 
 Miss Blatdihijs notes. 
 
 Station: Roof of college building. 
 
 No instrument. 
 
 4 h 52"'. Mississippi of a leaden color; geese cackle and run about; the land- 
 scape has a green tinge; the sky a lavender color. 
 
 4 h 55"'. Trees almost distinguished; sun visible to naked eye without pain; 
 darkness about equal to that of a cloudy moonlight night; sky yellow. 
 
 4 h 59'"- The horizon all around lighter than the rest of the sky; birds fly to the 
 bell -tower and flutter about; cries of birds heard. 
 
 5''. Twinkling light upon the leaves of the trees; pale-pink light at the west; 
 painful cry of birds. 
 
 3" 
 
 4 
 4 
 4 
 4 
 
 Miss Coffins notes of thermometer. 
 47 7Q S 11 l m - 
 
 68 
 
 7C c 27 . 
 
 72 
 
 4c 71 c c 42 
 
 76 
 
 c-j 70 ^ ^7 
 
 / " 
 74 
 
 Oo / w jo/ 
 
 /T- 
 
 ,tion of totality, 2 m 45*. 
 
 
 Miss Ely's notes. 
 
 Station: Roof of Mr. Foote's house. 
 No instrument. 
 
 4 h 1 5 m . Shadows lengthen; a flock of geese fly home; general appearance of land- 
 scape as before a thunder-storm. 
 
 4 h 30. College building not distinctly seen on account of smoke. 
 4 b 40. Swallows fly home. 
 4 h 45. Venus and Mercury seen. 
 8 E s 
 
58 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 4'' 56. Arcturus and Saturn are seen. Broad bands of yellow and red color 
 appear around the horizon. Corona seen. A band of blood-red color above the sun, 
 and two small bright points are visible, one below and the other at the right of the 
 moon's disk. 
 
 A bluish light pervades the landscape. As total phase ends, the bands about 
 the horizon change to purple and blue. 
 
 Miss Carter's notes. 
 (With binocular glass and photometer.) 
 
 Measurement of light by photometer showed a gradual decrease of illumination 
 until 4 b 30, when the light waned very rapidly and could not be seen at 4'' 56'". 
 
 4 h 56, Corona formed of irregular yellowish rays, with two ruby-colored leaf- 
 shaped flames. Blood-red band of light at the right, above. Dark body of moon 
 sharply defined and of greenish tint. 
 
 5 b 25 30". Venus still visible to the naked eye. 
 
 Miss Reynold's notes. 
 (Dollond glass, 2\ inches.) 
 
 Body of moon of inky blackness. Cusps' sharply defined. 
 The light did not appear like ordinary sunlight diminished. 
 4 h 54. Venus seen. 
 
 During totality two intensely bright lines were seen across the corona to moon's 
 disk, one from the right and one from below, as seen by the naked eye. 
 Fire-flies seen. Birds flew around as if lost. Crickets chirped. 
 
 Miss Glasier's notes. 
 (Glass by Clark, 3 inches.) 
 
 Sphericity of both moon and sun very evident. 
 
 At total phase I was surprised at the irregularity of corona; not clearly defined 
 against background of sky. Rays of light thrown over moon. 
 
 Light on terrestrial objects decidedly greenish; not half black, as in thunder- 
 storms. 
 
 I read writing with a moderately black pencil easily at totality. Protuberances 
 not rose but flame colored. 
 
REPORTS 
 
 MR. JOHN N. STOCKWELL AND PROF. D. G. EATON. 
 
 , IOWA.. 
 
REPORT OF J. N. STOCKWELL. 
 
 BURLINGTON, IOWA. 
 
 * 
 
 DEAR SIR : In conformity with your request, I herewith submit a brief account 
 of the solar eclipse of August 7, as it appeared to me, at Burlington, Iowa. As I 
 placed myself on the line of totality merely for the purpose of witnessing a total 
 eclipse, regarded as a wonderful celestial show, rather than for the purpose of making 
 valuable scientific observations, rny outfit corresponded in simplicity with the design 
 of my journey. The only optical appliances at my service consisted of a single 
 unmounted achromatic telescope of 25 inches focal length and 2 inches clear aper- 
 ture, with a magnifying power of about forty-five times. This instrument gave a very 
 sharply defined image of the sun's limb, and also of the spots on his surface. I con- 
 trived a very simple wooden mounting for the telescope, which steadied it sufficiently 
 for the purpose of observing the times of contact and the various other attendant 
 phenomena of the eclipse. 
 
 The observed times of the different contacts are as follows: 
 
 Beginning of eclipse 1 2 h 50^ 9" 
 
 Beginning of total eclipse 13 51 42 
 
 End of total eclipse 13 54 30 
 
 End of eclipse 14 50 42 
 
 It should be observed that the times here given are the chronometer times as 
 counted to the party. (Chro. Hutton, 202, p. 20.) 
 
 During the progress of the eclipse I noted the time of the occultation of the large 
 spot as 1 4 b 1 5 m 1 3 8 . No other phenomena were noted till near the time of totality, when 
 my attention was drawn to a very bright red spot,* situated very nearly in the lower 
 limb of the moon, and apparently considerably within the circumference of its disk, 
 and also extending a considerable distance beyond the border of the moon into space: 
 bvit the outline of a perfect limb of the moon was distinctly visible. It seemed as if 
 this spot was formed by the sun shining through a very large hole through the moon, 
 or perhaps the phenomenon might be more appropriately likened to the sun shining 
 through a tremendous chasm in the body of the moon with a magnificent arch span- 
 ning it from side to side and filling up the gap in its surface. The depth I should 
 estimate as at least equal to one-twentieth of the moon's diameter; and were it not 
 for the exceeding wildness of the idea, when we reduce such estimates to linear meas- 
 ures, I should be inclined to estimate it as 3 per cent, greater, or at one-fifteenth 
 of the moon's diameter! As soon as I recovered from the surprise occasioned by the 
 
 Probably No. 8 of Professor Mayer's diagram, Plate X, Fig. 1. C. 
 
 61 
 
62 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 imposing grandeur and magnificence of the spectacle I removed the red-screen glass 
 from the telescope, and what was before the bright-red spot was changed to a mag- 
 nificent rose-colored cloud or protuberance, having apparently the same form and 
 dimensions. 
 
 When the eclipse became total another large rose-colored protuberance* appeared 
 at about a quarter of the. circumference of the moon's disk, from the first spot, towards 
 the western limb. This spot continued to increase in magnitude and brilliancy while 
 the totality lasted, and in the mean time several smaller spots of a similar nature 
 appeared between the two which have just been mentioned. Three-quarters of the 
 moon's circumference was entirely barren of these rose-colored protuberances, and 
 also of all other phenomena of especial interest. As soon as the totality ceased and 
 a slender crescent of the solar disk appeared on the western limb of the moon, these 
 smaller protuberances disappeared, but not instantaneously, there being an appreciable 
 interval before they were wholly obliterated. The upper protuberance was visible 
 several seconds after the eclipse ceased to be total. But the large rose-colored 
 protuberance at the lower limb of the moon remained the most conspicuous local 
 phenomenon during the total phase. It also remained visible for some seconds after the 
 solar crescent had extended itself beyond the "hole in the moon," which permitted 
 this rose-colored cloud to be both a protuberance and an indentation, although the 
 two parts were apparently separated by a shadowy outline of the lunar disk. 
 
 In regard to the corona, I can only observe that I did not concentrate my attention 
 upon it to any great extent. Its color I noticed to be a pure white throughout its 
 whole extent, and its average breadth was about one-half the apparent radius of the 
 moon. The outer circumference of the corona was considerably distorted; its shape 
 somewhat resembled that of an elastic hoop which had been subjected to pressure from 
 the outside at several different points, producing concavities at the places where the 
 pressure was applied, and angular points midway between them. 
 
 The color of the moon I called a dark slate, instead of a jet black, as it is 
 sometimes said to be on such occasions. It was also sensibly uniform throughout its 
 whole extent. The darkness was not as great as I had anticipated, but I found some 
 difficulty in taking notes during the totality. The planets M ercnry and Venus, as well 
 as several of the fixed stars, were plainly visible. The darkness somewhat exceeded 
 that at the time of the full moon, but the color of the sky was unlike both that of 
 night and of twilight. The sky was also sensibly darker in the vicinity of the sun 
 than it was near the horizon. The belt of darkness also extended much farther from 
 east to west along the ecliptic than from north to south. 
 
 I have thus very briefly stated the main features of the eclipse as they presented 
 themselves to me, and I submit them for what they may be worth in the discussion of 
 those problems relating to the physical constitutions of the sun and moon. 
 Very respectfully, yours, 
 
 JOHN N. STOCKWELL. 
 
 Prof. J. H. C. COFFIN, 
 
 Superintendent American Ephemeris, and Chief of Burlington Eclipse Party. 
 (Communicated September 27, 1869.) 
 
 "Probably No. 11 of Mayer's diagram. C. 
 
REPORT OF PROF. D. G. EATON. 
 
 BURLINGTON, IOWA. 
 
 BROOKLYN, N. Y., September 14, 1869. 
 
 DEAR SIR : Yours of the i ith instant is just received, and I hasten to reply. My 
 observations on the late eclipse were made, as you may remember, with a small 
 telescope of about 2-inch object glass, belonging to Professor Young. Instead of 
 having a solar eye-piece, it was provided with a frame carrying a white disk for 
 receiving the image of the sun. During totality I used only the naked eye. I tried 
 in vain to view the corona through the telescope; but in so doing, while attempting to 
 thrust my head between the wires bearing the paper disk, I threw the sun out of the 
 field, and could not recover it without too great a sacrifice of time. My notes taken 
 during the eclipse, and written out soon afterwards, are as follows : 
 
 TIMES OF CONTACT BY THE CHRONOMETER. Hutton, 2O2. 
 
 Local mean time. 
 
 First contact 1 2 h 50 1 5" 3 h 56 23 8 .5 
 
 Beginning of totality 13 51 41 4 57 39-7 
 
 End of totality 13 54 33 5 o 31.2 
 
 Last contact 14 5 4 2 5 5 6 3 l - 2 
 
 The first contact was suspected some two or three seconds previous to the time 
 above noted, but I preferred not to record the time until the contact was so evident as 
 to leave no room for doubt. The time for the beginning of totality, I think, cannot 
 be more than one second in error. That for the end of totality I am not so confident 
 of, my attention being so much absorbed by the brilliant star-like protuberance near 
 the bottom of the moon's disk. I must also confess to a little excitement about that time. 
 Still I think the time above recorded cannot be more than one, or, at most, two seconds 
 in error. 
 
 The immersion of the large spot was noted as follows : 
 
 First contact - 1 3 h H 39 
 
 Second contact 1 3 J 5 2O 
 
 There seemed to be a slight repulsion between the spot and moon at the first 
 contact, so that the moon's edge, as it appeared on the screen, seemed indented by 
 
 63 
 
64 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 nearly the semi-diameter of the spot before contact actually occurred. I did not notice 
 either adhesion or repulsion at the second contact. At emersion the first contact was 
 not observed. The second contact was 14'' 9 27 s . 
 
 The following notes were taken as the eclipse was advancing : 
 
 4 h 25 (Burlington time). Landscape darkens. 
 
 4 35 Sky deepens its blue, especially overhead. 
 
 4 40 Wind N. E., lulling. 
 
 4 43 Wind increasing again. 
 
 4 45 Sky intensely blue overhead ; darkness coming on. 
 
 4 50 Sky darkens rapidly, but still retains its blue color. 
 
 4 53 Appearance of an approaching thunder storm, but without clouds, 
 lightning, or thunder. 
 
 4 56 Dark, weird and ghastly appearance of landscape. 
 
 4 57 Venus appeared very clear and bright. 
 
 Venus appeared to others before I saw it, and must have been visible nearly two 
 minutes before totality. During totality I could spare time for only a single glance 
 around the heavens; during which I recognized Mercury, Venus, Regulus, Arcturus, 
 and a Lyra?. Nothing peculiar in their color was noticed. I had not time to trace 
 out the sickle, or look for other stars as I had intended. The landscape appeared of 
 an ashy or leaden darkness. The light I judged to be not quite equal to the full moon 
 at night. I could not easily read my penciled notes; but a friend told me he could 
 read the print of a common newspaper. The appearance of the heavens was peculiar. 
 While the stars were shining overhead a beautiful twilight, tinted with the hues of 
 sunset, extended entirely around the horizon. 
 
 The Baily beads were very conspicuous. Just before totality the thin crescent 
 was suddenly broken up by dark lines shooting out from and perpendicular to edge 
 of the moon, and transverse to the crescent. The parts thus separated from each 
 other immediately gathered up into beads by an apparent mutual repulsion, like 
 globules of water on a dusty floor. I noticed very little if any lateral motion among 
 them. The Baily beads were not seen at emersion, because, as before remarked, I 
 had thrown the sun out of the field in my effort to see the corona through the teles- 
 cope. The corona was observed entirely with the naked eye. Its shape was irregular. 
 At first, it seemed more prominent a little to the right of the top. It changed its form 
 rapidly, however, until it approximated to a square or rhomboidal form. Its width was 
 not uniform, but I should judge it would average the radius of the moon, perhaps 
 more. It seemed to blaze out from behind the moon with a beautiful silver light, and 
 to consist of bright rays upon a thin flame or background of white light, less intense 
 but more uniform in brightness. The rays were perfectly straight and seemed to pro- 
 ceed directly from the centre of the sun. The corona appeared suddenly, at the 
 instant of, but not before, totality. It seemed to burst out like a blaze of glory, and 
 was inexpressibly beautiful. I was in a measure prepared for the grandeur and gloom 
 of the sky and the landscape, but not at all for the exquisite beauty of the corona. 
 Its light was peculiar. It had nothing of the dazzling, blinding light of the sun, but 
 a beautiful silvery light all its own, which was more pungent than moonlight, but 
 
EEPOET OF PKOF. D. G. EATON. 65 
 
 which failed to light up either air or earth so much as T should expect from its bright- 
 ness. I noticed two protuberances of great beauty : one about 1 20 * from the top 
 eastward, and the other about 1 70 f from the top westward, both of a bright red color. 
 The one on the east side seemed to lap over or enter the disk of the moon at least one 
 digit, The one near the bottom was the brightest, and shone with great brilliancy, 
 emitting short rays in every direction, even inwards over the edge of the moon. This 
 was perhaps the most beautiful object during the entire period of totality. Two or 
 three other protuberances were noticed, but my attention was so absorbed by these 
 two that I did not attempt to locate them. 
 
 The approach of the dark shadow from the west could not be observed because 
 the landscape in that direction was hidden by intervening houses. I attempted, how- 
 ever, to catch a view of the shadow in its flight eastward across the prairies on the 
 opposite side of the river; but, unfortunately, several gentlemen happening to stand 
 so as to intercept my view in that direction, I was compelled to change my position 
 some ten feet or more, and before this could be done the shadow was gone. I had, 
 however, instructed my wife and several friends to look specially for the flight of the 
 shadow eastward, but none of them were able to see it. 
 
 The effect of the whole scene on my own mind was peculiar, and quite different 
 from my expectations. Though I felt myself in a measure prepared for the scene by 
 a careful study of the subject, and by the descriptions of other eclipses given by 
 careful observers, I was completely surprised, and for a moment almost bewildered. 
 The whole scene the heavens above and the earth beneath had the appearance of 
 awful gloom, as if some strange and fearful calamity were impending. Just before 
 totality, as the shadow approached from the west, an undefined horror seemed 
 gathering in the sky a cloud, and yet not a cloud a tornado, and yet only a light 
 breeze! All nature seemed to hesitate, and everything was a contradiction. I can 
 well understand how such an event, not understood nor expected, would make the 
 stoutest heart quail and fill the sternest mind with fear and dread. 
 
 The time was all too short to make the observations I had intended, though I 
 think I could do much better another time. Never did three minutes seem to pass so 
 quickly; and on the other hand, never was so much enjoyment crowded into three 
 minutes! I have climbed the Alps and visited London, Paris, and Rome, but I 
 would sooner lose the memory of them all than of those three minutes on Burlington 
 heights. 
 
 On my way home, I spent several days at Indianapolis, which was only a 
 few miles outside of the shadow, and I have the testimony of several observers there 
 that the corona was plainly visible. If so, it will have some bearing on the question 
 whether the corona can be seen before totality. Some five or six intelligent observers 
 (among whom were Rev. Mr. Way, Mrs. Judge Roach, and Miss McLean) all agree 
 that at the time of greatest obscuration, when the crescent of the sun seemed, as they 
 expressed it, like a "mere pencil mark," the whole disk or outline of the moon was 
 visible, and well defined by the faint halo or corona shining out from behind. If 
 
 * Probably No. 6 or 7 of Mayer's diagram, Plate X, Fig. 1. C. 
 t Probably No. 8 of Mayer's diagram, Plate X, Fig. 1. C. 
 9 E S 
 
66 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 they really saw the whole outline of the moon, the corona must have been visible to 
 some extent. At the time of greatest obscuration, they all agree that the eclipse 
 could be viewed with the naked eye, and hence they were not likely to be deceived 
 by their smoked glasses. Shall we receive their testimony? At Burlington several 
 of my friends who were specially requested to notice the fact could not see the 
 corona even a second before or after totality. 
 Respectfully, yours, 
 
 D. G. EATON. 
 Prof. J. H. C. COFFIN. 
 
REPORTS 
 
 OP 
 
 MR. JOHN WEISSNER AND MR. E. P. AUSTIN. 
 
 67 
 
FROM THE REPORT OF MR. JOHN WIESSNER. 
 
 [Compiled by Professor COFFIN and combined with work of other parties.] 
 GEOGRAPHICAL POSITIONS AND TIME. 
 
 Mr. Wiessner was detailed to make observations at Mount Pleasant, Iowa. 
 Kewanee, 111., and Monroe, Mo., for the geographical positions of those places, and at 
 Monroe to observe the eclipse. 
 
 He used for the former a Gambey sextant, with which he was familiar from long 
 practice, and an artificial mercury horizon. The index correction of the sextant was 
 found by repeated measurements on each day and night when observations were made. 
 His observations of the sun included in each series a nearly equal number of altitudes 
 of each limb, also an equal number in each position of the roof of the horizon. His 
 two sons, who accompanied him, noted the times bv the chronometers. 
 
 The observations of Professor Watson at Mount Pleasant, and of Mr. Austin, at 
 Kewanee, are combined with those of Mr. Wiessner, to complete the determination 
 of the positions of those places. 
 
 MOUNT PLEASANT, IOWA, 
 
 is 28 miles from Burlington, on the Burlington and Missouri Railway. The observa- 
 tions were made at the station occupied by the parties of Professor Watson and Pro- 
 fessor Morton, in the Fair grounds, about i^ miles from the railroad station. 
 
 The following are the determinations of the latitude: 
 
 1869. ' 
 
 August 7. By 9 circum-meridian altitudes of the sun +40 56 59.9 
 
 1 1. By 1 8 circum-meridian altitudes of the sun 57 13.0 
 
 10. By 10 circum-meridian altitudes of a. Aquila? 57 17.0 
 
 10. By 1 2 altitudes of Polaris 57 27.2 
 
 Mean of sun and a. Aquilse 40 57 10.0 
 
 Adopted value +4 57 *8.6 
 
 The observations on the 7th were made by Professor Watson; the rest by Mr. 
 Wiessner. 
 
 For the longitude we have: 
 
 By chronometer Negus 1074 (see page 14). 
 
 Reduction to Reduction to Longitude from observations at Mount Pleasant. 
 
 18 9' Burlington mean time. Mount Pleasant mean time. Burlington. 
 
 August 10. 5 b ^ +S h 54 m 37"-0 + 1 " 1 44 8 - 7 P- m. alts, of sun. 
 
 g > + 5 h 56 2i".o 35-7 45-3 14 p. m. alts, of Tauri. 
 
 20 ) 34-3 46-7 28 a. m. alts, of sun. 
 
70 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 By chronometer Negus 1304 (see page 13). 
 
 Observations at Mount Pleasant. 
 
 August 10. 5 h + 5 h 55- 4^.2 + 5 h 542 3 *. 9 + z - 43 . 3 ^ 
 
 9 47-3 2 -3 45 -o > Same asforchron. 1074. 
 
 20 47.6 % 1.3 46.3) 
 
 By chronometer Negus 1233 (seepage 15). 
 
 August 7. o h +6 U 2 m 47 9 4 +6 h i m 3 8 .i +i m 44 8 . 3 5 p. m. alts, of sun. 
 The concluded result is: 
 
 Mount Pleasant, o h i m 45 s .o, west of Burlington, 
 
 o 57 58 . 7=14 2 g' 40", west of Washington. 
 6 6 10.8 91 32 42, west of Greenwich. 
 
 KEWANEE, ILLINOIS, 
 
 is on the Chicago, Burlington and Quincy Railway, 75 miles northeast from Burlington. 
 The observations were made at the eclipse station of Mr. Austin, in the yard of Mr. 
 A. Fiirst, about 5,500 feet, as estimated by telegraph poles and paces, or a little more 
 than a mile, northeast from the railway station. 
 
 The observations of Mr. Wiessner, July 31 and August i, and of Mr. Austin, 
 August 7, furnish the following results: 
 
 For latitude of the place of observation: 
 
 1869. o / // 
 
 July 31 and August i, by 46 circum-meridian altitudes of sun +41 15 15.8 
 
 July 31, by 9 circum-meridian altitudes of a. Ophiuchi 7.7 
 
 August i, by 14 circum-meridian altitudes of a AquilaB 10.9 
 
 , by 4 circum-meridian altitudes of Jj Ophiuchi 59.5 
 
 July 3 1, by 10 altitudes of Polaris 3 4.2 
 
 August i , by i 2 altitudes of Polaris 4 3- 5 
 
 by 4 altitudes of /? Ursse Minoris 45. 
 
 Mean by sun and south stars 14.5 
 
 Mean by north stars 40. i 
 
 Concluded latitude 4-41 15 27.3 
 
 For longitude : 
 
 By chronometers Negus 1074, 1304, and i 3 n (see pages 14, i 3 , and 12). 
 
 PI, Redaction to Reduction to Longitude from 
 
 on - Burlington mean time. Kewance mean time. Burlington. Observations at Kewanee. 
 
 August i. o, 1074 +5" 56 i7 8 .5 +6 h i m 2 8 . 3 4 m 44 S .8 28 Equal alts, of sun. 
 1.0,1304 5 55 42.2 6 o 26.8* 44.6 Comparison with 1074. 
 
 7.0,1131 5 48 30.8 5 53 15.7 44 .9 56 Equal alts, of sun. 
 
 The concluded longitude is : 
 
 Kewanee, o h 4 m 44 8 .8, east of Burlington, 
 
 o 51 28.9zzi252' 13", west of Washington. 
 5 59 41.089 55 15, west of Greenwich. 
 
 * Diminished by 0.3. See note page 13. 
 
EEPOET OF MR. JOHN WEISSNER. 7 I 
 
 MONROE, MISSOURI, 
 
 is on the Hannibal and Saint Joseph Railway, 30 miles southwest from Quincy, 111- 
 The observations, both for geographical position and of the eclipse, were made by Mr. 
 Wiessner at the "Seminary," about one-fourth of a mile northeast from the railway 
 station. He estimated the elevation above mean water of the Mississippi River to be 
 230 feet, and above the sea 600 feet. 
 
 His observations furnish the following- results: 
 
 For latitude of the place of observation. 
 1869. ' " 
 
 August 6. By 26 circum-meridian altitudes of sun +39 39 1 2 -5 
 
 7- By 35 circum-meridian altitudes of sun 39 1 1.4 
 
 8. By 2 1 circum-meridian altitudes of sun 39 34.2 
 
 5. By 4 circum-meridian altitudes of a Ophiuchi 38 37.5 
 
 7. By 1 7 circum-meridian altitudes of a Aquilre 38 33.0 
 
 August 5. By 6 altitudes of Polaris 39 2 1.8 
 
 7 By 14 altitudes of Polaris 39 31.2 
 
 Mean from sun and south stars +39 39 6.4 
 
 Mean from Polaris +39 39 26.5 
 
 Concluded latitude +39 39 J 6.5 
 
 For longitude: 
 
 By chronometers Negus 1074 and 1304 (see pages 14 and 13). 
 
 fi, Reduction to Reduction to Longitude from rn,aorrtinn at Mnnmo 
 
 Chron. Burlington mean time. Monroe mean time. Burlington. 
 
 August 6. o b 1074 +5 h 56 m i8 8 .2 +5 h 53 45 8 .8 +2 m 32 8 4 16 Equal alts, of sun. 
 
 7.0 18.7 46.5 32.2 91 Equal alts, of sun. 
 
 8. o 19.3 47-8 3 1 -5 2 1 Equal alts, of sun. 
 August 6. o h 1304 +5 h 55'" 44 9 -7 +5 h 53 m i2 8 .2 +2 m 32 8 .5* Comparisons with 1074. 
 
 7. o 45 .o 12 .8 32 .2* 
 
 8.0 45.6 14.2 31.4* 
 
 The concluded longitude is: 
 
 Monroe, o h 2 m 32 8 .o, west of Burlington, 
 
 o 58 45.7=14 41' 26", west of Washington. 
 
 6 6 57.8 91 44 28, west of Greenwich. 
 
 Observations of tJie Solar Eclipse, August 7, 1 869. 
 
 The eclipse was observed by Mr. Wiessner, at Monroe, with a dialytic telescope 
 by Pfossl, belonging to the United States Naval Academy; equatorially mounted; 3 
 inches aperture, and 37 inches focal length, and magnifying power 61. It was placed 
 in a window on the first floor and in the west front of the Seminary, whose geographical 
 position is given above. A dark-red shade glass was used for the beginning and end 
 of the eclipse, a light-red glass for the totality. The times of the several phases were 
 noted by his two sons. During the total obscuration "the seconds of the chronometer 
 were made visible by candle-light at a distance of 2 feet, but hardly plain enough." 
 
 * Diminished by O 1 ..-. See note p. 13. 
 
ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 Mr. Wiessner thinks that in the obscurity both of his assistants noted the times of the 
 sun's reappearance by the wrong end of the second-hand, and 30" too much. They 
 are given, however, as originally noted. 
 
 The chronometer corrections referred to Monroe mean time, obtained from the 
 tables on pages 13 and 14 and the longitude from Burlington, on page 71, are 
 
 August 7, 5 h + 5 h 53'" 46.8" for Negus 1074. 
 + 5 53 13- for Nef/us 1 304. 
 
 
 By chronometer, 1074. 
 
 By chronometer, 1304. Predicted 
 
 
 
 
 
 
 Chronometer 
 
 Monroe mean 
 
 Chronometer 
 
 Monroe mean 
 
 American 
 
 
 time. 
 
 time. 
 
 time. 
 
 time. 
 
 Ephemeris. 
 
 
 h. m. s. 
 
 h. m. s. 
 
 h. m. s. 
 
 h. m. s. 
 
 h. m. s. 
 
 Beginning of eclipse. 
 
 10 I II 
 
 3 54 57-8 
 
 10 I 46. 8 
 
 3 54 59- 8 
 
 3 55 4- 86 
 
 Beginning of totality. 
 
 ii 3 57-5 
 
 4 57 44-3 : ii 4 3i-5 
 
 4 57 44- 5 4 58 4"- 13 
 
 End of totality 
 
 1 1 5 24. 8 
 
 4 CO I I 6 
 
 ii <; 14 8 
 
 4. 5Q 78 * cK At) 11 
 
 End of eclipse 
 
 12 I 58.8 
 
 5 55 45' 6 
 
 12 2 31.3 
 
 5 55 44- 3 
 
 5 55 48.09 
 
 
 The sky appeared perfectly clear during the entire day. The following notes 
 were made of an aneroid barometer and thermometer, the former corrected 0.20 inch 
 by comparison with the barometer used at the eclipse station in Burlington. 
 
 Bar- Ther- 
 ometer. luometer. 
 in. 
 
 Q l /2 
 
 n a. m. 
 
 29.74 
 
 74' 
 
 2 
 
 p. m. 
 
 .60 
 
 80 
 
 3 
 
 p. m. 
 
 .62 
 
 78 
 
 5 
 
 p.m. 
 
 57 
 
 78 
 
 5 
 
 p. m. 
 
 57 
 
 77 
 
 August 7, 
 
 Just before totality. 
 Just after totality. 
 
 Mr. Wiessner speaks of the breaking up of the crescent just before the total 
 obscuration as presenting the appearance of "pearls moving from left to right." 
 
 During the total obscuration, Venus and Mercury were visible. The corona 
 appeared to the naked eye more extended on the southeast limb. The prominences 
 noticed were of a reddish color. 
 
 J. H. C. COFFIN 
 
REPORT OF MR. E. P. AUSTIN. 
 
 KEWANEE, ILLINOIS. 
 
 CAMBRIDGE, MASS., September 14, 1869. 
 
 SIR : I have the honor to submit the following report of operations at Kewanee, 
 111., to determine the longitude and observe the total eclipse of the sun of August 7, 
 1869. 
 
 I left Burlington at 10 a. m. on Thursday, August 5, accompanied by Mr. A. L. 
 Covert. The instruments consisted of a mean-time chronometer, Negus 1311, a sex- 
 tant by Gambey, and an artificial horizon of mercury, a binocular Navy glass magnify- 
 ing about four diameters, furnished with colored-glass shades, and a telescope by Mr. 
 Alvan Clark, with aperture of 3 inches and focal length 48 inches. 
 
 We arrived at Kewanee about 2 p. in., and set out immediately to find the station 
 previously selected by Mr. Wiessuer, which is situated on the farm of Mr. August 
 Fiirst, about three-fourths of a mile north-northeast* from Kewanee Railroad depot, 
 on a north and south road. 
 
 The weather had been cloudy all day, with occasional drops of rain, and con- 
 tinued until night; during the night some rain fell. 
 
 On the morning of the 6th, about 9 o'clock, the clouds broke away slightly, so as. 
 to give occasional glimpses of the sun, and I endeavored to take some double altitudes 
 of the sun in hopes that the weather would clear in the afternoon; but soon after 10 a. m. 
 it clouded up entirely and began to rain and rained with very little intermission till 
 about 4 p. m., and at intervals till 6. In the evening I went down to the telegraph 
 office pursuant to arrangements to compare chronometers and interchange signals with 
 Burlington. 
 
 The weather remained cloudy, but with some signs of breaking away, and about 
 half past 9 there were some stars visible, but by the time I had reached the station 
 the sky was completely overcast. 
 
 On looking out, however, some twenty minutes later, I was surprised to find it 
 had cleared off almost entirely, and I decided to try to get some observations of stars 
 for time. On attempting to observe it was found that the moisture in the atmosphere 
 condensed so rapidly on the glass shade of the artificial horizon as to render it impos- 
 sible to see the stars 
 
 On the morning of the 7th there was a cloudless sky, and the atmosphere had 
 been purified by the heavy rains so that its condition was nearly perfect. With the 
 
 * One mile uortheast, as estimated by Mr. Wiessner. 
 
 73 
 10 E S 
 
74 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 exception of a few patches of cirro-cumulus about 10 a. m., which disappeared soon 
 after, and faint traces of clouds about the time of totality, the sky remained cloudless 
 all day. 
 
 I began about half past 8 to take altitudes of the sun, and continued at short 
 intervals for two hours. 
 
 On measuring the diameter of the sun after the observations it was found that the 
 horizon glass was out of adjustment, so that the two images of the sun could be 
 brought to cover each other only about half way, but it was thought best not to dis- 
 turb the adjustments for the afternoon series, as it would be impossible to tell what 
 the correction would be to the forenoon altitudes. 
 
 In the afternoon the corresponding altitudes were observed for all but two or three 
 of the last sets, which were lost, owing to a mistake in the time. 
 
 The resulting correction of the chronometer at apparent noon is + S 1 ' 53 I5 8 -7O.* 
 
 The large telescope was mounted in the morning, and some attempts were made 
 to place it in such a position as to enable it to follow the sun with but one motion, but 
 it was not got very near in the meridian. 
 
 The instrument being provided with several eye-pieces, some experiments were 
 made to determine which one it would be best to use, and I decided to use the lowest 
 power, with a magnifying power of 34 diameters, the higher powers not giving a view 
 of the whole disk of the sun and the definition not being as good with them. The 
 instrument is provided with a diagonal eye-piece, having a thin glass plate in the angle, 
 to let most of the light pass through without reflection; several caps were made with 
 apertures of different sizes to shut off the light, but with the smallest aperture about 
 one inch in diameter it was found necessary to have a colored glass shade up to near 
 the time of the totality. 
 
 As no computation had been made of the time of beginning of the eclipse I did 
 not attempt to observe that, and the eclipse had been several minutes in progress at 
 the time it was first noticed. 
 
 The following in regard to the phenomena noted during the progress of the eclipse 
 was written out two or three days afterward. 
 
 The times noted are all chronometer times, Net/us 1311 being the chronometer 
 used. 
 
 The first phenomenon noted was the disappearance of the large spot, as follows: 
 breaking of the ring of the penumbra of the spot, io h 31"' 50"; final disappearance of 
 the umbra, 32 i". 
 
 Shortly afterwards there appeared to be a very slight elongation of the cusps of 
 the sun. 
 
 The next thing noted was the disappearance of a group of three small spots near 
 the center of the sun, forming a small triangle, thus, v, the middle spot being much 
 the smallest of the three. Disappearance noted as follows: first, io h 49 m 28 8 ; second, 
 io h 5 i m 3 8 ; third, io h 52'" 24". 
 
 The disappearance of the spot near the sun's limb was noted at i i h 7'" 5". Before 
 this time the sun's limb had begun to have a tremulous motion, and there was an ap- 
 
 * Altitudes of several stars gave 5.07 less, but they were vitiated by the inaladjiistmeut of the sextant. C. 
 
EEPOET OF MR. E. P. AUSTIN. 75 
 
 / 
 
 pearance of light streaming 1 from the extremity of the cusps, but I was not quite 
 certain whether it was an optical illusion or not. 
 
 About this time I removed the cap which was over the object-glass, reducing the 
 aperture to about one inch, and removed the colored glass, the small rim of light being 
 still so brilliant as to dazzle the eye; bright red flames burst out before the total obscura- 
 tion along a space of 10 or 20 of the moon's limb. 
 
 At about 1 1 1 ' 9 25 s a gentleman near by, who was on the lookout for the shadow, 
 called out, "Here it comes," and a few seconds after, "Here it is." The red flames 
 were so bright that I failed to recognize the instant of total obscuration, but at 
 1 1 h q m 40" (5 h 2 m 56" local mean time*) I saw the flames moving along the limb of the 
 moon and concluded that the sun had been gone 5 s or 6 a . 
 
 Expecting a duration only of 25" or 3O 3 , I at once began to look for the reappear- 
 ance. The red flames traveled along the moon's limb, and at i i h io m 38". 5 (5 h 3 54" 
 local mean timef) the light of the sun reappeared in the midst of the flames in two 
 distinct points which closed up in about half a second. I then looked at the sky for 
 the first time. The whole outline of the moon was surrounded by a brilliant halo, out 
 of one side of which came the dazzling light of the slender thread of the sun now 
 exposed. 
 
 By keeping the direct rays of the sun out of the field, the dark outline of the 
 moon was distinctly visible projected on the corona at n h 15 30". End of eclipse, 
 i2 h 7"' io 8 (6 h o m 26" local mean time). 
 
 Chickens went to roost several minutes before the totality, and turkeys came in 
 from the fields. 
 
 During the totality the only thing to which my attention was particularly attracted 
 besides the red flames already mentioned was a very large protuberance almost exactly 
 on the west side of the sun. 
 
 Mr. Fiirst noted the duration of totality with the naked eye to be 70". Venus 
 and Mercury were seen by the by-standers during the totality, and Venus for some 
 time before and after. 
 
 The day had been very hot, with considerable wind, which died out almost com- 
 pletely about the time the sun was half eclipsed. At this time everything had a som- 
 ber appearance, and the heat of the sun was no longer oppressive, while near the 
 totality there was a slightly chilly feeling. Near the time of totality slight traces of 
 clouds appeared in the west. 
 
 Mr. Covert noted the following phenomena with the binocular previously referred 
 to: 
 
 Disappearance of the large spot, io u 32 m 3". At i i h 8 m o" a candle flame no longer 
 casts a shadow on white paper about 3 inches distant. 
 
 Beginning of total phase 1 1 1 ' 9 53" 
 
 End of total phase 1 1 io 58 
 
 I may add to the above that about 20 or 3O m before the totality a number of 
 bright specks were seen both by Mr. Covert and myself to pass through the field of 
 
 * Time of disappearance, 5 b 2 m 45'.4i. Predicted from the Am. Ephemeris. 
 tTime of reappearance, 5 b 2 m 4S".7o. Predicted from the Am. Ephemeris. 
 
76 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 view. At the time I thought them to be small objects in the air near by, but they 
 were undoubtedly of the same nature as objects seen by other observers at different 
 points and thought to be meteors. 
 
 During the totality the moon appeared to be hanging free in the sky in front of 
 the corona. 
 
 The arc of the moon's limb along which the red flames were visible is very much 
 underestimated in the previous description. I think it could not have been less than 
 45, probably greater. 
 
 The red flames moved during the totality along the limb of the moon from the 
 point of disappearance to that of reappearance. 
 
 After the eclipse the weather became much warmer, although the sun was so near 
 the horizon. 
 
 In the evening, signals* were exchanged by telegraph with Burlington, Monroe, 
 and Kewanee. 
 
 Respectfully, yours, 
 
 E. P. AUSTIN. 
 
 Prof. J. H. C. COFFIN, 
 
 Superintendent Nautical Almanac. 
 
 % 
 
 * The results of these comparisons are given on page 13. C. 
 
REPORT 
 
 OT 
 
 PROF. JAMES C. WATSON. 
 
 MOUNT 
 
 77 
 
REPORT OF PROF. JAMES C. WATSON. 
 
 MOUNT PLEASANT, IOWA. 
 
 ANN ARBOR, October, 1869. 
 
 DEAR SIR: I have the honor to report that, in accordance with your request, I pro- 
 ceeded to Mount Pleasant, Iowa, to take part in the observation of the total eclipse of 
 August 7. I was accompanied by Assistant Prof. George B. Merriman, of the Uni- 
 versity of Michigan, and by Hon. D. Mclntyre, treasurer of the University of Michigan. 
 
 We were joined at Burlington by Prof. J. M Van Vleck, of Middletown, Conn., 
 and his assistant, Mr. William Johnston, and we arrived at Mount Pleasant on the 
 evening of Wednesday, August 4. Our arrival had already been preceded by that 
 of Prof. E. C. Pickering, of Boston, and Professor Henry Morton, of Philadelphia, 
 with a corps of skilled photographers. The object of our visit becoming known, we 
 were waited npon by Professor Mansfield, Mayor Strawn, and .other prominent citizens 
 of the place, by whom hospitalities were extended and a desire expressed to aid in any 
 way possible the successful completion of the arrangements preliminary to the obser- 
 vations to be made. 
 
 After visiting several points in the suburbs of the city, we selected the inclosed 
 grounds of the Henry County Agricultural Society as the proper place for an observ- 
 ing station, and on making known our selection to the authorities we were informed by 
 Mayor Strawn that the city government would provide any structures that it might be 
 necessary to erect. The point selected was on the south side of the building used as 
 a hall of fine arts, and the only additional requisites were a screen to protect the tele- 
 scope used for photography from the wind and a dark room for the preparation and 
 development of the plates. These preparations were partially completed on Thursday. 
 During the whole of Friday a rain-storm prevailed, with a northeast wind, and all the 
 indications seemed to be that our expedition would not be successful. 
 
 Toward night on Friday the barometer gave feeble indications of a favorable 
 change of the weather; and as nothing had been possible so far in the way of accu- 
 rately determining either our geographical position or our local time, it was deemed 
 advisable, in accordance with your programme, to compare our chronometer with yours 
 at Burlington by means of the electric telegraph. This comparison was duly effected 
 on this and the- following evening by transmitting signals in both directions. 
 
 On Saturday morning the clouds broke away and during the entire day the sky 
 was beautifully clear. The details of our observations I shall now proceed to give, 
 commencing with those for our geographical position and local time. 
 
 79 
 
80 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 I took with me from Ann Arbor a comet-seeker, by Fitz, of 4 inches aperture, 
 the finder ofour large equatorial, and a sidereal chronometer, Negus, No. 578. At 
 Burlington you provided me with an additional chronometer, Ney-iis No. i 233, regu- 
 lated to mean solar time, an aneroid barometer, No. 33509, and a sextant by Pistor 
 and Martins. If the weather had been favorable I intended to make observations on 
 Thursday and Friday for geographical position, but not succeeding an attempt was 
 made on Saturday. I soon found that the nature of the soil was such that no point 
 could be found within the space available where the work upon the building and 
 screen did not by vibration render the surface of the mercury of the artificial horizon 
 so unsteady that no definite reflected image could be obtained. After repeated 
 attempts during the forenoon I was obliged to abandon all hope of getting more than 
 an approximation. 
 
 At noon, when nearly all the workmen were absent, I succeeded in getting the 
 following altitudes for latitude : 
 
 Chrou. time. Negus 1233. 's upper limli. 
 
 6 h o m 8 s 65 35' 43" 
 
 1 13 65 35 45 
 
 2 21 65 36 15 
 36 65 36 15 
 
 4 12 65 36 20 
 
 5 21 65 36 15 
 7.1 65 36 20 
 
 8 i7 6 5 35 45 
 
 9 30 6 5 35 10 
 
 The corrections of the sextant have already been applied to these results. 
 
 The chronometer time of apparent noon was 6 h 4 25", and hence we obtained as 
 the resulting latitude +40 56' $9". 9. 
 
 Just before the commencement of the eclipse I endeavored to get a determination 
 of local time, to which we had thus far only a rude approximation. 
 
 The observations were as follows: 
 
 Chron. time. Negus 1233. ' upper limit. 
 
 9" 7'" 51" 43 46' 55" 
 
 8 46 43 37 15 
 
 9 36 43 27 50 
 
 10 32 43 18 15 
 
 11 40 43 5 i5 
 
 Means 99 4 1 - 43 27 6 .o 
 
 Refraction 1 o .8 
 
 Parallax . + 6.5 
 
 Semi-diameter 15 49 - 
 
 True altitude 0's center. . 43 10 22 .7 
 Sun's declination + 16 15' /'.8 
 
REPORT OP PROF. JAMES 0. WATSON. 81 
 
 The unsteadiness of the mercury occasioned by the vibrations produced by the 
 motion of carriages in the vicinity was such that the measurements were made with 
 extreme difficulty. The results from these measurements are as follows : 
 
 Hour angle 3 h 5'" i6".8 
 
 Mean time of apparent noon o 5 27 .3 
 
 Local mean time 3 10 44.1 
 
 Chroniometer, Negus 1 233 9 9 41 .o 
 
 Chromometer correction on local time . . . . + 6 [ 3.1 
 
 The foregoing are the best observations for latitude and time which were possible 
 during our stay at Mount Pleasant, and hence I suggested to you the propriety of 
 sending some person there to make a better determination of latitude and to determine 
 also the difference of longitude between Mount Pleasant and Burlington in order that 
 the telegraphic comparison of chronometers, might be available for accurate local time, 
 the observations at Burlington having been made with a transit instrument. This 
 service was performed by Mr. Wiessner.* 
 
 In obtaining the correction of the chronometer for the reductions of the times of the 
 phenomena observed it is of course proper to adopt only the results of the comparisons 
 of chronometers, in connection with Mr. Wiessner's longitude determination.f 
 
 Further comparisons were made, using at Mount Pleasant chronometer Negus 578, 
 it having been our intention to use both chronometers during the observations of the 
 eclipse, one for astronomical observations and the other for the records of the pho- 
 tographers. It was found advisable at the time of the observations to use but one 
 chronometer, and the mean-time chronometer, Negus 1233, was so used. 
 
 I have, therefore, adopted the following correction: August 7, 4 h Mount Pleasant 
 mean time, Negus 1233, -f 6 h i m 2 8 .26, with a daily variation of -f o s .22, with which 
 the observed times of contacts have been reduced. 
 
 Our arrangements for observations were completed only half an hour before the 
 first contact was observed. In addition to the telescopes already mentioned, Professor 
 Van Vleck had brought out a very fine portable equatorial, by Clark, with which his 
 spectroscopic observations were made, and also the finder of the Middletown equatorial, 
 also by Clark, and an equatorial stand. It was with the latter telescope, aperture y/* 
 inches, and magnifying power of about 80 diameters, that my own observations were 
 made. Professor Morton had the Philadelphia telescope for photographic purposes. 
 Since these gentlemen will make detailed reports of their operations, no further account 
 of their observations is here necessary. Professor Merriman observed with the Ann 
 Arbor comet-seeker, magnifying power 25, and Mr. Mclntyre observed as an amateur 
 with the finder of the Ann Arbor equatorial, magnifying power 30. 
 
 *|His results are given in his report, page 70. C. 
 
 tThe results of these comparisons are included in the tables, pages 15 and 16. C. 
 
 11 ES 
 
82 ECLIPSE OP THE SON, AUGUST 7, lS(i!. 
 
 The phases of the eclipse were observed as follows, the chronometer being Neyus 
 
 1233: 
 
 I'"trst contact. 
 
 Observer. Cliron. time. 
 
 Watson. . 9 " 53'" 3 . s 
 
 Merriman 9 53 4 .o 
 
 Van Vleck 9 53 o 
 
 Beginning of total eclipse. 
 
 Watson 10 54 27.5 
 
 Merriman i o 54 29 .o 
 
 Mclntyre 10 54 27.0 
 
 End of total eclipse. 
 
 Watson 10 57 19.5 
 
 Merriman 10 57 200 
 
 Mclntyre i o 57 20.0 
 
 Last contact. 
 
 Watson. ii 53 34.5 
 
 Merriman 1 1 ^3 32 .5 
 
 Van Vleck 11 53 30.5 
 
 Professor Van Vleck was occupied with spectroscopic observations during the 
 total phase, and hence he did not observe the times of beginning and end of that 
 phase. Mr. Mclntyre did not catch the first contact of limbs. 
 
 Applying the correction already determined as above for the chronometer, we 
 obtain the following results: 
 
 First contact. 
 
 Observer. Mount Pleasant mean time. 
 
 Watson 3 h 54 5*. 76 
 
 Merriman 3 54 6 .26 
 
 Van Vleck ... 3 54 2 .3 
 
 [Predicted from American Epheineris.] 3 53 41.20 
 
 Beginning of total eclipse. 
 
 Watson. 4 55 29.75 
 
 Merriman 4 55 31.25 
 
 Mclntyre . ... 4 55 29 .25 
 
 [Predicted from American Ephemcris.] 4 55 20 . 10 
 
 End of total eclipse. 
 
 Watson. 4 58 21.75 
 
 Merriman 4 58 22.25 
 
 Mclntyre 4 58 22 .25 
 
 [Predicted from American Ephemeris.] 4 58 9 .o 
 
REPOKT OF PKOF. JAMES C. WATSON. 83 
 
 ' Last contact. 
 
 Mount Pleasant moan time. 
 
 Watson. ..5 54 36.74 
 
 Merriman . . 5 54 34.74 
 
 Van Vleck 5 54 32.8 
 
 [Predicted from American Ephemeris.] 5 54 22 .07 
 
 The times of beginning 1 and end of the total phase were observed by me without 
 the interposition of a shade-glass. By the other observers the shade-glasses were 
 used. 
 
 During the progress of the eclipse I noticed particularly the form and extent of 
 the solar cusps, and the same was done by the other observers. These cusps were 
 observed by us to be remarkably distinct and attenuated at the extremities during the 
 entire period of their visibility. Mr. Mclntyre and myself both noticed a flash of 
 light from the upper cusp as seen in the telescope about five minutes before the 
 beginning of total obscuration, but careful scrutiny failed to reveal any repetition of 
 the phenomenon either before or after the total obscuration. 
 
 The formation of Baily's beads was very distinct a few seconds before the 
 beginning of total obscuration and immediately after the end of the total phase. 
 Those which preceded were, however, very different. 
 
 [NoTE. Professor Watson's drawings of these appearances are given in figures 
 3 and 4, Plate I]. C. 
 
 A very large protuberance was visible on the lower limb of the sun of a beautiful 
 rose color, and so brilliant that to the naked eye it appeared to indent the moon's limb. 
 [See Fig. 2, Plate I.] As seen in the telescope immediately after the beginning of the 
 total obscuration a chaiu of rose-colored prominences took the place of Baily's beads. 
 I wa,s careful to notice the interval of the moon's passage over these protuberances, 
 and I found that the principal chain was occulted in 20 seconds, while two higher 
 prominences near the point of internal contact were visible 10 seconds longer. At io h 
 56 2 5 s .o, chronometer time, a prominence became visible on the opposite limb of the 
 sun, and at i> h 57 6".o still another became visible about midway between this and the 
 one visible to -the naked eye. 
 
 At the middle of the eclipse I glanced for a moment at the appearance of the sky 
 and of surrounding objects. Stars of the third magnitude were distinctly visible. 
 The northeastern and southwestern portions of the sky in the- vicinity of the horizon 
 were illuminated strongly by the light beyond the limits of the shadow. The western 
 sky exhibited a greenish tint. Persons standing near whom I had requested to notice 
 particularly the approach of the shadow reported that they could not detect any change 
 in the appearance of distant objects as it approached, but that the sky exhibited it most 
 clearly. The gradual diminution of the sunlight, as the eclipse progressed, had unfitted 
 those who had been watching throughout for noticing contrasts of light, which would 
 otherwise have been so remarkable. The sudden appearance of the corona was greeted 
 with shouts of applause, heard from all parts of the city, and we noticed that cattle 
 grazing in the vicinity gave unmistakable signs of astonishment. The light during 
 the total obscuration was estimated as about equal to that of a moonlight night when 
 
84 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 the moon is ten days old, with this difference, however, that there were no distinct 
 shadows. The secondary tints of shade which give relief and reality to the image 
 were wanting, and as a consequence persons standing near had a peculiar ghost-like 
 appearance. The subsequent change from darkness to the full glare of day did not 
 appear so remarkable as the contrary had been. The first returning rays of the sun 
 darted forth instantaneously with extraordinary brilliancy, and the profound silence 
 which had reigned gave way to an audible hum. The world seemed to breathe again, 
 and at once life and animation took the place of what was an oppressive stillness. 
 
 In closing this report I must not fail to acknowledge our obligations for intelligent 
 assistance rendered by Professor and Mrs. Mansfield, of Mount Pleasant, and also by 
 Mr. B. C. Alexander arid Mr. Frank Krause, graduates of the engineering department 
 of the University of Michigan. Mrs. Mansfield made the record for Professor Van 
 Vleck's spectroscopic observations. Mr. Alexander called the seconds from the dial 
 of the chronometer, and Mr. Krause recorded the instants of the exposure of the 
 photographic plates. Professor Mansfield noted the readings of the aneroid barometer 
 as follows: 
 
 In. 
 
 30 minutes before total obscuration 29.590 
 
 1 5 minutes before total obscuration 2 9-595 
 
 At beginning of total phase 29.580 
 
 4 minutes after total obscuration 2 9-57 2 
 
 10 minutes after tetal obscuration . . 29.570 
 
 1 5 minutes after total obscuration 29-567 
 
 20 minutes after total obscuration 29.565 
 
 25 minutes after total obscuration 29.562 
 
 At the last contact 29.561 
 
 The reduction to be applied to these readings is o in .8oo, as determined August 8 
 at Burlington. Meteorological observations during the eclipse were made by Professor 
 Pickering at the hotel in the city, and hence no others were made by us at our station. 
 Our grateful acknowledgments are due to many citizens of Mount Pleasant for 
 courtesies extended, and especially to Colonel Root, proprietor of the omnibus line, 
 who furnished carriages at all times, free of expense, to convey members of our party 
 to and from the observing station. 
 Very truly, yours, 
 
 JAMES C. WATSON. 
 Prof. J. H. C. COFFIN, 
 
 Superintendent Nautical Almanac. 
 
REPORT 
 
 PROF. J. M. VAN VLECK 
 
 MOTJ^TT 
 
REPORT OF PROF. J. M. VAN VLECK. 
 
 MIDDLETOWN, October 15, 1869. 
 
 DEAR SIR: I respectfully submit the following report of my observations of the 
 solar eclipse of August 7: 
 
 My station was Mount Pleasant, Iowa, at which place I arrived in company with 
 Professor Watson and others on the evening of the 4th. 
 
 The special duty assigned to me was that of spectroscopic observation. I under- 
 took also to observe the first and last contacts. 
 
 The instruments which I employed were made under your direction by Messrs. 
 Alvan Clark & Sons, and were used for the first time on the day of the eclipse. 
 
 The spectroscope has a single prism of glass with a refracting angle of 60. It 
 is accompanied by a scale of equal parts, which is illuminated by a hand-lamp, and 
 read by reflection from the surface of the prism. 
 
 The telescope has an aperture of 3^ inches, and a focal length of 38 inches. It 
 is supported by a tripod, with an equatorial mounting adjustable to latitude, but with- 
 out slow-motion screws. 
 
 In observing the beginning and end of the eclipse I used a direct-vision eye- 
 piece, with the full aperture of the telescope. The magnifying power was 34. The 
 screen -glass was of a deep green color. I received it from Professor Watson in ex- 
 change for the screens of neutral tint which accompanied my telescope. 
 
 I watched carefully for any indication of the approach of the moon's limb before 
 the first contact, but could discover none. Neither did I see any traces of it after the 
 final contact. 
 
 The times at which I saw the contacts were, by the chronometer (Negus 1233), 
 as follows: 
 
 Time of first contact 9 h 53 o s 
 
 Time of last contact 1 1 53 30.5 
 
 For the guidance of the telescope during the spectroscopic observations, I was 
 indebted to my friend, Mr. W. A. Johnston, of this city. In the absence of slow- 
 motion screws this was a task of much delicacy, and it was skillfully performed. 
 
 Our telescope had a small finder, which, though adequate to the usual demands 
 upon it, was probably not made with reference to the requirements of the spectro- 
 scope. A slight examination of it convinced us that it would be safer to depend upon 
 the image of the sun or corona at the slit of the spectroscope. The diameter of this 
 image was about an inch and a quarter. It was obtained from the smaller image at 
 
 87 
 
88 ECLIPSE "OF THE SUN, AUGUST 7, 1869. 
 
 the focus of the telescope by inserting a negative eye-piece at the proper place in the 
 tube which connected the two instruments. As a finder it gave all the precision that 
 was needed. The principal objection to it was its faintness at the time of totality. 
 It was with difficulty that any of the protuberances could be distinguished upon it, 
 and we were obliged to depend mainly on the spectroscope to determine their position. 
 
 Anticipating that this would be the case, it was my intention to examine the sun's 
 border before the eclipse, in order to ascertain the position of the largest prominences. 
 But the unfavorable weather of the two preceding days had delayed the work of our 
 party so much that our time on the 7th had to be devoted to other preparations. 
 
 At the beginning of the totality, we had the slit of the spectroscope in contact 
 with the moon's limb, about 30 south of the east point. A spectrum of bright lines, 
 which appeared as soon as the light of the sun vanished, indicated that we were upon 
 a protuberance.* I attempted at once to determine the positions of these lines, but the 
 difficulty of holding our instruments in position was such that we found it necessary 
 to seek a larger protuberance. For this purpose the telescope was moved, without 
 changing the direction of the slit, towards the east point. Not far from this point we 
 found a prominence of such size that it could be distinguished by Mr. Johnston in the 
 image of the corona. It was probably the large protuberance f described by Professor 
 Morton as resembling in shape the letter X. The spectrum in this place appeared to 
 me to be identical with the former one. The unsteadiness of the instrument still inter- 
 fered somewhat with the precision of my measurements ; but I think that there can be 
 no difficulty in identifying my results with the more accurate determinations of other 
 observers. The following are my readings for the bright lines compared with the 
 positions of a few of the principal dark lines of the solar spectrum. The latter were 
 measured before the eclipse. 
 
 Bright lir 
 
 1 43.5 
 
 2 51.5 
 "? 6l.5 
 
 tJ *J 
 
 4 72 
 
 5 85 
 
 6 91 
 
 7 103? 
 
 The readings for the first and last of the bright lines were not precise. They are, 
 however, well-known lines whose positions had been previously determined with great 
 accuracy. The first, fourth, sixth, and seventh are hydrogen lines whose places on 
 Kirchhoff's scale are C, F, 2796 and h, respectively. The second is the well-known 
 line D 3 of the chromosphere, situated just above I). Its place on the same scale is 
 1017 5. The third is a little below E, and is, I presume, Kirchhoff's 1474 which cor- 
 responds to an iron line, and had been previously discovered as a chromosphere line 
 "by Mr. Lockyer, also at a later date by Professor Young. So far as I can judge from 
 a graphic comparison of the two scales, the fifth line corresponds nearly with Kirch- 
 hofPs 2600. 
 
 * Probably No. 5 of Mayer's diagram, Plato X, Fig. I. C. 
 tNos. 3 and 4 of Mayer's diagram. C. 
 
 es. 
 
 c 
 
 Dark lines. 
 A-l 
 
 D 
 
 to 
 
 C T 
 
 
 j 
 
 61 9 
 
 F 
 
 72 
 
 G 
 
 
 .h 
 
 IO2 
 
REPORT OF PROF. J. M. VAN VLECK. 89 
 
 While the measurements were in progress, the instrument was held, of necessity, 
 with as much steadiness as possible directly upon the protuberance. At first it seemed 
 to be oscillating between the lower part of this object and the dark surface of the moon 
 At this time all of the lines were visible in quick flashes, alternating with darkness ; 
 but I perceived no light from the corona. Presently, however, a slight movement 
 brought us upon the corona, which gave a continuous spectrum, with none of the dark 
 lines of the solar spectrum. There was also, at the same time, a noticeable change in 
 the appearance of the bright lines. In the former position I had observed little or no 
 difference in their lengths. But now, the second and third lines of the above list, or 
 those near D and E, respectively, extended entirely across the spectrum, though none 
 of the others had half as great a length. Once, also, when a small displacement of the 
 telescope put the others just out of the field, these two lines continued in view with 
 the same length, in connection with the corona-spectrum. This appearance lasted 
 only for an instant, and was not repeated. Whether the two lines had equal lengths, 
 or to what distance they extended, I cannot tell. My efforts were directed, at the 
 time, to the identification of the lines above E, and I failed to give the phenom- 
 enon the attention it deserved. But so far as I have described it, 1 am confident of my 
 correctness. 
 
 A short time before the reappearance of the sun, we moved to some distance from 
 the protuberance. But I saw nothing besides the continuous spectrum of the corona. 
 Most respectfully, your obedient servant, 
 
 J. M. VAN VLECK. 
 
 Prof. J. H. C. COFFIN, 
 
 Superintendent of the Nautical Almanac, Washington, D. C. 
 
 12 E 8 
 
REPORT 
 
 OF 
 
 PROF. E. C. PICKERING. 
 
 MOUNT PLEASANT, IOWA.. 
 
 91 
 
REPORT* OP PROFESSOR EDWARD C. PICKERING. 
 
 MOUNT PLEASANT, IOWA. 
 
 [Professor Pickering was a member of the "Philadelphia Photographic Expedi- 
 tion." His report is inserted here from its close connection with that of Professor Van 
 Vleck. J. H. C. COFFIN.] 
 
 MOUNT PLEASANT, IOWA, August 9, 1869. 
 Prof. HENRY MORTON: 
 
 DEAR SIR : The following experiments were conducted at the Brazelton House in 
 this town. Latitude, 40 57' north; longitude, 91 38' west. The room used was in 
 the third story, and had an unobstructed view to the west. 
 
 TABLE I. 
 
 Time. 
 
 A. 
 
 B. 
 
 C. 
 
 Time. 
 
 A. 
 
 B. 
 
 C. 
 
 h. m. 
 
 O 
 
 
 
 o 
 
 h. m. 
 
 o 
 
 O 
 
 O 
 
 3 7 
 
 23-3 
 
 23-1 
 
 40.8 
 
 5 10 
 
 23.0 
 
 23.1 
 
 26.4 
 
 20 
 
 23-5 
 
 23.0 
 
 40.8 
 
 5 
 
 23.2 
 
 
 27.6 
 
 2 9 
 
 23-7 
 
 23.2 
 
 40.8 
 
 20 
 
 23-4 
 
 23-4 
 
 28.7 
 
 36 
 
 23.8 
 
 23. 2 
 
 41-7 
 
 25 
 
 23. 6 
 
 23.6 
 
 29. 6 
 
 4 
 
 23-9 
 
 23-4 
 
 41.7 
 
 30 
 
 23-8 
 
 
 31.0 
 
 5 
 
 24-3 
 
 24.0 
 
 . 42.2 
 
 35 
 
 24.0 
 
 24. o 
 
 32.0 
 
 55 
 
 24.7 
 
 24. o 
 
 42.0 
 
 40 
 
 24.3 
 
 24.0 
 
 32-4 
 
 4 o 
 
 24.7 
 
 24.0 
 
 41.8 
 
 45 
 
 24.4 
 
 24.2 
 
 33- i 
 
 5 
 
 24.9 
 
 24.0 
 
 40.8 
 
 50 
 
 24.5 
 
 24.2 
 
 32.90 
 
 10 
 
 24.9 
 
 24. o 
 
 40. 6 
 
 55 
 
 24.7 
 
 24-3 
 
 35-4 
 
 '5 
 
 25.0 
 
 24. o 
 
 39-7 
 
 6 o 
 
 24. 6 
 
 
 36.9 
 
 20 
 
 25-3 
 
 24.0 
 
 38-0 
 
 5 
 
 24-5 
 
 24.2 
 
 35-8 
 
 25 
 
 25.2 
 
 24. 1 
 
 37-4 
 
 18 
 
 24.2 
 
 
 34-8 
 
 30 
 
 24.7 
 
 24. o 
 
 34-9 
 
 20 
 
 24-3 
 
 24.0 
 
 34.1 
 
 35 
 
 24.4 
 
 
 33-o 
 
 25 
 
 24.2 
 
 24.0 
 
 33-9 
 
 40 
 
 24-3 
 
 .... 
 
 31-8 
 
 3 
 
 2 3-9 
 
 
 32-9 
 
 45 
 
 23-9 
 
 23.8 
 
 28.6 
 
 35 
 
 23-8 
 
 
 30.7 
 
 48 
 
 23-7 
 
 
 27.2 
 
 40 
 
 23-5 
 
 23-7 
 
 29.7 
 
 57 
 
 23-3 
 
 23-3 
 
 24.8 
 
 45 
 
 23.2 
 
 
 27.1 
 
 5r\ 
 
 ?1 A 
 
 
 2d 7 
 
 CQ 
 
 
 
 2<,. 2b 
 
 u 
 
 ?3* 4 
 
 
 ^^r- / 
 
 J" 
 
 
 
 j 
 
 5 
 
 23 
 
 
 25-3 
 
 55 
 
 22.7 
 
 23.0 
 
 23-4<- 
 
 a, shadow fell on C, causing the depression seen in the curve. 
 
 b, sun reaches cloud near horizon. 
 
 c, sun appears red through, cloud. 
 
 Reprinted from Journal of the Franklin Institute, vol. LVIII, third series, p. SJ1. 
 
 93 
 
94 
 
 ECLIPSE OF THE SUN~, AUGUST 7, 1869. 
 
 The most important experiments during the partial phase were thermometric. 
 For this purpose three delicate thermometers were used. An alcohol thermometer, A, 
 divided to half degrees, and two filled with mercury, B and C, the latter having a 
 blackened bulb. A was hung in the room in the shade ; B kept in its case, so that its 
 temperature was very nearly constant; and C'was exposed dii'ectly to the sun's rays. 
 
 Observations were made every 5 minutes after the eclipse began; at longer intervals 
 before. The time is about a minute and a half slower than the local time, or 56 50" 
 slower than Washington mean time. The temperatures are centigrade, estimated to 
 tenths of a degree. 
 
 The curves in the adjoining figure represent these results; vertical distances give 
 temperatures ; horizontal distances, times. For use in the following table, they have 
 
 FIG. 1. 
 
 also been drawn on a much larger scale, and the accidental errors in part eliminated 
 by passing a curve through all the points ; the difference was generally only a small 
 fraction of a degree. The times were then computed at which i, 2, 3, 4, &c., digits 
 were eclipsed, and the corresponding temperatures obtained by interpolation. 
 
 In Table II the first column gives the number of digits eclipsed; negative 
 numbers denoting distances between the two limbs. The second column gives the 
 local time ; the third, the temperature of A ; the fourth, the estimated temperature, if 
 there had been no eclipse. Of course this is a very rough approximation, and was ob- 
 tained by drawing a continuous curve through the beginning and end of the eclipse. 
 It is only intended as a guide, and too much dependence must not be put upon it. 
 The last column gives the fraction of the sun's disk obscured. 
 
 By examining the third column of this table, it will be seen that shortly before 
 the eclipse the thermometer rose, attaining its maximum at the instant of contact, 
 so that when three digits, or 25 per cent, of the sun's disk was obscured, the tempera- 
 ture was about the same as before the eclipse. Again, the thermometer continued to 
 rise after the eclipse was over. 
 
REPORT OF PROF. E. C. PICKERING. 
 TABLE II. 
 
 
 Digits. 
 
 Time. 
 
 Temperature. 
 
 Obscur. 
 
 Digits. 
 
 Time. 
 
 Temperature. 
 
 Obscur. 
 
 Real. 
 
 Assumed. 
 
 Real. 
 
 Assumed. 
 
 8 
 
 - 7 
 6 
 
 5 
 - 4 
 3 
 
 2 
 I 
 
 
 I 
 2 
 
 3 
 4 
 S 
 6 
 
 7 
 8 
 
 9 
 
 10 
 
 ii 
 
 12 
 
 li. m. 
 3 8 
 13 
 19 
 25 
 3 
 36 
 42 
 47 
 53 
 58 
 4 4 
 9 
 '5 
 20 
 
 25 
 3" 
 36 
 4i 
 46 
 
 5' 
 56 
 
 o 
 
 40.8 
 
 40.8 
 40.8 
 40.8 
 40.9 
 41.5 
 41.8 
 42.0 
 
 42. 1 
 
 42. o 
 
 41-3 
 40.7 
 
 39-6 
 38.6 
 
 37-4 
 34-9 
 33- 
 3'-7 
 28.6 
 26.4 
 24.8 
 
 o 
 
 
 12 
 
 II 
 
 IO 
 
 9 
 
 8 
 
 7 
 6 
 
 5 
 4 
 3 
 
 2 
 
 I 
 
 
 2 
 
 - 3 
 - 4 
 
 
 
 6 
 
 - 7 
 8 
 
 1). m. 
 4 59 
 5 4 
 9 
 M 
 '9 
 24 
 28 
 
 32 
 
 37 
 41 
 45 
 5o 
 5 
 58 
 
 6 2 
 
 7 
 ii 
 
 '5 
 '9 
 23 
 26 
 
 O 
 
 24.7 
 25.1 
 25.9 
 27.1 
 28.2 
 29-3 
 3- i 
 3i-3 
 32-' 
 32-8 
 33-5 
 34-4 
 35-2 
 36.1 
 36.1 
 35-7 
 35-3 
 35-o 
 34-4 
 33-9 
 33-5 
 
 o 
 
 39.5 
 
 39-3 
 39- i 
 38.9 
 38.7 
 38.5 
 38.3 
 38-0 
 37-8 
 37-6 
 37-3 
 36.9 
 36.6 
 
 36.3 
 
 I.OOO 
 
 893 
 789 
 .685 
 .586 
 .486 
 
 39" 
 .302 
 .219 
 
 '44 
 .079 
 .029 
 .000 
 
 
 
 
 
 
 
 40.8 
 40.8 
 40.8 
 40.7 
 40.7 
 40.7 
 40. 6 
 40. 6 
 40.5 
 40.4 
 
 40.3 
 40. 2 
 40. I 
 40.0 
 
 39-9 
 39-8 
 39-6 
 
 
 
 
 
 
 .029 
 . 029 
 144 
 . 219 
 
 .302 
 
 391 
 .486 
 
 .586 
 .685 
 .789 
 893 
 
 I. 000 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 Columns A and B, in the first table, show that the temperature of the air falls 
 but slightly. As the instruments were in the room, they were protected from radiation. 
 Their maxima occurred some time after the first contact, owing^to the gradual warming 
 of the room by the sun. In the last column of the second table, the disks of the sun 
 and moon are supposed to be of the same size; as the latter, in reality, exceeded the 
 former by about one twenty-fifth, the area obscured would be somewhat greater. The 
 error, however, is only about one per cent, for eleven digits, aiid much less for other 
 parts of the eclipse. 
 
 Actinometric experiments by the method of Bunsen and Roscoe were made, 
 exposing pieces of sensitive paper every five minutes for one 
 minute to the sun, and then comparing them with a fixed scale. 
 The'results are given in Table III and in Fig. 2, but the delicacy 
 of the method does not appear to lead to important results. 
 
 Fig. 2. 
 
96 
 
 ECLIPSE OF THE SUN, AUGUST 7, 1809. 
 TABLE III. 
 
 Time. Intensity. 
 
 Time. Intensity. 
 
 Time. Intensity. 
 
 h. m. 
 
 h. in. 
 
 h. in . 
 
 3 40 85 
 
 4 35 20 
 
 5 10 25 
 
 4 5 60 
 
 4 40 15 
 
 5 20 25 
 
 4 20 50 
 
 4 45 8 
 
 5 35 36 
 
 4 25 45 
 
 4 5 i 
 
 5 40 3 
 
 4 3 3 
 
 5 5 8 
 
 5 59 25 
 
 THE TOTAL PHASE. 
 
 On the approach of totality the thermometric and acti no metric experiments were 
 given up, and the following observations made instead: 
 
 GKNKRAL, OBSERVATIONS. A pocket telescope magnifying about ten diameters was 
 used. It was tied to the baqk of a chair by a piece of cloth just tightly enough to 
 make it remain in whatever position it was placed. This forms a convenient mounting, 
 and by it the telescope can be moved steadily, and the sun or a star followed without 
 difficulty. 
 
 The corona appeared as an irregular four-pointed star, with, of course, a black 
 center. Two of the rays were nearly vertical, and two horizontal, the left hand one 
 pointing somewhat downward, while between it and the lower ray was a fifth smaller 
 point. Its color was pure white, very different from the full moon, but resembling a 
 cumulus cloud. Possibly the reddish tint noticed by many observers heretofore may 
 be a subjective effect due to the green color of surrounding trees or grass. Its texture 
 resembled the ragged edge of a thunder cloud, or the crest of a wave torn by the wind. 
 The striae were not radial but spiral, as if the sun had been turned in such a way that 
 the upper edge moved towards the east. 
 
 A very bright protuberance was seen on the lower edge of the sun ; also, two 
 others on the western side. The first, to the naked eye, appeared as much within as 
 without the moon's limb, and, by irradiation, appeared to send rays some distance 
 towards the center. The sky presented the appearance it has during the morning 
 twilight, the western horizon, however, being bright yellow. 
 
 I did not notice the sudden lowering of the temperature during totality, although 
 this was very perceptible to those in the open air; it would, therefore, seem that this 
 is an effect mainly due to radiation. 
 
 After the reappearance of the sun the corona remained visible for several seconds. 
 Cocks in the neighborhood crowed repeatedly as the light returned. 
 
 The following star observations were made by Dr. C. Pearson, who also assisted 
 in the actinometric observations. Mercury became visible at 4 b 54, or two minutes 
 before totality, and disappeared at 5 b . Venus was visible from 4 h 51 to 5 h 12, or 
 twenty-one minutes. 
 
 SPKCTROSCOPIC OBSERVATIONS. A chemical spectroscope with one 60 prism was 
 loaned me by Professor Van Vleck, and was mounted in the way above described for 
 the telescope. As no lens was placed in front of it, all the light that fell on the slit 
 from a circle about 7 in diameter passed through the instrument. Turning it towards 
 
EEPOET OF PEOF. E. C. PICKEEING. 97 
 
 the sun before totality, the latter remained in the field. This is probably the best 
 way to obtain the spectrum of the corona, as there is very little loss of light. The 
 protuberances are so small that their spectra would be faint. The spectrum appeared 
 to be continuous, with two or three bright lines, the brightest in the. neighborhood of 
 E, and the next near C; but as no dark solar lines were visible, these positions cannot 
 be relied upon. The absence of the dark lines may be due to the want of brilliancy 
 of the spectrum, although this was bright enought to have its upper and lower edges 
 well defined. 
 
 POLARIZATION. The form of polariscope used was that adopted by Arago in his 
 experiments on sky polarization. It consists of a tube about 20 inches long and two 
 inches in diameter, one end of which is closed by a double image-prism of Iceland 
 spar, and the other by a plate of quartz. Looking through the former we see two 
 images of the latter, which, when the light is polarized, assume complementary tints. 
 If, now, the corona was polarized in planes passing through the center of the sun (as 
 is generally admitted) when viewed through the polariscope, in one image the upper 
 and lower parts should have appeared blue and those on the right and left yellow; 
 while in the second image these colors would be reversed, the yellow being above 
 and below and the blue on the sides. In reality the two images were precisely alike, 
 and both pure white, but one was on a blue, the other on a yellow, back ground. 
 From this we may infer that the corona was unpolarized, or, at least, that the polarization 
 was too slight to be perceptible.* 
 
 Although this does not prove that it shines by its own light, since polarization is 
 produced only by diffuse reflection, yet these observations, and also those with the 
 spectroscope, seem to render it probable. This view is also strengthened by the fact 
 that as the most distant portions are but about one hundredth part of the distance of 
 the earth, they receive over ten thousand times as much heat per square foot. 
 
 The colored background mentioned above shows that the sky close to the corona 
 is strongly polarized, and since the tint is uniform on all sides of the sun, the plane of 
 polarization is independent of the position of the latter ; that is, the same on the sides 
 that it is above or below it. The most probable explanation of this most unexpected 
 result is that the earth beyond the limits of the shadow being strongly illuminated 
 acts as an independent source of light, and this being reflected by the air becomes 
 polarized in planes perpendicular to the horizon. 
 
 I am indebted to Mr. E. L. Wilson for the use of two Vogel's photometers, and also 
 to Messrs. Hover and Leisenring for assistance in the photographic experiments. 
 
 In conclusion, the new facts elicited may be summed up as follows : An increase 
 of heat and actinic power is observed in the beginning of the eclipse, caused by an 
 increased brightness of the sun's disk near the moon's limb. The spectrum of the 
 corona appears to be free from dark lines, but may contain two or three bright ones. 
 Its striae are spiral rather than radial, and its light is unpolarized. The sky adjoining 
 it, however, reflecting light from the earth, shows strong signs of polarization. 
 
 Respectfully submitted. 
 
 EDWARD C. PICKERING. 
 
 * A similar result was obtained with this instrument in 1870 by Mr. Waldo O. Ross (U. S. Coast Survey Report, 
 1870, p. 173). In 1878 Mr. W. H. Pickering obtained a different result (Monthly Notices Roy. Astron. Soc., XXXIX, 
 138). E. C. P. 
 
 13 ES 
 
98 ECLIPSE OP THE SUN AUGUST 7, 1869. 
 
 NOTE ON THE SUPPOSED POLARIZATION OF THE COKONA.* 
 
 BY PROF. E. C. PICKERING. 
 
 An observation on this subject is given in my report on page 285 of the current 
 volume of this Journal, but as the form of the instrument used has been in one or two 
 
 cases misunderstood, I inclose a sketch of it. A B 
 (Fig. i) is a sheet-iron tube, closed at A with a plate 
 of quartz and at B with a prism of Rochon. The 
 latter has the property of giving two images of any 
 object seen through it, separated by an angle of nearly 3. Looking through the 
 tube we therefore see two images of the quartz touching, but not overlapping. When 
 the light is polarized these images assume complementary tints, which vary with the 
 plane of polarization and the thickness of the quartz. On turning this instrument 
 towards the sun during totality, the images presented the appearance shown in Fig. 2. 
 The hexagons represent in form and size the plate of quartz; the black circles 
 
 the moon, here drawn a sixth of an inch in diameter, 
 as the scale is about 3 to the inch. The corona 
 appeared white, but the sky surrounding it was 
 colored in one image blue, in the other yellow, 
 represented in the figure by vertical and horizontal 
 lines. The conclusion to be drawn from this is, that 
 the light of the corona is unpolarized, or, more 
 strictly, that the amount of polarized light, if any, 
 is too slight to be perceptible with this instrument. 
 Its delicacy, although not equal to Savart's polariscope, is very great, giving colored 
 images with paper, wood and other bodies which reflect a small amount of light 
 specularly. The day before the eclipse it showed, in a very marked manner, the 
 polarization of the wet pavements and roofs. To measure its sensitiveness, I viewed 
 the light reflected by a piece of plate glass, at different angles of incidents, and found 
 that the color ceased to be visible when this angle was about 10, which, allowing for 
 the reflection from the second face, would give about one part of polarized to twenty- 
 four of natural light. 
 
 Observers heretofore have generally attached their polariscope to a telescope, 
 and thus introduced a source of error, avoided in my instrument. For, light 
 passing through the object-glass and field lens would be polarized by refraction before 
 reaching the polariscope by the obliquity of the incidence, caused both by the curva- 
 ture of the surfaces and the fact that the edge of the field of view receives its light 
 not parallel to the axis. The plane of polarization would be perpendicular to a plane 
 falling through the axis of the instrument. Now, if any part of the corona was 
 brought into the center of the field of view, the adjoining portions would appear 
 polarized in planes parallel to the edge of the field, or passing through the sun's center. 
 In sweeping around the sun's edge the plane of polarization would continually change, 
 
 From Journal of the Franklin Institute, Iviii, 372. 
 
EEPORT OF PEOF. B. C. PICKERING. 99 
 
 as the corona passed through different parts of the field, and the comparative darkness 
 of the moon's disk and the exterior sky prevent the polarization of the other portions 
 of the field from being visible. The degree of polarization by refraction would be 
 very slight and perhaps imperceptible, but the agreement of observation with this 
 hypothesis is certainly a curious coincidence. 
 
 The strongest argument against the polarization of the corona is furnished by the 
 spectroscope, the presence of bright lines and absence of dark ones, as observed by 
 Prefessor Young, denoting incandescence, a view strengthened by the consideration 
 that each square centimeter of the surface of the corona would receive several 
 thousand units of heat per minute. I am well aware that my results are at variance 
 with those obtained by previous observers, including some of the most eminent 
 astronomers of the day, but as far as I can learn this form of polariscope has not been 
 used for the purpose, and therefore hope that my experiment may be repeated during 
 the next eclipse. 
 
 [NOTE. Since writing the above I learn from Prof. F. H. Smith that an excellent Arago's polariscope was used 
 at Eden Ridge, Tenn., in observing the eclipse. The result agreed with mine, namely, that no traces of polarization 
 could be detected in the corona with this instrument]. E. C. P. 
 
REPORT 
 
 OF 
 
 PROF. STEPHEN ALEXANDER, 
 
 OTTTJMWA, IOWA.. 
 
 101 
 
REPORT OF PROFESSOR STEPHEN ALEXANDER. 
 
 OBSERVATIONS AT OTTUMWA, IOWA. 
 
 COLLEGE OF NEW JERSEY, Princeton, December, 1869. 
 
 SIR: Having as astronomer occupied one of the stations which, in your official 
 capacity, you had selected for the observation of the total eclipse of the sun of August 
 7, 1869, I beg leave respectfully to report: 
 
 That after special consultation with yourself, at Burlington, Iowa, I fixed upon 
 Ottumwa as my own place of observation, because of its special advantages for our 
 purpose. On the day of the arrival there of myself and assistants, i. e., August 2, I, 
 in company with my assistant, Gen. Norris Halsted, made choice of a station on an 
 eminence about a mile and a quarter to the northeast of the center of the city ; the 
 station being indeed one of several which had been personally inspected by you 
 several days before. From it we had an unobstructed view of the whole circumfer- 
 ence of the horizon except a small portion toward the northeast. 
 
 I forthwith made arrangements for the construction of a temporary observatory 
 for the accommodation of the photographic party, which was to be stationed at the 
 same place, in accordance with your own arrangements; the construction, position, 
 &c., of the observatory being all in accordance with the plan prescribed by yourself. 
 Associated with me as assistants were Gen. Norris Halsted, of Kearney, N. J.; and 
 Mr. Thomas L. Graham, of Pennsylvania ; and as supernumeraries, four members of 
 the senior class in the college of New Jersey, viz: George H. Hooper, Charles H. 
 Moore, John E. Peters, of New Jersey, and George C. Yeisley, of Maryland. 
 
 We had with us 4 mounted telescopes, besides field-glasses; my own being an 
 achromatic refractor by Utschneider and Fraunhb'fer, aperture nearly 3 English inches, 
 and focal distance of object-glass 5 1 inches. I had with me a filar micrometer adapted 
 to this. We had also i pocket and 2 box chronometers, 9 thermometers, a Daniels 
 hygrometer, an aneroid barometer, and 2 thermo-electric piles with attached apparatus. 
 
 We had, withal, the valuable co-operation of the photographic party, detailed by 
 Professor Morton to occupy the Ottumwa station, consisting of Prof. Charles F. Himes, 
 Ph. D., of Dickinson College, Carlisle, Pa. ; Messrs. J. Zentmayer, E. Moelling, of Phil- 
 adelphia; and J. C. Browne, of Buffalo. 
 
 Professor Himes has himself reported to you, and also put you in possession of 
 the results which the photographers obtained, of which, it seems to me, it may well 
 be said that they are unequaled of their kind. 
 
 It is here only necessary to advert to some arrangements which we had in common. 
 A chronograph was set up just outside of the observatory, on which the astronomical 
 
 103 
 
104 
 
 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 assistants (in turn) "tapped" the seconds shown by the standard chronometer (Daniel's 
 g'g), which were also audibly called out, and the minute also marked, as the limit of 60" 
 was reached, by the assistant specially charged with that duty. It was also intended 
 that the records of times of the phenomena and those of taking the photographic im- 
 pressions should be marked on the fillet of the chronograph, each observer being 
 furnished with his own key to make connection. The success of the arrangement 
 was but partial, and the other box chronometer (Negus 2335) was passed over to 
 Professor Himes, in the observatory, and by the aid of it he made his own record of 
 the times of taking the photographs. 
 
 Observations for time were obtained on the 3d, 4th, 7th, and gth days of the 
 month. [The results are incorporated in the table for chronometer, Daniel's ^, on page 
 1 6. The correction for this chronometer referred to Burlington mean time, August 
 7 5 b was + 5 h 57 6 s . 7,* and to Ottumwa time, was assumed to be -f- 5 h 52 o 8 . o, and 
 the hourly change + o s .O3.] 
 
 OBSERVATIONS OF THE ECLIPSE. 
 
 The observed times of the principal phenomena and the corresponding Ottumwa 
 times were as follows,' the names of the observers being annexed: 
 
 FIRST CONTACT. 
 
 Chronometer time. 
 
 Ottumwa time.j- 
 
 Observer. 
 
 h. m. s. 
 
 h. m. s. 
 
 
 9 57 54-3 
 
 3 49 54- 3 
 
 Alexander. 
 
 57-4 
 
 57-4 
 
 Halsted. 
 
 SECOND CONTACT. 
 
 Disappearance of all the sun's limb, except part broken into drops, which rather 
 seemed to adhere to the moon, as recorded on the chronograph. 
 
 Chron. time, u h o m 49 8 .24; Ottumwa time, 4 h 52 49 8 .2. (Alexander.) 
 
 Total immersion of the drops, chron. time, n h o m 49".44; Ottumwa time, 4 h 52 
 49 8 4. (Alexander.) 
 
 Disappearance of two small bright prominences (flames) on the side of the corona 
 toward which the moon was advancing, as noted by Peters in his telescope, 4 h 53 35", 
 Ottumwa time. 
 
 THIRD CONTACT. 
 
 Chronometer time. 
 
 Ottumwa time. 
 
 Observer. 
 
 h. m. s. 
 
 h. m. s. 
 
 
 ii 3 40 
 
 4 55 40. o 
 
 Halsted. 
 
 40.8 
 
 40.8 
 
 Peters.}:. 
 
 * This correction and Ottumwa mean times of observations should be diminished i".5, p. 16. C. 
 t Professor Alexander thinks these times should be l nl later. C. 
 
 t Mr. Peters noticed in his telescope a manifest increase oP light near the end of the total eclipse, along that 
 part of the moon's limb where the sun was about to emerge. 
 
REPORT OF PROF. STEPHEN ALEXANDER. 
 
 LAST CONTACT. * 
 
 105 
 
 Chronometer time. 
 
 Ottumwa time. 
 
 Observer. 
 
 h. m. s. 
 
 h. m. 
 
 s. 
 
 
 o o 11.3 
 
 5 52 
 
 "3 
 
 Alexander. 
 
 (or possibly 12. o) 
 
 (or 
 
 12. 0) 
 
 
 12-3 
 
 
 12-3 
 
 Halsted. 
 
 NOTE. The Ottumwa mean times computed from the American Ephemeris for latitude 40 58' N. and longitude 
 ih jm 2 o".7 W. from Washington are for 
 
 Beginning of eclipse 3 h 49 44'.82 
 
 Beginning of totality 4 n 5i m 45".58 
 
 End of totality 4 t S4 m 36 I .i3 
 
 End of eclipse 50 5i m I4".92 
 
 The record of the total immersion needs an explanation. The seconds had been 
 audibly called and tapped by the assistant on the key of the chronograph until within 
 a few seconds before the total immersion, when the putting forth of my hand to 
 obtain access to the key when immersion should take place was mistaken by the 
 assistant as a signal that I meant to go on with the tapping myself, and he therefore 
 stopped doing so, as well as the calling of the seconds. The time was not one for expla- 
 nations; but my own impressions of the key, both when the drops were all that re- 
 mained visible of the sun, and when they disappeared, have produced their very distinct 
 marks on the fillet of the chronograph, though the taps for seconds failed to be im- 
 pressed. The assistant, however, began his calling of seconds anew before the occur- 
 rence of the limit of the next 60", and the termination of the minute was marked on the 
 fillet by the assistant in charge of that matter. The lengths due to minutes being thus 
 ascertained, and the interval of the record of total immersion of limb and that of the 
 drops from the nearest minute mark carefully measured, the seconds and fractions have . 
 been deduced from these by proportion; the value of the interval thus deduced being 
 io 9 .76 for the disappearance of the limb, and io*.56 for the vanishing of the drops; 
 the duration of the drops after every other portion of the sun had disappeared being, 
 as thus recorded, o 8 .2o. The weight of the observation thus recorded is, of course, 
 diminished by the circumstances here detailed, but the result would seem to be very 
 closely consistent with the record of the other phenomena, and, among them, with the 
 duration of the total eclipse due to the position of Ottumwa. 
 
 The corona and its appendages. The total immersion was scarcely complete f when 
 General Halsted earnestly called the attention of the other observers to an unlocked 
 for and striking phenomenon. The greater portion of the corona appeared doubled as 
 if by reflection; the seeming image being to the right of the real and the line joining 
 the centers of the object, and this image inclining downward toward the right, the 
 outline of the whole being that of a figure 8 turned very nearly sidewise.J In color 
 and appearance the outline of the strange appendage to the corona closely resembled 
 
 * These times were i m less as first reported. C. 
 
 tGeneral Halsted's phenomenon was seen just after the total eclipse began, instead of just before, as I learned 
 subsequently by personal interview, but the light was no doubt brighter on the side where the sun was last seen. 
 
 }A communication to the writer of this report from Mr. S. Fountain, postmaster at Rocky Mount, N. C., states 
 that "during the observation two rings were visible elongated east and west, broader on the southern limb of the 
 dark disk of the moon. Just under the outer ring appeared a red spot." 
 14 E S 
 
106 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 that of the "old moon in the arms of the new" that portion of the border of the 
 moon which is seen soon after the new moon illuminated by earth light. The drawing* 
 of the appearance sent with this report has been submitted to General Halsted and 
 approved by him. The appearance was of very short duration. 
 
 The corona had a clear, white, very brilliant and almost sparkling appearance, 
 its light being very like that of the planet Venus as seen in the early evening twilight. 
 It had a flame-like outline, but the projecting portions were not so far extended, nor 
 did they present so great an appearance as seems to have been noticed elsewhere. 
 Some of the observers spoke of the upper left-hand portion on the east limb as being 
 brighter than the rest and also of its being a little wider there. 
 
 Seven protuberances in all were noted, and the enlarged copy of the photograph 
 of the "totality," (Plate VII), shows protuberances in nine places. Some of these pro- 
 tuberances were conspicuous to the bare eye, and to most of the observers the colors 
 of these appeared to be a lively red. Such was their color as seen by my own eye 
 on a first inspection. I then turned away to arrange the thermo-electric pile, arid 
 while the screen of that was removing, examined the corona with the telescope. The 
 protuberances appeared with all the distinctness that is characteristic of so fine a 
 refractor, but at first view, thus seen, they were white, and yet, within the few seconds 
 which I could devote to their inspection, these white prominences, portions of them, 
 became tinted with a pale rose color, so that they appeared not unlike pinnacled 
 glaciers or icebergs illuminated by the setting sun an appearance which explained 
 why some European observers of the total eclipse of 1842, in their descriptions, spoke 
 of the protuberances as "fiery mountains." The lithograph in Schumacher's Astrono- 
 
 misclie Nachsichten fur 1843, vol. 20, represents all this exceedingly well. The outlines 
 of two of those observed at Ottumwa were as they appeared to me, very nearly as 
 here represented, the shape of the larger one being withal justified by a comparison 
 with the enlarged copies of photographs. 
 
 As to the color of the protuberances, as seen by some of the other observers, 
 General Halsted saw the protuberances red with the bare eye, and also at first with 
 his telescope, though they afterwards appeared white. He removed his eye from 
 the telescope to see how that could have happened, and when he looked again with 
 the instrument the protuberances appeared of a rose color. 
 
 Professor Himes, who wears glasses, states that "at the first instant of totality my 
 
 "This drawing, and another subsequently furnished, exhibit two images of the eclipsed sun, that to the right 
 being the fainter and less distinct, and lapping each other about one-sixth of the diameter of each. It would seem 
 to have been a case of binocular vision but for the implication that the duplication was seen by more than one person 
 The drawings show no appearance of a corona, but only a narrow fringe of light. C. 
 
REPORT OF PROF. STEPHEN ALEXANDER. 107 
 
 I 
 
 eyes were directed to the moon, and I perceived dazzling white prominences projecting 
 apparently from the moon. My attention was then attracted to the photographic 
 apparatus, and after about, half a minute, upon looking up I found the former white 
 prominences of a brilliant decided rose color, bordering on crimson, and they remained 
 of this color to the close of the totality." According to my note of conversation with 
 him two days after the eclipse he also saw the protuberances rose color with a field- 
 glass. 
 
 Mr. Browne had been confined to the "dark room" of the photographic observa- 
 atory, which was coated with orange-colored curtains, and in it were two candles 
 burning guarded by quite yellow tissue paper. The view which he had at the middle 
 of the totality lasted but for three seconds. Everything appeared to him as if tinted 
 with smoke. As seen with the bare eye the protuberances appeared white, bordered 
 with a delicate rose color. Mr. Zentmayer and Mr. Moelling had been looking on the 
 screen-glass of the photographic apparatus. Mr. Zentmayer last saw the protuberances 
 white with a slight tinge of blue. Mr. Moelling saw them white all the time.* 
 
 Most persons saw with the bare eye an intrusion of light on the moon's disk, of a 
 nearly triangular shape, issuing from the base of a protuberance. Especially was this 
 true of the largest of all of those appendages near to the lowest point of the moon's 
 edge. In the photograph, Plate VIII of the totality, the place of this is partly occupied 
 by a white spot nearly parallel to the protuberance and also to another spot outside of 
 the disk. This photograph distinctly recalls to General Halsted what he saw in his 
 telescope. 
 
 It was in accordance with your own suggestion that I endeavored to obtain some 
 indication, if it so might be, of the heat of the corona. Disappointed in obtaining a 
 lens of rock salt, I had provided several convex lenses of glass of short focus, and 
 also a concave mirror of 9 inches diameter, to concentrate heat, and a very sensitive 
 thermo-electric pile to indicate the effect of the concentration. It seemed right to make 
 the experiment, though without the rock salt there seemed almost no hope of success, 
 the mirror not being arranged for, as it could not be known beforehand how bright 
 the image of the corona would be. The image by refraction through a glass lens was 
 thrown on the end of the pile for a ver)' short time without any sensible effect, and 
 was still held there when the first beam of sunlight emerged. Trying this experiment 
 interfered with even the setting of the web in the filar micrometer so as to read off 
 afterward the measurement of the height of the protuberances, and there was too much 
 else doing to enable us to make efficient use of the Daniel's hygrometer. Some of 
 these things had to be abandoned, though not without the expectation that they would 
 be used elsewhere, while it was feared that the attempt to obtain the heat of the corona 
 would not elsewhere be made. 
 
 OTHER OBSERVATIONS. 
 
 The degree of darkness during the total eclipse was such that large print could 
 with difficulty be read. Animals behaved as they usually do when night is coming on. 
 
 *Mr. H. P. Norton, of Moniuouth. 111., saw the protuberances red at first, but white just after the emersion of 
 sunlight. 
 
108 
 
 ECLIPSE OF THE SUK, AUGUST 7, 1860. 
 
 The increasing darkness was painted on the sky toward the west some time before 
 the total eclipse, and again the same tint was visible eastward after the total eclipse 
 was over, and those who were at liberty to do so observed with what frightful rapidity 
 we were plunged into the dark shadow, and the contrary effect as we emerged into 
 sunlight. No wind was perceptible during the total eclipse. The white light of Venus 
 and the ruddy light of Mercury appeared in beautiful comparison, and contrast as well, 
 as soon as the sun was totally hidden. Saturn, also, and at least four fixed stars, were 
 seen. Arcturus appeared white to both General Halsted and Mr. Graham. 
 The Ottumwa times of other miscellaneous observations were as follows: 
 
 
 Time. 
 
 Observer. 
 
 A distortion of the upper cusp 
 
 } h IS 01 ?? 
 
 
 Bright band bordering the moon near the cusps of the eclipsed sun . 
 Contact with a large spot 
 
 411 40 
 
 Do. 
 Do 
 
 Total immersion of large spot 
 
 
 Do 
 
 Emersion of two small round spots 
 
 S-JI 
 
 Do 
 
 Bright band bordering the moon 
 
 5-i(\ 
 
 Do 
 
 Bright band bordering the moon 
 
 1 dl 
 
 Do 
 
 Bright band bordering the moon (seen very plainly) 
 
 
 Do 
 
 Emersion of a long spot 
 
 
 Do 
 
 
 
 
 OBSERVATIONS OF TEMPERATURE BY MR. YE[8LEY. 
 
 The thermometers have the initials of the maker's nameappended: F., for Faulkner; 
 P., for Pike, and R, for Russell. Those designated by a * were alcoholic, the others 
 mecurial thermometers. The degrees are those of Fahrenheit. The dates are in local 
 mean time. 
 
BBPOET OF PEOF. STEPHEN ALEXANDER. 
 
 Thermometers. 
 
 109 
 
 1869. 
 
 In sun. 
 
 In shade. 
 
 
 August 7. 
 
 P. 
 
 P.* 
 
 R. 
 
 R. 
 
 P.* 
 
 P. 
 
 P. 
 
 F. 
 
 F.* 
 
 Remarks, 
 
 h. m. 
 
 
 
 
 
 O 
 
 
 
 
 
 O 
 
 
 
 O 
 
 o 
 
 
 2 10 
 
 93 
 
 91 
 
 72 
 
 72 
 
 72 
 
 72 
 
 72 
 
 74 
 
 73 
 
 
 20 
 
 9" 
 
 92 
 
 72 
 
 72 
 
 72 
 
 74 
 
 74 
 
 74 
 
 73 
 
 
 3 
 
 90 91 
 
 7' 
 
 7" 
 
 72 
 
 72 
 
 74 
 
 74 
 
 74 
 
 
 40 
 
 90 91 
 
 7' 
 
 7 
 
 72 
 
 72 
 
 74 
 
 74 
 
 74 
 
 
 5 
 
 92 
 
 93 
 
 7 
 
 7 
 
 72 
 
 74 
 
 74 
 
 74 
 
 74 
 
 
 "? o 
 
 96 
 
 95 
 
 70 
 
 7i 
 
 72 
 
 74 
 
 74 
 
 74 
 
 74 
 
 
 IO 
 
 96 
 
 95 
 
 7' 
 
 72 
 
 72 
 
 74 
 
 74 
 
 74 
 
 74 
 
 
 20 
 
 96 
 
 96 
 
 7i 
 
 72 
 
 72 
 
 74 
 
 74 
 
 74 
 
 74 
 
 
 30 \ 
 
 
 
 
 
 
 
 
 
 
 Thermometers moved. 
 
 40 / 
 
 
 
 
 
 
 
 
 
 
 
 5 
 
 90 
 
 9' 
 
 7 
 
 72 
 
 72 
 
 73 
 
 73^ 
 
 73'/2 
 
 73^ 
 
 Beginning of eclipse. 
 
 4 o 
 
 gg 
 
 90 
 
 70 
 
 7i 
 
 7 
 
 72 
 
 73 
 
 73 
 
 73 
 
 
 10 
 
 86 
 
 88 
 
 69 
 
 70 
 
 72 
 
 72 
 
 72^ 
 
 72^ 
 
 72^ 
 
 
 20 
 
 84 
 
 85 
 
 69 
 
 70 
 
 70 
 
 72 
 
 72 
 
 72 
 
 72 
 
 
 3 
 
 76 
 
 78* 
 
 68 
 
 68 
 
 69 
 
 70 
 
 70 
 
 7' 
 
 7' 
 
 
 4 
 
 
 
 
 
 
 
 
 
 
 
 5 
 
 7 
 
 7' 
 
 65 
 
 66 
 
 68 
 
 68 
 
 6g 
 
 68 
 
 68 
 
 Before totality. 
 
 5 
 
 67 
 
 68 
 
 64 
 
 65 
 
 68 
 
 68 
 
 6g 
 
 68 
 
 68 
 
 After totality. 
 
 10 
 
 70 
 
 7i 
 
 64 
 
 64 
 
 65 
 
 66 
 
 66^ 
 
 68 
 
 68 
 
 
 20 
 
 74 
 
 75 
 
 64 
 
 64 
 
 65 
 
 66 
 
 68 
 
 68 
 
 68 
 
 
 3 
 
 73 
 
 76 
 
 66 
 
 66 
 
 65 
 
 68 
 
 68 
 
 68 
 
 68 
 
 
 40 
 
 78 
 
 80 
 
 64 
 
 64 
 
 66 
 
 66 
 
 68 
 
 68 
 
 68 
 
 
 50 
 
 78 
 
 80 
 
 64 
 
 66 
 
 66 
 
 68 
 
 68 
 
 68 
 
 68 
 
 End of eclipse. 
 
 6 o 
 
 74 
 
 75 
 
 64 
 
 64 
 
 66 
 
 67 
 
 68 
 
 68 
 
 68 
 
 
 Barometric observations by Mr. Peters. 
 
 These may be useful as indicating to some extent the changes of the aneroid 
 barometer which was used, its index-error not having been determined. 
 
 ig6 9 . 
 
 An. barometer. 
 
 Ig6g. 
 
 An. barometer. 
 
 Remarks. 
 
 h. m. 
 
 in. 
 
 h. m. 
 
 in. 
 
 
 August 5. 6 o a. m. 
 
 29.25 
 
 August 7. 3 15 p. m. 
 
 29-44 
 
 
 5 45 P- m - 
 
 . 22 
 
 3 3 P- " 
 
 44 
 
 
 6. 5 30 a. m. 
 2 10 p. m. 
 
 . 20 
 3' 
 
 3 45 P- m. 
 4 o p. m. 
 
 42 
 42 
 
 Beginning of eclipse. 
 
 7. 703. m. 
 
 .48 
 
 4 15 P- m - 
 
 42 
 
 
 g 30 a. m. 
 
 5 
 
 4 30 p. m. 
 
 .42 
 
 
 i o p. m. 
 
 .48 
 
 4 45 p. m. 
 
 .42 
 
 
 2 o p. m. 
 
 .46 
 
 5 o p. m. 
 
 .40 
 
 Total eclipse. 
 
 2 15 p. m. 
 
 .46 
 
 5 15 p.m. 
 
 .40 
 
 
 2 30 p. m. 
 
 44 
 
 5 3P- m - 
 
 .40 
 
 
 2 45 p. m. 
 3 o p. m. 
 
 44 
 44 
 
 5 45 P- m - 
 6 o p. m. 
 
 .40 
 29.40 
 
 End of eclipse. 
 
110 ECLIPSE OP THE SUN, AUGUST 7, 1869. 
 
 OBSERVATIONS FOE LATITUDE OF OBSERVATORY HILL, OTTUMWA. 
 
 These have been exclusively confined to altitudes of the sun; and because of 
 his northern declination, were obliged to be more extra-meridian than was at all 
 desirable. But the interruptions occasioned by the whole two days' storm of the 5th 
 and 6th of the month, and clouds and other interruptions at night afterwards, pre- 
 vented any successful observations north of the zenith, except one of Polaris, and that 
 ill-conditioned. The results consequently must be affected by error in centering of 
 sextant, as well as some uncertainties of refraction, &c. Eight observations of the alti- 
 tude of the sun's lower limb, on the 4th of the month, gave for the latitude, 
 
 + 40 58' 33".o; 
 and ten observations of altitude of the upper limb gave for the latitude, 
 
 + 40 58' 21^.45* 
 
 half weight being allowed to two observations in each case, which differed unduly 
 from the mean. 
 
 The mean of both results is: 
 
 + 40 58' 27"-2; 
 
 and the same is the mean of the whole eighteen observations. Yet four observations 
 of the lower limb and three of the upper limb on the gth give a mean of 41 o' 22" ; two 
 other observations being rejected for their great discrepancy from the means of the 
 others. 
 
 The double altitudes were in this case near to the extreme limit of 1 20, where 
 the arc may have been slightly bent, or its graduation faulty. It is, moreover, possible 
 that the bottom of the basin containing the oil used to give the artificial horizon may 
 have interfered by its reflection, as it was not everywhere sufficiently blackened. The 
 pent-house [roof] covering the horizon has been tested, without an indication of any 
 marked discrepancy, when ends are interchanged in their position with regard to the 
 observer. 
 
 When the times, by single altitudes, are separately computed and compared (as 
 they have been largely for different days) with those deduced by corresponding alti- 
 tudes, the latitude deduced on the 4th being employed, the coincidence is close (the 
 effect of the error in centering being nearly the same for both). 
 
 The first result (the mean of observations on the 4th) seems to be preferable ; 
 and as far as these necessarily imperfect determinations can indicate we should not 
 admit the latitude of our position to be greater than 40 59', or that of the center of 
 the city more than 40 58^'. Its latitude by estimate, heretofore, seems to have been 
 
 41 3' or 4'. 
 
 The report of the comparison with Burlington of telegraphic signals for longitude 
 has been already transmitted.! 
 
 Very respectfully, your obedient servant, 
 
 STEPHEN ALEXANDER, 
 
 PRINCETON, December, 1869. 
 Prof. JOHN H. C. COFFIN, 
 
 Superintendent American Ephemeris and Nautical Almanac. 
 
 "The result from double altitudes for time is given hereafter. C. 
 tTho results are included in tables on pages 16 and 17. 
 
SUPPLEMENTAL REPORT BY PROF. J. H. C. COFFIN. 
 
 OBSERVATIONS FOR TIME AND LONGITUDE OP OTTUMWA. 
 
 Professor Alexander's observations for time at Ottumwa were made with a sextant 
 and artificial horizon. Each set consisted of altitudes, of each limb and the center of 
 the sun, observed with the same reading of the sextant. The index correction 
 -25' 13", found by coincidence of the direct and reflected images of the sun, was 
 regarded as constant. The P. M. observations of each day were in part of the same 
 altitudes as the A. M. observations. I have, however, reduced all the observations 
 separatelv with the assumed latitudes +40 58' 30". 
 
 August 3. Five sets A. M. and two sets P. M. observations. 
 
 To reconcile the A. M. observations, it is necessary to suppose the sextant reading of the 1st set to be 1' too 
 small, and of the 3d and 4th, to be 1' too great. The two sets of P. M. observations can be reconciled by supposing 
 the sextant reading of the 1st sot, which corresponds to the 2d A. M. set, to be 1' too great. The A. M. and P. M. ob- 
 servations may then be more fully reconciled by diminishing the latitude 42", or the altitudes 14". 
 
 August 4. Five sets of A. M. and five sets of corresponding P. M. 
 
 The P. M. observations agree if the sextant reading for the 2d set is supposed to be 1' too great, and that for 
 the 5th to be 1' too small. The A. M, and P. M. observations are further reconciled by diminishing the latitude 35", or 
 the altitudes 8". 
 
 August 7. Six sets of altitudes were observed at 10 a. m. 
 
 These observations give as the correction of Chronometer Daniels yfo, -f 5 52' 2".0 + O.060 A L + OM07 A 
 A, A L and A h being corrections, respectively, of the latitude and altitudes in seconds. 
 
 August 9. Five sets of A. M. and four sets of P. M. observations. 
 
 They are reconciled by supposing the sextant readings for the 5th A. M. and the corresponding 1st P. M. sets 
 to be each 1' too small ; and more closely agree by diminishing the latitude 24", or the altitudes 8". 
 
 Occasionally on each day there was obviously an error of io 8 in noting time, 
 which has been corrected. 
 
 Correcting the altitudes as indicated, the latitude found by combining the A. M. 
 and P. M. observations is: 
 
 August 3, + 40 57' 48" 
 4, 57 55 
 
 9, 58 6 
 
 Mean, + 40 57' 56" 
 
 This combined with + 40 58' 27", obtained by Professor Alexander from his 
 observations for latitude on August 4 (page i io), gives as the concluded latitude of the 
 eclipse station, -f 40 58' 12". 
 
 The following are the results of the time observations (that for August 7 being 
 corrected for A L 18"), combined with the chronometer corrections in the table, 
 page r6; found by comparisons with Hutton 202. 
 
112 
 
 ECLIPSE OP THE SUN, AUGUST 7, 1869. 
 
 Chronometer Daniels j-fy. 
 
 Date. 
 
 Corrections referred to 
 Ottumwa mean time. 
 
 Corrections referred to 
 Burlington mean time. 
 
 Longitude from Bur- 
 lington. 
 
 h. 
 
 h. m. s. 
 
 h. m. s. 
 
 m. s. 
 
 August 3 o 
 
 + 5 51 54- 2 
 
 + 5 57 2-9 
 
 5 8-7 
 
 4 o 
 
 57.6 
 
 4-5 
 
 6.9 
 
 6 22 
 
 60. 9 
 
 5-9 
 
 5.0 
 
 9 o 
 
 61.7 
 
 8-3 
 
 6.6 
 
 Giving half weight to August 3 and August 6, the mean difference of longitude 
 is 5 6 8 .8, Ottumwa W. of Burlington. 
 
 From comparisons of Chronometer Negus 2335 with Daniels ~, and from the 
 table p. 1 7, using the variable rate stated at the bottom, the longitude deduced is 5 m 7". 0. 
 But as this is not independent of that from Chron. -^ and the rate of 2355 is quite 
 irregular, I have adopted 
 
 Ottumwa, o h 5 m 6".8 west of Burlington, 
 
 i i 20.5 =. 15 20' 8" west of Washington. 
 6 9 32.6 92 23 9 west of Greenwich. 
 
 J. H. C. COFFIN. 
 
It E P OUTS 
 
 PHILADELPHIA PHOTOGRAPHIC EXPEDITION. 
 
 PltOF. HENRY MORTON. 
 
 PEOF. A. M. MEYER, 
 
 liurlington, Iowa. 
 
 PEOF. C. F. HIMES, 
 
 Ottumwa, Iowa. 
 
 113 
 
 15 E s 
 
REPORTS OF THE PHILADELPHIA PHOTOGRAPHIC EXPEDITION.* 
 
 REPORT OF PROF. HENRY MORTON, Ph. D. 
 
 '. PHILADKLPHIA, August 18, 1869. 
 
 SIR: On receipt of your letter of May 3, in which you proposed that I should 
 undertake the organization and conduct of a party to make photographic observations 
 of the total eclipse of August 7, I proceeded to make inquiry as to the material which 
 might be available for the purpose and, in concert with and assisted by yourself and 
 Prof. E. 0. Kendall, found that \ve might readily procure two fine Munich Equatorials 
 of 6-inch aperture, and with clockwork, belonging, respectively, to the high school of 
 this city and the Pennsylvania College at Gettysburg, and also an excellent Dollond 
 of 4-inch aperture equatorially mounted, but without clockwork, belonging to the 
 University of Pennsylvania, in this city. 
 
 On further consultation with yourself, it was concluded that, on account of the 
 risk of local clouds, it would be desirable, if possible, to take all these instruments and 
 distribute them over some distance on or near the central line. 
 
 On careful reflection, I came to the conclusion that at least five skilled operators 
 would be necessary to each instrument, and that, therefore, something must be done 
 to diminish the expense of transportation, or the Government appropriation available 
 for this department of the general eclipse observations would be insufficient. 
 
 It also appeared that some arrangement by which trans-shipment of the numerous 
 weighty and delicate pieces of apparatus might be avoided would be highly condu- 
 cive to success and security. 
 
 I therefore called upon my friend, Mr. R. H. Lamborn, secretary of the American 
 Steel Manufacturing Company, whose extensive connection with our great lines of 
 interior transportation would give him opportunity of affording the best advice, and 
 explained to him my ideas. He went with me at once to Col. Thomas A. Scott, vice- 
 president of the Pennsylvania Central Railroad, and stated the case to him with ad- 
 mirable brevity and precision. 
 
 Colonel Scott, with the greatest kindness, acceeded at once to our request, and 
 promised to provide us with a special car, from which some seats should be removed 
 to accommodate our apparatus, and which should go with us to the end of our route, 
 and there remain until our return. Free transportation over the entire route of the 
 Pennsylvania Central and Fort Wayne Railroads (i. e., as far as Chicago) for our 
 party, and several others besides, was included in or added to this generous gift. 
 
 I then wrote to Mr. Robert Harris, of Chicago, general superintendent of the 
 Chicago, Burlington and Quincy Railroad, asking him to forward our car and its con- 
 tents over the road in his charge. To this he also most kindly agreed, and, although 
 
 " These reports were published iu the Journal of the Franklin Institute for September and October, 1869, and 
 are here reproduced with revisions made in January, 1871. All additions and important changes are noted. C. 
 
 115 
 
116 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 it will anticipate subsequent events, I may as well say in this place that this gentleman 
 also facilitated our movements in every way, sending a locomotive to meet us at the 
 intersection of his road with the Pittsburgh, Fort Wayne and Chicago line, and carrying 
 us to the depot for Burlington on our way out, and transferring our vehicle again on 
 our return journey. Mr. Norton, from Mr. Harris's office, also met us at the junction, 
 to explain the proposed disposition, and kindly acted as our guide through the city. 
 
 Provision being thus made for transportation, by which an expense of about $1,500 
 was spared to the Government appropriation, the plan of taking out a triple party 
 became feasible, and was accordingly adopted. 
 
 The next point was the selection of the party, and this was proceeded with at 
 once, communications being exchanged with many of our leading photographers and 
 others, to learn their views and inclination. It was soon found that an excellent selec- 
 tion might be had from among those whose position or engagements would allow them 
 to volunteer without other compensation than the moral one contingent on success, 
 and, after a few changes rendered necessary by sickness or other inevitable cause, the 
 party, as finally constituted, consisted of Prof A. M. Mayer, Ph. 1).; Prof. C. F. 
 Himes, Ph. D.; Messrs. J. Zentmayer, O. H. Willard, E. L.' Wilson, H. C. Phillips, E. 
 Moelling, J. C. Browne, W. J. Baker, James Cremer, H. W. Clifford, O. H. Kendall, 
 J. Mahoney, W. V. Ranger. 
 
 We were also joined, as volunteers, on the ground, by Mr. John Carbutt, of 
 Chicago, and Mr. Miles Rock, of Bethlehem, Pa., and Mr. Leisenring, of Burlington. 
 Professor Coffin having suggested that some general physical observations should be 
 carried out in connection with this party, I applied to Prof. E. C. Pickering, of the 
 Massachusetts Institute of Technology, Boston, who consented to take charge of these, 
 and accompanied us to Mount Pleasant, Iowa, as will be seen from a subsequent por- 
 tion of this report. Prof. James McClune, of the Philadelphia Central High School, 
 and Prof. S. G. Gummere, also accompanied the expedition, and were stationed at 
 Oscaloosa. 
 
 The next point to which attention was directed, was the arrangement of the instru- 
 ments for their photographic work. It was a question of much moment to decide 
 whether we would follow the plan adopted by the French and German expeditions of 
 last year, and make the photograph iTl the principal focus of the object-glass, thus 
 securing great intensity of light in a small image, or follow the method employed by 
 De la Rue in 1 860, when he used an ordinary Huygenian eye-piece so placed as to 
 produce an enlargement of the first image from the objective. 
 
 After a careful study of De la Rue's report and pictures, as also those of the later 
 expeditions, I came to the conclusion that the plan of enlargement presented many 
 advantages, and should be followed by us with certain modifications, which I will 
 proceed to describe 
 
 The work of designing and constructing these lenses, and also the different attach- 
 ments to the cameras for securing exposures of various degrees of rapidity, from a 
 very small fraction of a second to any desired length, was placed in the hands of Mr. 
 Joseph Zentmayer, whose extended scientific attainments, combined with unrivaled 
 skill in the construction of optical instruments, peculiarly fitted him for such a task. 
 
REPORT OF THE PHILADELPHIA PHOTOGRAPHIC EXPEDITION. 
 
 117 
 
 The camera, as finished, is represented in the accompanying woodcut, which shows 
 it as seen from directly in front. 
 
 Here A is represents the face-plate of the camera, to which the eye-piece tul>e was 
 attached, its other end being screwed to the telescope. The diaphragm plate D E, 
 moved across the axis of the instrument, being drawn downwards by the combined 
 spring E K. The strength of this spring could be reduced by raising the outer end of 
 one or both the upper strips so as to disengage the forks at their end from the lower 
 spring, and then turning them forward in a direction normal to the front of the box, 
 out of the way. 
 
 The spring was attached to the diaphragm plate by a swivel hook, which, while 
 in no instance falling out, could be detached and readjusted with the greatest facility. 
 
 A number of diaphragm plates were provided, with slits respectively of -i, ~, -i, 
 and ^ of an inch in width. These plates could be readily interchanged, and, in 
 combination with the springs,- gave a very wide and yet delicate series of fixed 
 adjustments for the times of exposure. 
 
 To make the exposure, the plate was drawn up until the projecting pin D could 
 be caught on the lever K, which would then retain it. On depressing the outer end 
 of this lever, however, with the finger, the hold on the pin was disengaged, and the 
 plate flashed across the axis_of the tube, allowing light to traverse the narrow slit as 
 it flew past. The plate was then arrested on the end of the second lever G. When 
 an exposure of some seconds was required, as during the totality, a plate, having a round 
 orifice exposing the entire field of the eye-piece was substituted for the one with the 
 narrow slit, and was so arranged that, when caught by the upper lever, it covered the 
 lens, but when fallen to the second lever exposed it entirely; when, however, this 
 lever was in turn touched, the plate descended again far enough once more to close the 
 lens. By touching these two levers in succession it was then possible to make a "time 
 
118 ECLIPSE OP THE SUN, AUGUST 7, 18C9. 
 
 exposure" with great nicety and accuracy, as proved by actual experience during the 
 eclipse. 
 
 To secure a chronographic record of each exposure a binding screw was provided, 
 to make one connection with the general mass of the face-plate, including lever K, and 
 another at L, to carry on the circuit when the downward motion of the lever brought 
 the spring at its side in contact with the point projecting from L. In raising the lever 
 for a new exposure, the spring at its side was pressed back so as to pass the point 
 without contact. A more substantial break-piece would have been made had time 
 allowed, but this was found to operate in a perfectly satisfactory manner. 
 
 As the operation of the eye-piece, when employed to produce an image on the 
 screen or ground glass of a camera, is essentially different from that which it performs 
 in its usual office, it was judged best by Mr. Zentmayer to make some alterations in 
 its form. Thus, in the first place, since in the present case the ."eye-lens" of the eye- 
 piece undoubtedly makes a, secondary image of the primary image formed within the 
 eye piece by the combined action of the objective and the field lens of the eye-piece, 
 it is clearly desirable to make this lens of a longer focus than usual, so that its errors 
 may be of less account. It was also essential to give the new eye-piece a wide angle, 
 so as to secure a sufficient field not only for the solar disk, but also for the corona. 
 
 While, therefore, the ratio of focal lengths in the two lenses of the ordinary eye- 
 piece is usually 1-3, it was in this case as 1-2. While the distance between the lenses 
 is usually the sum of their focal lengths divided by 2, it was here made equal to the 
 sum of the focal lengths divided by 2 plus .24 inch. This was to give space for the 
 introduction of the reticule of spider-lines, which would otherwise have been brought 
 too near the field lens, and also to keep this lens beyond the conjugate focus of the 
 eye lens, as otherwise particles of dust on the former would have been too faithfully 
 portrayed by the latter. 
 
 The elements actually adopted were as follows: 
 
 ft. in. 
 
 Focal length of objective 8 6. 
 
 Radius of field lens '-375 
 
 Radius of eye lens 0.687 
 
 Focus of field lens 2.6 
 
 Diameter of field lens (zrR) 1-375 
 
 Focus of eye lens 1.3 
 
 Diameter of eye lens ( zzR) 0.687 
 
 Distance between lenses, 1.95+0.25 2.2 
 
 Equivalent 1.75 
 
 Distance of reticule from eye lens for 5-inch distance of ground glass . 1.62 
 
 The reticule was mounted on a short tube with a fine thread on the outside 
 running in a corresponding thread on the inside of the eye-piece tube. This being 
 approximately adjusted beforehand, was moved to its exact place by turning it with a 
 sharp point through a little slot cut in the eye-piece tube. 
 
 One of the cameras with its eye-piece, being finished, experiments were at once 
 made with the telescope of the University of Pennsylvania, which, by reason of its 
 
KKL'OliT OF THE PHILADELPHIA PHOTOGRAPHIC EXPEDITION. 119 
 
 smaller size, was most readily available for such purpose. These were conducted by 
 Mr. Willard, Mr. Zentmayer, and myself, at the establishment of Mr. Willard, 1 206 
 Chestnut street, where all conveniences for the work were at hand, and were of the 
 greatest value in affording data on which the construction of the other apparatus could 
 be based. 
 
 It was found that, with a clear sun, it was necessary to reduce the ap*erture of this 
 telescope (which was 4 inches, with 50 inches focus), to if> inches, and to use all three 
 springs and the diaphragm-slide of / inch aperture, in order to get a proper exposure 
 when the solar image was enlarged from 6. incli (its diameter at the principal focus of 
 the objective) to 2\ inches on the ground glass. The same size of aperture was adopted 
 for the larger instruments during the partial phases, the entire aperture, in all cases, 
 of course, being used during totality. 
 
 There being no place in the city where the larger instruments could, with con- 
 venience, be set up, adjusted, and practiced with by the party who were to use them, 
 I applied to Mr. John Sellers for permission to use a very conveniently located portion 
 of his grounds in West Philadelphia, and having prepared a design for a temporary 
 building (with roof, in part, removable by sliding), caused it to be erected, and had 
 the large instruments set up in it. 
 
 Matters being thus far advanced, Prof. A. M. Mayer, Ph. D., of the Lehigh Uni- 
 versity, Bethlehem, Pa., who had agreed to join our party, came down to the city and 
 spent some days here, during which the telescopes were adjusted by him, in a very 
 perfect manner, by a rapid and convenient method, which has been made the subject 
 of a full discussion by him, as will be seen in his own report appended hereto. 
 
 A number of experiments were made by Mr. Willard, at this time, in photograph- 
 ing the moon, which were of great value in settling the time of exposure which would 
 probably be required in the total phase. 
 
 He found that a good impression could be obtained of the full moon in about one 
 minute, and that an abundantly strong one could be secured with an exposure of three 
 minutes. From this and the deductions of De la Rue, that the light of the promi- 
 nences was 1 80 times as great as that of the full moon, it appeared that an exposure 
 of from \ of a second to 1 second, during totality, would have been sufficient to secure 
 images of these bodies. For the corona, of course a much longer exposure would be 
 required, but no estimate could be made as to what would be its duration. 
 
 In connection with these experiments, it is but just that I should call attention to 
 the unwearied patience and enthusiastic energy with which Mr. Willard devoted him- 
 self to the prosecution of this preliminary work. Day and night, whenever any 
 observations were to be made, or any experiments tried, he was on the ground, and 
 on certain occasions displayed an energy and determination, combined with sound 
 judgment, seldom to be encountered. Thus, it becoming desirable to shift the position 
 of the building in which the telescopes were placed, he arranged and accomplished this 
 in a most successful manner, though the operation was considered, by the professional 
 builders present, impossible without derangement of the instruments. 
 
 Mr 0. H. Kendall also rendered invaluable services in connection with the pre- 
 liminary arrangements. 
 
120 ECLIPSE OF T1IK SUN, AUGUST 7, ISli'.i. 
 
 Much interruption was experienced from bad weather after this, but the rainy 
 days were utilized by Mr. Zentmayer in putting the driving 1 clocks of both instruments 
 (which were in very bad order) in admirable adjustment, so that, on the few occasions 
 that the sun did shine, enough work was done by the rest of the party to make them 
 familiar with the necessary manipulations. 
 
 The instruments were dismounted, boxed, and packed in the special car furnished 
 us by Colonel Scott, on Saturday, July 31, when it was found that, with the various 
 photographic appliances, they made no less than five furniture cart loads of material. 
 
 On Monday, August 2, we started, and on Wednesday, the 4th, about noon, 
 reached Burlington, Iowa, on the bank of the Mississippi. 
 
 In arranging the division of our party into three sections, with the three tele- 
 scopes, so that they might be distributed along the line of totality, and thus diminish 
 the chance of universal extinction by local clouds, I was chiefly guided by the desire 
 of securing in each section such a diversity of special ability as might make each self- 
 dependent and complete ; also, to leave nothing undone to secure content and harmony 
 of feeling. I assigned myself to the University telescope, which, being of smaller size, 
 and without clock-work movement, coul,d not be expected to do as good work as the 
 others; though, should they by chance be overclouded, its result would be invaluable. 
 
 I therefore divided the party as follows : 
 
 With the High School telescope, 6-inch aperture, 9 feet focal length, Prof. A. M. 
 Mayer, Ph. D., and Mr. O. H. Kendall in charge of the adjustment of the instrument 
 and management of the apparatus for exposures, and Messrs. O. H. Willard, H. C. 
 Phillips, and J. Mahoney having charge of the entire photographic work. This sec- 
 tion was stationed at Burlington, 40 48' 20" N., o 1 ' 56 13" West of Washington. 
 
 With the Gettysburg telescope, 6-inch aperture, 8 feet focal length, Prof. C. F. 
 Himes, Mr. J. Zentmayer, and Mr. E. Moelling, in charge of the instrument, &c., and Mr. 
 J. C. Browne and Mr. W. J. Baker, who managed all the photographic processes. This 
 party was stationed at Ottumwa, about seventy-five miles nearly west of Burlington. 
 
 With the University telescopes were Mr. E. L. Wilson, and myself, in charge of 
 the instrument, and Messrs. H. W. Clifford, James Cremer, and W. V. Ranger, as pho- 
 tographers. We were also joined by Mr. John Corbutt, of Chicago, as a volunteer, 
 who gave us most efficient aid. This section was placed at Mount Pleasant, between 
 the other stations. The various parties having reached their destinations during Wed- 
 nesday, arrangements were at once made to get the instruments into position in the 
 locations previously prepared by Professor Coffin. In the case of the Burlington 
 party, all went smoothly, and the dark weather alone prevented final adjustment until 
 the night of the 6th or morning of the 7th, when this was secured with great nicety 
 by Professor Mayer, who sat up all night for the purpose. 
 
 With the Ottumwa instrument it was, however, found that the clockwork had 
 become seriously deranged in carriage, so that Mr. Zentmayer was obliged to take it 
 entirely apart and refit it. This he accomplished with great. success, and it may be 
 regarded as one of our many pieces of providential good fortune, that since one of 
 the clocks was to go wrong on the journey, it was that one which was within reach of 
 this gentleman's skill. The trouble and anxiety which this cause of delay occasioned, 
 
REPOKT OF THE PHILADELPHIA PHOTOGRAPHIC EXPEDITION. 
 
 was, however, no small trial of fortitude to the Ottumwa party. The final adjustment 
 was also given to this instrument during the morning of the 7th, by Mr. Zentmayer, 
 who had watched all night, vainly, for a star. 
 
 This party, beside the above-mentioned difficulties, were unable to obtain any ex- 
 pert assistance on the ground, from resident photographers and others, as was done by 
 both the other divisions, so that they were left entirely to their own resources, and 
 acquitted themselves, under the exceptional difficulties of their position, in a most 
 creditable manner. 
 
 In this connection, special reference should be made to Prof. C. F. Himes, who, 
 by his skill, judgment, and coolness in a serious emergency (occasioned by accidental 
 derangement of the chronograph attached to the telescope), preserved the record of 
 this series of pictures which must otherwise have been in great part lost. 
 
 The telescope at Mount Pleasant having no clockwork, and being otherwise unfit 
 for any fine adjustment, required no arrangement, except what could be given during 
 the morning of the 7th. 
 
 As all know, the weather on the eventful day of the eclipse was, at all our 
 stations, perfect, so rendering needless, but none the less judicious, our policy of 
 distribution. 
 
 At the. Burlington station, a photographic record of the first contact was secured, 
 by exposing plates, in rapid succession, about the calculated time. A very good result 
 was thus obtained. 
 
 At Mount Pleasant, we placed a plate ready in the camera, and then waited a 
 signal from Professor Watson, of the University of Michigan, who, with his party, 
 was on the ground with us, and was watching for the first contact. We thus obtained 
 a picture showing a very slight indentation. By measurement of this, the time of actual 
 first contact can be reached by calculation, yet more precisely than would be possible 
 with any eye observation. 
 
 During the partial phases, accurately timed exposures were made by all parties, 
 at intervals varying from a few seconds to ten minutes. 
 
 PARTIAL PHASE PICTURES.* 
 
 These pictures are chiefly of interest in a photographic point of view, as showing 
 the accurate adjustment of the several instruments, and the excellent condition of the 
 photographic material as well as the precision of the various manipulations. 
 
 The serrated character of the moon's edge is clearly manifest, and the same promi- 
 nent peak or ridge may be readily identified throughout an entire series of pictures. 
 
 In the negative, taken immediately after first contact at Burlington, a prominent 
 mountain, producing a notch in the solar edges is perhaps the most conspicuous 
 indication of the contact. 
 
 I have selected an enlargement from negative No. 21, taken at Burlington, as a 
 specimen of this partial phase pictures, because it combines most satisfactorily several 
 features of interest. It is given in Plate IX. 
 
 The serrated lunar edge, the well-defined sun spot with its border of faculse, and 
 
 * This article supplied in Jauuary, 1871. C. 
 16 E S 
 
122 ECLIPSE OF THE SUN, AUGUST 7, ISfii). 
 
 the irregular masses of faculons matter at other points, and the strange light band or 
 glow adjoining the lunar edge, are remarkably distinct. 
 
 As regards the cause of this last-mentioned phenomenon, a careful inspection of 
 the original negatives convinced me at once (as stated in a rough draft of this report 
 published in the Journal of the Franklin Institute for September, 1869) that it was 
 "a question of deposited silver and not contrast of light and shade." 
 
 A similar phenomenon was noticed by Prof. Stephen Alexander in 1831 and 1860, 
 and also by Mr. De la Rue in his pictures of the latter date. Professor Alexander and 
 Professor Challis* considered this as evidence of a lunar atmosphere. Mr. De la Rue, 
 and the Astronomer Royal of England, Mr. Airy, however, agreed in ranking this as 
 a peculiar effect of contrast, and Mr. Airy had shown f that no such effect would be 
 produced by a lunar atmosphere if it were present. 
 
 A repetition of the experiments suggested by the Astronomer Royal and Mr. De 
 la Rue to prove the subjective nature of the phenomenon failed to produce the effect 
 described by them, in a satisfactory manner, thus proving that the subjective theory 
 was insufficient to explain the entire phenomenon as exhibited in tlicsc. pictures. 
 
 I have, therefore, made the following experiments, which I believe will aid in 
 throwing light upon this obscure subject. 
 
 I converted an enlarged print from one of the solar pictures taken soon after first 
 contact into a crescent by pasting partly over it a circular piece of dark paper taken 
 from the background of another print. This exhibited a very faint band of light, 
 such as might be expected to result from contrast with the sharply denned dark edge, 
 but which in no way approached in intensity or extent the bright line found on the 
 prints of the actual eclipse negatives. 
 
 I then had this artificial eclipse-picture photographed (through the kindness of 
 Mr. James Cramer, one of the members of our party,) when negatives were produced, 
 showing a dense deposit along the lunar edge, and giving prints which showed a 
 "bright line" in the same place fully equal, and in some cases even superior, in intensity 
 to that produced by the eclipse negatives. 
 
 From this it would appear that the cause of the bright line was to be sought, not 
 in the heavens, but in the camera or photographic manipulations. 
 
 The explanation which at first suggested itself, and was published by me at the 
 time, was the following : 
 
 It is well known that the development of a negative depends upon the presence 
 of free nitrate of silver in the film, and that a great strengthening or intensifying may 
 be produced by re-immersion in the silver bath, and a repeated application of the 
 developer. In the case before us, that part of the plate representing the dark disk of 
 the moon, and therefore not acted upon, furnishes a reservoir of nitrate of silver, 
 imbibed by the film which, during the development, penetrates for a short distance 
 into the portion representing the luminous surface of the sun, whose supply of free 
 nitrate was exhausted by the reaction which occurred on the first application of the 
 developer. A similar action no doubt occurs on the outer margin of the sun, but it 
 can there only diminish the graduated shade which we know to exist in that part. 
 
 * Monthly notices of the Royal Astronomical Society, 1863, p. 234. 
 
 t Monthly notices of the Royal Astronomical Society, 1863, November 13, and 1864, June 10. 
 
KEPORT OF THE PHILADELPHIA PHOTOGRAPHIC EXPEDITION. 123 
 
 A number of ingenious experiments made by Dr. Edward Curtis, of New York, 
 and which he has communicated to me, have drawn my attention to other points, and 
 have led me to make further trials, which in conjunction with his results have convinced 
 ine that the r/ututtittj of tree nitrate of silver in connection with the sfre>if/th of the 
 actinic action to which the film was exposed, and lastly the drainage of the plate 
 during exposure, exerted very important modifying influences in the production or 
 non-appearance of the "bright line." Thus suppose that in a given case the actinic 
 impression was so faint as compared with the amount of free nitrate present that there 
 is a large excess of the latter everywhere present at the end of the exposure, no line 
 will be developed. If, on the other hand, during the exposure the actinic influence 
 is sufficiently strong to exhaust the capacity for impression .in any part of the 
 plate, then the drainage over this part of free nitrate will tend to develop an increased 
 deposit in such parts as it reaches, or an infiltration in a lateral direction may have 
 a like effect. I have thus observed in several cases a marked increase of the bright 
 lines in a vertical direction as regards the position of the plate when in the camera. 
 
 As regards the absence of the bright line, I have found it invariably wanting when 
 a short exposure was made on a plate fresh from the bath, and Dr. Curtis has obtained 
 on the same stereoscopic plate one image of an object with the "bright band," and 
 another without the exposures being simultaneous, but the lens which gave no band 
 being reduced in aperture. 
 
 I would then conclude that the phenomenon of the "bright band" so conspicu- 
 ously illustrated in the accompanying impression is one of photo-chemical origin, and 
 originates in the sensitive film during its employment, but that it depends upon the 
 co-existence of several conditions and may either be absent or suffer certain special 
 modifications as these vary. 
 
 TOTALITY PICTURES : THE PROMINENCES. 
 
 During the totality thirteen pictures in all were taken with the three instruments. 
 Of these six were made at Burlington, with exposures of five to seven seconds; four 
 were made at Ottumwa, with times of exposure ranging from six seconds to sixteen.* 
 
 These are all admirable negatives, which show abundant detail, and, in some 
 cases, much of the corona. Three pictures in totality were also made at Mount Pleasant, 
 but, for want of a clock-movement, are of little value. One of the Ottumwa pictures, 
 exposed at the very last instant before totality, gives a photographic record of the 
 curioiis phenomenon known as Bailly's beads, being simply the last glimpse of the 
 sun's edge cut by the peaks of lunar mountains into irregular spots. 
 
 One of the objects which it was considered desirable to secure, if possible, was 
 a view of the "corona. It was with this intent that some of the exposures were made 
 so long. 
 
 Examination of the negatives shows us that five seconds was more than sufficient 
 to secure all the details of the protuberances, although it gave no decided indication 
 of the corona. 
 
 The development proceeded slowly in all but a few spots where very massive 
 
 'Two of the Burlington and three of the Ottumwa pictures are given it. Plates IV to VIII. C. 
 
[24 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 prominences were located, and thus it was not thought, at the moment, judicious to 
 try shorter exposures; but, in the light of our present experience, we would judge 
 that exposures of even one or two seconds, with persistent development, such as could 
 be best carried out on albumeni/ed plates, would be of value to secure details in the 
 rounded and massive prominences which appear at some points. 
 
 The most conspicuous prominence (see Plate X, Fig. i) is that which, at a hasty 
 glance, seems to resemble the letter X, but, on more careful inspection, is perceived 
 to be like an ear of corn. It consists of a solid central mass inclined at an angle of 
 about 45 to the normal at the solar surface, and with three branches from near its 
 end, one sweeping backwards in a direction generally parallel to the solar surface, 
 another forward, as concerns the direction of the general mass, and a third branching 
 out a little below and running in the same direction as this last. The appearance of 
 the main body, which is of a spindle shape, and with spiral markings, is highly sug- 
 gestive of a vortical motion which has swept these whiffs of light matter into their 
 peculiar positions. 
 
 It was believed by several observers that this object moved rapidly while they 
 were watching it; but as the same positions are shown in the eight different negatives 
 (taken at Burlington and Ottumwa) which contain it, there can be no doubt of its per- 
 manent character. 
 
 It appears, however, beyond doubt that motion, amid the light surrounding the 
 sun, was observed, as there is much accordant testimony on the subject. But this 
 motion, as we shall presently see, there is every reason to believe existed in the 
 corona, and not in the prominences, which, however, might easily have the appear- 
 ance of movement, if seen against a background of shifting light. To this subject 
 we shall refer again when speaking of the corona. 
 
 Immediately to the right of this ear of corn is seen a region of soft light, among 
 which rise two similar spindle-shaped masses inclining toward the corn ear. 
 
 To the left appears a mass of rolling cloud disposed in beautiful streams and 
 curls, like the smoke from a bonfire or burning meadow, swept gently toward one 
 side by a light wind. In connection with these are some small masses, entirely 
 detached and floating above the general body, as was the case in De la Rue's pictures. 
 
 Other solid nodular masses appear at other points ; but the next most notable 
 prominence is one which attracted the attention of all observers, and appeared to 
 occupy a position on the lowermost edge of the sun. It is most clearly shown in the 
 last totality pictures taken at each station, and resembles in shape a great whale with 
 a body made up of dense cumulous cloud matter, with a long tail clinging close to the 
 solar edge, and stretching some 40,000 miles along. The length of the entire mass is 
 about 110,000 miles, and the height of its more bulky portion about 28,000 miles, 
 while its length is about 70,000 miles. 
 
 To the right of this, and only showing its entire length in the last picture of each 
 series, is a caterpillar-like mass of cloud matter, very much like the solid rolls of hori- 
 zontal vapor which are sometimes seen passing over a sheet of water. At one end 
 rises a projecting head, but the rest clings closely to the solar edge, and is indented 
 with ring-like divisions, giving it much the aspect of a huge worm. 
 
KEPOKT OF THE PHILADELPHIA PHOTOGRAPHIC EXPEDITION. 125 
 
 THE CORONA.* 
 
 [Universal experience has shown that the actinic power of the coronal light ]is 
 extremely feeble, and the successful photographic record of its detail and extent would 
 therefore have been inconsistent with securing any valuable representation of the 
 prominences. In fact, the best or most extensive photograph of the corona obtained 
 during this eclipse was a picture taken by the Messrs. Houver, photographers at Mount 
 Pleasant, at the suggestion of Professor Pickering, with a globe lens of 1 2 inches 
 focal length. The camera was previously pointed- toward the sun and the plate 
 exposed during the entire totality. The accompanying wood cut gives a fair repre- 
 sentation of the negative obtained enlarged two diameters, and shows the marked 
 predominance of rays in the direction of the sun's equator and axis. 
 
 The following cut represents the position of the corona as it appeared in the sky 
 at Mount Pleasant, the edges of the black ground being vertical and parallel with 
 the horizon respectively.] 
 
 The Ottumwa pictures, of long exposure, give us some idea of the true structure 
 of the corona. One of them (Plate VIII), the last and longest exposed, gives the 
 curved structure of the rays, and the varying intensity with which they are emitted 
 in different points is most marked. 
 
 The brightest outbursts of the corona light are evidently associated with those 
 prominences which are of a pointed and flame-like shape; those of a massive descrip- 
 tion, on the contrary, seeming to cast a shadow on the corona; this, we think, is to be 
 noticed in De la Rue's pictures. 
 
 These facts have peculiar significance, when taken in connection with others 
 developed by observations made during this same eclipse In the first place, Prof. E. 
 C. Pickering, of the Massachusetts Institute of Technology, who was with our party at 
 Mount Pleasant for the purpose of making various physical observations, found that 
 while the sky was strongly polarized all around, close up to the corona, that object 
 itself was not a source of polarized light. 
 
 The instrument employed was a tube, having at one end a large plate of quartz, 
 and at the other a double image prism of Iceland spar, made in the manner known as 
 the prism of Rochon. 
 
 On looking through this at the corona, the entire circle was in field with a part of 
 the surrounding sky, and two entirely distinct images of the entire area were seen, the 
 corona in both being colorless, but projected on a ground of tints, complementary in 
 the two images. 
 
 * The portion of this article in [brackets] was supplied in January, 1871. See in connection with it Professor 
 Pickering's article on "Photographing the Corona," in Journal of the Franklin Institute, LX1I, p. 54, and given 
 hereafter. C. 
 
126 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 This would certainly indicate that the light of the corona was not reflected sun- 
 light. With a spectroscope arranged to analyze the entire light from the totality phase, 
 Professor Pickering also found no dark lines in the spectrum. This also points in 
 the same direction. 
 
 The observations of Prof C. A. Young, of Dartmouth College, Hanover, N. H., 
 who was stationed at Burlington, are most conclusive. He found bright lines in the 
 spectrum of the corona corresponding with those given by the aurora. In a letter 
 which I have just received from him, he says: 
 
 ince returning, I have seen the July No. of Silliman, and in it the positions 
 given by Winlock for 5 aurora borealis lines.* You will be interested to learn 
 that, so tar as I can ascertain by graphical construction, the aurora line at 1550 of 
 Huggins' chart exactly coincides with my principal corona line 1474 Kirchhoff; and, 
 moreover, the aurora lines 1280 and 1400 (Huggins) agree, as far as I can judge, 
 with the two fainter corona lines between D and K, which I saw and recorded, but had 
 not time to measure accurately. 
 
 "Perhaps I am too bold in my conclusions, but at present I feel persuaded that 
 the solar corona is a permanent aurora." 
 
 It would thus seem almost certain that the corona is simply an electric discharge, 
 no doubt varying with great rapidity, as we see in the case of the aurora, and to its 
 variations we may attribute those apparent motions of the prominences which have 
 been observed by so many, but which our large series of photographs so conclusively 
 shows not to have had any actual existence.! 
 
 Before closing this report, I cannot refrain from saying a few words in reference 
 to the members of my party. 
 
 Our labor was eminently a cooperative one, and the pleasing success which has 
 attended our efforts is largely due to the thorough harmony of effort and the self- 
 denial and devotion to the general cause, irrespective of individual interest, which has 
 characterized the entire history of this expedition. 
 
 The work we had in hand was of a nature which, in the first place, required the 
 combination of a high order of ability in many distinct branches. It was necessary 
 that the best optical skill should be enlisted in the structure and arrangement of the 
 lenses; it was essential that the very best mechanical ability should be applied to the 
 details of the various adjustments of clockwork and cameras; the largest experience 
 in photographic operations was equally necessary; so, also, was a thorough and ready 
 skill hi the refined details of practical astronomy. Besides this, it came of necessity 
 that the failure of any one would ruin the work of all, as each step must be secure, 
 or the pinnacle of success could not possibly be reached. 
 
 Under these circumstances, when we say that we have no failure to regret, and 
 
 * Silliman' * Journal, Vol. XLVI1I, p. 123. "We are indebted to Prof. Winlock for the following interesting 
 notices. The light of the beautiful Aurora of the evening of April 15tb, examined with the spectroscope, gave five 
 bright lines corresponding in position to the following lines of Mr. Hugging' scale. 1280 (brightest), 1400, 1550, 1680, 
 near F, 2640 near G. On the evening of June 6th, the same lines were again observed, the brightest corresponding 
 with 1280 of Mr. Huggius' scale. These lines could readily be seen and measured with an ordinary chemical spectro- 
 scope, with the collimator poiuted directly towards the heavens." 
 
 t Mr. Zeutmayer observed some bright objects, eleven or thirteen in number, crossing the lunar disk, generally 
 from one cusp to the other. These were noticed by other observers in other places. C. 
 
KEPOKT OF THE PHILADELPHIA PHOTOGRAPHIC EXPEDITION. 127 
 
 that no reproach lias had cause to be uttered, the highest commendation possible has 
 been implied towards all and every one concerned. 
 
 Where all were unremitting- in effort and excellent in execution, it is not easy, without 
 injustice to any, to indicate the special merit developed, by opportunity or trying emer- 
 gency in some; but we cannot refrain from drawing especial attention to the very 
 valuable aid which was afforded by Professor Mayer, Ph. D., through his intimate 
 familiarities with all the niceties and most refined improvements in practical astronomy; 
 by Mr. Joseph Zentmayer, through his admirable ingenuity in the devising and con- 
 struction of the various mechanical and optical details required in the several instru- 
 ments; by Mr. (). H. Willard, through the unsparing devotion of time and energy, 
 and the indomitable perseverance by which all the preliminary arrangements were 
 pushed to a successful issue, and his own department developed to its highest perfec- 
 tion; and by Prof. C. F. Himes, through the sound judgment and presence of mind 
 displayed on a trying and sudden emergency. 
 
 While affording gladly this special distinction to some, we repeat that all were 
 equally meritorious, and that the work of no one would have been of the least value 
 without the aid of the others. 
 
 I have also, on my own behalf, as well as on that of my colleagues, to thank you 
 for that uniform kindness, courtesy, and consideration which has rendered all our re- 
 lations of the most agreeable character, and made our labor of love in an equal degree 
 a labor also of pleasure. 
 
 Very respectfully, yours, 
 
 HENRY MORTON. 
 Prof. J. H. C. COFFIN, 
 
 Superintendent of the Nautical Almanac, WasJiint/ton, I). C. 
 
REPORT OF ALFRED M. MAYER, PH. .D. 
 
 (Chief of the Burlington Section of the Photographic Expedition). 
 
 To Prof. HENRY MORTON, PH. I).: 
 
 DEVR SIR: I herewith present to you my report, as chief of the Burlington section 
 of the Photographic Expedition, organized by you under the authority of Prof. J. H. 
 
 C. Coffin, U. S. N., Superintendent of the Nautical Almanac. 
 This report is given under the following heads: 
 
 1. Diary of work at Burlington up to the time of the eclipse. 
 
 2. The station. 
 
 3. The equatorial and its adjustments in altitude and azimuth 
 
 4. The camera and chronograph. 
 
 (..) The adjustment of the reticule of the camera. 
 
 (i.) The experimental determination of the time of exposure during 
 partial phase. 
 
 5. The work during the eclipse. 
 
 6. Description of the photographs taken. 
 7 Results : 
 
 (a.) Time of first contact. 
 
 (J>.) Position-angles of first and fourth contacts. 
 (c.) Angles of position and heights of the protuberances. 
 (<t) Measurements on the solar spot in SW quadrant. 
 
 8. Observations on the application of photography to the determination of the 
 times of contacts during the transit of Venus in 1874 and 1882. 
 
 I. DIARY OF WORK AT BURLINGTON UP TO THE TIME OF THE ECLIPSE. 
 
 Our party, consisting of Messrs. O. H. Willard, H. C. Phillips, J. Mahoney, O. 
 II. Kendall, Miles Rock (who accompanied the expedition as my special assistant), and 
 myself, arrived at Burlington, Iowa, about noon on Wednesday, August 4. 
 
 We were here received by Professor Coffin, who had previously selected our station 
 of observation, and on it had erected a building to contain the equatorial, with adjoin- 
 ino- rooms suitable for photographic purposes. The afternoon was occupied in the 
 transportation of our boxes to the observatory and in unpacking and mounting the 
 telescope, while Mr. Willard made some additions to the photographic rooms and 
 modifications in their arrangement. We had progressed so well with our work that 
 by sundown we had put together the base and frame of the telescope, had mounted 
 bed-plate, polar and declination axes and circles and the cradle which holds the tel- 
 escope tube. 
 
 On Thursday, August 5, the tube was placed in the cradle and all the parts of 
 the telescope were put together and oiled. The verniers were now adjusted opposite 
 each other, and the instrument was brought into altitude adjustment to within i' by 
 the process described below. 
 
 17 E g 129 
 
130 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 Mr. Austin, of the Nautical Almanac Office, at the request of Professor Coffin, had 
 previously run a meridian line on the cross-timbers which supported the base of the 
 telescope, and, as near as could be determined, I brought the polar axis and this line 
 into one plane. This forethought of Professor Coffin greatly expedited the bringing 
 of the equatorial into position, and I afterwards found from star observations that the 
 azimuth adjustment required to be touched but slightly. 
 
 We rose on Friday morning, August 6, to see a driving rain, with an east wind 
 and the same dull murky atmosphere which we had had all the day before. Yet we 
 went on attending to the details of arrangements for the coming day as though we 
 could not be disappointed after weeks spent in previous preparation for the work of to- 
 morrow, and after having come over a thousand miles to carry back with us the long 
 thought of eclipse, fixed on our plates in appearance, time, and position. 
 
 As we retired there appeared a breaking away in the clouds, and Dr. Gould told 
 the clerk in the office to "wake us up if the stars came out." We had barely lost 
 ourselves in cloudy slumber when the clerk knocked at the door with "Get up! jtlniifi/ 
 of stars!" We were soon dressed, and Professor Coffin, Dr. Gould, and I were up all 
 night, putting our own special instruments in adjustment, and, at the same time, help- 
 ing each other as we could. . When all was finished the sun was rising over the trees 
 on the opposite bank of the Mississippi and the air was as pure and as serene as one 
 could wish. 
 
 On Saturday morning the chronograph was mounted and wires were led to the 
 camera, to Prof. C. A. Young's spectroscope and to the station of Dr. Gould outside 
 the building. The two threads of the reticule of the camera were placed one parallel 
 and the other at right angles to the celestial equator. Mr. Willard now began experi- 
 ments to ascertain the chemical focus, and his success in this delicate adjustment will 
 speak for itself to all who examine the beautiful details of the photographs. 
 
 Is is here important to remark that the chemical focus was obtained after the tube 
 had been following the sun for an hour or more, and after the focus was fixed the 
 clock-work was kept going so that no change in focus should supervene from a change 
 in temperature in the lenses and tube, which change of focus certainly would have 
 occurred if we had closed the roof of the observatoiy and had uncovered only a short 
 time before the eclipse. 
 
 By 3 p. m. all was in readiness and each one at his allotted post of duty ready 
 for work. We were now surrounded by a clear, soft atmosphere without the slightest 
 haze, and no trace of clouds except a small low bank on the western horizon. The 
 temperature of the air was 71 Fahr. 
 
 2. THE STATION. 
 
 The station selected for us by Professor Coffin was situate on an eminence known 
 as South Hill, in the southwest part of the town of Burlington. The inclosure was ;i 
 level square of ground thickly covered with clover grass and surrounded by a hedge. 
 It was elevated about 175 feet above the river, and its quiet and freedom from dust 
 rendered it admirably suited to our purposes. 
 
 The latitude of our station in .Burlington is 40 48' 20" N. Longitude, o 1 ' 
 56 m I3 8 .8 W of Washington. It was about 7 miles north of the center of the moon's 
 shadow. 
 
REPORT OF THE PHILADELPHIA PHOTOGRAPHIC EXPEDITION. 131 
 
 3. THE EQUATORIAL AND ITS ADJUSTMENTS. 
 
 The equatorial was borrowed from the observatory of the Central High School 
 of Philadelphia, and is by Merz and Mahler, of Munich. It is of 9 feet focus and 6.42 
 inches aperture, and was mounted on one of Fraunhofer's wooden stands. It has a 
 driving clock, the movement of which is governed by the friction of revolving arms 
 against the inner surface of a cone, and by bringing the knobs (which terminate the 
 arms and are attached to them by springs) to run against a larger or smaller circum- 
 ference of the cone we obtain a greater or less velocity of clock-movement. 
 
 The stand of the telescope rested on massive cross-timbers firmly rammed in the 
 ground. 
 
 The object-glass of this instrument had a light brownish tinge, which it is im- 
 portant to remember, as it may have had some effect on the chemical action at its 
 focus. 
 
 The probability of cloudy weather immediately preceding the eclipse caused me 
 to use the following method of adjustment ; and it is well I did, for otherwise I should 
 not have been able, in the few hours when the stars did appear, to have brought 
 my telescope into the exact position I did. 
 
 I had the cap, which covers the object-glass, centered on a lathe and pierced with 
 a hole. The object-glass and eye-lenses were removed and a plumb-line was let fall 
 from the hole in the center of the cap through the hole of the cap of the ocular. 
 When the line was brought to the center of the hole of the eye-cap, the axis of the 
 telescope was vertical. The vernier was now read, the tube brought to a vertical posi- 
 tion on the other side of the polar axis, and the vernier read again. The difference of 
 readings gives twice the angle formed by the vertical with the polar axis, and, if the 
 polar axis is elevated to the latitude of the place, will equal twice the co-latitude of the 
 station. If the angle obtained is too great, close it by elevating the polar axis; if too 
 little, open it by depressing the axis. 
 
 I thus, assisted by Mr. Rock, adjusted the telescope to within i'. The error read 
 was 30". I say within i', for i' on a radius of 9 feet is .03132 inch, and a deflection 
 of the line ,00 of an inch from the center of the ocular cap will give a deviation from 
 centrality of twice that quantity, or ^ (about ^ inch) ; for we measure with the eye 
 from the sides of the hole to the line and not from its center to the line, so the differ- 
 ence of these measures is twice the deviation. 
 
 As stated above, the polar axis was brought as near as could be in one plane with 
 the meridian line previously traced, and the azimuth adjustment, tested in the following 
 manner, required only a slight alteration. 
 
 To bring polar axis into the plane of the meridian. Select an equatorial star and 
 place micrometer thread so that the star glides along the thread when the telescope is 
 moved in right ascension. The thread is now nearly parallel to the equator. Select 
 a star about three hours off the meridian, say W , and bring it on equatorial thread of 
 micrometer and set the clock going. If the star (as seen in a refractor with a direct 
 eye-piece) rises above the thread, then N. end of polar axis, is E. of the meridian; if 
 the star falls below the thread, then N. end of axis is W. of meridian plane. If an 
 E. star is used, then the above rule is reversed (E. for W., &c.) 
 
132 ECLIPSE OP THE SUN, AUGUST 7, 1809. 
 
 After each adjustment the equatorial wire is reset to the equator, and the opera- 
 tions are continued until the star neither rises nor falls. 
 
 On the night of the 6th~7th this adjustment was effected and the clock, after 
 much trouble, regulated until it drove the tube so that a star was closely bisected for 
 about twenty minutes. During the adjustment of the clock the precaution was taken 
 to place the tube to about the same elevation it would have the next day during totality. 
 
 4. THE CAMERA AND CHRONOGRAPH. 
 
 The image of the sun was formed on the plate of the camera by the action of a 
 negative eye-piece, the lenses of which were so placed by Mr. Zentmayer in relation 
 to the object-glass and to each other, that the diameter of the sun's image, on a 4^ by 
 $% inch plate, was 2.04 inches. This image was therefore not the direct image formed 
 by the object-glass, but, according to De la Rue's plan, adopted and judiciously mod- 
 ified by you, it was the magnified image of the direct image which was used. 
 
 (a) The adjustment of the reticule of the camera. 
 
 Mr. Zentmayer had so constructed the camera eye-piece that the image of a 
 reticule of two spider threads, at right angles to each other, was formed on the plate 
 with the image of the sun, and these threads were so mounted that they could be 
 adjusted respectively parallel and at right angles to the celestial equator, and thus fix 
 on the photographs the positions of the sun and moon, and give the position-angles 
 of points on the surface and periphery of the sun. This adjustment I deemed of 
 great importance, as without it we would not obtain the position-angles of contact nor 
 the positions of the protuberances during totality. The lines are nearly as sharply 
 defined on the pictures of totality as on those taken during partial phase. 
 
 The adjustment was made as follows : The camera was firmly screwed to the tel- 
 escope and the focussing tube was moved until the images of the sun and threads of 
 the reticule w.ere brought to exact focus on the ground plate. The well-defined spot 
 in the SW. quadrant of the sun was now made to travel along the thread, by clamp- 
 ing the telescope in right ascension, and the reticule plate revolved until the spot was 
 accurately bisected during all its progress across the field. The telescope was then 
 undamped in right ascension (still remaining clamped in declination), and moved 
 around the polar axis so that the spot ran along the thread; it was found to be bisected 
 throughout all its transit. 
 
 Dr. Gould, at my request, now examined the adjustment and pronounced it precise. 
 
 (ft) The experimental determination of the time of exposure during partial phase. 
 
 The tube carrying the camera lenses screwed into a plate, in which, immediately 
 in front of the anterior lens, was a guide in which a thin plate, having a horizontal 
 slot of .0224 inch in width, was caused to descend by the action of a spring.* Any 
 integral ray of the beam whose rays successively passed this slot traversed the plate 
 only during the time it took the slot to fall its own breadth, or the .0224 of an inch; 
 and the determination of this time being the time of exposure has been the object 
 of an experimental investigation which is given below. 
 
 During totality the full aperature of object-glass was employed and a slide-plaie 
 
 "The construction was such that the plate could lie made to descend by the action of 1, 1, or :{ springs only one 
 was used by me for the exposures of both partial phase and of totality. 
 
REPORT OF THE PHILADELPHIA PHOTOGRAPHIC EXPEDITION. 
 
 133 
 
 was used which had a circular opening, which allowed the full beam to pass. This 
 plate had two falls instead of one, as was the case with the .02 24-inch slide used during 
 partial phase. On setting the plate free by the top trigger it fell, and the collodion 
 plate was exposed to the entire beam; after the desired exposure a lower trigger was 
 relieved and the plate made a second fall, and, the lens being covered by the top of 
 the plate, the exposure ceased. 
 
 After my examination of the photographs, I realized the importance of an accurate 
 determination of the time of exposure during partial phase, so that those who should 
 hereafter attempt similar work might have the full benefit of our experience. This I 
 considered all the more important because our results are apparently as perfect as any 
 heretofore attained, and therefore the time which gave these results should be accurately 
 known. 
 
 A reference to the diagram of the camera will render clear the method of register- 
 ing on the chronograph and also the process by which I determined the duration of 
 the Hash of the sun which fixed his image on our plates 
 
 During the eclipse the registration on the chronograph was effected as follows- 
 
 A circuit passed from the face-plate A B to the chronograph through the trigger'K, 
 and the spring attached to the binding screw L, which latter was insulated from the 
 slide by being fixed to the wooden camera box. On, tapping the trigger K, the pin p 
 of the slide being relieved of support, the slide fell, and the circuit was broken by the 
 spring under the trigger no longer touching the top of the spring L. Thus a break 
 circuit was obtained at the instant of each exposure, which was duly registered on the 
 chronograph. (See diagram, page 1 1 7.) 
 
 The arrangement of apparatus and circuit for the determination of the time of 
 exposure was as follows: 
 
 From the break-circuit clock of my observatory I led a wire to one pole of a 
 battery, thence by the other pole to the place at H; from this plate the current went 
 
134 ECLIPSE OF TBE SUN, AUGUST 7, 1869. 
 
 through the trigger K and spring at L to a Morse register; from the register by a wire 
 which led back to the clock, and thus completed the circuit. Another short stiff wire, 
 o A, was attached to the binding screw L, and reached from L to a short distance 
 beyond the slot A, and was in front of the surface of the face-plate A B, but so near 
 to it that when the slide fell the projecting pin p would strike the wire about one-tenth 
 of an inch above its lowest point of fall.* 
 
 Now, suppose the projecting pin p to rest on the trigger K, while the spring under 
 the trigger rests on the top of the steel spring attached to L, and that a paper fillet is 
 running through the Morse register; then at every second the clock will for an instant 
 open the circuit, and there will be a very short break made in the line marked by the 
 pen on the fillet, and thus the seconds of time are stepped off in space on the paper 
 ribbon. Suppose, now, that the long end of the trigger K be sharply driven by the 
 blow of a hammer against the face of the camera ; the circuit will be open during the fall 
 of the pin from the top of trigger to the point where it strikes the wire o A projecting 
 from L, and there will be produced in the line on the fillet a break, whose length 
 compared with the length of the second in which it occurs will give the time required 
 for the plate to fall the above-mentioned distance. It is evident that as soon as the pin 
 strikes the wire the circuit is again closed, and the clock breaks the circuit as before 
 the fall. I always struck the trigger at about a half second, so that the comparison could 
 be readily and accurately made. 
 
 The fall being accurately measured and the time of that fall known, the time the 
 plate takes to fall .0224 inch, which is the time of exposure, can be accurately computed. 
 
 Before giving the results of these experiments, I should remark that the plate 
 descends with an increasing velocity produced by the action of the decreasing force of 
 the spring, and what I obtained was the mean velocity of the plate. Also, the time it 
 took the pen of the register t > leave the fillet at demagnetization and return to the fillet 
 at magnetization is neglected, and as I had no means of determining it I adjusted the 
 force of current and of spring so that these motions were as rapid as.possible. I do not 
 think the time required for these motions has affected the results appreciably, especially 
 as the fall was a large multiple of the breadth of the slot. 
 
 The breadth of the slot was measured under the microscope and the mean of three 
 measures at ends and middle gave .0224 inch. 
 
 As an example of the mariner of determining the time of exposure from the above 
 data, we will take the results of fillet No. i. 
 
 Inch. 
 
 Length of second on fillet 83 
 
 Length of break during the fall of slide 1 05 
 
 Fall of slide i .340 
 
 Width of slot in plate 0224 
 
 Time of fall of slide through i .34 inch, ^~ o 8 . 1 26. 
 
 O 
 
 Time of exposure, = O "- 126 * ' 224 - O 8 .oo2 1 1. 
 
 1-34 
 
 The wire A is represented in the engraving, bent upward at its end A; it should bo straight, 
 
REPORT OF THE PHILADELPHIA PHOTOGRAPHIC EXPEDITION. 
 
 135 
 
 Number of fillet. 
 
 Length of I s on 
 
 fillet. 
 
 Length of break 
 on fillet (luring 
 fall of plate. 
 
 ('all of plate. 
 
 Time of exposure. 
 
 
 huh. 
 
 fact. 
 
 Inch.. 
 
 Stc. 
 
 I 
 
 .830 
 
 .105 
 
 '34 
 
 . 002 i i 
 
 2 
 
 .765 
 
 .090 
 
 i-34 
 
 . 00196 
 
 3 
 
 79 
 
 .0975 
 
 i-34 
 
 .00205 
 
 4 
 
 795 
 
 . 100 
 
 i-34 
 
 .00208 
 
 5 
 
 .840 
 
 . 120 
 
 '34 
 
 .00237 
 
 6 
 
 78s 
 
 .095 
 
 i-34 
 
 . OO2O2 
 
 7 
 
 755 
 
 . no 
 
 1.36 
 
 .O023I 
 
 8 
 
 .860 
 
 . 120 
 
 1.36 
 
 .00228 
 
 9 
 Mean time of ex 
 
 75 
 posure 
 
 . 100 
 
 1.36 
 
 . OO2II 
 
 . OO2I^ 
 
 
 The greatest departure in these results from the mean is .0002, No. 2 being that 
 quantity below, and No 5 that amount above the mean. 
 
 The sum of the last column of figures equals 39; their mean 4.33; which shows 
 that they are entirely of an arbitrary value, and if the experiments had been extended 
 would no doubt eventually have equaled 4.5; we therefore reject the last decimal 
 place, and adopt for our final result .002 1 of a second. The time of exposure was 
 therefore almost exactly one five hundredth of a second ! 
 
 5. THE WORK DURING THE ECLIPSE. 
 
 As before stated, by 3 p. m. of August 7 all was in readiness fpr our work. Mr. 
 Willard had used every precaution to insure success in the details of photographic 
 manipulation, and the results which he reached will show with what judgment and 
 skill he had organized all the workings of this department. 
 
 It was my duty to keep the telescope in adjustment and to manipulate the apparatus 
 of exposure and chronographic registration, while Mr. Willard placed the plate in the 
 camera and gave me the several times of exposure he desired during totality. Mr. H. 
 C. Phillips coated the plates and handed them to Mr. Montfort (photographer of Burling- 
 ton), who carried them to Mr. Willard, and thence after exposure to Mr. Mahoney, who 
 developed, assisted by Mr. Leisenring. 
 
 Mr. Miles Rock was detailed to attend to the very important duty of calling 
 and tapping the seconds on the chronograph fillet; in this duty he was relieved by Mr 
 Bonsall, of Burlington. Mr. ( ). H. Kendall called out the minutes at each 60 second 
 call of Mr. Rock and wrote it on the fillet. He also had charge of the chronograph, 
 and started it when I called ''clock," while at the same signal Mr. Rock began the 
 registration of seconds. 
 
 I laid out the following programme of work: (i) To take in rapid succession, 
 beginning ten seconds before the computed time of first contact, a series of five photo- 
 graphs. (2) One just before second contact, one just after second contact, as many 
 as possible during totality, one just before the end of totality, and another just after 
 the sun appeared. (3) To take again a series in rapid succession about the end of 
 
1 36 ECLIPSE OP THE SUN, AUGUST 7, 18C9. 
 
 the eclipse. (4) During partial phase to take a photograph every four or five 
 minutes. 
 
 To accomplish this I placed on a table before me a watch set to the face of the 
 chronometer, whose indications we used during the eclipse, and on a slip of paper 
 pasted to the table I wrote in very black, lead pencil the computed times of ist, 2d, 3d, 
 and 4th contacts, obtained from Professor Coffin. I thus could give Mr. Willard due 
 notice when the plates should be prepared. 
 
 When the face of the chronometer marked i 2 h 48, Mr. Rock began to count and 
 register the times oh the fillet. Every one was at his post, the lanterns lighted, and 
 nothing could be heard but the count and the tap of the chronograph. At i 2'' 49'" 45", 
 1 took the first photograph, and following at intervals of 11, 10.*, 15.2, and 12 seconds 
 we secured five perfect negatives. The contact is first visible on the third. We now 
 leisurely took photographs at intervals of about four minutes, until \ve had taken twelve 
 plates in all. The moon's limb had now advanced to about three minutes of the time of 
 the spot in the SW. quadrant. Professor Young, of Dartmouth College, who was 
 stationed near me, stated his intention to signal as soon as the umbra was bisected by the 
 border of the moon. The plate was prepared and all was ready. Professor Young 
 signaled; I tapped the trigger; he remarked, "You must have shot it on the wing." 
 The 1 3th plate (No. 15) shows the spot, as nearly cut in half as I can estimate by a 
 careful comparison of this drawing with another of the spot, as photographed on the 
 preceding Plate . 
 
 About five minutes before totality Mr. Willard removed the diaphragm of two 
 inches aperature, which was vised during partial phase, and exposed the full aperture 
 of the object glass, while I changed the slide with .02 24-inch slot for the one which 
 admitted the whole beam at once on the plate of the camera. 
 
 The order was given to prepare the plates. We took the first plate at 1 3*'5 1 '" 39". i 5 , 
 or 7" before the time of second contact, as observed by Professor Coffin. I soon had 
 the slide reset for another exposure, and as Mr. Willard desired the first plate of total- 
 ity to be exposed five seconds, T kept on counting zero, zero, zero, with the taps of 
 the chronograph when, striking the upper trigger at zero, I counted i, 2, 3, 4, 5, when 
 the lower trigger was struck and the plate removed. 
 
 Counting the first plate, taken seven seconds before second contact, I took six 
 photographs in 2 3". After the sixth was removed I looked at the watch and saw 
 50" yet of total phase. There was a delay in the plate. I grew impatient. I called 
 plate! plate! but, alas, it was found impossible to manipulate more than six plates in 
 two minutes and three seconds. We had used up our store too rapidly, and so did 
 not succeed in getting an impression just before the sun came forth. The next plate 
 was taken 29". 2 after third contact, and is a valuable photograph of a thin crescent 
 with the cusps sharply cut, 
 
 As has already been explained, under the head of camera, at each fall of the slide 
 the electric circuit was broken, and a registration made on the fillet alongside of Mr. 
 Rock's second marks taken from the chronometer, and it is evident that all of these 
 registrations are vitiated with whatever personal equation affected him at that time. 
 This was not determined. 
 
i;i:roi;T OF THE PHILADELPHIA PHOTOGRAPHIC EXPEDITION. 137 
 
 A!M nit fifteen minutes before totality it became so cool that I was obliged to put 
 on my coat. A minute or two before totality the sky grew ashen, or rather leaden, in 
 hue, and as, with face turned toward the sun, I kept the count from the chronometer 
 for the first exposure, Venus and Mercury came out shining beautifully on a ground 
 of bluish gray. 1 thought I sa\v a Hashing, twirling motion in the corona, or in the 
 last rays of the sun; but of this 1 will not In; positive, for my attention was not at the 
 time specially directed to minute observation. Moths and insects in profusion passed 
 between me and the sun, while a Hock of birds with troubled irregular Hight seemed 
 seeking cover from the unnatural gloom which surrounded them. A low moaning 
 wind now sprang up, and the whole atmosphere seemed filled with a leaden-colored 
 vapor, and I experienced an indescribable feeling of oppression when I tapped the 
 trigger, and from that instant until the sun appeared 1 had nothing but an instrumental 
 consciousness, for I was nothing but part of the telescope, and all my being was in 
 the work which I had to perform. I reset slide, made circuit, exposed, and so over 
 again, until the six photographs were taken. 
 
 Photographs were now taken leisurely, at intervals of about four minutes, until 
 i4 b 47" 1 /)8 S 4, when the first of the series for the end of the eclipse was secured; this 
 was followed by four others at intervals of i m i6".84, 19". 26, 24 8 .3, and 2i".55. Our 
 work was finished, and in a few seconds the eclipse of August 7, 1869, was of the past, 
 but its history we had faithfully recorded in forty-one perfect photographs. 
 
 Such good success as attended our efforts speaks for the entire devotion of each 
 one to his allotted duties. Without this devotion on the part of each and all we would 
 have failed, and the harmony and efficiency which pervaded our corps need no other 
 witness. 
 
 6. DESCRIPTION OF THE PHOTOGRAPHS "TAKEN. 
 
 We took forty-one photographs during the eclipse. They are all good, but some 
 are superior to the others, and these will be designated as I proceed. 
 
 The plates were numbered with a diamond before the work began, and the 
 numbers corresponding to those on the plate are given below, and opposite them the 
 times when they were severally taken. These times were measured off from the 
 chronograph fillet, and correspond to the face of the chronometer.* 
 
 * //lit/on, 202, the correction of which referred to /urn/ mean time of the Coast Survey station, was + I5 11 6 16". 70 9". 63 
 (t I2 b ), / being the chronometer time in hours (p. 20). C. 
 18 E S 
 
138 
 
 ECLIPSE OF THE SUN, AUGUST 7, isti'.t. 
 
 No. of plate. 
 
 Time when taken. 
 
 No. 
 
 of plate. Time when taken. 
 
 
 h. ra. s. 
 
 
 h. m. .s. 
 
 ) 
 
 .... 12 49 45. 25 
 
 25 
 
 (7 seconds exposure) totality. . 13 52 31. 3 
 
 3 : 
 
 .... 12 49 56.0 
 
 23 
 
 (7 seconds exposure) totality. . 13 52 54.5 
 
 4 (after 1st contact) 
 
 .... 12 50 5. 8 
 
 26 
 
 (7 seconds exposure) totality. . 13 53 12. 37 
 
 5 
 
 .... 12 50 21. I 
 
 27 
 
 (7 seconds exposure) totality. . 13 53 42. 2 
 
 6 
 
 .... 12 50 32.95 
 
 28 
 
 '3 55 1-2 
 
 8 
 
 12 53 5-3 
 
 29 
 
 '3 57 20. 5 
 
 9 
 
 12 56 3-2 
 
 3 
 
 13 5 5-5 
 
 10 
 
 - 12 57 33-4 
 
 ji 
 
 14 2 41. 
 
 ii 
 
 . . . . 12 59 17.6 
 
 32 
 
 14 7 14-67 
 
 12 
 
 .... 13 2 IS. I 
 
 33 
 
 H H 33-5 
 
 '3 
 
 - . 13 7 23. 3 
 
 34 
 
 14 16 59. 6 
 
 '4 
 
 . . . . 13 12 19.27 
 
 35 
 
 M 23 1.5 
 
 s 
 
 .... 13 15 14.24 
 
 36 
 
 ; . . ; 14 29 21.5 
 
 16 
 
 - '3 22 57.5 
 
 37 
 
 14 3" 33-5 
 
 17 
 
 .-...'. 13 20 55.6 
 
 38 
 
 - - - H 44 33- ' 
 
 18 . : 
 
 - 13 32 5 8 - 
 
 39 
 
 H 47 4& 4 
 
 19 
 
 . ... '13 37 4i-5 
 
 40 
 
 .... 14 49 5-24 
 
 20 
 
 .... 13 41 50. 6 
 
 41 
 
 14 49 24- 5 
 
 21 
 
 .... 13 46 34. i 
 
 42 
 
 just before end <>f eclipse . . 14 49 48. 8 
 
 
 
 
 
 22 (5 seconds exposure) 
 
 totality. . 13 51 39- 15 
 
 43 
 
 14 50 10. 35 
 
 24 (5 seconds exposure) 
 
 totality. . 13 52 3. I 
 
 
 
 All the photographs show a beautiful gradation of shade from the border of the 
 sun inwards. This shading of the source of light is due to the absorption of the periph- 
 eral rays, which necessarily pass through a greater thickness of the dense solar 
 atmosphere than those which emanate from the central portion of the disk. 
 
 On a more searching examination of the relative intensities of light of different 
 portions of the solar disk, we observe on all of these photographs, close to the limb of 
 the advancing or retreating moon, a bright glow like that of early dawn, which 
 extends from the moon to a distance of about 1 5". 
 
 Thinking that this might be subjective and due to the strong contrast existing 
 between the bright image of the sun and the contiguous black lunar disk, I made the 
 following experiments: 
 
 I covered the image of the moon with a disk of white paper of its exact diameter. 
 The plate was now inclined to the light, so that the sun and the paper surface had as 
 nearly as possible the same white tint, while the photograph was viewed against an 
 illuminated ground formed by a sheet of white paper placed before the window 
 Under these circumstances the glow remained the same in all the photographs 
 examined Among others, plate No. 1 1 (which is the' best photograph of partial phase 
 in the series) shows this glow unequivocally. 
 
 Plates Nos. 21 and 30 are excellent photographs of thin crescents of the sun; the 
 first taken 5 12" before and the second 3 33". 5 after totality. This glow, if it really 
 exist, should show 'in these pictures an increased illumination in the points of the 
 cusps when the light of these portions of the periphery of the sun is compared with an 
 equal breadth of the sun's border, taken on that portion of its limb the farthest from 
 
K'KI'ORT OF TIIK I'HILADKU'HIA PHOTOGRAPHIC KXPKDITION. 139 
 
 the moon's. To make this comparison T covered with white paper both the moon and 
 the dark ground surrounding the sun, and inclined the plates as in the above experi- 
 ments, so as to destroy irradiation from juxtaposition of the light and dark surfaces. 
 This method of examination showed a distinct illumination in the narrowest portions 
 of the horns of the crescents. 
 
 No such glow is seen on the periphery of the sun, althongh this is contiguous to 
 the dark ground of the plate, and on covering the latter the appearance remains the 
 same. 
 
 T am therefore convinced that this glow really exists, and if it cannot be accounted 
 for in mode and in mnix/n-c, by diffraction, it must be due to a lunar atmosphere; 
 though I confess I cannot understand how an atmosphere capable of producing such 
 marked effects, when projected against the intensely lighted disk of the sun, should 
 have no appreciable refractive effect on small stars, and especially on double stars, 
 when occulted by the moon.* 
 
 This glow can be distinctly traced on plate No. 11 to 18" beyond the limb of 
 the moon. 
 
 A minute examination of these photographs reveals a coarsely granulated or 
 mottled surface extending over the sun, and especially well defined as we near its 
 border. < )ne is tempted at first to imagine that this is the well known solar granula- 
 lion observed in the telescope; but familiarity w'th that appearance, as well as the 
 reasons given below, soon decided me to reject the idea that this appearance on the 
 photographs \vas really an impression produced by the image of the sun's granulation 
 on the plate. 
 
 First, the granulations are many times larger than any ever yet observed, those on 
 the photographs averaging 7". 5 in diameter, while those on the sun average i", and 
 never exceed 3" in diameter; secondly, on plate No. 14 the mottling is very apparent, and 
 encloses a space entirely free from granulation in the NE. quadrant; no corresponding- 
 vacant space occurs in any of the other photographs; thirdly, the positions of these 
 granulations are not the same on any two plates, as I found from very careful 
 measurement; and fourthly, they are arranged in rows parallel to the sides of the 
 plates, thus showing conclusively that they have been produced in the photographic 
 manipulation. 
 
 According to the photographs, sixteen well-defined solar spots were on the sun 
 during the time of the eclipse. In the NE. quadrant, close to the sun's limb, and 
 about 90 E. of N. is a remarkably beautiful and characteristic spot, greatly fore- 
 shorte'hed from its position, so that the penumbra has disappeared on the west side of 
 the umbra against which rest the large bright facula?, which enclose the spot. Looking 
 at it through a lens, you are immediately struck with the idea of a depression in the 
 
 "Since the lir.-t publication of this report (Jour. Frank. lust., Oct., 1*69), Prof. H. Mortou (Jour. Frank. lust., 
 Dec., 181)9) has shown that tin.-) "glow" is produced as follows: * * " Part of the plate representing the dark 
 
 edge of the union, anil, therefore, not acted upon, furnishes a reservoir of nitrate of silver, imbibed by the collodion 
 film, which, during the development, penetrates for a short distance into the lumiiioiu area of the sun, whose supply 
 of free nitrate was exhausted by the reaction which occured at the first moment when the developer was applied." 
 My own experiments, given above, show that the glow is not subjective, and cannot be accounted for by irradiation, 
 while Prof. E. C. Pickering (Jonr. Frank. Inst., Apr., 1870) has proved that diffraction exerts no npprenable effect in 
 causing this phenomenon. 
 
140 ECLIPSE OF THE SUN, AUGUST 7, 1860. 
 
 sun's surface, and you cannot help remarking how like it is in appearance to a lunar 
 crater, for you are convinced that you look down into it, while the surrounding bright 
 faculae give a border similar to the white walls of some of the lunar mountains. From 
 the southwestern portion of this apparently elevated ridge a large bright facula bridges 
 over the cavity in a northeast direction, and divides the spot into two portions. 
 
 Plates Nos. 11, 16, and 21 show this object in perfection. 
 
 In the SE. quadrant we see three small and w^ll-defined spots, and several 
 largely developed faculse near the sun's limb. 
 
 In the SW. quadrant is a large and well-developed spot, and near it, to the N., 
 a group of four smaller ones. This large spot exhibited remarkable chain es during 
 the time of the eclipse, as will be seen from the drawings and measurements found 
 under the head of "Measurements on the solar spot in the SW. quadrant." 
 
 On close inspection, there is observed a very white projection from the surrounding 
 bright surface of the sun, which stretches into the northwestern border of the penumbra 
 of this spot and reaches nearly to its umbra. 
 
 In the NW. quadrant no solar spots are visible on the photographs. About 
 NNW. of the intersection of the threads of the reticule are observed what, at first 
 sight, we might take for a group of spots, but they are specks of dust on the lens of 
 the ocular, as they change their place on the disk with the threads, always preserving 
 the same position in reference to them. This test will serve to distinguish other spots 
 on the photographs, produced by the same cause as, for example, the four spots on 
 the SE. quadrant. 
 
 Plate No. 4, which, fortunately, is one of the best photographs, was taken 
 2 8 .8 after first contact, as observed by Dr. Gould. It shows a depression in the 
 sun's limb at the point of contact, and from this depression shoots into the sun a high 
 lunar mountain, whose position, measured from the S. point of the cusp, is one-fourth 
 of the distance to the N. point of the same. Mr. W. S. Oilman, of New York, who 
 observed at Sioux City, Iowa, informed me that he determined first contact by seeing 
 this mountain peak thrust itself into the limb of the sun before a flattening took place 
 from contact of the lower general surface of the moon. This mountain shows itself 
 on all the photographs of the eastern limb, while other peaks appear as the moon 
 progresses over the sun. The photographs show that the eastern limb of the moon is 
 far more mountainous than the western. 
 
 Plates Nos. 4, 9, and 1 1 best show the mountains on the following limb ; plates 
 Nos. 31, 35, and 42 on the preceding limb. 
 
 The best method of examining these mountains is to cut with a sharp knife a disk 
 of paper of the exact diameter of the image of the moon, and make its circumference 
 coincide with the general level of the moon's periphery; the lunar mountains will then 
 appear as black protuberances rising above the white circle of the paper. 
 
 Plates Nos. 39, 40, 41,42, and 43, taken in rapid succession, as the moon was leaving 
 the sun's disk, previous to fourth contact, show two prominent lunar mountains on the 
 northern part of the cusp, followed by a long depression in the moon's limb. 
 
 Five photographs (Nos. 23-27) were taken during total eclipse, and one 6".85 
 before, and one 29 S .2 after totality. The one (No. 22) taken 6 8 .85 before the disap- 
 
REPORT OF THE IMIILADKU'H I A PHOTOGRAPHIC EXPEDITION. 141 
 
 pearance of the sun shows all the prominences of the eastern limb; but on account of 
 the long exposure, the thin crescent of the sun which then remained caused a blurring 
 of the details. The picture is a mixture of crescent and protuberances. The promi- 
 nences, 6 and 7, are entirely isolated, while the intervening ones are enveloped in the 
 ght of the crescent. 
 
 Plate No. 28, taken 28". 2 after totality, is the photograph of a very thin 
 solar crescent, whose cusps are sharply defined throughout. The northern horn is 
 narrower than the southern, which causes the moon's disk to appear to depart from a 
 circle curve.* 
 
 No. 24, taken at i3 h 52 3".! that is. iy s .i after beginning of totality- 
 shows the full development of the prominences on the eastern limb, while on the 
 western only the top of the large southern protuberance (No. 8) is visible, and a slight 
 glow appears on the NW. and S\V. border. 
 
 Nos. 25, 23, 26, and 27, f taken respectively 45^.3, i m 8 s , i" 1 26 8 .37, and i . 56 8 .2, 
 after the disappearance of the sun, show the advance of the moon eastward, and the 
 gradual appearance of the prominences and glow on the western limb, while those on 
 the eastern are being gradually cut off from view. 
 
 In No. 25, protuberance No. 8 is yet alone visible, while the glow appears along 
 all the western border of the moon. Protuberances i and 2 are covered by the moon. 
 
 In No. 23, the glow on the western limb is about equal to that on the eastern. 
 The tops of protuberances 10 and i i are just visible, while 7 is just fading from sight. 
 
 In plate 26, on the western limb, prominences Nos. 9 and i 2 have not yet come 
 into view: No. 8 has already taken the form of the albatross head; No. 10 only ap- 
 pears like a grain of rice set on and; while No 1 1 resembles two such grains standing- 
 oil end near each other. The glow is now greatest on the western limb. 
 
 In plate No. 27, taken 50 seconds before the sun came forth, we see No. 8 as a 
 fully-developed albatross head with bill and throat close to the moon's border. 
 
 The small protuberance No. 9 now comes in view, and No. 10 assumes the shape 
 of a caterpillar; i i appears as a grain of wheat with a groove around its middle, and 
 No 12 comes in sight. On the moon's eastern border a mere trace of 6 appears, while 
 4 exactly resembles a bird sailing close to the surface of the moon. The group of 
 protuberances, No. 5, which formerly appeared high above the body of the moon, 
 floating in cloud, now rest upon its border. 
 
 This sketch will, I hope, give a general idea of the development and disappear- 
 ance of the several flames, and show how rapid was the shifting of scenes during 
 totality. All the changes I have described took place in i'"39 s .i, the time in which 
 the five photographs were taken. 
 
 The diagram Plate X, Fig. i, has been very carefully drawn from the results of 
 measurements and calculations on the position-angles of the prominences. 
 
 I wish it to be understood that all of the measurements on the photographs given 
 in this preliminary report were made on copies on glass, and not on the original iict/a- 
 also, that no micrometric apparatus was used, but only an accurate scale divided 
 
 * Sc.i I'hite IX. tNo. a~ is- uivmi in Plate VII. 
 
142 ECLIPSE OF THE SUN, Aldl'ST 7, ISIi'.i. 
 
 into halt' millimeters, the readings on which were made with a lens. These numerical 
 results (except those of the position-angles and heights of protuberances) are therefore 
 only approximative, and the numbers to be used in a thorough discussion of the 
 eclipse will be given as soon as accurate micrometric measurements can be made on 
 the original negatives. 
 
 The protuberances are designated by numbers, from i to 12, going from N. through 
 E. to N. The position-angles and heights are tabulated under the head of "Results." 
 
 The drawing and measurements of the prominences on the E. limb of the sun 
 are from the first photograph taken, while those on the W. are from the last picture 
 obtained. The diagram therefore shows the greatest visible development of these 
 objects on the eastern limb, and those on the western are as they appeared 50 seconds 
 before the end of totality. 
 
 Proceeding from the N. by the E. we perceive a glow of light which begins 
 a little E. of N., and extends nearly to the S. point. This luminous fringe to the pho- 
 tograph (represented on the diagram by the irregular dotted line) reaches its maximum 
 height about midway between the prominences 2 and 4, there attaining an ele- 
 vation of 2' 15". Another maximum of altitude occurs a few degrees S. of No. 5, 
 where it has the same height. In the midst of this bright glow and near its greatest 
 height appears at 3 and 5 detached sheets of bright flame floating above the lower 
 .mass of the conflagration. 
 
 The bases of the other protuberances are on the periphery of the moon, and all 
 except No. 4 rest below the general circle of the moon's border. This appearance is 
 ptirtidllji explained by the fact that the telescope follows the motion of the protuber- 
 ances, while the moon, therefore, has the difference of angular velocity between it and 
 the sun At the instant of exposure the portion of the prominence resting against 
 the moon's limb is photographed; but as the moon moves eastward during all the time 
 of exposure, the prominence will appear as a (Irjii-cxxioi/ iu tlic moon' 1 * I'nitb, for the latter 
 has moved to a higher portion of an eastern prominence, and to a lower portion of a 
 western, by the time the exposure is ended. 
 
 From the relative motion above referred to, it must necessarily follow that the 
 border of the moon will not be well defined; but the eastern one will be more sharply 
 cut than the western. All of the photographs of totality show this distinctly. 
 
 On plate No. 26, the apparent depression of prominence 1 1 is nearly all due to 
 its being in the hazy limb, its base resting in a very slight depression. 
 
 The amount of depression of the prominences I have accurately represented in 
 the accompanying diagram. (Plate X, fig. i.) 
 
 Proceeding from the north point to the east, we first meet with prominence No. i ? 
 having the position-angle of about 56 30'. It is of the shape of a rice grain, with 
 its base but slightly below the circumference of the moon. In breadth it is 2 50' and 
 in height 22". As i' on the circumference of the sun equals 124 miles and i" of arc 
 at the sun's distance, on August 7, subtends 449 miles, it follows that its actual dimen- 
 sions are 21,000 miles long, and 9,900 miles high. 
 
 Protuberance No. 2 lies imbedded in the moon's border, and has in form the ap- 
 
REPOKT OF THE PHILADELPHIA PHOTOGRAPHIC EXPEDITION. 143 
 
 peararice of a short, deeply articulated worm. Its mean position is 69 17'; its length 
 6 if, or 46,700 miles, and its greatest height equals 22" or 9,900 miles. 
 
 Between proturberances Nos. 2 and 3 arc two flames in the midst of the glow 
 previously described; one near to No. 2, the other quite close to No. 3. Midway 
 between Nos. 2 and 3 rises the diffused light to an elevation of 2' 15", or 60,500 
 miles. The position of protuberance 3 is 87 15', and it rises to a height of i' 15", 
 or 33,600 miles. 
 
 We now come to that curiously-formed protuberance No. 4. Some have com- 
 pared it to an ear of corn, but on the photographs it appears like an eagle, with out- 
 spread wings, resting on the trunk of a tree, which leans toward the north. On plate 
 27, where the tree-stump is cut off by the advancing moon, the resemblance to an 
 eagle on the wing is perfect 
 
 The form of this object indicates instability, and impresses one with the idea that 
 it is a great traveling Whirl of Hame, the direction of whose rotation as indicated 
 by the position of the "wings" and the projection of one on the other is retrograde 
 or in the s;ime direction as the motion of the hands of a watch. I have examined 
 with care the successive photographs of it, and although at first I thought that the 
 last, impression differed from those preceding, in that the wings had become longer 
 and more in a line with each other, yet, on subsequent examination, 1 could not really 
 decide that a perceptible motion had taken place during the time of totality. 
 
 The position-angle of the north side of the base of this object is 96 25'; its 
 height is i' 22", or 36,700 miles, and the spread of the wings, as measured on plate 
 27, is 9 31', or 70,800 miles. 
 
 Protuberance No. 5 reaches from B to an ill-defined point beyond c of the diagram; 
 it is of very irregular outline, and shows portions of its substance detached from the 
 general mass, and floating freely above it, The most elevated and bright of these 
 detached flames float at a height of at least. 20,000 miles above the surface of the sun. 
 Beyond the point c, a white nebulous cloud rises to the elevation of 2' 1 5", or 
 60,500 miles. 
 
 Protuberance No. 6 of the diagram has a mean position of 148; its length is 
 3 5', or 22,900 miles; its height is 45", or 20,000 miles. 
 
 The position of the center of No. 7, shaped like a grain of wheat, is 159 22'; 
 its length 5 13', equal to 38,800 miles; its height 37", or 16,600 miles. 
 
 We now pass to the western limb of the sun, and meet with the remarkably 
 large and massive protuberance No. 8. It is shaped like an albatross head, with the 
 beak and under side of the head resting on the limb of the moon. On a photograph 
 taken at Ottumwa, Iowa, just before the sun came out, this protuberence had the 
 exact appearance of an albatross head, with the beak open, holding a rounded mas s 
 between the extremity of the jaws. It lies between the position-angles of 230 13' 
 and 245 46'; its length is 15 33', or 1 15,700 miles, and its greatest height is 75", or 
 33,600 miles. 
 
 The small prominence No. 9 has a position of 273 27'. 
 
144 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 Protuberance No. 10 bears the most striking- resemblance to a caterpillar. Its 
 mean position is 287 33', and its extends through an angle of 11, or 81,800 miles.. 
 Its maximum elevation, which is at the head of "the caterpillar," is 52" or 23,300 
 miles. Out of the head issue two horns; the one nearest the front being the higher 
 of the two, and is terminated with a knob or ball, from which curves a broken line of 
 light to the border of the moon. 
 
 The center of prominence No. 11 has a position of 318 33' and its extent is 
 5 18', 01-37,400 miles, with an elevation of 44', or 20,100 miles. It lias the shape of 
 a grain of rice, slightly restricted in the middle. 
 
 The small protuberance No. 12 has a mean position of 343. Its length is 
 i 51', or 13,800 miles, and its greatest height is 15", or 6,700 miles. 
 
 The faintly-dotted circle, inside the circumference of the moon, shows the relative 
 diameter and position of the sun at the middle of total eclipse. The scale on which 
 the diagram is made fails to show want of coincidence of the centers of these circles. 
 The arrow marks the points of contact, and shows the direction of the motion of the 
 moon. 
 
 7. RESULTS. 
 
 Under this head I give a few approximate results deduced from measurements 
 on the glass positives, it be'ing useless to attempt more until an accurate micrometric 
 apparatus is brought to bear on the original negatives. 
 
 (a) The time of first contact: 
 
 This determination was made by taking the mean of several measures of diameters 
 of the sun's image on one of the plates, and from the known angle subtended by the 
 moon deducing its diameter in the same unit of length; then the chord of the cusp 
 was measured, and from these data the distances of the chord from the limbs of the 
 sun and moon (or the versed sines) were calculated 
 
 From the known hourly motion of the moon (allowance being made for parallax) 
 we obtained the time of first contact. 
 
 It is evident that if this measure be accurately made on the negatives, and the 
 effect of refraction be also taken into account, we have precise data for determining 
 the corrections necessary to be applied to the elements of the eclipse. 
 
 The time of first contact thus deduced from two plates gave i 2'' 50'" 2 S .94, which 
 is I s . i before contact, as observed by Professor Coffin, and o".i before Dr. Gould's 
 observation. From measures on another plate (No. 5) we deduced i2 h 49'" 59", which 
 is 4 8 before contact, as observed by Dr. Gmild, and six-tenths of a second after contact, 
 as determined by Professor Young with his new spectroscopic method of observation. 
 
 (&) Position-angles of first and fourth contacts: 
 
 These position-angles we determined on plates 8 and 41 from the following 
 measures : 
 
liBPOBT OF THE PHILADELPHIA PHOTOGRAPHIC EXPEDITION. 
 
 145 
 
 PLATE No. 8. 
 
 Radius of sun zz 3 1.4. 
 
 Length of > chord from N. point to point of contact = 18.25. 
 
 _ Q , _. 
 
 5 =.5793 = sin 35 24'; X2rr70 48' 
 
 O * i 
 
 Hence angle of first contact is 70 48' or + 289 12' 
 Computed angle 
 
 Difference. . 
 
 o 12' 
 
 PLATE No. 41. 
 
 Radius of 31111 = 30.835. 
 
 Length of y 2 chord from S. point to point of fourth contact 18. 
 
 39:|35 =>5837 _ s ; n35 o 43 , ; X 2 = 7 i 26' 
 
 Position-angle of fourth contact rr 108 34' 
 
 Computed angle =. io8 c 
 
 o' 
 
 Difference. 
 
 The points where the inner dotted circle of the diagram is cut by the arrow shows 
 the positions of contact as determined from the photographs. 
 
 (() Position -uni/tex /uid lir/gJits of the protuberances : 
 
 The determinations of the position-angles and heights of the protuberances on the 
 eastern limb of the moon are derived from measures on plate No. 24, the first taken 
 during totality, and those on the western limb, from No. 27, the last plate of totality. 
 
 The measures were made in the following manner: On plate 24 only the reticule 
 line on the eastern border is visible; but on plate No. 25, taken 28". 2 after, both 
 eastern and western lines are sharply cut; and prominence No. 6 is nearly as fully 
 developed on this plate as on that just preceding. I therefore obtained the exact 
 angle of position of the south side of prominence 6, on plate 25 ; then, from this 
 position, as point of origin of chords on plate 24, I determined the positions of promi- 
 nences 4, 5, and 7. As the chords drawn from the south side of prominence 6 to 
 protuberances i, 2, and 3 were too long to give accurate determinations from their 
 measures, I fixed the position of these prominences from measures made from the 
 north side (point B) of protuberance No. 5, previously determined by reference to the 
 south side of prominence No. 6. 
 
 On plate No. 27 the reticule line on both eastern and western limb is distinctly 
 photographed, and so this plate was alone used in determining the positions of the 
 western protuberances. 
 
 The measurements were made on glass positives, taken directly from the original 
 negatives by means of an orthoscopic lens, which enlarged the moon's image to a 
 diameter of 2.47 inches. The plates, firmly held by a wooden clamp, were supported 
 about six inches above a board covered with white paper, and placed before a large 
 north window. Sometimes the plates were parallel to the board, at others inclined, 
 19 E s 
 
146 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 with the angle opening towards the window. This, I found, was the best illumination 
 with which to examine the details of the " photographs and to make measurements 
 thereon. The legs of finely-pointed dividers were clamped to the proper opening, 
 and with this radius arcs were struck (cutting through the dark film of the photograph 
 to the glass below), having as their centers the points on the moon's border cut by the 
 declination line of the reticule. Through the intersections of these arcs a line was 
 carefully drawn, which gave the diameter of the moon's disk, which joined the N. and 
 S. points of its periphery. Chords were now measured from the N. and S. sides of 
 each protuberance to either the N. or S. points of position, according as the protuber- 
 ance was in the N. or S. semicircle. Half of a chord being the sine of half the angle 
 required, we can having previously obtained the moon's radius deduce therefrom 
 the position-angle. 
 
 These measures have been made with the greatest care, and can, I think, be relied 
 upon as accurate determinations. We do not think that in this case subsequent 
 micrometric measures will add to their precision, for, from the difficulty of defining 
 the exact boundary of the moon (especially on plate No. 24), the accuracy of the 
 determination of radii will not be increased by attempting a micrometric measure of 
 what we cannot see. 
 
 In the measurements a finely- divided millimeter scale was used, and the readings 
 were made through a lens magnifying eight diameters. 
 
 The adopted radius of the moon, on each plate, is derived from the measures of four 
 diameters, inclined 45 to each other. Every chord used is the mean of three measure- 
 ments. 
 
 The measures, in millimeters, serving as data for the position, are as follows : 
 
 Plate No. 29 second of totality. 
 No. of measure. Diameter of moon. 
 
 I 66. 4 
 
 2 66. o 
 
 3 66.2 
 
 4 66. 2 
 
 Mean diameter 66. 2 
 
 Radius 33. i 
 
 From S. point to S. side of prominence No. 6 17. 4 
 
 Length (measured on plate 24) prominence No. 6 '1.8 
 
 Plate Ac. 24 first of totality.* 
 No. of measure. Diameter of moon. 
 
 I 66.3 
 
 2 66. i 
 
 3 66.25 
 
 4 66. 3 
 
 Mean diameter 66. 24 
 
 Radius 33. n 
 
 S. side of prominence 6 to N. side of prominence 7 4. 2 
 
 S. side of prominence 6 to S. side of prominence 7 7. 2 
 
 S. side of prominence 6 to N. side of prominence (point B) 5 27. o 
 
 S. side of prominence 6 to S. side of prominence (point C) 5 17. 65 
 
 S. side of prominence 6 to N. side of base of prominence 4 29. 6 
 
 S. side of prominence 6 to S. side of base of prominence 4 28. 75 
 
 N. side (B) of prominence 5 to tip of S. wing of "eagle" 4 7 
 
 * See Plate IV. 
 
REPORT OF THE PHILADELPHIA PHOTOGRAPHIC EXPEDITION- 
 
 147 
 
 N. side (I?) of prominence 5 to tip of N. wing of " eagle "4 6. 2 
 
 N. side (H) of prominence 5 to center of prominence 3 8. 15 
 
 N. side (H) of prominence 5 to S. side of prominence 2 16. 6 
 
 N. side (15) of prominence 5 to N. side of prominence 2 ........ 20.0 
 
 N. side (I!) of prominence 5 to S. side of prominence I 24. 5 
 
 N.side (1!) of prominence 5 to N. side of prominence I 26.0 
 
 Plate No. 27 the last of totality.' 
 
 No. of measure. 
 
 1 .... 
 
 2 .... 
 
 3 .... 
 
 4 .... 
 
 Diameter of rnoou. 
 ... 66. I 
 ... 65.9 
 65.75 
 ... 65.9 
 
 Mean diameter 65. 94 
 
 Radius 32. 97 
 
 S. point to S. side of prominence 8 28. 5 
 
 S. point to N. side of prominence 8 35. 8 
 
 N. point to center of prominence 9 45. 2 
 
 N. point to S. side of prominence 10 41-4 
 
 N. point to N. side of prominence 10 36.3 
 
 N. point to S. side of prominence 1 1 24. 75 
 
 N. point to N. side of prominence 12 10.25 
 
 N. point to S. side of prominence 12 9.2 
 
 Table of the position-angles and heights of the prominences. 
 
 No. prominence. 
 
 Position-angles. 
 
 Height. 
 
 Remarks. 
 
 i 
 
 o / o / 
 
 cc q to $7 so 
 
 // 
 
 22 
 
 
 
 66 14 to 72 21 
 
 22 
 
 
 -i 
 
 8? is . 
 
 7< 
 
 
 4 (base of) .... 
 
 96 25 to 98 4 
 
 QO 3.Q 
 
 82 
 
 
 
 . IOO IO 
 
 
 
 
 101 23 to 118 36 
 
 136 
 
 Nebulous cloud. 
 
 6 .... 
 
 146 25 to 149 30 
 
 45 
 
 
 7 . 
 
 156 46 to 161 59 
 
 37 
 
 
 8 
 
 230 13 to 245 46 
 
 75 
 
 
 
 277 27 
 
 
 
 10 
 
 282 13 to 293 12 
 
 52 
 
 
 ii , . 
 
 3IS S4 to 121 12 
 
 44 
 
 
 12 
 
 342 7 to 343 58 
 
 15 
 
 D 
 
 
 
 
 
 
 As the moon glides over the solar disk the angle of position of any protuberance 
 referred to the disk of the moon is constantly changing, and the amount of displace- 
 ment depends on its position in reference to the line of the moon's motion. 
 
 The position-angle of the S. side of prominence 6 was first determined on plate 
 No. 25, and this point, thus determined, was taken as origin of chords on plate No. 
 24, taken 28 8 .2 before; but I find by computation that the position-angle of the 
 S. side of prominence 6, on plate 24, is 32' 32" N. of what it is on plate 25, 
 assuming in the computation that the prominence is stable in form and position on 
 
 * See Plate VII. 
 
148 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 the sun's circumference. Therefore, it follows that the position-angles of prominences 
 i, 2, 3, 4, 5, 6, and 7, as given in the above table, should be diminished by 3 2'. 5 to 
 make them correspond to the position-angles they had at the time plate No. 24 was 
 taken. 
 
 (d) Measurements on the solar spot in the SW. quadrant : 
 
 The drawings marked " plate 4" and "plate 42 "* were made with a camera lucida, 
 the spots being magnified under the microscope to exactly 2 1 diameters. They show 
 better than can be described the changes which took place in the dimension and form 
 of this spot in the interval between the times of 12'' 50'" 5 8 .8 and i4 h 49 48 8 .8. 
 Through each spot two lines are drawn, in the directions of the minimum and maxi- 
 mum diameters of the spot on "plate 42." The lines on 4 are respectively parallel to 
 those on 42, thus having the same position-angles. 
 
 On "plate 4" we see umbra and penumbra of a general circular outline; the intensely 
 bright projection into the margin of the penumbra is shown in the depression in the 
 northwest border. The breadth of the umbra in the direction of the northeasterly 
 and southwesterly line is 14". 2, which equals, at the distance of sun on the 7th of 
 August, 6,375 miles. Its width in the northwesterly and southeasterly line is 15". 5, 
 or 6,960 miles. 
 
 " Plate 42 " shows the change of dimension and of form which took place in i h 59 
 33", the circular outlines of umbra and penumbra having changed to elliptical 
 boundaries, the direction of the longer axis being northwest and southeast. The 
 umbra has widened in this direction 4", or 1,796 miles, and has, in the transverse 
 direction, narrowed its breadth 5".25, or 2,357 miles, while the outward projections of 
 the umbra (which can be identified in Plate 4) have become greatly lengthened. 
 
 The breadth of the umbra in northeast and southwest direction is 9". 6, or 4,3-10 
 miles; in the northwest and southeast line it is 19". 6, or 8,800 miles. 
 
 After the drawings had been made with the camera lucida a micrometer plate 
 was placed under the. microscope, without deranging the instrument, and the magnified 
 image of hundredths of inches on the plate was marked on the drawings. This gave 
 directly the value of the magnifying power used, and, by computation, the value on 
 the drawing, in fraction of an inch, of i" on the sun's disk. 
 
 8. OBSERVATIONS ON THE APPLICATION OF PHOTOGRAPHY TO THE DETERMINATION OF 
 THE TIMES OF CONTACTS DURING THE TRANSITS OF VENUS IN 1874 AND 1882. 
 
 We here venture a few remarks showing the peculiar value of photography in 
 the observations of the transits of Venus. 
 
 It has been shown that the sun's image was photographed on the camera plate 
 with an exposure of only 5 J of a second ; and the duration of exposure for any 
 other instrument can be determined with as great precision by the method which I 
 employed. 
 
 The instant the mechanical movement exposes the plate it also records the time 
 of that exposure on a chronograph connected with a break-circuit clock, and thus we 
 have an accurately delineated figure of the transit corresponding to a time marked on 
 
 * Plate X, Figs. 3 and 4. 
 
REPORT OF THE PHILADELPHIA PHOTOGRAPHIC EXPEDITION. 149 
 
 the face of the clock employed; and this correspondence of figure and time is unaffected 
 with personal equation either of sight or of hearing. Now, if the error and rate of the 
 clock can be entirely freed from the personal equation of the observer who determined 
 them, and if* the longitude of the station be found by the coincidences of the beats of 
 a sidereal clock with those of a break-circuit mean solar clock placed at the observatory 
 of the first meridian, we have the most accurate means of obtaining the absolute times 
 of contacts at the station of observation. 
 
 Thus we see how applicable will be photography to these observations, for the 
 data of the solar parallax will be given either by observing the absolute time of the 
 ingress or of the egress (which method is alone of value in the transit of 1874), or by 
 determining the iln ration of the transit of Venus over the solar disk. The photographs 
 are permanent phenomena, on which we can repeat our measures at leisure, with every 
 appliance of precision, while it is impossible to attain a similar degree with eye and ear, 
 from the difficulty of micrometrirally measuring at a precise instant the distance of 
 Venus from the sun's limb, and from the (recorded) distortions of Venus at contacts. 
 
 It will also be of great value to have a photographic record of the appearance of 
 Venus at the contacts, for if the disk of the planet then should appear on the plate 
 to depart from a circle and have attachments to the sun's limb, these distortions can 
 be measured and allowed for. 
 
 An idea may be formed of the apparent size of Venus during its transit of the 
 sun's disk from the fact that the umbra of the solar spot in the southwest quadrant is 
 15" in diameter, and that Venus at transit will subtend an angle of about 70"; so 
 that the planet would appear on the plate as a disk 4^3 times the diameter of this spot, 
 or as a disk of .107 inch diameter on an image of the sun of 3 inches in diameter. 
 
 The negatives of these photographs I find, from trial, will stand a magnifying 
 power of 50 under the micrometer, and as i" of arc will equal one seven-hundredth 
 inch on a solar image of 3 inches diameter, we can, with the above-mentioned power, 
 divide a second into ten parts. This supposes, however, that the bisection by the 
 micrometer thread is on a perfectly well defined point, and this does not exist in 
 the outlines of any photograph, and especially is the limb of the sun indistinct on 
 account of its shading, and of the manner in which the silver is deposited in the col 
 lodion film. 
 
 From actual experience in measurements under the micrometer, I find that we 
 cannot, as yet, hope to make a bisection on the sun's limb closer than one -half of 
 a second. On the boundary of the umbra of a well-defined solar spot we can read 
 to one-quarter of a second, and from this I should think that two-tenths of a second 
 might probably be attained as the limit in a reading on the limb of the image of 
 Venus. 
 
 But with measures as close as these, and the tables of Venus brought to the 
 accuracy which existing unreduced observations can give, we may reasonably hope 
 for a determination of the solar parallax comporting with the most exact astronomical 
 measures of this century. 
 
 A. M. MAYER. 
 
 THE LEHIGH UNIVERSITY, PA., September 7, 1869. 
 
REPORT OF PROF. C. F. HIMES, PH. D., OF DICKINSON COLLEGE, 
 
 PENNSYLVANIA. 
 
 DICKINSON COLLEGE, August 31, 1869. 
 
 MY DEAR SIR: According to request I make the following report of the operations 
 of the section of the photographic corps organized by you, consisting of Messrs. J. 
 Zentmayer, J. C. Browne, E Moelling, W. J. Baker, and myself, stationed at Ottumwa 
 City, Iowa, on the Des Moines River and Burlington and Missouri Railroad about 75 
 miles west of Burlington. 
 
 Our outfit consisted of 
 
 (1) The equatorial belonging to Pennsylvania College, Gettysburg, Pa., made by 
 Merz & Sohn, of Munich, of 6-inch aperture, 8)4 feet focal length, with spring-governor 
 driving clock, and mounted on a heavy wooden Fraunhofer stand. It was adapted 
 to the work to be done, as the other telescopes of the corps, by means of a modified 
 Huygenian eye-piece, camera with spring exposure-slide, and so forth. 
 
 (2) Photographic apparatus and chemicals, in regard to which a report will be 
 made to you by J. C. Browne, esq., who had charge of the purely photographic work. 
 
 (3) A make-circuit chronograph, with two pens and accessories. Other astro- 
 nomical and physical apparatus, including chronometers, was expected from a co- 
 operating astronomicla party stationed at the same place in charge of Prof. Stephen 
 Alexander. 
 
 We arrived at our destination on Wednesday evening preceding the eclipse. On 
 Thursday our apparatus was transported to the point of observation, finely located on 
 a bluff about a mile northeast of the city by Professor Coffin, and upon which, under 
 his instructions, a very convenient shelter-shed had been constructed 16 by 1 6 feet, with 
 photographic dark-room 4 by 9 feet in the southeast corner; the building in its length 
 occupying a position nearly north and south. The roof was constructed in six movable 
 sections of pine frames, covered with building paper, which could be slid up and down 
 wholly or partially very readily upon rafters projecting to the ground. According to 
 determinations from observatio .s by Professor Alexander it had a latitude of 40 58' 
 12" N., and longitude i h i ra 2O 8 .5 W. of Washington. 
 
 The telescope was set upon a cross of timber firmly let into the earth. It was 
 soon discovered that the clock-work, not of very superior construction, had become 
 deranged by transportation. Mr. Zentmayer, who fortunately for us formed one of 
 our party, took it apart and put it in as good running order as it was susceptible of, 
 thus enabling us with care to give the length of exposure necessary during totality 
 to secure the amount of detail and corona which our negatives show. 
 
 Cloudy weather set in on Thursday, and on Friday morning a severe thunder- 
 storm unroofed a portion of our shed. The sky continued overcast until about 4 
 
 151 
 
152 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 a. m. on Saturday, when Polaris exhibited himself, but for an instant. Regardless of 
 the depressing circumstances, we continued such preparations as could be made, with 
 apparently as much faith in clear weather as astronomical prediction. The adjust- 
 ment of the telescope in the absence of any assistance from the astronomical party 
 was mainly accomplished by Mr. Zentmayer, but the limited amount of fair weather 
 prevented an equally satisfactory adjustment of the reticule for determining angles of 
 position photographed upon the plates with the sun. The dawn of the ;th found the 
 sky still overcast, but gradually with a dry wind from the east the clouds gave way, 
 until at noon not a trace of cloud or haze was to be seen. These few hours afforded 
 us an opportunity to determine the actinic focus with great accuracy, which, owing to 
 a modification of the eye-piece just before leaving Philadelphia, had not been deter- 
 mined before. The chronograph assigned to us was by mistake left at Burlington, and 
 did not reach our observatory until Friday afternoon. Upon placing it in position, 
 and connecting one pen with the exposure-slide of the camera and the other with the 
 key upon which the seconds were to be tapped, it was found that, although it was not 
 in the best condition, it could be made to act satisfactorily by constant attention. As 
 it was necessary, however, to intrust it to volunteer assistants, and there was not 
 sufficient time to drill them properly, fearing that it might become deranged at a 
 critical moment, I did not deem it advisable to trust our record to it alone, and imme- 
 diately before the beginning of the eclipse, determined to make a record of the times 
 from a chronometer kindly placed at my disposal by Professor Alexander, the correction 
 for which will be found with the annexed schedule of negatives. I found it very easy 
 to note the fraction of a second by the click of the exposure-slide during the partial phase, 
 warning -having been given me before touching the trigger. I send this record because 
 that ma,de by the chronograph is not complete, and, perhaps, not reliable as far as it goes 
 as the instrument became deranged during the progress of the eclipse. During totality 
 an unforeseen delay of about a minute occurred in changing the exposure-slide to one of 
 full opening, and the plates were afterward exposed as rapidly as possible without an 
 opportunity to note the~time by the chronometer. Fortunately the chronographic 
 record at this place, though not as accurate as might be desired, furnishes very good 
 proximate data. Knowing from accounts of previous observers the liability to 
 encounter unforeseen obstacles at this point, I had adjusted the chronograph a short 
 time before totality, and although the seconds were not tapped during that time, the 
 pen connected with the camera-slide left a very distinct record of each exposure, 
 and an examination of the record of seconds for several minutes preceding totality 
 shows that the fillet had a very uniform motion, from which by measurement from the 
 last second mark to the marks recording exposures, the times of exposure of the totality 
 negatives, as given in the schedule, were obtained. The key by which the seconds 
 were recorded was also used by Professor Alexander to note several of his observations, 
 his records being interpolated between the seconds on the fillet. 
 
 It was found necessary to increase the length of exposure by detaching two of 
 the springs attached to the exposure-slide as the total phase was approached. The 
 exposure during the partial phase was made with the aperture of the telescope 
 reduced to two inches by a diaphragm placed over the objective. During totality 
 
EBPOET OF THE PHILADELPHIA PHOTOGRAPHIC EXPEDITION. 153 
 
 the full aperture was used, and exposures of six, twelve, and sixteen seconds given, 
 producing negatives of exquisite sharpness and detail, including a portion of the corona. 
 On account of the unreliable character of the clock-work it was deemed advisable that 
 Mr. Moelling should pay exclusive attention to it during the progress of the eclipse, in 
 order to detect and correct any irregularity it might occasion. The general plan of 
 exposure was to obtain five negatives, if possible, near the first and last contact, and 
 three near the beginning and end of totality, and at intervals of five and ten minutes 
 during the other phases. Thirty-four excellent, accurately timed negatives were 
 obtained, as given in the annexed schedule, in which D indicates diaphragm of two 
 inches, Ffull aperture; under Length of Exposure, under Drop, i indicates exposure-slide 
 with slit one-fortieth of an inch wide ; 2, with slit one-thirtieth ; 3, with slit one-twentieth; 
 and 4., with circular aperture size of eye-piece. Under Spring, i, 2, 3 denote that one, 
 two, or three springs were used upon the exposure-slide. Lost indicates that the 
 negative is worthless by reason of accident in manipulation or because the image of 
 the sun is only partially on the plate. The one immediately preceding totality displays 
 the limb of the sun beautifully cut up into Baily's beads, and the one taken at the instant 
 of the close of the total phase received the first rays of the emerging sun, and is of 
 interest in this connection as showing the red prominences. The first after totality 
 was taken with the full aperture of the telescope, and on that account is much fogged. 
 
 The coating and developing of the plates were exclusively committed to Messrs. 
 Browne and Baker, and the negatives obtained are photographically perfect. 
 
 Whilst we all feel fully satisfied with the results of our efforts, the success of which 
 has been so largely due to the thoroughness of preparation in all details, and the use 
 made of the experience of previous parties by you, we confess, with observers of this 
 phenomenon generally, that we feel that our present experience would have been of 
 great value. The distribution by you of the prints from negatives of last year at Aden 
 aided much in regulating developments and exposure. 
 
 The risk of failure, however, was much increased by our limited number and 
 limited time at the place of observation. 
 
 We were necessarily excluded from extended observations beyond our special 
 work, but there are several notes made that may be of interest in this connection. 
 
 I had watched the approach of totality anxious, if possible, to obtain a negative 
 with Baily's beads, and was surprised with the sudden transition to comparative 
 darkness at the instant of totality, and the peculiar brilliancy with which the stars 
 seemed to spring out without the long struggle through twilight. 
 
 The corona approached much more nearly in regularity the four-rayed form 
 generally given, and which had always seemed idealized or conventional. The SW. 
 ray was, however, unequally subdivided with the smaller part toward the north. 
 The whole seemed of a fibrous, slightly curled or twisted character, somewhat like a 
 cirrus cloud, and of silvery whiteness. The prominences, especially the large one a 
 little to the left of south, seemed, at the first instant, of a dazzling white, but after my 
 attention had been diverted for a few moments, it appeared of a brilliant decided rose 
 color, bordering on crimson, and remained of this color to the close. To Mr. Zent- 
 mayer, who was engaged at the camera and had used neither telescope nor screen, it 
 
 20 E S 
 
154 
 
 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 appeared white, with a slightly roseate hue. To Mr. Moelling, under similar condi- 
 tions, it appeared white throughout. Messrs. Browne and Baker, who had a short 
 glimpse of it from the door of the dark room, rather incline to the opinion that they 
 were white. 
 
 During the progress of the eclipse, Mr. Zentmayer, who examined the ground 
 glass of the camera from time to time to notice the position of the image of the sun, 
 called my attention to an appearance of small luminous bodies like meteors crossing 
 the dark image of the moon from cusp to cusp. Subsequently they were seen to pass 
 over the ground glass from outside of the field on to the image of the sun, where, of 
 course, they were lost, always coming from the same side. We were led by this 
 circumstance to regard them as most likely to be optical illusions, perhaps insects with 
 transparent wings or bodies, but the fact that other observers report a shower of 
 meteors between the moon and the earth, which seemed to be, as far as I can gather from 
 a hasty description, identical in appearance with the objects noticed by us, our obser- 
 vation may be of considerable value, especially as Mr. Zentmayer, who saw most of 
 them, is disposed not to regard them as optical illusions, since they must have been 
 caused by objects not less than 2,000 feet distant. 
 
 I cannot omit to mention the friendly manner in which we were treated by the 
 authorities and citizens of Ottumwa. 
 
 Favored as we were with a sky free from cloud or haze, and a beautiful point of 
 view, this phenomenon left an inerasible impression upon our minds and hearts. 
 
 CHARLES F. HIMES. 
 
 Prof. HENRY MORTON, PH. D. 
 
 PHILADELPHIA PHOTOGRAPHIC CORPS OTTUMWA SECTION. 
 
 Record of the chronometer times ami 'lengths of 'exposures of the photographic plates exposed during total eclipse of the sun, at Ottumwa, 
 
 Inua, August 7, 1869, as noted by C. F. Himes.* 
 
 No. 
 
 Chron. time of exposure. 
 
 Length of exposure. 
 
 Aperture. 
 
 
 Drop. 
 
 Spring. 
 
 I 
 
 2 
 
 3 
 
 4 
 5 
 6 
 
 7 
 8 
 
 9 
 
 10 
 
 ii 
 
 12 
 '3 
 '4 
 
 15 
 
 h. m. s. 
 o ^o 30 
 
 
 3 
 
 3 
 3 
 3 
 3 
 3 
 3 
 3 
 3 
 3 
 3 
 3 
 3 
 i 
 
 D 
 D 
 D 
 D 
 D 
 D 
 D 
 D 
 D 
 D 
 D 
 D 
 D 
 D 
 
 D 
 
 Lost. 
 
 Lost. 
 Lost. 
 
 Lost. 
 
 
 to i c 
 
 TO 2 St 
 
 
 
 
 10 14 57 glass second quality ..... 
 IO JO ^7 
 
 10 28' c 
 
 IO 32 5O 
 
 IO 37 28 
 
 10 41 41 
 
 10 49 22^ glass second quality .... 
 10 ?s s6 . 
 
 
REPORT OF THE PHILADELPHIA PHOTOGRAPHIC EXPEDITION. 
 
 Record of the chronametff times and lengths of exposures of the photographic plates, etc. Continued. 
 
 155 
 
 No. 
 
 C'hron. time of exposure. 
 
 Length of exposure. 
 
 Aperture. 
 
 
 Drop. 
 
 Spring. 
 
 16 
 
 "7 
 18 
 
 19 
 20 
 
 21 
 22 
 
 23 
 24 
 
 25 
 26 
 
 27 
 28 
 2 9 
 
 3 
 3i 
 32 
 33 
 34 
 35 
 36 
 37 
 38 
 39 
 
 h. m. s. 
 TO <;6 ^i\4 
 
 I 
 I 
 4 
 4 
 4 
 I 
 I 
 I 
 
 I 
 I 
 I 
 I 
 I 
 I 
 I 
 I 
 I 
 I 
 I 
 I 
 I 
 I 
 
 I 
 I 
 
 D 
 D 
 V 
 
 F 
 F 
 y 
 
 D 
 I) 
 D 
 D 
 L> 
 D 
 D 
 D 
 D 
 D 
 D 
 D 
 D 
 D 
 D 
 D 
 D 
 D 
 
 Baily's 
 Beads. 
 
 Fogged. 
 
 10 S7 ^6i 
 
 1 58 33. 32 about 6 seconds "| 
 
 10 59 19. 76 about 1 2 seconds I *- x , p * ure 
 f Totality. 
 
 II o 12. 62 about 16 seconds J 
 1 1 4 15 ... 
 
 
 
 I 
 
 3 
 3 
 
 . 3 
 
 3 
 3 
 3 
 3 
 3 
 3 
 3 
 3 
 3 
 3 
 3 
 3 
 3 
 
 11 6 12 
 
 ii 6 52 . . 
 
 ii 7 57% 
 
 ii 10 6^ 
 
 ii 16 i6j( 
 
 II 22 45 J^ 
 
 II 2O 27 . 
 
 II 17 ?7!4 . 
 
 II 47 ?8 . 
 
 II C? 1 1 A . 
 
 II C.1 41 
 
 II 54. 12}^ . 
 
 II ?? 12 . 
 
 II <? 4O . 
 
 II 56 IO 
 
 II ?7 58 . 
 
 II ?Q 54 . 
 
 II en 75/ . 
 
 
 D denotes aperture of two inches in diaphragm on objective. 
 
 F denotes full aperture. 
 
 Drop I indicates drop with slit in slide one-fortieth of an inch wide. 
 
 Drop 4 indicates drop with circular aperture size of eye-piece. 
 
 Spring I, 2, 3, indicates number of springs used on drop. 
 
 *The time for No. 39 was noted by chronometer Daniels jfr> " le reduction of which to Ottumwa mean time was 
 -|-jh j!m 58'.5; the times for the others were noted by chronometer Negus 2335, the reduction of which to Ottumwa mean time 
 was +5" 50" s8.o (p. 16). 
 
 f Within a second. 
 
156 ECLIPSE OF THE SUN, AUGUST 7, 1869. 
 
 The following article from the Journal of the Franklin Institute, Ixii, 3d series, 
 p. 54, is appropriately introduced here. J. H. C. C. 
 
 PHOTOGRAPHING THE COKONA. 
 
 BY PROFESSOR EDWARD C. PICKERING. 
 
 The difficulty in photographing the corona visible around the sun during a total 
 eclipse is mainly due to its small actinic power. To remedy this we must increase the 
 light in our camera as much as possible, and therefore when attached to Professor 
 Morton's Eclipse Party, in August, 1869, I proposed that a common portrait camera 
 should be used. As with such instrument we can obtain an impression of objects in a 
 comparatively dark room in a few seconds, it seemed probable that in two or three 
 minutes so bright a body as the corona would produce a very distinct impression, 
 even of its more remote portions. We found in Mount Pleasant, where we were sta- 
 tioned, two photographers, Messrs. Hoover Bros., who undertook to give this plan a 
 trial, and as a result they obtained a photograph, which is represented in the accom- 
 panying figure to double its original size. I believe the exposure lasted during nearly 
 
 the whole period of totality, the apparent motion of the sun being avoided by follow- 
 ing it with the camera. The aperture of the lens being much greater compared with 
 its focal length than that of any telescope, so .much light is concentrated that an im- 
 pression of a large part of the corona is obtained, giving one of the best photo- 
 graphs of this body yet taken. 
 
 A comparison with the view taken by Mr. Whipple in Shelby ville shows many 
 points of resemblance, and greatly strengthens any conclusions based on either. It 
 also proves that the structure common to both is solar, or at least not due to any local 
 irregularities in our own atmosphere. The indentation in the moon's limb marks the 
 position of the large protuberance then visible, and we readily perceive the bases of 
 the five points or streamers which were noticed at the same time,. The line N S gives 
 the direction of the sun's polar axis, and shows the increased height of the corona at 
 its equator, and the corresponding diminution at its poles. The experiment is so easily 
 tried by any photographer on the line of totality as to encourage the hope that in 
 future eclipses, views may be taken from a great many points Avith the largest portrait 
 cameras, and thus eliminating all local effects, show with certainty how much of the 
 corona is really solar. 
 
 MASSACHUSETTS INSTITUTE OF TECHNOLOGY, May 15, 1871. 
 
SUPPLEMENTARY NOTE BY PROFESSOR COFFIN. 
 
 The photographs of tho eclipse taken at Burlington have been measured by Mr. 
 Henry G. Fitz, under the direction of Mr. Lewis M. Rutherfurd, with the apparatus 
 constructed by the latter. Measurements were made of the N-S and E-W diameters 
 of the sun's disk as determined by the lines in the eye-piece of the telescope (which 
 appear clear and distinct in the photographs); the vertical and horizontal diameters of 
 the sun's disk when practicable; the distances and position-angles of the cusps, and 
 the distance of the limbs of the sun and moon on a line perpendicular to the line of 
 cusps. Care was taken to center the plate to correspond with the center of motion 
 of the instrument. 
 
 The photographs were taken with great care, and every known precaution used 
 to obviate error and secure work of a high order of precision. I had hoped to obtain 
 from them the apparent path of the moon across the sun and the times of contact 
 with a good degree of accuracy. But failure of health and latterly a disorder of the 
 eyes, which precluded the study and arrangement of formulas and all work in com- 
 putations, have prevented the contemplated discussion. A tentative discussion, how- 
 ever, has been made with the aid of Mr. H. L. Hodgkins, of Columbian University, 
 to determine the times of the first and last contacts. 
 
 For the first contact, plates 4 to 16* (see table p. 138), inclusive, gave the chro- 
 nometer time of i 2 h 50 o", which is almost identical with that noted by Professor 
 Young (p. 44). But the times derived from the several plates vary from 1 2 h 49"' o s to 
 i2 h so m 38 s . 
 
 For the last contact, plates 30 to 43 inclusive give the chronometer time, 
 14'' 50 47 s ; Dr. Gould's being 14'' 50 45" (p. 36), and Professor Coffin's 14'' 50'" 41" 
 (p 25); but the several plates give times varying from 14'' 50"' 30" to 14'' 52'" o 8 . 
 The angles of position have been determined from the E and W lines of each plate, 
 as the adjustment of the diaphragm of the telescope was made by that line. The N and 
 S line makes an angle of 89 30'. 4 with the E and W line from the E point toward 
 the N point. 
 
 The angles of position of the normal to the disks of the sun and moon, i. e., of 
 
 the center of the moon's disk from that of the sun, on plates 4 .to 17, vary from 
 
 70 40' to 71 28', the mean being 71 10^2'; and on plates 35 to 43 from 
 
 + 108 5' to +109 3', the mean being +108 35'.8, reckoned from the N point of 
 
 the sun's disk + toward the east. 
 
 Correcting the measurements for refraction and for defective adjustment of the 
 center of the sun's disk to the center of motion of the measuring machine would 
 
 * Plates uumbered 7 and 34 are not included ; it is doubtful if they were takjn 
 21 E S 1W 
 
158 ECLIPSE OF THE SUN, AUGUST 7, 180!). 
 
 probably diminish the discordances, particularly in the linear measurements, but not 
 to any great extent. The scale-readings for the moon's limb and the cusps are the 
 most discordant It has been suggested as quite probable that a higher magnifying 
 power was used in making these measurements than the plates would bear. 
 
 Still it is very doubtful that the most careful measurements and refined discussion 
 would produce results of the precision desirable in eclipse observations, and which 
 would secure preference of photographs to eye-observations. With all the care possi- 
 ble, the suspicion will remain that the development of the plates may have produced 
 changes, very small perhaps, but sufficient to produce distrust. 
 
 The Ottumwa photographs appear to have been taken with equal care with those 
 at Burlington, but imperfect adjustment of the lines of the reticle of the telescope 
 impairs their value for the determination of angles of position. 
 
 It is proper to state that the original reports of observations of the eclipse are 
 published as communicated to me at the dates of each (except some of Professor Alex- 
 ander's reports of times, the changes of which are noted in the text) ; and that all 
 changes in the original remarks or speculations on the eclipse and its results, when of 
 sufficient importance, are stated. 
 
 In conclusion, I express my obligations to Dr. Morrison and Mr. E. J. Loomis, of 
 the Nautical Almanac Office; to the former for computing predicted phases of the 
 eclipse, the latter for aid in preparing and arranging manuscripts and correcting proofs. 
 
 J. H. C. COFFIN, 
 Professor of Mathematics, United States Navy. 
 
 WASHINGTON, May, 1885. 
 
Solar fMipM,Auffust 7. fftM Sy Pro r Coffrfi.Bur/inff fort 
 
 HtfipurfintHff. 
 
 vv 
 
 fly Pro/ 1 HJrlson, M? Mffrsant. 
 
 Fit/. 3 
 
olnr Ecffpsr. August 7 /<*, By J>r OoiiM,Jinrli.ngtn. 
 
 Pfatt ff 
 
 fr m 
 
 I.. 'ill 
 
 / . 
 
r Kflipxi ..lutfunt 7 ItidU. 
 
 I'rof f .1. )'n/i/ir/ K ifr/i/i I//IIH . 
 
 MM 
 
 iliiiiliiiihiiilinili 
 
 r ai. 
 
 500 600 70O 800 OU IOOO 1100 1200 1300 MOO 1500 1600 1700 UOO 19OO 2000 2100 
 
 1900 2000 2100 2200 2300 2400 2600 2600 27OO 2800 29OO 2000 .1100 3200 55OO 3400 
 
 . <-/ne mtm/>fl<> u'ljjttfri frytrmj frf/fai/i f/fti/- f///fj ale Msur 
 /;/ir/>f fiin'.i in //if t/'/l/- f'Hua f'ftr'it' aif Mfjf f f'jfi i'r</ in i/tf .j/trrf;ti//t // f/if rfii-fm t/rta ///t' 
 
S,i/dr AV////.SV . .1 uplift 7 ."' /W6'.<V. /> in-tin rjti>ii , Ir>wa/. 
 
 PLATE IV 
 
 l-'rnni rimtot/raftli 3'C'J-/: Krf>t>.-mrr . r > * . 
 nVHUNGTOff MKAN TIME <t" .1H"L" OR It! 'AFTKH HKC.INXIKC. OF TIITsUJTY 
 
k~^ f\ t? 'lYrr 'a * 
 
 OP 
 
 [UHI VARSITY) 
 
Solcu-Eclifise. , August 7 ?* 1869. (^ttumii>a/: Iowa/. 
 
 PLATE V. 
 
 From Photograph N? 18. Exposure (5:* 
 
 OTTITMWA MEAN TIME 4-f 52? tfSi' OR44fAFTKlt HE G1NKIKC OJ-' TOTALITY 
 WASHINGTON ,, ., 5. 53 54, 
 
Solar Eclipse! Jiugust 7$* 1869. Oftotrnwa,', Iowa/. 
 
 ] 'LATE VI. 
 
 OTTl'MWA MEAN T1MK 4*' 53*? -JO 
 
 , , . , 5 . M- +it 
 
 From Photograph. Jf"J9. Exposure* l- s w 
 
 07? /-f.-JJ-i At'TKK HKCJNNlNt: OF TDTAI.1TY 
 
Salnrh'r/f/w. Jm/uKt 7 "' 
 
 VI.ATE vn. 
 
 From Photograph A'? i'7 /.*.x'"- s '" /r 
 
 JIVHLINGl'Off MEAlf TIMK 4" r>?41? OR l*SJfAFTKll 
 WASHINGTON ,i // 5 35 55 
 
 OF TOTALITY 
 

 
7f* IHti'J. Ottuniwa. Iowa. 
 
 PLATK VI 11. 
 
 From Photograph N"20. Exposure jffi-" w 
 
 OTTVMWA MEAN TIME / f .7 / f l:i > Oft L'H * Bf.TOItf:' THK f:.\D Of TOTALITY 
 , . , . .i 55. H3. 
 
Solar Eclipse-, .Ini/nxi 7. lilli'.i. 
 
 Prof. A.M.Mtii/er. liurlimjton , lown . 
 
 Plate X. 
 
 X 
 
 E 
 
 S 
 
 Plate 15. 
 
 4h. 21m. 18.9 s. 
 
 Fy.3. 
 
 Fy.4. 
 
 
 -E 
 
 Plate 4. 
 
 3h. ~id in. 14..") 
 
 t ..... i ; 
 
 CT 1O' 20* 3O* 
 
 1 ori drawings =.027 inch. 
 Ion the Sun = 449 miles 
 
 Plate 42 . 
 
 , r )h.55m. 38. 
 

 
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