y 7 THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA LOS ANGELES > '* ' PAPERS COMPARATIVE MERITS CATOPTRIC AND DIOPTRIC OR CATADIOPTRIC SYSTEMS LIGHT-HOUSE ILLUMINATION AND OTHER SUBJECTS RELATING TO AIDS TO NAVIGATION COMPILED FROM BRITISH, FRENCH, AND UNITED STATES REPORTS AND AUTHORITIES, FOR THE USE OF THE UNITED STATES LIGHT-HOUSE ESTABLISHMENT SERVICE. WASHINGTON: GOVERNMENT PRINTING OFFICE. 1861. Tc 377 TABLE OF CONTENTS. 1. Papers on the Comparative Merits of the Catoptric and Dioptric Lights for Light- houses, (British Parliamen- tary Eeport of 1857) 140 2. Plan for distinguishing Sea- coast and other Lights by Occultation, by CHARLES BABBAGE, Esq., &c., &c., &c., London 4357 3. Letter from LEONOE FBESNEL, Divisionary Inspector of Bridges and Koads, and member of the Light- house Commission, to Lt. Thornton A. Jenkins, U. S. Navy, Secretary Light- house Board, Washington City 58-61 4. Letter from L. BEYNATJD, En- gineer- in -chief, Secretary to the Light-house Com- mission, charged with the direction of the service, Paris, France 6166 5. Letter from HENBY LEPAUTE, Constructor of Lens Appa- ratus, Paris, France 6771 6. Letter from T. LETOTJENEAU, Constructor of Lens Appa- ratus, Paris, France 7177 7. Letters from WILLIAM LOED, B. N., Marine Surveyor to the Port of Liverpool, Eng- land 77-84 8. Letter from THOMAS STEVEN- SON, F. B. S. E., F. E. S. S. A., Edinburgh, Scot- land 9. Proceedings of the Northern Lights Lens Committee.. 10. Letter from Sir DATD BBEWS- TEE on the Dioptric System of Light-house Illumina- tion... 8590 I 9095 11. Letters from Messrs. ALEXAN- ASUKR MITCHELL & SON, on Screw-pile Foundations for Light-houses and Screw- Moorings for Buoys, and accompanying papers. .95 99 & 188 12. Eeport on Lightning Eods for Light-houses, by M. FAB- ADAY, London 100 101 13. Irish Lights, (Extract from Senate Document No. 488, 1st session, 2 9th Congress) . 1 01 103 14. Eapeseed Oil 103110 15. EefugeBuoy Beacon 110 16. Letter from JACOB HEEBEET, Secretary to the Trinity House, London 113118 17. Eeport of Hon. E. J. WALKBE, Secretary of the Treasury, Extracts from, on Improv- ing the Aids to Navigation in the United States 118-123 967GO TABLE OP CONTENTS. 18. Report of Lieuts. THORNTON A. JENKINS and EICHARD BACHB, U. S. Navy, to the Secretary of the Treasury, August 5, 1846, Extracts from, 123154 19. Comparison of the two sys- tems of Light-house Illu- mination, by LEONOR FRKS- NEL, &c., &c., &c 155175 20. Light-house service of France 176 188 21. Captain CANFIELD, U. S. Topo- graphical Engineer's, plan for giving warning of the extinction of lights 189 22. Mr. ALEXANDER SxEVENSON.on Light-house Illumination, Extract from Treatise on. 190221 23. An account of the construc- tion of the light-house at Havana, Cuba 221234 24. Report of the Chamber of Commerce of New York on PAGE. Lights and other Aids to Navigation 234240 25. The Electric Light, by Mr. FARADAY, &c., &c. , &c., Royal Institution of Great Britain 240244 26. Light dues levied on the ship- ping of the United States in Great Britain 244252 27. Report of the Light-house Board, March 13, 1858, comparing the economy of the present system in the United States with the old ' one, embracing a period of 5| years under each sys- tem of management 252 271 28. Letter from LEONOR FRESNEL, &c.,&c.,&c., May 7, 1861, to Commander Thornton A. Jenkins, U. S. Navy, Secretary of the Light- house Board, Washington City 272 CATOPTRIC AND DIOPTRIC LIGHTS. BRITISH PARLIAMENTARY REPORT, 1857. CATOPTRIC AND DIOPTRIC LIGHTS, PAPER BY MONS. LEONOPv FRESNEL ON THE OLD AND NEW SYSTEMS OF LIGHTS FOR LIGHT-HOUSES. [REPORT of Lieut. THORNTON A. JENKINS and Lieut. RICHABD BACHB, U. S. Navy, "On Improvements in the Light-house System and Collateral Aids to Navigation." Senate Doc., 1st session 29th Congress, No. 488, August, 1846, page 12-1.] After having balanced the advantages relative to the two systems of lights in view of their useful and economical effects, I ought to con- sider them with reference to their security and the facility with which they are served. I will reproduce, upon this subject, the observations inserted in a memoir of the 20th of April, 1830, in which I replied to the ques- tions which were addressed to me by the government of Sweden and Norway, in relation to the necessary measures to be taken to improve the lighting of its maritime coast : "The service of lenticular lights is, in the aggregate, less labo- rious than that of the reflector lights. The first demand at all times during the night the unremitted attention of the keeper. If, for example, the central lamp should become extinct during the absence of the keeper from the lantern, or while he is asleep, the horizon of the light would remain some hours plunged in total darkness, and the greatest objection which has been urged against our new system of illumination is the fear of such accidents. Happily an experience of seven years has dissipated that fear, and the lenticular lights have been distinguished up to this time by the regularity of their service. However, every precaution has, besides, been taken to replace promptly the lamp or its burner in case of extinction. The extreme simplicity of the day duty compensates the keepers for that to which they are subjected during the night. To snuff and replace the wicks, renew the oil, sweep the chambers of the lantern and the stairs of the tower, dust the apparatus, and sometimes wash with a little spirits of Avine the tarnished spots upon it, and, lastly, to wipe dry the glass of the lantern ; such is the principal daily duty which is divided between the keepers of the new lights, and which rarely occupies them more than two hours." Opinions thus expressed fifteen years since, based upon an experi- ence of seven years, have been greatly strengthened up to the present time, embracing a period of twenty-two years since the establishment of the Cordouan light, and sustained by the results daily offered of more than one hundred lenticular lights of the three first orders, established along the coasts as well of France as of different foreign powers. In this important point of view, then, the question seems to be irrevocably settled, and I Avill only add a few considerations relative to the application, more or less exterded, which may be made of the new system of illumination to the vast maritime coasts of the United States. FIRST. It has been objected that it would require too great sacrifices to be made to procure in that country keepers possessing the amount of intelligence requisite for the superintendence of lenticular lights. SECOND. That from distant points or stations the necessary repairing and renewing of the mechanical lamps would be attended with great difficulty. I will reply, with regard to the keepers, that the difficulty of obtaining proper persons to fill these subaltern stations appears to be most singularly exaggerated. In France they belong almost al \vays to the class of ordinary mechanics, or laborers, who make from 1.50 francs to 2.50 francs (27 to 46 cents) per day. Eight or ten days will suffice, ordinarily, to instruct a light-keeper in the most essential parts of his duty, receiving lessons from an instructor conversant with all the details of service; and two instruct- ing officers will be sufficient to prepare keepers for all the lenticular lights which could be successively established upon the coasts of North America. The information thus imparted would never be lost, and these officers might, besides, be aided by foremen or assistants, who could supply the place in case of necessity. In defence of this assertion I will cite the example of the administration of Norway and Sweden, which, after having obtained the assistance of a French 5 agent to put up the apparatus of the two first lenticular lights, which were sent from Paris in 1832 and 1836, has provided since, without any foreign assistance, for the placing as well as the organization of the service, of all the lights of the new system which it has succes- sively established. With reference to the eventual repairs of the mechanical lamps, it is to be considered FIRST. That, in consequence of the great strength of the pieces of which the new model of mechanical lamps is composed, they will perform well for a number of years without requiring anything more than a proper attention to their cleanliness. SECOND. That the ordinary assortment of a dioptric light-house comprises three of these lamps, which afford a sufficient guarantee against the chances of accident ; and, besides, we may, by increasing a little the mean expense, increase the number to four under some circumstances, as an exception to the general rule. THIRD. That the repairs of the implements under discussion may be easily made by all the clock or watchmakers, or other mechanicians, to whom we have recourse for repairing the revolving machinery of light-houses. I conclude with the remark that, if it be determined to multiply the application of the new system of maritime illumination in the United States, it seems to me that it will be expedient to engage one of the foremen employed in the manufactory of our mechanical lamps to go to, and remain in the country for several years. By that measure, which would be attended with very little expense, all the difficulties which might presnet themselves at first in establishing lenticular lights would be removed, and the perfect regularity of the service of these new establishments would be insured. LEONOR FRESNEL. PARIS, December 31, 1845. PAPER ON FRENCH LIGHTS ACCOMPANYING REPORT OF THE LIGHT-HOUSE BOARD OF THE UNITED STATES. [REPORT or Lieuts. THORNTON A. JENKINS and RICHARD BACHE, U. S. Navy, to the Secretary of the Treasury, June 22, 1846. Senate Doc., 1st session 29th Congress, No. 488, p. 70.] The Light-house Department of France is attached to the official duties of the minister, Secretary of State for the Interior, and is under the immediate control and direction of the Minister of Public Works, charged with the administration of the bridges and roads. A central public board has the management of all light-houses, buoys, beacons, and sea-marks on the coasts, which is composed of eleven distinguished scientific and professional individuals, who are appointed by the government, including the engineer, secretary to the commission, and his assistant. This board is presided over by the Minister of Public Works, and in his absence by the Under Sec- retary of State for that department. This mixed commission, called the "Commission des Phares," is composed of naval officers, (of whom there is a majority,) of inspectors of the corps of bridges and roads, and of members of the institute. It prepares the projets for all new lights, and the general council of bridges and roads judges of the propriety of all schemes for that branch of service, under the four heads of Architectural Design, Mode of executing the Works, Estimate -of the Expense, and the Preparation of the Specifications of the Works. The light-house commission of France is not an administrative body, but is occupied solely in questions of principle or design, and leaves to the general directory of bridges and roads the care of providing the necessary means for the construction of new works, the expenses of illumina- tion, y T. Letour- neau. The floating lights at present in use are composed of a greater or less number of metallic parabolic reflectors, adjusted around the masts of the vessels upon Avhich they are placed. They are divided into fixed lights, and varied by flashes. Besides the inconvenience due to the multiplication of lamps, there is not a sufficient quantity of light produced by this apparatus. NEW SYSTEMS. The new floating lights are, in the first place, of four refracting apparatus for fixed lights, embracing an angle of 212 degrees. Sec- ondly, of spherical reflectors, making for the optical part the same focus which it should have with the horizontal amplitude of 148 de- grees. These apparatus represent very nearly a weight equal to that of eight reflectors which they replace, and an illumination each by a lamp consuming 0.045 grammes per hour. They are placed in suspension, equidistant from each other, and in whatever manner, always directed to the horizon, and whatever point occupied by the observer, a light greatly increased. The prices of these apparatus are fixed for the set of four optical parts, reflectors and lamps, 4,800 francs. For the lantern 3,000 francs. In general the old lanterns may be used for new apparatus. Revolving machinery for floating lights, by T. Letourneau. As much from communicated as personal observation, I have been convinced of the inconveniences arising from the placing of rollers 75 between plane parallel surfaces, as very little time suffices for them to make a succession of haclmres or indentations sufficiently marked to change the regularity of the revolutions, and in the hands of incom- petent keepers are operations of difficulty. To obviate these inconveniences, this is the way I have proceeded. Preserving the same number of rollers, I caused them to be placed between two conical surfaces having a common centre; in that way I have obtained the regular development of movement following the generation of the surface of revolution. Lens apparatus for lighting sea steamers from their wheel-louses and boivs, by T . Letourneau. I find myself conducted in descending the ladder of applications of optics, to acquaint you with the last modification, that of lights to prevent collision at sea. The result of detailed experimental researches made by some of my friends among the officers of the French navy, has been to engage me to construct, according to the ordinance regulating it, small ap- paratus for colored lights to produce a light sufficiently intense to be distinguished (if a white light) ten miles in good weather. In conse- quence of the success with which I have met in these lamps, I find myself within the last two years charged with the supplying of all that are required for the navy and for the commercial marine, both of which are subjected in the ordinance to the same general rules. I do not know if the United States has taken steps in this impor- tant matter similar to those of the British Parliament and of the ordinance of Gen. Cavaignac, to insure a uniformity in the manner of distinguishing steamers at night at sea, and to determine at con- siderable distances the courses steered. SERVICE AND REPAIR OF THE APPARATUS. No changes worthy of note, so far as I know, have been introduced into the regulations relating to the lighting service, except such as relate specially to the modification of the apparatus, and which may have been considered worthy of the attention of those to whom they were entrusted with a view to test their applicability. Lamps. There are at present two descriptions or systems of lamps, that of Mr. Henry Lepaute and mine; there is also a third one undergoing 76 trial, but which, however highly recommended for its simplicity, is yet suffering from doubts as to its durability and the regularity with which it will perform. I have had for two months one of these new lamps placed on board of a steamer running at night on the river Rhone; but. besides not having received reliable intelligence in relation to it, that experiment would not prove any thing, even if it were satisfactory. The present question is between the two first lamps. As you are already aware, sir, that while M. Henry Lepaute's lamp succeeded the Carcel lamp, mine has succeeded his. The sys- tem of M. Henry Lepaute was announced, at its introduction, as pos- sessing superior qualities of combination, while mine has travelled on its own way noiselessly. My lamp is the counterpart of Mr. Lepaute's: it is the solidity of it which gives it the most merit, in my opinion. To bring at once this delicate subject to a close, I would desire that the commission make a trial of both lamps. Lamp icicks. For some time past I have been making trial of different tissues for wicks. The object of these researches was to get rid of the ope- ration of trimming the wicks during the night. I have long known how prejudicial the operation is to the service, but I have been com- pelled to abandon the subject. Lens apparatus constructed ly me for Frame, England, Scotland, Ire- land, Spain, cC-c., since 1835. In furnishing the list of apparatus constructed for these different countries, I cannot say that it contains all; by other hands you will receive the complement. Mr. Wilkins, of London, informs me that he will forward to you a list of the lights put up in England, Ireland and Portugal, the great part of the optical parts of which I have supplied. You will find from page 3 to 7 of my notice, the table of apparatus constructed by me before and since 1845. excepting those of England, Ireland and Portugal, which I have sent often without knowing their destination. Value of tJie apparatus. The price of the apparatus has not changed. 77 Oil for illuminating light-houses. All the experiments which have been making for u long time upon the different kinds of oils, have given results showing them to be in every respect inferior to that obtained from colza. The rich oleagin- ous quality of that grain, and the quantity of land prepared for its culture, have rendered it of great importance ; besides which, the oil is now prepared in the most perfect manner. A friend of mine in Normandy, who is familiar with the modes of preparing the land for the culture of this plant, has promised to address me shortly on the subject, and furnish to me in detail an exact account of the process. For the present, I must confine myself to the following hints : Rich land is preferred for the cultivation of the colza : but, how- ever, it is commonly the custom in Normandy to sow the colza upon the fields from which wheat has been cut. The north of France is its peculiar region. Markets. The principal markets for colza oil are : for the north of France, Lille and Coutrai, and for the west, Caen and Rouen. The price is necessarily variable, its average rate is 72 francs the hectoliter for the first quality clarified.* The prices may differ greatly at certain ports for transhipment, depending upon the small or large number of emigrants applying for passage. MARINE SURVEYOR'S OFFICE, V Liverpool, November 20, 1851. SIR : I regret that my absence from Liverpool for a long period, in consequence of ill health, should have caused your letter from the Light-house Board of the United States to remain so long unanswered. Having only recently returned to my official duties, I now hasten to reply to the question proposed in your communication of May last, which, I trust, will be found satisfactory, and should further informa- tion, or explanation of any matter connected with the marine depart- A hectoliter is a little over 26 gallons, making the price of the first quality clarified colza oil in France 55 cents per gallon, while sperm oil ranges in this country from $1 to $1 50 per gallon. 78 ment at this port, be required by the Light-house Board of the United States, both the dock committee and myself will have much pleasure in furnishing it. 1. No change has been made in the mode and materials for light- houses at this port. 2. The best description of mortar for resisting the action of salt water, &c., is that composed of sand, lime, smithy ash ; and the best coating for light towers, is paint made of pure white lead, with sand thrown on it while the paint is in a liquid state. 3. No Fresnel lights have been introduced here. Parabolic re- flectors of twenty-one inch diameter are in general use at the light- houses, with the exception of the two Hoylake light-houses, in which parabolas of twenty-nine and twenty-seven inches are used. Refined olive oil has been introduced and burnt at the various light-houses and light ships, instead of sperrn oil. Since the year 1847, the saving in cost price, as compared with sperm oil, is about forty per cent. : and the illuminating powers are fully equal, if not superior, to those of sperm oil. 4. The best reflector in use is the parabolic. The proportion of silver used here is six ounces to the pound avoirdupois of copper. They are made of various prices and qualities, varying from two ounces to six ounces of silver to the pound of copper. Their illumi- nating powers and focal distance of lamp burner from reflector, are tested with those in use by means of the intensity of the light re- flected by them. 5. Argand lamps are used in reflector shore lights. (j. The ventilation in the shore lights is effected by a chimney and turn-cap on the summit of the light-room or lantern ; air valves in window frames and sides of light-room ; and copper tubes over the lamp cylinders to carry oif the smoke. 7. The materials of lanterns in the light-houses and sizes of glass vary considerably. In the Crosby light-house, (one of the last erect- ed,) the lantern is of wood, lined with sheet iron ; the window frames of iron ; the panes of glass, of which there are three, are of the di- mensions of six feet by three, glazed with putty and pins. The as- tragals are vertical, and although very strong, obstruct very little light. In the Rock light-house, built after the plan of the Eddy- stone light-house, the window frames and roof of lantern are of copper ; there are sixteen squares of glass in the round, four ditto 79 in depth ; the squares are two feet five inches by two feet ; the lan- tern is fifteen feet six inches in diameter : the astragals are vertical and horizontal. 8. The burners of the lamps are tipped with silver to prevent their too rapid decay from the action of the flame. 9. The best parabolic reflectors, after being twenty years in use with good care and attention, are not perceptibly deteriorated. The inferior quality are not used here. 10. A set of the best lamps, with silver-tipped burners, with good cure and attention, will last twenty or thirty years, with occasional repairs and the renewal of the burners, which last on an average three or four years. 11. The repairs of illuminating- apparatus are made under the di- rection and superintendence of the dock and marine surveyors. 12. The lamps and reflectors in the light-ships are not mounted on gimballs ; but parabolic reflectors of 21 inches diameter, similar to those in the light-houses, are used in the light ships, and lamps with a flat wick two inches wide ; the oil cistern is placed at the back of the reflector, and the cistern is ingeniously subdivided by partitions perforated with holes, to prevent the flooding of the oil by the ship's motion. The introduction of these improved light-ships, lanterns, and reflectors, by which a light is produced equal to that shown from the light-houses, is due to Mr. Hartley, dock surveyor to the Liver- pool dock trustees. 13. The greatest improvement made in the light-ship's moorings, is the introduction of wrought-iron welded studs in the chains, in- stead of the common cast-iron studs. These improved chains arc used in the thirty fathom lengths next the bows of the light-vessels, and the chains have been found to break much less frequently than they did prior to their introduction. The remaining portion of the light-ship's moorings are of the ordinary stud-chain. The buoy moorings vary in size, according to the dimensions of the buoys ; the chains are made without any studs ; the sinkers are of the shape and size shown in the accompanying drawing. 14. The fog signals in use at the light-houses and light-ships con- sist of bells and gongs. 15. The material I should recommend for buoys, floating beacons, and light-vessels, is iron. The colors, shapes, distinguishing marks, =. r =32.4 burners. 16 Maximum lustre or brilliancy corresponding to the axis 66 burners. Economical effect 62 ' 160 35 grammes=:l,776. (C.) "Sideral" reflector of Bordier Marcet, formed of two para- bolic metallic mirrors, with a diameter of 0.344 metre, (13.54 inches,) and an aperture of 0.187 metre, (7.364 inches,) illuminated by a lamp burning 50 grammes (1 oz. 12.25 drachms avoirdupois) of oil per hour. Uniform brilliancy or lustre in all the azimuthsizi4 burners. The extent illuminated, after deducting the spaces occupied b}~ the lamp and the frame, is about 285 degrees, or 17,100 minutes. Useful e/ect=4: x 17, 100=68,400. Economical e/ect= ~~= 1 8 6 8 . 157 The foregoing results confirm the following principles, the evidence of which springs moreover from a simple enunciation of them : 1st. The useful effect of a parabolic reflector increases with its di- mensions and with that of the illuminating body. 2d. The economical effect of a reflector of given dimensions is great- est when the lamp-burner is smallest. 3d. The divergence is greatest when the flame is most voluminous, or when the reflector is smallest. We cannot, then, (all other things being equal,) augment the economical effect of a reflector, without di- minishing its useful effect that is to say, without reducing its bril- liancy or intensity, and consequently its range. The reduction of the volume of light within certain limits is particularly objectionable when it appertains to eclipse apparatus, in which case it limits the width of the luminous cone, and consequently augments the length of the eclipses.* The same reduction applied to the crowns (foci) of reflectors composing a fixed light apparatus, may weaken the light in their intervals to such a degree as to produce dead angles, or be- come completely obscured to the observer beyond certain distances. It is further proper to remark that the horizontal divergence is not lost for useful effect, but that the divergence in the vertical sense only profits the navigator in the limited angular space comprised be- tween the tangent at the surface of the sea and the ray terminating at the distance of some miles from the light. Finally, there is for the calibre of the lamp-burners applicable to reflectors of given dimensions, and destined for the illumination of an equally determined range, a maximum beyond which prodigality of light ensues, and a minimum within which the illumination becomes insufficient." Useful and economical effect of dioptric apparatus. "Before commencing an analysis of the effect of the light of the lenticular or dioptric apparatus, I will state First, That these lenses always contain, independently of the fixed or movable dioptric drum, a subsidiary catoptric or catadioptric part, the useful effect of which is combined with that of the principal part. It was to obviate the defect of divergence that Bordier Marcet invented his large double parabolic reflectors with double focus ; but that combination caused too great a loss of light. 158 Second. That when these lenses are not required to illuminate the whole of the horizon, that side which remains deprived of light is fitted with spherical reflectors (metallic) in place of the dioptric drum, which adds about one-fifth to the intensity of the sector directly corresponding. That being stated, I now proceed to present the photometric results obtained from different lenses of the four orders of dioptric apparatus. [Lenticular apparatus of the first order.] (A.} First order lenticular apparatus for a fixed light, with accessory catoptric part. * Lustre or brilliancy of the dioptric drum =360 burners. Mean brilliancy of mirrors 7 upper zones=80 ) _ 12Q burnprs 4 lower zones = 40 j- Total amount of brilliancy=480 " Calculation of the useful effect. 1st. The dioptric drum illuminating equally the whole of the horizon, (except about 26, being computed the amount of space occupied by the frames of the apparatus, and that of the lantern, )=360 burn- ersx20,000' = 7,200,000 2d. 7 zones of upper mirrors =80 burners X 20, 000'= 1,600,000 3d. 4 zones of lower mirrors, omitted for one-eighth of the circumference, for the necessary passage of the keepers,= 40 burners X 17, 500'= 700, 000 Total of useful effect 9,500,000 ci i * 9,500,000 Economical effect = -- 750 gramrnes= 12,667. Notwithstanding the decided adv.xi,tages which the catadioptric zones present, com- pared to the mirrors, we may, by reason of their economy, prefer, under some circum- stances, the second combination to the first for lenticular apparatus of the first order. 159 If the apparatus illuminate only three -fourths of the cir- cumference of the horizon, the useful effect will be re- duced to 7,200,000 To which must be added the effect of the reflector occu- pying the vacant space in the dioptric drum, one -fifth (360 burners X 5, 000'=: 360, 000 Useful effect of the apparatus, for 270= 7,560,000 7,560,000 1st order, economical effects ^r^- 1A AOA 750 grammesr=10,080 (a 1 ) First order lenticular apparatus for a fixed light, luith accessory catadioptric part. Lustre or brilliancy of the dioptric drum 360 burners. Cupola or upper zones=:. 140 burners ) 9AA tl Lower zones= 60 " J Total brilliancy 560 Calculation of the useful effect. 560 burners X 20, 000'= 11,200,000 From which must be deducted for the passage of the keepers, 60 burners X 2, 500'=. 150,000 Remainder of useful effect= 11,050,000 11,050,OCO Economical effect =^50" grammes = 14,733. If the apparatus illuminate only three-fourths of the cir- cumference of the horizon, the useful effect becomes reduced to 560 burners x 15, 000'= 8,400,000 To which must be added, as in the other case, for the advantages of the reflector occupying the open space in the dioptric drum, one-fifth (360 burners X 5, 000')=: 360,000 Useful effect of the apparatus, for 270 8,760,000 8,760,000 Economical effect = 720~~grammeB = 11,680. 160 (a?) First order revolving lenticular apparatus, with accessory catop- tric part. Brilliancy or lustres, measured upon one-half of the amplitude of the luminous beam, emitted from a lens of one metre (39.38 inches) in height, and occupying a space of 45: Brilliancy or Lustre. Answering to the divisions BURNERS. BURNERS. 210' 4(?) 77 The annexed brilliancies of light are the results 180' 150 of means of different experiments. 150' 120' 90' 800 2,000 2,900 1,400 2,450 3 300 It is just to remark that all the divisions have intervals of thirty minutes, BO as to distribute, in effect, the partial products of the mean GO' 30' 3,700 3, 900 3,800 intensities into the angular distances. 0' 4,200 4,050 15,552 The useful effect of a lens = 2 x 15,552 X 30'= 933,120 Ditto of the 8 lenses of a dioptric drum Ditto of 11 zones of mirrors, as before Total useful effect 9,764,960 Economical effect -w^. 7oO grammes = 13, 020. *7,464,960 2,300,000 9,764,960 If the apparatus illuminate only three-fourths of the horizon, the useful effect will be reduced to 7,758,720; and the economical effect to 10,345. We have given 7,200,000 to the dioptric drum of a. fixed UgMa.n amount which seems satisfactory, in consideration of the degree of uncertainty attending photometric opera- tions. 161 (b) Second order lenticular apparatus for a fixed light, with a catadi- optric accessory part.* Lustre or brilliancy of the dioptric drum = 160 burners. Upper part, or cupola = 76 Lustre or brilliancy of the catadioptric zones lower zones = 28 Total lustre or brilliancy in burners 264 Calculation of useful effect. 264 burners x 20, 000'= 5, 280, 000 From which must be deducted for the space of one-sixth of the circumference, which is not supplied with the catadioptric zones below the lenticular drum 93,333 Remainder of the useful effect =: 5, 186, 667 5,186.667 Economical effect = 500 grammes = 10, 373. If the apparatus illuminate only five-sixths of the circumference of the horizon, a reflector is placed on the side of the earth; the useful effect then becomes reduced to 4,706,667, and the economical effect to 9,413. For an illumination embracing only three-fourths of the circum- ference of the horizon, the useful effect is then reduced to 4,120,000, and the economical effect to 8,240. (ty) Second order revolving lenticular apparatus, with catadioptric accessory part. The lustres or brilliancies measured upon half of the amplitude of the luminous beam emitted from a lens of 80 centimetres in height, occupying a space of 30 degrees. * For the second order (and with greater reason for the inferior orders) we dispense with the use of the concave mirrors for the subsidiary part of the apparatus. The increased use- ful effect of that part which is always faced is, above all, important in the revolving dioptric drum apparatus to prevent, at a certain distance, the complete disappearance of the light or positive eclipses. 11 162 Brilliancy or Lustre. Azimuths. Angular distances. Products. Observations. Answering to the divisions. Means. BUBNEBS. 210' 180' 150' 120' 90' 60' 0' 3(?> 61 274 492 907 933 1,080 32(?) 167.5 383 699.5 920 1,006.5 30' 30' 30' 30' 30' 60' 960 5,025 11,490 20,985 27,600 60,390 126,450 Useful effect of a lens 2 X 126,450 = 252,900. Useful effect of 12 lenses of the drum 3,034,800 Useful effect for catadioptric zones 1,986,667 Total useful effect == 5,021,467 5,021,467 grammes = 10,043. Economical effect = 500 (c) Lenticular apparatus for a fixed light of the third order (larger size) ivith catadioptric accessory part. Brilliancy of the dioptric drum = 50 burners : brilliancy of the catadioptric dome or cupola 20 burners; total 70 burners. Useful effect = 70 burners X 20,000'= 1,400,000. 1,400,000 190 grammes = 7, 368. Economical effect = If the apparatus illuminate only four-fifths of the circum- ference of the horizon, the useful effect is reduced to- 1,120,000 To which add for spherical reflector 40, 000 Total useful effect = 1, 160, 000 1,160,000 Economical effect -.^ nr . c 190 grammes = 6, 105. Catadioptric apparatus of the third order (smaller size) for a fixed light. Brilliancy of the apparatus = 31 burners. Useful effect = 31 burners x 20,400' = 632,400. 632,400 Economical effect = ^-? 115 grammes = 54,999. 163 If the apparatus illuminate only three-fourths of the circumference of the horizon, the useful effect will be reduced to 474, 300, and the economical effect to 124. It must bo remembered that this apparatus may be illuminated with a decided advantage by means of an ordinary Argand lamp with one ivick, with which we will obtain the following results: Brilliancy of the apparatus = 25 burners.* Useful effect = 25 x 20,400' = 510,000. 510,000 Economical effect . = TT~ 60 grammes 8,500. Fourth order catadioptric apparatus for a fixed light (larger model) Brilliancy of the apparatus =. 15 burners. Useful effect = 15 X 20,400'=: 306,000. v . , . 306,000 ~4 grammes =5, 100. If the apparatus illuminate only three-fourths of the horizon, the useful effect will become reduced to 229,500. and the economical effect to 3,825. Fourth order catadioptric apparatus (smaller model) for a fixed light. Brilliancy of the apparatus = 9 burners. Useful effects 9 X 20,400'= 183,600. 183,600 Economical effect = -45 grammes = 4> 080 . If the apparatus illuminate only three -fourths of the circumference of the horizon, the useful effect becomes reduced to 137,700, and the economical effect to 3,060. General observations upon photometric measures. The photometric results from which I have deduced the values of the useful effects and of the economical effects of the various orders of catoptric and dioptric apparatus should only be considered as simple approximations. New experiments upon apparatus of the same kind The catadioptric apparatus of 50c. (19.69 inches) diameter, illuminated thus by an ordinary constant level lamp, burning 60 grammes (2 ounces 1.9 drachm avoirdupois) of oil per hour, offers a very advantageous combination for the illumination of the entrances to ports and roadsteads, with ranges of 12 to 15 nautical miles. One keeper is sufficient to perform with ease all the service ; and the ordinary annual expenti does not exceed (in France) one thou- sand to eleven hundred francs ($187. 50 to $206.25. ) 164 would show, without doubt, very remarkable differences, not only because of the greater or lesser precision which the construction of the optical pieces may present, and of the difficulty of obtaining the identity of brilliancy, in the unity of light, but also in consequence of the nature of the photometric experiments, where it becomes neces- sary to estimate by the eye the equal intensities of shadows produced by light, often of different tints. These approximations are always sufficient to establish results exact enough between the effects of the different illuminating apparatus to be compared, and give much more correct ideas as to their relative values than can be deduced from observations upon the absolute range of the lights. Service of the Catoptric lights. The fixed catoptric lights established upon land, and illuminated by a small number of reflectors, say from six to eight, may be attended by a single keeper, especially if he be assisted by his family. If the apparatus be a revolving one, or if the number of reflectors be greater than six or eight, it will become, ordinarily, necessary to employ two keepers, as well to superintend the light during the night, as to maintain in a proper manner the illuminating apparatus and fixtures. If the light be placed in an isolated position at sea, three keepers at the least are necessary to assure regular attendance. In such cases, these agents (keepers) are relieved at regular intervals, and permitted to return to the continent for fifteen days or a month. Service of the Lenticular lights. The lenticular lights of the fourth order, and of the third order smaller model, require but a single keeper to superintend them, except in cases when situated at isolated points at sea. Two keepers are required to superintend the lights of the third order larger model, and the second order, in consequence of the use of the mechanical lamps in those lights. Three keepers are required for the superintendence of lights of the first order. For lights of the second and third orders, in isolated positions at sea, it is necessary to employ three keepers, and four keepers for lights of the first order similarly situated. 165 COMPARISON OF THE TWO SYSTEMS OF LIGHTS. Parallel beticeen the Catoptric and Dioptric lights. The preceding developments have appeared to nie indispensable, as preliminaries to the establishment of a parallel between the two systems of illuminating light-houses. I will consider the two systems under the following heads : 1st. The absolute useful and economical effects. 2d. The first cost of the establishment, and of the repairs and main- tenance. 3d. The facility and safety of the service. Apparatus of the fourth order, smaller model. SEC. 1. Absolute useful and economical effect of the illuminating appa- ratus. The brilliancy of a catadioptric apparatus of 30c. (11.8 inches) interior diameter, illuminated by a lamp burning 45 grammes (one ounce, nine and four-tenths drachms avoirdupois) of oil per hour, has been found equal to eight or nine burners. The brilliancy of a "sideral" reflector, illuminated by a lamp burn- ing 50 grammes (one ounce, twelve and tiventy-flve hundredths drachms avoirdupois) of oil per hour, is equal to four burners. This brilliancy of the first is at least double that of the second. The useful effect of the catadioptric apparatus of the fourth order, illuminating three-fourths of the circumference of the horizon, is represented by 137,700. The useful effect of the "sideral" reflector is equivalent to 68,400. Comparison of the second to the first =: 1 to 2. Economical eifect of the catadioptric apparatus = 3060. Economical effect of the "sideral" reflector == 1368. Comparison of the second to the first = 1 to 2.24. If we take for a term of com- parison the ordinary reflector, (a coquille plate, ) the superiority of the catadioptric apparatus will be still more decided. With regard to the concave parabolic reflectors, or " photophores," I will not introduce them into this parallel, in consideration that they can only serve in isolated cases for the ordinary .illumination of the entrances to har- bors, upon an amplitude of not more than twenty degrees. Apparatus of the- third ordet, smaller model. The apparatus of the third order, smaller size, illuminated by an ordinary fountain, or constant level lamp, carrying one burner and one 166 wick, consuming 60 grammes (two ounces one and nine-tenths drachm avoirdupois) of oil per hour, or one burner with t ico wicks, consuming 115 grammes (four ounces and one drachm) of oil per hour, have no equivalents in the catoptric apparatus in use at present. A "sideral" apparatus, of the same useful effect, would be of a dimension which would render the construction of it very difficult and very expensive, and would require, relatively, a very great con- sumption of oil. Neither could we supply it in a proper manner by the use of parabolic reflectors, except they were made expressly for the purpose, of very small dimensions, to allow a sufficient number to distribute properly the light upon three-fourths of the horizon. It is evident, moreover, that that embarrassing combination would require a consumption of more than 200 grammes (7 ounces) of oil per hour. The old light of Cette. (Herault.) provisionally illuminated by a eatadioptric apparatus of 50 centimetres (19.69 inches) diameter, with a lamp of two concentric wicks, is easily seen, in ordinary weather, at the distance of 15 to 18 nautical miles, although it is given a range in the official table of only 12 nautical miles. Apparatus of the third order, larger model. The brilliancy of catadioptric apparatus of the third order, one metre (39. 38 inches) in diameter in the interior, illuminated by a mechanical lamp of double wick, burning 190 grammes (6 oz. 11.35 drachms) of oil per hour, has been found = 70 burners. I will sup- pose, moreover, that it embraces only four-fifths of the horizon. To illuminate, by means of reflectors, the same angular space of 238-. with an effect of light about equal, it will be necessary to employ 14 parabolic reflectors (photophores) of 57. 5c. (10.8 inches) diameter, each burning 35 grammes (1 oz. 3.8 drachms) of oil per hour. The brilliancy in the axis of each of the 14 reflectors will be about = 66 burners. The brilliancy in the intervals, the least illuminated, will be = 36 burners. The useful effect will be represented by 14 x 62,160 = 870,240. But the useful effect of the catadioptric appa- ratus has been found to be = 1, 160,000. In this case, notwithstand- ing the very great difference in the consumption of oil, the dioptric or lenticular apparatus is superior, in useful effect, to the catoptric apparatus. The economical effect of the first apparatus is repre- sented by 1786 : comparison =1 to 3.44 : that is to say, without estimating the expenditure of oil by unity of light, the lenticular 167 apparatus will be nearly three and a half times more advantageous than the catoptric apparatus. With regard to the effective expendi- ture of oil, it will be in the proportion of 190 grammes to 14x35 grammes, or of 1 to 2.6. Apparatus for a fixed light, second order. The brilliancy of a catadioptric apparatus of the second order, having an interior diameter of 1m. 40c. (4 feet 7. 13 inches) illumi- nated by a mechanical lamp of three concentric wicks, burning five hundred grammes (17 oz. 10.5 drachms) of oil per hour, has been found to be = 264 burners. Let us suppose it only embraces three- fourths of the horizon. To obtain an effect about equal in an angular space of 270, it will be necessary to employ at least thirty-four parabolic reflectors, having fifty centimetres (19.69 inches) diameter. The brilliancy in the axis of each of these thirty-four reflectors will be =: 270 burners. But the lustres in the intervals are only = 148 burners. The useful effect of the catadioptric apparatus will be 4,120,000, and that of the thirty-four reflectors by 34x103,680 = 3,525,120. The comparison between the absolute expenditure of oil 34 X 42 will be = . =, 2.86 to 1 ; and the comparison of the quantity of oil expended by unity of light = = 1 to 3.33 ; thus, in this last respect, the lenticular apparatus will be three and one-third times as advantageous as the catoptric apparatus. Revolving apparatus of the second order. The maximum brilliancy or lustre of the revolving apparatus of the second order, with twelve lenses, has been found to be := 1,184 burners, as follows : 1st. Brilliancy in the axis of a lens =. 1,080 burners. 2d. Brilliancy in the fixed catadioptric zones = 104 " Total amount of brilliancy = 1, 184 And the minimum corresponding to the eclipses, is equivalent to one hundred and four burners. To construct a catoptric apparatus, possessing an equivalent effect, without multiplying beyond bounds the reflectors, (photophores,) it will be requisite, without doubt, to take those with diameters of fifty-five centimetres to sixty centimetres (21.66 inches to 23.63 inches;) but for want of sufficiently precise data as to their lustres, 168 I will suppose the employment of reflectors of fifty centimetres (19.69 inches) diameter, which give, in their axis, a lustre equal to two hundred and seventy burners. I will suppose, also, that the frame has six faces, each fitted with four of these reflectors. I will admit, lastly, as the succession of flashes ought to be the same in both systems, that the lenticular apparatus makes its revolution in six minutes, and the catoptric apparatus in three minutes. The maximum lustre of the catoptric system will be equal to 4 X 270 = 1,080 burners. The amplitude of the lustres of the reflectors being, moreover, of sixteen degrees at most, there will be six angles of forty-four degrees each almost entirely obscured : and the length of these eclipses will be twenty-two seconds, while the length of the flashes will be only eight seconds. Without pressing further the comparison of the effects of the two kinds of apparatus, we will perceive, without doubt, the evident advantages of the dioptric or lenticular combination, which, in fine weather, will not present an absolute edipse at a less distance than fifteen to eighteen nautical miles. If we now consider the expendi- ture of oil, we will find First. That they are as 24x42 : 500, or : : 1 to 2 ; Second. That the economical effects will be as 2,460: 10,043, or as 1 to 4.07. Thus the lenticular apparatus will be four times as advantageous as the catoptric or reflector apparatus. I admit that this result might be modified by the employment of larger reflectors ; but as their divergence would be less, the length of the flashes would be diminished, and consequently that of the eclipses would be augmented too much. Let us remark before proceeding further, that in employing 25 parabolic reflectors (photophores) of 50 centimetres (19.69 inches) diameter for such an apparatus, we reach the utmost possible limit, without admitting the employment of lanterns of a size beyond all proper bounds ; and we may also affirm that very few of the catop- tric lights, considered as lights ofihejirst order, equal the lenticular lights of the same character of the second order. Apparatus of the first order. With the view not to multiply unnecessarily the comparisons, I will omit the details relative to the first order of the catadioptric combination, which is the most advantageous; and I will suppose, in 169 consequence, the lenticular apparatus fitted in its accessory part with eleven zones of fixed mirrors. Now, we have found that the total lustre or brilliancy of an apparatus of that kind is equal in all its azimuths to 480 burners. But it will be practically impossible to obtain a like effect in the catoptric system, without having recourse to the employment of 36 reflectors with apertures (diameters) of 60 centimetres (23.63 inches.) The difficulty becomes still greater if it be necessary to attain with these parabolic reflectors the effect of a revolving lenticular light with eight large lenses, the lustres or flashes of which exceed 4,000 burners of the Carcel lamp. Let us limit ourselves, then, without entering into more full details, to the observation that the economical effect of a fixed light of the first order, illuminating three-fourths of the horizon, is to the economical effect of a light composed of parabolic reflectors (" photophores") of 50 centimetres (19.69 inches) diameter as 10.080 to 2.469, or as 4.08 to 1. That is to say, that the first will be (as to the expense of oil only) four times as advantageous as the second. Apparatus for lights varied by flashes. I will only here refer to the apparatus for lights varied by flashes, (otherwise called of short eclipses,) for the purpose of remarking that the catoptric or reflector system is not susceptible of producing, without great difficulty, that combination which unites to the permanence of fixed lights the advantage of presenting a very decided character. SEC. 2. Expenses offlrst establishing and of maintaining light-houses. So far, I have compared the economical effects of the different kinds of apparatus only with reference to the expenditures of oil ; but it will not fail to be objected that the advantages which I point out in favor of the lenticular system ought to be very greatly diminished in a fiscal point of view, in consequence of the high price of the appa- ratus, and the excess of keepers necessary to their service. To appreciate the value of that objection, I will compare several lights of both systems, taking into the account all the expenses to which they could be subjected, and for the first example I will take the harbor lights. HARBOR LIGHTS. A harbor light, placed at the entrance to a port, being often ex- posed to the force of the sea, ought (to insure proper attendance, &c.) 170 to be erected securely in a bronze lantern, fitted upon the summit of a small tower constructed of masonry, and sufficiently spacious for the purposes of illumination and attendance at all times, and in every description of weather. That being established, we may state the expenses for the first establishing for both systems, (in France,) as follows : 1. Small "sideral" light. Small tower in masonry 5, 000 fr. Octagonal lantern, 1m. 40c. (4 feet 7. 13 inches) in diameter. . 2, G50 "Sideral" reflector, with subsidiary pieces 500 = $1,528 12. 8,150 Interest at 5 per cent 407 fr. Annual expense of the service 800 = $226 31. 1,207 2. Catadioptric harbor light, (smaller model.) Tower and lantern 7, 650 fr. Catadioptric apparatus 1,531 = $1,721 43. 9,181 Interest at 5 per cent , 459 fr. Annual expense of the service 800 = $236 06. 1,259 The useful effect of the ' ' sideral" (reflector) light having been found equal to 68,400 68,400 Its economical effect will be represented here by = 57. 1,207 The useful effect of the Catadioptric light, illuminating three-fourths of the horizon, has been found to be equal to 137,700 137,700 After the same manner, its economical effect will be =109. 1,259 The comparison of the economical effects of these two will be, then, in the proportion of 57 to 109, or 1 to 1.91. 171 Then, besides the advantage of a double lustre or brilliancy, the catadioptric apparatus, in an economical point of view, is nearly twice as advantageous as the catoptric apparatus. Lights of the third order. It is difficult to establish a precise comparison between the fixed lights of the third order in the old and in the new system, because Ave cannot obtain with the ordinary parabolic reflectors a passably equal distribution of light, without multiplying these reflectors to such a number as would require a much greater expenditure of oil than could be allowed for lights of that class. I will merely observe that I have every reason to believe, from the indications contained in the table of light-houses in the United States, that among all the lights of that country illuminated by reflectors, the diameters of which do not exceed sixteen English inches, there are very few whose useful effect is superior, or even equal to that of a catadioptric light of the third order, larger model. [Revolving lights of the second order ] 1st. Catoptric light. In the comparative examination of the useful and economical effects of the two systems of maritime illumination, I have supposed the re- volving catoptric apparatus of the second order, composed of twenty- four parabolic reflectors of fifty centimetres (19.69 inches) of aperture distributed equally upon the six faces of prismatic frame. I will sup- pose, also, that the lantern is three metres (9 feet 10.14 inches) in diameter, the same as required for a lenticular apparatus of the sec- ond order, but with a little less height. I will admit, moreover, the same perfection in the works that is to say, that the frame and sashes, constructed of iron, are covered with bronze exteriorily ; and that the roof or dome of the lantern is of copper, the glazing of glass of eight or ten milimetres (0.39 to 0.31 of an inch) in thickness, ), lighted by a lamp of three concentric wicks, consum- ing three hundred and eighty-four gallons of oil per annum. 3. Lights of the third order, lighted by a lamp of two concentric wicks, consuming one hundred and eighty-three gallons of oil por annum, and having a focal distance of 19.68 inches (50 cm -) 4. Lights of the fourth order, or harbor-lights, having an internal radius of 9.84 inches (25 cm< ), and a lamp of two concentric wicks, consuming about one hundred and thirty gallons of oil per annum. 5. Lights of the fifth order, having a focal distance of 7.28 inches (18.5 cm -); and 6. Lights of the sixth order, having an internal radius of 5.9 inches (15 om '), and lighted by a lamp of one wick, or Argand burner, con- suming forty-eight gallons of oil per annum, The more minute sub- divisions of orders I consider to be unnecessary. 13 194 Those orders are not intended as distinctions, but are character- istic of the power and range of lights, which render them suitable for different localities on the coast, according to the distance at which they can be seen. This division, therefore, is analogous to that which separates our lights into sea lights, secondary lights, and harbor lights, terms which are used to designate the power and position, and not the appearance of the lights to which they are applied. Each of the above orders is susceptible of certain combinations, which produce various appearances, and constitute the distinctions used for dioptric lights; but the following are those which have been actually employed as the most useful in practice : The first order contains, first, lights producing, once in every minute, a great flash, preceded by a smaller one, by the revolution of eight great lenses and eight smaller ones combined with eight mirrors; second, lights flashing once in every half minute, and com- posed of sixteen half lenses. Those lights may have the subsidiary parts simply catoptric, or diacatoptric : and, third, fixed lights, composed of a combination of cylindric pieces, with curved mirrors or catadioptric zones ranged in tiers above and below them. The second order comprises revolving lights with sixteen or twelve lenses, which make flashes every half minute; and fixed lights varied by flashes once in every four minutes an effect which, as already noticed, is produced by the revolution of exterior cylindric pieces. The third order contains common fixed lights, and fixed lights varied by flashes once in every four minutes. The fourth order contains simple fixed lights, and fixed lights varied by flashes once in three minutes. The fifth order has fixed lights varied by flashes once in every three minutes, and fixed lights of the common kind. It has been thought necessary to change the term "fixed lights varied by flashes" for "fixed lights with short eclipses," because it has been found that at certain distances a momentary eclipse precedes the flash. The sixth order has only fixed lights. These distinctions depend upon the periods of revolution rather than upon the characteristic appearance of the light ; and therefore seem less calculated to strike the eye of a seaman than those em- ployed on the coasts of Great Britain and Ireland. In conformity 195 with this system, and in consideration of the great loss of light which results from the application of colored media, distinctions based upon color have been generally discarded in the French lights. The distinctions are in fact only four in number, viz : fixed ; fixed, varied by flashes ;* revolving, with flashes once a minute ; and revolving with flashes every half minute. To those might be added, revolving, with bright periods once in two minutes, and perhaps flashing once in Jive seconds, ( as introduced by me at the Little Ross, but I cannot say with such complete success as would induce me to recommend its general adoption.) My own experience would also lead me to reject the distinction called "fixed, varied by flashes," which I do not consider as possessing a marked or efficient character. Having thus fully described the nature of the catoptric and dioptric modes of illuminating light-houses, I shall conclude with a com- parative view of the merits of both systems, deduced from the experiments made at Gullan-hill during the winters of 1832 and 1833, under the inspection of the commissioners of Northern lights. The chief practical result of those trials was, that the light of one of the great annular lenses used in the revolving lights of the first order, was equal to the united effect of eight of the large reflectors em- ployed in the revolving lights on the Scotch coast. It may be said, however, that the diacatoptrict combination of pyramidal lenses and plane mirrors of Cordouan, adds the power of more than two reflectors to the effect of the great lens ; but it ought to be re- membered that in the French lights this additional power is used only to compensate for one of the defects of the system by lengthen- ing the duration of the flash, and therefore contributes, if at all, only in a very indirect manner to render the light visible to the mariner at a greater distance. M. Fresnel found that from the smaller divergence of the lens the eclipses were too long and the bright periods of the revolution too short, and he therefore determined to adopt the horizontal deviation of 7 for the upper lenses, with a view to remedy this defect. Assuming, therefore, that it were required to increase the number of reflectors in a revolving light of three sides, so as to render it equal in power to a dioptric revolving light of the first order, it would be necessary to place eight reflectors on each face, so that the greatest number of reflectors required for this a The " Feu fixe, varie par des eclats," or "Feu fixe, a courtes eclipses," of Fresnel. f I use this word to designate the arrangement of pyramidal lenses and plane mirrors, by which the light is first refracted and then Ttfleded. 196 purpose may be taken at twenty-four. M. Fresnel has stated the expenditure of oil in the lamp of four concentric wicks at seven hundred and fifty grammes of colza oil per hour ; and it is found by experience at the Isle of May and Inchkeith that the quantity of spermaceti oil consumed by the great lamp is equal to that burned by from fourteen to sixteen of the Argand lamps used in the Scotch lights. It therefore follows that by dioptric means the consumption of oil necessary for between fourteen and sixteen reflectors will produce a light as powerful as that which would require the oil of twenty- four reflectors in the catoptric system of Scotland ; and consequently that there is an excess of oil equal to that consumed by ten reflectors, or four hundred gallons in the year, against the Scotch system. But in order fully to compare the economy of pro- ducing two revolving lights of equal power by those two methods, it will be necessary to take into the calculation the interest of the first outlay in establishing them. The expense of fitting up a revolving light with twenty-four re- flectors, ranged on three faces, may be estimated at 1,298, and the annual maintenance, including the interest of the first c st of the apparatus, may be calculated at 418 8s. 4c. The fitting up a revolving light with eight lenses and the diacatoptric accessory apparatus, may be estimated at 1,459, and the annul maintenance at 354 10s. 4d. It therefore follows that to establish and after- wards maintain a catoptric light of the kind called revolving ivhite, with a frame of three faces, each equal in power to a face of the dioptric light of Cordouan, an annual outlay of 63 18s. more would be required for the reflecting light than for the lens light; while for a light of the kind called revolving red and white, whose frame has four faces, at least thirty-six reflectors would be required in order to make the light even approcah an equality to that of Cordouan ; and the catoptric light would in that case cost 225 more than the dioptric light. The effect produced by burning an equal quantity of oil in revolving lights on either system may be estimated as follows : In a revolving light like that of Skerryvore, having eight sides, each lighting with its greatest power a horizontal sector of 4, we have 32 (or units) of the horizon illuminated with the full power of three thousand two hundred Argand flames, and consequently an aggre- gate effect of one hundred and two thousand four hundred flames, produced by burning the oil required for sixteen reflectors ; while in 197 a catoptric apparatus, like that of the old light at Inchkeith, having seven sides of one reflector, each lighting with its greatest power a sector of 4 25', we have nearly 31 (or units) of the horizon illuminated with the full power of four hundred Argand flames, and consequently an aggregate effect of twelve thousand four hun- dred flames as the result of burning the oil required for seven re- flectors. Hence the effect of burning the same quantity of oil in revolving lights on either system will be represented respectively "by . 12,400 = 28,343 for the catoptric, contrasted with 102,400 for the dioptric light; or, in other words, revolving lights on the dioptric principle use the oil more economically than those on the catoptric plan, nearly in the ratio of 3.6 to 1. Let us now speak of fixed lights, to which the dioptric method is peculiarly Avell adapted. The effect produced by the consumption of a gallon of oil in a fixed light, with twenty-six reflectors, which is the smallest number that can be properly employed, may be esti- mated as follows : The mean effect of the light spread over the horizontal sector, subtended by one reflector, as deduced from measurements made at each horizontal degree, by the method of shadows, is equal to 174 unassisted Argand burners. If, then, this quantity be muliplied by 360 degrees, we shall obtain an aggregate effect of 62,640, which, divided by 1,040, (the number of gallons burned during a year in twenty-six reflectors,) would give sixty Argand flames for the effect of the light maintained throughout the year by the combustion of a gallon of oil. On the other hand, the power of a catadioptric light of the first order, like that lately established at Girdleness, may be estimated thus : The mean effect of the light produced by the joint effect of both the dioptric and catadioptric parts of fixed light apparatus, may be valued at 450 Argand flames, which, multiplied by 360 degrees, gives an aggregate of 162,000 ; and if this quantity be divided by 570 (the number of gallons burned by the great flame in a year ) we shall have about 284 Argand flames for the effect of the light produced by the com- bustion of a gallon of oil. It would thus appear that in fixed lights, the French apparatus, as lately improved, produces, as the average effect of the combustion of the same~quantity of oil over the whole horizon, upwards of four times the amount of light that is obtained by the catoptric mode. But the great superiority of the dioptric method chiefly rests upon 198 its perfect fulfilment of an important condition required in a fixed light, by distributing the rays equally in every point of the horizon. In the event of the whole horizon not requiring to be illuminated, the dioptric light would lose a part of its superiority in economy, and when half the horizon only is lighted, it would be more expen- sive than the reflected light ; but the greater power and more equal distribution of the light may be considered of so great importance, as far to outweigh the difference of expense. In the latter case, too, an additional power, as already noticed, can be given to the dioptric light, by placing at the landward side of the light room, spherical mirrors with their centres in the focus of the refracting apparatus.* The luminous cones, or pyramids, of which such reflectors would form the bases, instead of passing off uselessly to the land, would thus be thrown back through the focal point, and finally refracted, so as to increase the effect of the light seaward by nearly one-third of the light which would otherwise be lost. The expense of establishing a fixed light composed of twenty-six reflectors may be estimated at 950, and its annual maintenance, including interest on the first cost of the apparatus, may be reckoned at 425 10s. ; and the expense of fitting up a fixed light on the diop- tric principle with catadioptric zones is 1,511, while its annual maintenance may be taken at 285 6s. 4c?. It thus appears that the annual expenditure of dioptric fixed light is 140 3s. Sd. less than that of a fixed light composed of twenty-six reflectors ; while the average effect, equally diffused over the horizon, is four times greater. The comparative views already given of the catoptric and dioptric modes of illuminating light-houses, demonstrate that the latter pro- duces more powerful lights by the combustion of the same quantity of oil ; while it is obvious that the catoptric system insures a more certain exhibition of the light, from the fountain lamps being less liable to derangement than the mechanical lamps used in dioptric lights. The balance, therefore, of real advantages or disadvantages, and consequently the propriety of adopting the one or the other system, involves a mixed question, not susceptible of a very precise solution, and leaving room for different decisions, according to the A similar arrangement can also be made in revolving lights by making the radius of the mirrors somewhat less than that of the inscribed circle of the octagon bounded by the lenses, so that they may circulate freely round the backs of the mirrors. The shortness of the radius of the reflecting surface would, of course, increase the divergence of the beam of light refracted through the lenses, as the flame would, in this case, subtend a greater angle at the face of the mirrors. 199 value which may be set upon obtaining a cheaper and better light on the one hand, as contrasted, on the other, with less certainty in its exhibition. Experience, however, goes far to show that, in prac- tice, the risk of extinction of the lamp in dioptric lights is very small. A few general considerations, serving briefly to recapitulate the arguments for and against the two systems, may not be out of place. And, first, regarding the fitness of dioptric instruments for revolving lights, it appears from the details above given 1. That by placing eight reflectors on each face of a revolving frame, a light might be obtained as brilliant as that derived from the great annular lens ; and that, in the case of a frame of three sides, the excess of expense by the reflecting mode would be 63 18s. ; and in the case of a frame of four sides, the excess would amount to 225. 2. That for burning oil economically in revolving light-houses, which illuminate every point of the horizon successively, the lens is more advantageous than the reflector in the ratio of 3.6 to 1. 3. That the divergence of the rays from the lens being less than from the reflector, it becomes difficult to produce, by lenses, the appearance which characterizes the catoptric revolving lights, already so well known to British mariners; and any change of existing lights which would, of course, affect their appearance, must, therefore, involve some practical objections, which do not at all apply to the case of new lights. 4. That the uncertainty in the management of the lamp renders it more difficult to maintain the revolving dioptric lights without risk of extinction an accident which has several times occurred at Cor- douan and other light-houses, both in Prance and elsewhere. A more extended experience, however, has tended to moderate any fears on this head. 5. That the extinction of one lamp in a revolving catoptric light is not only less probable, but leads to much less serious consequences than the extinction of the single lamp in a dioptric light ; because, in the first case, the evil is limited to diminishing the power of one face by an eighth part ; whilst, in the second, the ivliole horizon is totally deprived of light. The extinction of a lamp, therefore, in a dioptric light, leads to evils which may be considered very great in comparison with the consequences which attend the same accident in a catoptric light. 200 In comparing the fixed dioptric and the fixed catoptric apparatus, the results may be summed up under the following heads : 1. It is impossible, by means of any practicable combination of paraboloi'dal reflectors, to distribute round the horizon a zone of light of exactly equal intensity ; while this may be easily effected by diop- tric means, in the manner already described. In other words, the qualities required in fixed lights cannot be so fully obtained by reflect- ors as by refractors. 2. The average light produced in every azimuth by burning one gallon of oil in Argand lamps, with reflectors, is only about one-fourth of that produced by burning the same quantity in the dioptric appa- ratus ; and the annual expenditure is X140 3s. Sd, less for the entire dioptric light than for the catoptric light. 3. The characteristic appearance of the fixed reflecting light in any one azimuth would not be changed by the adoption of the dioptric method, although its increased mean power would render it visible at a greater distance in every direction. 4. From the equal distribution of the rays, the dioptric light would be observed at equal distances in every point of the horizon; an effect which cannot be fully attained by any practicable combination of para- boloi'dal reflectors. 5. The inconveniences arising from the uncertainty which attends the use of the mechanical lamp, are not perhaps so much felt in a fixed as in a revolving light; because the greater simplicity of the apparatus admits of easier access to it in case of accident. 6. But the extinction of a lamp in a catoptric light, leaves only one twenty -sixth part of the horizon without the benefit of the light, and the chance of accident arising to vessels from it, may, therefore, be considered as incalculably less than the danger resulting from the extinction of the single lamp of the dioptric light, which deprives the whole horizon of light. 7. There is also, in certain situations, a risk arising from irregu- larity in the distances at which the same fixed catoptric light can be seen in the different azimuths. This defect, of course, does not exist in the dioptric light. There can be little doubt that the more fully the system of Fresnel is understood, the more certainly will it be preferred to the catoptric system of illuminating light-houses, at least in those countries where this important branch of administration is conducted with the care and solicitude which it deserves. It must not, however, be imagined, that there are no circumstances in which the catoptric system is not absolutely preferable to illumi- nation by means of lenses. We have hitherto attended only to hori- zontal divergence and its effects, and this is unquestionably the more important view; but the consideration of vertical divergence must not be altogether overlooked. Now while it is obvious that vertical divergence, at least above the horizon, involves a total loss of the light which escapes uselessly upwards into space, (in which respect the reflectors are much less advantageous,) it is no less true, that if the sheet of light which reaches the most distant horizon of the light- house, however brilliant, were as thin as the absence of all vertical divergence would imply, it would be practically useless; and some measure of dispersion in the arc below the horizon is therefore ab- solutely indispensable to constitue a really useful light. In the re- flector, the greatest vertical divergence below the horizontal plane of the focus is 16 8', and that of the lens is about 4 30'. Let us consider for a moment the bearing of those facts upon the applica- tion of the two modes of illumination to special circumstances. The powerful beam of light transmitted by the lens peculiarly fits that instrument for the great sea-lights which are intended to warn the mariner of his approach to a distant coast which he first makes on an over-sea voyage ; and the deficiency of its divergence, whether hori- zontal or vertical, is not practically felt as an inconvenience in lights of that character, which seldom require to serve the double purpose of being visible at a great distance, and at the same time of acting as guides for danger near the shore. For such purposes, the lens applies the light much more advantageously as well as more economically than the reflector; because, while the duration of its least divergent beam is nearly equal to that of the reflector, it is eight times more power- ful. A revolving system of eight lenses illuminates an horizontal arc of 32 with this bright beam. The reflector, on the other hand, spreads the light over a larger arc of the horizon; and, while its least divergent beam is much less powerful than that of the lens, the light which is shed over its extreme arc is so feeble as to be practically of no use in lights of extensive range, even during clear weather. When a light-house is placed on a very high headland, however, the defi- ciency of divergence in the vertical direction is often found to be productive of some practical inconvenience; but this defect may be partially remedied by giving to the lenses a slight inclination out- wards from the vertical plane of the focus, so as to cause the most 202 brilliant portion of the emergent beam to reach the visible horizon which is due to the height of the lantern. It may be observed, also, that a lantern at the height of 150 feet, which (taking into account the common height of the observer's eye at sea) commands a range of upwards of twenty English miles, is sufficient for all the ordinary pur- poses of the navigator, and that the intermediate space is practically easily illuminated, even to within a mile of the light-house, by means of a slight inclination of the subsidiary mirrors, even where the light from the principal part of the apparatus passes over the seaman' s head. For the purpose of leading lights, in narrow channels, on the other hand, and for the illumination of certain narrow seas, there can be no doubt that reflectors are much more suitable and convenient. In such cases, the amount of vertical divergence below the horizon forms an important element in the question, because it is absolutely necessary that the mariner should keep sight of the lights even when he is very near them; while there is not the same call for a very powerful beam which exists in the case of sea-lights. Yet even in narrow seas, where low towers, corresponding to the extent of the range of the light, are adopted, but where it is, at the same time, needful to illuminate the whole or the greater part of the horizon, the use of dioptric instruments will be found almost unavoidable, especially in fixed lights, as well from their equalizing the distri- bution of the light in every azimuth, as from their much greater econ- omy in situations where a large annual expenditure would often be disproportionate to the revenue at disposal. In such places, where certain peculiarities of the situation require the combination of a light equally diffused over the greater portion of the horizon, along with a greater vertical divergence in certain azimuths, than dioptric instru- ments afford, I have found it convenient and economical to add to the fixed refracting apparatus a single paraboloidal reflector in order to produce the desired effect, instead of adapting the whole to the more expensive plan for the sake of meeting the wants of a single narrow sector of its range. In other cases, where the whole horizon is to be illuminated, and great vertical divergence is at the same time desi- rable, a slight elevation of the burner, at the expense, no doubt, of a small loss of light, is sometimes resorted to, and is found to pro- duce, with good effect, the requisite depression of the emergent rays. In certain situations, where a great range, and, consequently, a powerful light must be combined with tolerably powerful illumina- tion in the immediate vicinity of the light-house, we might, perhaps, 203 advantageously adopt a variation of the form and dimensions of the mirrors employed, so as to resemble those formerly used at the Tour de Cordouan, which were of considerably larger surface and longer focal distance than those which are used in Britain. If such a form were adopted, the power of the light for the purpose of the distant range would be increased ; and I would propose to compensate for the deficiency of divergence consequent on a long focal distance, by placing a second burner in some position between the parameter and the vertex, and slightly elevated above the axis of the instrument, so as to throw the greater portion of the beam resulting from this second burner below the horizontal plane of the focus. Such an expedient is no doubt somewhat clumsy, and would at the same time involve the consumption of twice the quantity of oil used in an ordinary catoptric light; but I can still conceive it to be preferable, in certain situations, to the use of the lenses alone. Thus it appears that we must not too absolutely conclude against one, or in favor of the other mode of illumination for light-houses; but, as in every other department of the arts, we shall find the neces- sity of patiently weighing all the circumstances of each particular case that comes before us, before selecting that instrument, or com- bination of instruments, which appears most suitable. The mode of distinguishing lights in the system of Fresnel depends more upon their magnitude and the measured interval of the time of their revolution, than upon their appearance; and no other very marked distinctions, except fixed and revolving, have been success- fully attempted in France. As above stated, I consider the distinc- tion of the fixed light varied by flashes, to possess an appearance too slightly differing from that of a revolving light, to admit of its being safely adopted in situations where revolving lights are near. The trial which I made at the Little Ross, in the Solway Frith, of pro- ducing, by means of lenses, a light flashing once in five seconds of time, although successful so far as mere distinction is concerned, has several practical defects, arising from the shortness of the duration of the flashes compared with the powerful effect of the fixed part of the apparatus, which I consider sufficient to prevent its adoption in future, especially considering that a much more marked appearance can be produced by means of reflectors, as has been done at the Buchanness in Aberdeenshire, and the Rhinns of Islay in Argyle- shire. Colored media have never, so far as I know, been applied to dioptric apparatus, except in the case of the Maplin light at the 204 mouth of the Thames, and Cromarty Point light at the entrance to the Cromarty Frith, Nosshead in Caithness, and Ship Rock of Sanda in Argyleshire, but in all those instances successfully. In the case of the fixed light at Sanda, in particular, I would observe that it is seen at the distance of sixteen nautical miles, and occasionally observed even so far off as twenty-two nautical miles. The enormous loss of light, however, amounting to no less than 0-80 of the whole incident rays, forms a great bar to the adoption of color as a distinc- tion; and any means which could tend to lessen that absorption, and at the same time produce the characteristic appearance, would be most valuable. I have tried some glasses of a pink tinge, prepared by M. Letourneau of Paris, in which the absorption does not exceed 0-57 of the incident rays; but the appearance of the light, at a dis- tance, is much less marked than that produced by the glasses used in Britain. Such deficiency of characteristic color might lead to serious consequences, as the transmission of white rays, through a hazy atmosphere, too often produces, by absorption, a reddish tinge of the light, for which the less marked appearance given by the paler media might be easily mistaken. This coloring power of absorption is so well known, that red lights are seldom used except in direct contrast with white ones; but, on a coast so thickly studded with light-houses as that of Great Britain, the number of distinctions is insufficient to supply all our wants, so that we are sometimes reluc- tantly compelled to adopt a single red light in some situation of lesser importance, or which, from some local circumstances and the appear- ance of the lights which must be seen by the mariner before passing it, is not likely to be mistaken for any other. The great loss of light by colored media causes the red beam, in a revolving light, to be seen at a shorter distance than the white; and it is conceivable that, in certain circumstances, this might lead the mariner to mistake a red and white light for a white light revolving at half the velocity. Such a mistake might perhaps prove dangerous; but the lights are generally so situated that there is ample time for the mariner, after first discovering the red light, and thus correcting any mistake, to shape his course accordingly. All other colored media, except red, have been found useless as distinctions for any lights of extensive range, and fail to be efficient, owing to the necessity of absorbing almost all the light before a marked appearance can be obtained. In a few pier or ferry lights, green and blue media have been tried, and found available at the distance of a few cables' lengths.* It seems to be a natural consequence of the physical distribution of light, that fixed lights, which illuminate the whole horizon, should be less powerful than revolving lights which have their effect con- centrated within narrow sectors of the horizon. Any attempt to increase the power of fixed lights is, therefore, worthy of attention; and when the late Captain Basil Hall proposed a plan for effecting this object, it received, as it deserved, the full consideration of the Scotch Light-house Board, who authorized me to repeat Captain Hall's experiments, and verify his results by observations made at a consid- erable distance. The familiar experiment of whirling a burning stick quickly round the head, so as to produce a ribbon of light, proves the possibility of causing a continuous impression on the retina by intermittent images succeeding each other with a certain rapidity. From the moderate velocity at which this continuity of impression is obtained, we should be warranted in concluding, a priori, that the time required to make an impression on the retina is considerably less than the duration of the impression itself ; for the continuity of effect must, of course, be caused by fresh impulses succeeding each other before the preceding ones have entirely faded. If it were otherwise, and the time required to make the impression were equal to the duration of the sensation, it would obviously be impossible to obtain a series of impulses so close or continuous in their effect as to run into and overlap each other, and thus throw out the intervals of darkness ; because the same velocity which would tend to shorten the dark intervals, would also curtail the bright flashes, and thus prevent their acting on the eye long enough to cause an impression. Accordingly, we find that the duration of an impression is in reality much greater than the time required for producing the effect on the retina. It is stated by Professor Wheatstone, in the London Transactions for 1834, that only about one millionth part of a second is required for making a distinct impression on the eye; and it appears from a statement made by Lame, at p. 425 of his Cours de Physique, that M. Plateau found that an impression on the retina preserves its intensity unabated during one ~ In some late experiments which I made with very powerful instruments, green lights were visible, in very clear weather, at the distance of seven miles. The blue could only once be seen, with great difficulty, at five miles. 206 hundredth of a second, so that, however small those times may be in themselves, the one is ten thousand times greater than the other. It has been ascertained, by direct experiment,* that the eye can receive a fresh impression before the preceding one has faded ; and, indeed, if this were impossible, absolute continuity of impression from any succession of impulses, however rapid, would seem to be unattainable; and the approach to perfect continuity would be in- versely at the time required to make an impression. From the property Avhich bright bodies passing rapidly before the eye possess of communicating a continuous impression to the sense of sight, the late Captain Basil Hall conceived the idea, not merely of obtaining all the effects of a fixed light, by causing a system of lenses to revolve with such a velocity as to produce a continuous im- pression, but, at the same time, of obtaining a much more brilliant appearance, by the compensating influence of the bright flashes, which he expected would produce impulses sufficiently powerful and durable to make the deficiency of light in the dark spaces almost imperceptible. The mean effect of the whole series of changes would, he imagined, be thus greatly superior to that which can be obtained from the same quantity of light equally distributed, as in fixed lights, over the whole horizon. Now this expectation, if it be considered solely in reference to the physical distribution of the light, involves various difficulties. The quantity of light subjected to instrumental action is the same whether we employ the refracting zones at present used in fixed dioptric lights, or attempt to obtain continuity of effect by the rapid revolution of lenses ; and the only difference in the action of those two arrangements is this, that while the zones distribute the light equally over the whole horizon, or rather do not interfere with its natural horizontal distribution, the effect of the proposed method is to collect the light into pencils, which are made to revolve with such rapidity that the impression from each pencil succeeds the preceding one in time to prevent a sensible occurrence of darkness. To expect that the mean effect of the light, so applied, should be greater than when it is left to its natural horizontal divergence, certainly appears at first to involve something approaching to a contradiction of physical laws. In both 3 Lame, Cours de Phyrique, p. 424. " L' impression peut subdster encore lorsque la suivantc a lien." 207 cases, the same quantity of light is acted upon by the instrument; and, in either case, any one observer will receive an impression sim- ilar and equal to that received by any other stationed at a different part of the horizon ; so that, unless we imagine that there is some loss of light peculiar to one of the methods, we are shut up, in the physical view of the question, to the conclusion that the impressions received by each class of observers must be of equal intensity. In other words, the same quantity of light is by both methods employed to convey a continuous impression to the senses of spectators in every direction, and, in both methods, equality of distribution is effected, since it does not at all consist with our hypothesis, that any one ob- server in the same class should receive more or less than his equal share of the light. Then, as to the probability of the loss of light, it seems natural to expect that this should occur in connection with the revolving system, because the velocity is an extraneous circum- stance, by no means necessary to an equal distribution of the light, which can, as we already know, be more naturally, and at the same time perfectly attained by the use of the zones. On the other hand, it must not be forgotten that, although the effect of both methods is to give each part of the horizon an equal share of light, there is yet this difference between them, that while the light from the zones is equally intense at every instant of time, that evolved by the rapidly circulating lenses is constantly passing through every phase between total darkness and the brightest flash of the lens ; and this difference, taken in connection with some curi- ous physiological observations regarding the sensibility of the retina, gives considerable countenance to the expectation on which Captain Hall's ingenious expedient is based. The fact which has already been noticed, and which the beautiful experiments of M. Plateau and Professor Wheatstone have of late rendered more precise, that the duration of an impression on the retina is not only appreciable, but is much greater than the time required to cause it, seems to en- courage us in expecting that, while the velocity required to produce continuity of effect would not be found so great as to interfere with the formation of a full impression, the duration of the impulse from each flash would remain unaltered, and the dark intervals which do not excite the retina would, at the same time, be shortened ; and that, therefore, we might, in this manner, obtain an effect on the 208 senses exceeding the brilliancy of a steady light distributed equally in every direction by the ordinary method. Some persons, indeed, who have speculated on this subject, seem even to be of opinion. that so far from the whole effect of the series of continuous impres- sions being weakened by a blending of the dark with the bright intervals, the eye would in reality be stimulated by the contrast of light and darkness, so as thereby to receive a more complete and durable impulse from the light. It is obvious, however, that this question regarding the probable effect to be anticipated from a revo- lution so rapid as to cause a continuous impression, could only have been satisfactorily answered by appeal to experiment. In experimenting on this subject, I used the apparatus formerly employed by Captain Hall. It consisted of an octagonal frame, which carried eight of the discs that compose the central part of Fresnel's compound lens, and was susceptible of being revolved slowly or quickly at pleasure, by means of a crank handle and some intermediate gearing. The experiments were nearly identical with those made by Captain Hall, who contrasted the effect of a single lens at rest, or moving very slowly, with that produced by the eight lenses, revolving with such velocity as to cause an apparently continuous impression on the eye. To this experiment I added that of comparing the beam thrown out by the central portion of a cylin- dric refractor, such as is used at the fixed light of the Isle of May, with the continuous impression obtained by the rapid revolution of the lenses. Captain Hall made all his comparisons at the short dis- tance of one hundred yards; and, in order to obtain some measure of the intensity, he viewed the lights through plates of colored glass until the luminous discs became invisible to the eye. I repeated those experiments at Gullan, under similar circumstances, but with very different results. I shall not, however, enter upon the discus- sion of those differences here, although they are susceptible of explanation, and are corroborative of the conclusions at which I arrived by comparing the lights from a distance of fourteen miles, but shall briefly notice the more important results which were ob- tained by the distant view. They are as follows : 1. The flash of the lens revolving slowly was very much larger than that of the rapidly revolving series; and this decrease of size in the luminous object presented to the eye became more marked as 209 the rate of revolution was accelerated, so that, at the velocity of eight or ten flashes in a second the naked eye could hardly detect it, and only few of the observers saw it, while the steady light from the fixed refractor was distinctly visible. 2. There was also a marked falling off in the brilliancy of the rapid flashes as compared with that of the slow ones ; but this effect was by no means so striking as the decrease of volume. 3. Continuity of impression was not attained at the rate of five flashes in a second, but each flash appeared to be distinctly sepa- rated by an interval of darkness ; and even when the nearest ap- proach to continuity was made, by the recurrence of eight or ten flashes in a second, the light still presented a twinkling appearance, which was well contrasted with the steady and unchanging effect of the cylindric refractor. 4. The light of the cylindric refractor was, as already stated, steady and unchanging, and of much larger volume than the rapidly revolving flashes. It did not, however, appear so brilliant as the flashes of the quickly revolving lenses, more especially at the lower rate of five flashes in a second. 5. When viewed through a telescope, the difference of volume be- tween the light of a cylindric refractor and that produced by the lenses at their greatest velocity was very striking. The former presented a large diffuse object of inferior brilliancy, while the lat- ter exhibited a sharp pin-point of brilliant light. Upon a careful consideration of these facts, it appears warrant- able to draw the following general conclusions : 1. That our expectations as to the effects of light, when distrib- uted according to the law of its natural horizontal divergence, are supported by observed facts as to the visibility of such lights, con- trasted with those whose continuity of effect is produced by collect- ing the whole light into bright pencils, and causing them to revolve with great velocity. 2. It appears that this deficiency of visibility seems to be chiefly due to a want of volume in the luminous object, and also, although in a less degree, to a loss of intensity, both of which defects appear to increase in proportion as the motion of the luminous object is accel- erated. 3. That this deficiency of volume is the most remarkable optical 14 210 phenomenon connected with the rapid motion of luminous bodies, and that it appears to be directly proportional to the velocity of their passage over the eye. 4. That there is reason to suspect that the visibility of distant light depends on the volume of the impression in a greater degree than has perhaps been generally imagined. 5. That, as the size and intensity of the radiants causing these various impressions to a- distant observer were the same, the volume of the light, and, consequently, cceteris paribus, its visibility, are, within certain limits, proportionate to the time during which the object is present to the eye. Such appear to be the general conclusions which those experi- ments warrant us in drawing ; and the practical result, in so far as light-houses are concerned, is sufficient to discourage us from at- tempting to improve the visibility of fixed lights in the manner pro- posed by Capt. Hall, even supposing the practical difficulties con- nected with the great centrifugal force generated by the rapid revo- lution of the lenses to be less than they really are. The decrease in the volume of the luminous object caused by the rapid motion of the lights is interesting from its apparent connec- tion with the curious phenomenon of irradiation. When luminous bodies, such as the lights of distant lamps, are seen by night, they appear much larger than they would do by day ; and this effect is said to be produced by irradiation. M. Plateau, in his elaborate essay on this subject, after a careful examination of all the theories of irradiation, states it to be his opinion, that the most probable mode of accounting for the various observed phenomena of irradia- tion is to suppose, that, in the case of a night-view, the excitement caused by light is propagated over the retina beyond the limits of the day-image of the object, owing to the increased stimulus pro- duced by the contrast of light and darkness j and he also lays it down as a law, confirmed by numerous experiments, that irradiation increases with the duration of the observation. It appears, there- fore, not unreasonable to conjecture, that the deficiency of volume observed during the rapid revolution of the lenses may have been caused by the light being present to the eye so short a time, that the retina was not stimulated in a degree sufficient to produce the amount of irradiation required for causing a large visual object. 211 When, indeed, the statement of M. Plateau, that irradiation is pro- portional to the duration of the observation, is taken in connection with the observed fact, that the volume of the light decreased as the motion of the lenses was accelerated, it seems almost impossible to avoid connecting together the two phenomena as cause and effect. Before leaving this part of the subject, I will call attention to some late plans for combining dioptric and catoptric apparatus, the object of which is to subject to the corrective action of instruments, a greater proportion of the luminous sphere than it has yet been found practicable to do, especially in revolving lights. Reflectors act chiefly on the posterior portion of the flame, and generally re- ceive about twelve-seventeenths of the whole luminous sphere ; while a series of dioptric instruments can only affect an anterior zone, amounting to about two-fifths of the whole light which is emitted by the lamp. Certain deductions due to the form of the lower part of the burners, and to the loss of light at reflection, which is not less than one-half of the incident light, as well as to that by refraction through the lens, (which, however, cannot exceed one-tenth of the incident light,) will reduce those numbers from twelve-seventeenths to one-third, and from two-fifths to three-tenths, thus making the ratio of the proportion of the whole flame actually given forth by the reflectors to the amount by lenses equal to that of ten to nine. In fixed lights, on Fresnel's system, we have already seen that nearly the whole of the available light is turned to a useful purpose by means of the curved mirrors or catadioptric zones, which are added to increase the effect of the central dioptric belt ; and, in revolving lights, an approximation to a similar result is obtained by the addi- tion of the diacatoptric combination of pyramidal lenses and plane mirrors placed above the great lenses. Catoptric lights, however, to which such auxiliary arrangements are inapplicable, had still the great disadvantage of leaving the anterior cone of light to pass oft' in the useless state of naturally divergent light ; and anything cal- culated to increase the power of that class of lights, without alter- ing that simplicity and security of the burners employed in them, which renders them so suitable for remote situations in the colonies, deserves careful attention. It will be remembered that the propo- sal of Mr. Barlow for effecting this object, has already been noticed; and it is needless now to do more than remind the reader that the 212 practical disadvantage of the great aberration in the path of the rays reflected from the subsidiary hemispherical mirror, which must necessarily be of very small dimensions, together with the great loss of light by the second reflection, must go far to neutralize the effect of Mr. Barlow's plan. A combination of dioptric and catop- tric instruments, intended to produce a similar effect, has been pro- posed by Mr. Alexander Gordon, and is described at page 385 of the tenth volume of the Civil Engineers' and Architects' Journal. It consists of a paraboloi'dal mirror, of a very short focal distance, with some of the outer zones of one of Fresnel's smaller lenses in front of it. The zones are intended to refract some of the rays that es- cape past the edges of the mirror, while the pencil of light reflected from the mirror itself is supposed to pass through the circular space which is generally occupied by the central portion of the lens. This arrangement is a step in the right direction, only in so far as it im- plies the union of the two modes of illumination ; but, as it is by no means skilfully designed, it is liable to several palpable objections. 1. The actual gain of light has been greatly overrated by the writer in the Journal, who expects to turn twenty-seven-twenty- eighths of the whole light to a useful account ; but so great a gain of light can never consist with the form and position of the lower part of the flame. 2. Upwards of twenty-four-twenty-eighths of the estimated quan- tity would be intercepted by the paraboloid alone, and little more than two-twenty-eights by the rings of the lens, an addition far too insignificant to warrant the adoption of so expensive an appendage to the reflector. 3. The great aberration of the rays reflected by the conoid behind the parameter, and its small reflecting surface, must render it prac- tically useless ; and. perhaps, nearly one-half of the whole light would thus be lost to the mariner. The accurate formation of a paraboloid of such depth would also be difficult; and, considering the practical inutility of the conoid behind the parameter, would seem to be a mis- application of labor. 4. The union of such an instrument with the lenticular zones in front, which require that the pencil of parallel rays should be reflect- ed with the greatest accuracy, so as to enable them to pass through the circular space bounded by the zones, is an obvious misapplica- 213 tion of a paraboloid with a short focal distance, to a purpose for which it is singularly unsuitable. 5. Mirrors somewhat of the same form were in use at Scilly light- house, and were long ago discarded as disadvantageous, at the sug- gestion of the late eminent Captain Huddart. 6. The outer zones, which form the least efficient, and at the same time the most expensive portion of the compound lens have been pre- ferred to the central portion of that instrument j and by this means the anterior cone of rays is at the same time lost. * * * * * # * # A considerable practical defect in all the light-house lanterns which I have ever seen, with the exception of those recently constructed for the Scotch light-houses, consists in the vertical direction of the astra- gals, which of course tend to intercept the whole or a great part of the light in the azimuth which they subtend. The consideration of the improvement which I had effected in giving a diagonal direction to the joints of the fixed refractors first led me to adopt a diagonal arrangement of the framework which carries the cupola of zones, and afterwards for the astragals of the lantern. Not only is the direction of the astragals more advantageous for equalizing the effect of the light, but the greater stiffness and strength which such an arrange- ment gives to the framework of the lantern, make it safe to use more slender bars, and thus also absolutely less light is intercepted ; the panes of glass at the same time become triangular, and are necessarily stronger than rectangular panes of equal surface. This form of lan- tern is extremely light and elegant, and is shown, with detailed drawings of some of its principal parts, in plate X. To avoid the necessity of painting, which, in situations so exposed as those which light-houses generally occupy, is attended with many inconveniences and no small risk, the framework of the lantern is now formed of gun-metal and the dome is of copper. A lantern for a light of the first order, twelve feet in diameter, and with glass frames ten feet high, costs, when glazed, about ,1,260. In order to give the light- keepers free access to cleanse and wash the upper panes of the lan- tern, (an operation which in snowy weather must sometimes be fre- quently repeated during the night, ) a narrow gangway, on which they may safety stand, is placed on the level of the top of the lower panes, and at the top of the second panes rings are provided of which the light-keepers may lay hold for security in stormy weather. A light trap-ladder is also attached to the outside of the lantern by 214 means of which there is an easy access to the ventilator on the dome. Great care is bestowed on the glazing of the lantern, in order that it may be quite impervious to water, even during the heavy gales. "When iron is used for the frames, they are carefully and frequently painted ; but gun-metal, as just noticed, is now generally used in the Scotch light-houses. There is great risk of the glass plates being broken by the shaking of the lantern during high winds; and as much as possible to prevent this, various precautions are adopted. The arris of each plate is always carefully rounded by grinding ; and grooves about half an inch wide, capable of holding a good thickness of putty, are provided in the astragals for receiving the glass, which is quarter of an inch thick. Small pieces of lead or wood are in- serted between the frames and the plates of glass against which they may press, and by which they are completely separated from the more unyielding material of which the lantern -frames are composed. Panes glazed in frames padded with cushions, and capable of being temporarily fixed in a few minutes, in the room of a broken plate, are kept ready for use in the store-room. Those framed plates are called storm panes, and have been found very useful on several occa- sions when the glass has been shattered by large sea-birds coming against it in a stormy night, or by small stones violently driven against the lantern by the force of the wind. The ventilation of the lanterns forms a most important element in the preservation of a good and sufficient light. An ill-ventilated lan- tern has its sides continually covered with the water of condensation, which is produced by the contact of the ascending current of heated air; and the glass, thus obscured, obstructs the passage of the rays and diminishes the power of the light. In the northern light-houses, ventilators, capable of being opened and shut at pleasure, so as to admit from without a supply of air when required, are provided in the parapet wall on which the lantern stands ; the lantern roof also is surmounted by a cover which, while it closes the top of an open cylindric tube against the entrance of rain, and descends over it only so far as is needful for that purpose, still leaves an open air-space between it and the dome. This arrangement permits the current of heated air, which is continually flowing from the lantern through the cylindric tube, to pass between it and the outer cover, from which it finally escapes to the open air through the space between the cover and the dome. The door which communicates from the light-room 215 through the parapet to the balcony outside, is also made the means of ventilating the light-room ; and, for that purpose, it is provided with a sliding bolt at the bottom, which, being dropped into one or other of the holes cut in the balcony for its reception, serves to keep the door open at any angle that may be found necessary. A useful precaution was introduced by my predecessor, as engineer to the Northern lights Board, in order to prevent the too rapid condensa- tion of heated air on the large internal surface of the lantern roof, which consists in having two domes with an air-space between them, as shown in the enlarged diagrams in plate X. An important improvement in the ventilation of light-houses was some years ago introduced by Dr. Faraday into several of the light- houses belonging to the Trinity House, and has since been adopted in all the dioptric lights belonging to the commissioners of Northern light-houses. After mentioning several proofs of extremely bad ventilation in light-houses, Dr. Faraday thus describes his appa- ratus :* "The ventilating pipe or chimney is a copper tube, four inches in diameter; not, however, in one length, but divided into three or four pieces; the lower end of each of these pieces for about one and a half inch is opened out in a conical form, about five and a half inches in diameter at the lowest part. When the chimney is put together, the upper end of the bottom piece is inserted about half an inch into the cone of the next piece above, and fixed there by three ties or pins, so that the two pieces are firmly held together; but there is still plenty of air-way or entrance into the chimney between them. The same arrangement holds good with each succeeding piece. When the ventilating chimney is fixed in its place, it is adjused so that the lamp-chimney enters about half an inch into the lower cone, and the top of the ventilating chimney enters into the cowl or head of the lantern. "With this arrangement, it is found that the action of the venti- lating flue is to carry up every portion of the products of combustion into the cowl ; none passes by the cone apertures into the air of the lantern, but a portion of the air passes from the lantern by these aper- tures into the flue, and so the lantern itself is in some degree ventilated. " The important use of these cone apertures is, that when a sudden gust or eddy of wind strikes into the cowl of the lantern it should not have any eifect in disturbing or altering the flame. It is found that Q Minutes of Institution of Civil Engineers, vol. i., p. 207. 216 the wind may blow suddenly in at the cowl, and the effect never reaches the lamp. The upper, or the second, or the third, or even the fourth portion of the ventilating flue might be entirely closed, yet without altering the flame. The cone junctions in no way inter- fere with the tube in carrying up all the products of combustion; but if any downward current occurs, they dispose of the whole of it into the room without ever affecting the lamp. The ventilating flue is in fact a tube, which, as regards the lamp, can carry everything up but conveys nothing doivn." The advantages of this arrangement, as applied to the Northern light-houses, were much less palpable than those which are described in the beginning of Dr. Faraday's paper, because their ventilation was very good before its introduction; and the flame in particular was perfectly steady, being by no means subject to derangement from sudden gusts of wind from the roof in the manner noticed above. All the light-houses in the district of the Scotch Commissioners are under the charge of at least two light-keepers, whose duties are to cleanse and prepare the apparatus for the night illumination, to mount guard singly after the light is exhibited, and to relieve each other at stated hours, fixed by the printed regulations and instruc- tions under which they act. The rule is, that no keeper on watch shall, under any circumstances, leave the light-room until relieved by his comrade; and, for the purpose of cutting off all pretext for the neglect of this universal law, the dwelling-houses are built close to the light-tower, and means are provided for making signals directly from the light-room to the sleeping apartments below. The signals are communicated by air tubes (Plate XII) which pass from the light-room to the sleeping apartments in the houses, and through which, by means of a small piston, or puff of wind from the mouth, calls can be exchanged between the keepers. The man on guard in the light-room, at the end of the watch or on any sudden emergency, may thus summon his comrade from below, who, on being thus called, answers by a counter-blast, to show that the summons has been heard and will be obeyed. For the purpose of greater secu- rity, in such situations as the Bell Rock and the Skerryvore, four keepers are provided for one light-room, one being always ashore on leave with his family, and the other three being at the light-house, so that in case of the illness of one light-keeper an efficient establish- ment of two keepers for watching the light may remain. At all the 217 land light-houses, also, an agreement is made with some steady per- son residing in the neighborhood, who is instructed in the manage- ment of the light and cleansing of the apparatus, and comes under an obligation to do duty in the light-room when called upon, in the event of the sickness or absence of one of the light-keepers. This person is called the occasional keeper, and receives pay only while ac- tually employed at the light-house; but in order to keep him in the practice of the duty, he is required to serve in the light-room for a fortnight annually in the month of January. For the more minute details of the light-keepers' duty, I would refer the reader to the in- structions already alluded to, which will be found at the end of this volume. Each of the two light-keepers has a house for himself and family, both being under a common roof, but entering by separate doors, as shown in Plates XI and XII, which exhibit the buildings for the new light-house at Aduarmurchan point, on the coast of Argyleshire. The principal keeper's house consists of six rooms, two of which are at the disposal of the visiting officers of the board, whose duty in in- specting the light-house or superintending repairs may call them to the station; and the assistant has four rooms, one of which is used as a barrack-room for the workmen who, under the direction of the foreman of the light-room works, execute the annual repairs of the apparatus. The early light-houses contained accommodation for the light- keepers in the tower itself, but the dust caused by the cleaning of those rooms in the tower was found to be very injurious to the deli- cate apparatus and machinery in the light-room. Unless, therefore, in situations such as the Eddystone, the Bell Rock, or the Skerry- vore, where it is unavoidable, the dwellings of the light-keepers ought not to be placed in the light-tower, but in an adjoining building. Great care should be bestowed to produce the utmost cleanliness in everything connected with a light-house, the optical apparatus of which is of such a nature as to suffer materially from the effect of dust in injuring its polish. For this purpose, covered ash-pits are provided at all the dwelling-houses, in order that the dust of the fire-places may not be carried by the wind to the light-room ; and, for similar reasons, iron floors are used for the light-rooms instead of stone, which is often liable to abrasion, and all the stone work near the lantern is regularly painted in oil. 218 If, in all that belongs to a light-house, the greatest cleanliness be desirable, it is in a still higher degree necessary in every part of the light-room apparatus, without which the optical instruments and the machinery will neither last long nor work well. Every part of the apparatus, whether lenses or reflectors, should be carefully freed from dust before being either washed or burnished ; and without such a precaution, the cleansing process would only serve to scratch them. For burnishing the reflectors, prepared rouge (tritoxide of iron) of the finest description, which should be in the state of an impalpable powder of a deep orange-red color, is applied, by means of soft chamois skins, as occasion may require; but the great art of keeping reflectors clean consists in the daily, patient, and skilful application of manual labor in rubbing the surface of the instrument with a per- fectly dry, soft and clean skin, without rouge. The form of the hol- low paraboloid is such that some practice is necessary in order to acquire a free movement of the hand in rubbing reflectors ; and its attainment forms one of the principal lessons in the course of the preliminary instruction to which candidates for the situation of a light-keeper are subjected at the Bell Rock light-house. For cleans- ing the lenses and glass mirrors, spirits of wine is used. Having washed the surface of the instrument with a linen cloth steeped in spirits of wine, it is carefully dried with a soft and dry linen rubber, and finally rubbed with a fine chamois skin, free from any dust which would injure the polish of the glass, as well as from grease. It is sometimes necessary to use a little fine rouge with a chamois skin, for restoring any deficiency of polish which may occur from time to time; but in a well managed light-house this application will seldom, if ever, be required. The machinery of all kinds, whether that of the mechanical lamp or the revolving apparatus, should also be kept scrupulously clean, and all the journals should be regularly and carefully oiled. * * There are now no fewer than twenty-six floating lights on the coast of England. By the kindness of the Elder Brethren of the Corporation of Trinity House of Deptford Strond, I am enabled to give the following brief sketch of the nature and peculiarities of floating lights, which was communicated to me by Mr. Herbert, the secretary of the corpora- tion : ' ' The annual expense of maintaining a floating light, including the wages and victualing of the crew, who are eleven in number, is on 219 an average XI, 000 ; and the first cost of such a vessel, fitted complete with lantern and lighting apparatus, anchors, cables, &c., is nearly 5, 000. The lanterns are octagonal in form, five feet six inches in diameter ; and, where fixed lights are exhibited, they are fitted with eight Argand lamps, each in the focus of a parabolic reflector of twelve inches diameter ; but, in the revolving lights, four lamps and reflectors only are fitted. The greatest depth of water in which any light-vessel belonging to the Corporation of Trinity House of Dept- ford Strond at present rides, is about forty fathoms, (which is at the station of the Seven Stones between the Scilly islands and the coast of Cornwall. ) "The corporation's light- vessels are moored with chain-cables of 1-2 inch diameter, and a single mushroom anchor of 32 cwt., in which cases the chain-cables are 200 fathoms in length ; some of said vessels are moored to span-ground moorings, consisting of 100 fathoms of chain to each arm, and a mushroom anchor of similar weight at the end of each ; a riding cable of 150 fathoms being in such cases attached to the centre ring of the ground chain. The tonnage and general dimensions of the light-vessels are given on the drawing of the lines." Still lower in the scale of "signs and marks of the sea,'*' are bea- cons and buoys, which are used to point out those dangers which, either owing to the difficulty and expense that would attend the placing of more efficient marks to serve by night as well as by day, are necessarily left without lights, or which, from the peculiarity of their position, in passages too intricate for navigation by night, are, in practice, considered to be sufficiently indicated by day-marks alone. Beacons, as being more permanent, are preferred to buoys ; but they are generally placed only on rocks or banks which are dry at some periods of the tide. On rocks, in exposed situations, beacons are some- times of squared masonry, secured by numerous joggles; but, in situa- tions difficult of access, and in which works of uncompleted masonry could not be safely left during the winter season, an open frame-work of cast-iron pipes, firmly trussed and braced, and secured to the rock with strong louis-bats, is preferred. The details of this frame-work are shown at plate XIII. A stone beacon, of about forty feet high, may be erected for about .700, and an iron beacon for about 640. In less exposed places, where the bottom is rock, gravel, or hard sand, a conical form of beacon, composed of cast-iron plates, united with flanges and screws, with rust joints between them, and partially 220 filled with concrete, is sometimes used. A beacon of that kind can be erected for about 400. Lastly, buoys, which may be regarded as the least efficient kind of mark, and as bearing the same relation to a beacon that a float- ing light does to a light-house, are used to mark by day dangers which are always covered even at low water, and also to line out the fairways of channels. They are of three kinds, viz : the nun-buoy, in the form of a parabolic spindle, generally truncated at one end, so as to carry a mast or frame of cage-work, and loaded at the other end, so as to float in a vertical position ; the can-buoy, which is a conoid floating on its side ; and, lastly, the cask-buoy, which is a short frustum of a spindle truncated at both ends, but almost exclusively used for carrying the warps of vessels riding at moorings. Those buoys are of various sizes and differ in cost. Mast buoys, from ten to fifteen feet in length, cost from '23 15s. to 48 ; and those of the Kibble and the Tay, which are twenty-one and twenty-four feet long, cost respectively 105 and 79 ; the can-buoys are from five to eight feet long, and cost from 13 13s. to 20 5s. Smaller buoys are also used in narrow estuaries or rivers. Large buoys are often built on kneed frames, resembling the timbers of vessels. The cask-buoy is generally six feet long, and costs 22 15s. All those buoys are formed of strong oaken barrel-staves, well hooped with iron rings, and shielded with soft timber ; and the nozzle-pieces at the small end of the nun and caw-buoys are generally solid quoins of oak or iron, formed with a raglet or groove to receive the ends of the staves. Much skill on the part of the cooper is required in heating and moulding the staves to the required form; and great care must be taken that they be of well-seasoned timber. Buoys are not caulked with oakum, but with dry flags, which are closely compressed between the edges of the staves, and swell on being wet ; and they are care- fully proved by steaming them like barrels, to see if they be quite tight. Sheet iron is sometimes used in making buoys, and they are then sometimes protected with fenders of timber; but they have been found more troublesome for transport, and, for most situations, are considered less convenient than those of timber. An attempt has lately been made, under my direction, to construct buoys of gutta percha, stretched on a frame of timber; but I cannot at present speak confidently of the result. In the beginning of 1845, I suggested the idea of rendering beacons and buoys useful during night, by coating them with some phospho- 221 rescent substance, or surmounting them with a globe of strong glass filled with such a preparation, whose combustion is very slow, and emits a dull whitish light and little heat. Some experiments were accordingly made; but no practically useful result has been obtained. In laying down beacons or buoys, their position is fixed either by the intersection of two lines draAvn through two leading objects on the shore, (the magnetic bearings of which are given for the sake of easy reference on the spot, in finding out the marks,) or by means of the angles contained between lines drawn to various objects on the shore, which meet at the beacon or buoy from which they are meas- ured by means of a sextant. In the latter case, the angles are always measured around the whole horizon, thus affording a check by the dif- ference of their sum from 360. The magnetic bearing of one of those lines is afterwards carefully ascertained by means of the prismatic compass, (if possible from one of the objects on shore, and if not, conversely from the beacon or buoy,) so as to afford the means of translating the whole into magnetic bearings for the use of seamen. The buoys are moored by means of chains and iron sinkers, with a suf- ficient allowance in the length of the chain to permit them to ride [Extract from the Journal of the Franklin Institute.] AN ACCOUNT OF THE CONSTRUCTION OF THE NEW LIGHT- HOUSE AT THE PORT OF HAVANA, CUBA. By Senor Don Jose Benites, Colonel of Royal Engineers. [Translated from the Spanish for the Journal of tbe Franklin Institute ] The improvement of the light at the Moro Castle, which serves as a guide to vessels entering the port of Havana, in such manner as to correspond not only with the importance of its commerce, but also with the perfection to which the construction of this kind of appara- tus has now attained, having been determined upon by the royal junta of protection, the department of the marine was naturally consulted with regard to the most eligible situation and the proper altitude of the new light. That illustrious body was of opinion that a light placed at the same entrance to the port as the former one would be preferable to a light 222 elsewhere, although it might be situated on a more elevated point of the coast, owing to the particular configuration of which it might be seen from further to the windward. With regard to the height, it was judged sufficient to give an additional elevation of twenty-five feet to the old tower, because the light, being thus placed at one hundred and forty-two feet* above the level of the sea, would over- look the point called Del Pajonal, which bears about N. 71 E., and might, therefore, be readily distinguished and recognized by vessels approaching the port from that direction, within not less than eight nor more than fifteen miles of the coast, and affording still greater ad- vantages to those standing in more from the northward. And, more- over, that with the proposed elevation, this light-house would be one of the highest which are known. In accordance with this report, the junta determined, on the 22d of April, 1840, to proceed with the execution of the work ; and its president, the most excellent Captain General, directed that the corps of engineers should make the proper examination, in order to ascertain the practicability of giving to the old tower the desired ad- ditional elevation. By a report of the commandant, June 2d, 1840, it was declared practicable to add the proposed twenty-five feet to the height of the tower, provided the work were carefully done, and with materials of the best kind. In this state the project rested until the 16th of October, 1843, when the junta, through its president, asked that the funds necessary for the work should be remitted, inasmuch as it would also be neces- sary, in addition to the projected increase in the height of the tower, to order from Paris a lenticular lantern of the most improved kind, by Fresnel, to be placed therein. The requisite funds having been provided, it was resolved, on the 7th of April, 1844, to proceed with the work, but with the indispensable condition that the light should not be interrupted for a single night. Accordingly, the construction of a small temporary tower was commenced on the 22d of May, for the purpose of sustaining the light while the height of the old tower was being increased by additional mason-work. The great height of the platform upon which the temporary tower was constructed, rendered it unnecessary to give it an elevation of more than seven yards in order to maintain the light at the same height as that at which it was placed in the old tower. Its immediate proximity to this, and the removal of the light to the temporary tower in a single day, rendered ~- The Spanish foot here used is equal to 11.1 inches, and the vara, or yard, is 33.3 inches. it unnecessary to give that notice in the public papers which would otherwise have been requisite in order to avoid dangerous conse- quences to vessels. On the 23d of July, 1844, the temporary light- house was first put into use; its cost, including the lantern, amounting to the sum of $1, 800. Its strength, and the judicious principles upon which it was constructed, were fully proved in the terrible hurricane of the 5th of October last ; during which, though exposed, without the least protection from other buildings, to the force of the wind and the beating of the waves, it remained firm, and without other injury than a total destruction of the glass in the lantern. The next step was the taking down of the lantern from the old tower, and to proceed with other preparations for increasing its height, when, on the 14th of August, 1844, notice was received by the board of engineers, from his excellency, the Captain General, that, by a resolution of the junta, adopted in virtue of a report from their commissioners, it was determined to suspend the work, and inquire whether it would not be more expedient, provided the funds were sufficient, to construct a tower upon a new plan, which should combine all the beauty, convenience, and facility which would bo required for the proper management of an apparatus so complicated as that of Fresnel ; advantages which could not be afforded by the old tower on account of its limited dimensions, and its total want of accommodations for the persons entrusted with the care of the light during the night, as well as its narrow and inconvenient stairway. The board of engineers, as was to be expected, reported in favor of the new project, and at the same time submitted a plan and an esti- mate for the new tower. Both of these were approved by the junta at its session on the 16th of August, and the work was ordered to be carried into effect. On the following day the demolition of the old tower was commenced, and, at the same time, the excavation of a foundation for the new one was begun, in order that the old materials might be used in it. Situation of the nciv tower. Of the rock upon which the Moro cas- tle is built, that point which extends farthest towards the N. W., and on which the old tower stood, is divided from the rest by a cleft or fissure, and is also undermined by a large cavern, washed out by the continual beating of the waves. In order to avoid these defects, which might, in time, endanger the stability of the new edifice, and also because the space afforded, for the ground plan was not sufficient, a place was chosen eighty-four feet farther back than the position 224 occupied by the old tower, and on the broadest part of the glacis of the Morillo a position combining all the advantages of the former one, besides leaving free the extreme point of the Morillo for the erection of a battery of three Paixhan guns, of large calibre, in such a very advantageous position. Care was also taken to leave sufficient space about the new tower for the free use and management of the cannon which defend the entrance to the port, as well as of those on the opposite side. Description of the tower. It is composed of two parts ; the first representing a column seventy-nine feet high, twenty-five feet in diameter at the base, and twenty at the top. The cornice of this serves as the floor of a corridor with a circular parapet, enclosed by a grated railing of copper, which surrounds the upper, or second part, upon which the lantern is supported. The first or lower part is constructed of hewn stone, the wall being seven feet thick at the base, vertical in the interior, and sloping on the outside, thirty inches in the whole height. The interior space of eleven feet in diameter serves for a circular staircase, the steps of which are four feet long, seven and a half inches high, nineteen inches broad at the wide end, and six at the other, or immediately at the spindle or central column of three feet in diameter, which extends up through the whole height. The stairway begins inside, at thirty-eight inches in the clear from the door, in order to leave an open landing place ; the steps being covered with slabs of marble one and a half inch in thickness, with a moulding which extends an inch beyond the step. The doorway in the lower part of the tower, which gives entrance to the stairway, is four feet wide and eight feet high, with pilasters at the sides, and its cornice and frontispiece in the form of a circular arch. Over the door is a block of marble containing an inscription in Spanish of the following purport : In the year 1844 : Isabella the Second reigning ; The Junta of Protection under the Presidency of the Captain General of the Island, Don Leopold O'Donncll ; This work was executed under the direction of the Corps of Engineers of the Army. The stairway is lighted and ventilated by three i ets of windows, placed equi-distant from one another throughout the whole height. They are four feet high and two feet wide, and in six of them the lower part of the niche, or recess in the wall which forms the win- 225 dow, is level with the steps, and serves as a landing or resting place. BeloAV the stairway, and at the level of the lower floor of the tower, is a spacious room, enclosed by a wooden railing, which is used as a place of deposit for oil and the more heavy and bulky articles used about the light-house. At the height of sixty-three feet nine inches the stairway, which has been described, terminates in an apartment called the attendant's room, twelve feet in diameter and twelve and a half in height, cov- ered by an arch two feet in the crown. This chamber, lined with marble, is intended for the two persons who have charge of the light during the night. It is furnished with windows, and the requisite conveniences for containing a supply of lamps, funnels, wicks, oil, e made up by the arched ceiling of this room, which has not been taken into the account. The solid contents of the circular wall which forms the upper sec- tion of the tower, upon which the lantern is placed, is twenty-seven 231 cubic yards, deducting the opening for the door; so that the whole amount of solid masonry is 902 cubic yards. A cubic yard of the masonry used in this tower weighs eighty-five arrobas, (twenty-five pounds each,) and the arm of the lever of resist- ance being four yards, (a little less than the radius of the base,) it fol- lows that the power of the resistance will be 902 X 4 X 85 = 306, 680. A central perpendicular section of the lower portion of the tower contains 195 square yards: of the upper portion, 13; and of the lan- tern, 26, presenting a total sectional superfice of 234 square yards. The centre of gravity of these three superfices is found at thirteen 3'ards from the base of the tower; consequently the momentum of pressure from the wind is f 386 x 234 X 13=31,504 arrobas, and the ratio of the resistance to the pressures 3 j )6 ' 680 9.7. 31,504 By this result it will be seen that the tower at the Moro has a stability equal to nearly one and a half times that of the tower at L' Orient, which was taken for comparison, and consequently that its dimensions are sufficient, although indispensable for the reasons already mentioned, to warrant the undertaking of its construction with entire confidence. Details of the construction. Foundation. As the tower is twenty- five feet in diameter at its base, a circle 28^ feet in diameter was traced around the centre of the area to be occupied by it so that the excavation for the foundation being larger than the body of the tower, a berm or offset of twenty-one inches would be left by the extension of the foundation wall beyond that of the tower itself. The excavation was carried through the surface soil down to the rock which underlies the glacis of the Morillo, which was reached and laid bare at an average depth of fifteen feet. The rock presented an irregular surface, in consequence of which, together with its extreme hardness, the operation of cutting it down to a level would have been very expensive. It was therefore deemed preferable to construct the foundation by steps, (enescaiones,) using blocks of stone of the best kind, disposed in circular horizontal layers, (formando anillos en capos Jiorizontales,) properly placed, and the joints filled with a mixture of lime and sand ; taking care, as in all masonry of hewn stone, that the joints of each layer should be covered by the course immediately above it. The foundation is nine and a half yards in diameter by five in depth, and consequently contains three hundred and fifty-five cubic 232 yards of masonry. The cost of its excavation and refilling was $1,554, being $4.375 per cubic yard. In the calculation of the original estimate it was assumed that the foundation would be only three yards in depth ; consequently containing two hundred and thirteen cubic yards, of which the cost, estimated at $7.50 per yard for the masonry, including the excavation, amounted to $1,597.50, being an excess of $43.50. In calculating this estimate of $7.50 per cubic yard of masonry, it was proposed to use all the materials of the old tower : but as this would not be sufficient, it was supposed that the stone still to be provided would have to be purchased and transported from the opposite shore. The great reduction which was made in the cost per cubic yard of this work, from that originally estimated, was owing to the following causes : First. Instead of buying from in- dividuals the stone which were required, those were procured which remained unused from the erection of the fortifications at that place, and which has been taken from quarries opened for that purpose ; on which account they were obtained at a much lower price, while, at the same time, the expensive transportation in vessels was avoided. Second. Because it was not necessary to purchase sand for making the cement, having used that which was found in the fosses of the fortifications. The digging of the foundation was commenced on the 17th of August, 1844, and by the 24th of September it was completed and leveled off to nine inches below the glacis of the castle ; being then in order for receiving the first layer of stone for the tower. Daring the same time the old tower was completely taken down, its materials, as has been already said, being used for the new foun- dation. The lower part of the tower. Upon the level top of the basement, or foundation, the first layer of stone forms a solid floor over the whole twenty-five feet in diameter ; its outer boarder being vertical and forming a projection or socle of nine inches around the tower, as well as a step, of the same height, for entrance into it. The building is then continued to the requisite elevation by successive courses of eighteen inches in height. In order to give an exterior slope to the wall, and consequently to diminish its thickness in due proportion, the width of the blocks in the interior courses was gradually contracted, while those on the exterior were of the same breadth, so that the vertical joints might recede gradually to- 233 wards the interior, and the masonry be well united together ; thus avoiding the defect which would result from an equal diminution in the breadth of the blocks used in both the inner and outer faces of the wall, in which case, the vertical joints of each course would con- tinue to be one above another, thus forming two distinct walls, with- out further connexion than that of the extending ties. The circular stairway is composed of entire blocks of stone, which are inserted six inches into the Avail, each of them forming two steps, together with the corresponding part of the central column, or nave, of the staircase. It was carried up at the same time with the wall of the tower, in order to insure the proper connexion and binding together of the work, and also served for use during the construction of the building ; the order of proceeding being first to set the block of stone which formed two steps, and then to lay the corresponding course on the wall, and so on successively. The nave, or central part of the stairway, is cylindrical throughout its whole height, except at the top, where it increases in diameter, with a view of gaining a certain space on the floor of the attendants' room. In order to give this proper form to the central column, its diameter was gradually en- larged, beginning at the seventeenth step from the top, and so con- tinuing to the last ; so that the stairway is only twenty-seven inches wide in the last six feet of its flight. The upper part of the tower. This is a simple circular wall of cut stone, composed of blocks in alternate order, and presenting nothing worthy of special notice. Arch of the attendants' room. This arch is in the form of a simple dome, and presents nothing remarkable in its construction. The thickness of the wall which supports it is that which is strictly necessary for the equilibrium, since the excess in the weight of its masonry, from the spring of the arch to the key, and that of the upper part of the tower, which also contributes to its stability, are more than sufficient to compensate for the weight of the apparatus for illumination, which rests upon the summit of the arch. But not- withstanding this, as the three openings in it somewhat diminish its strength, the precaution was taken, in order to avoid the least dis- placement, to fasten all the arch stones of the second and third courses, together with those of the first, with iron clamps, one and a half inch thick by three inches wide, let into the arch stones and fastened to each of them by a bolt, which passes through two-thirds of their thickness, well secured with lead. 234 Materials. The stone used in the construction of the tower was taken from the quarries known here by the name of playa de chivos immediately at the point where the tower stands, and preferable to the stone found at any other place in the vicinity, because, although not of the hardest quality, they are still sufficiently so, and of a more equal and homogeneous texture than the others. Great care was also taken to use blocks of the most durable kind in the exterior sur- face of the wall, and for the steps of the stairway. The lime and sand employed were both of excellent quality; the former made of a very hard and clean stone, and the latter containing no saline matter. The mortar was made with great care, composed of two-fifths of lime and three-fifths of sand, mixed with fresh water and well stirred, so as perfectly to incorporate the ingredients. The doors, windows, interior balustrades, and hand rails of the staircase are of mahogany. After the completion of the edifice, in order to preserve it from the effects of moisture and of nitrous salts, inasmuch as the stone, as already stated, is not of the hardest kind, it was covered, both on the interior and exterior surface, with a very thin and well laid coat of painted stucco. The cost of the structure, when completed, was very nearly that calculated in the original estimate. CHAMBER OF COMMERCE, NEW YORK. The Committee appointed to consider the condition of the light-houses of tiie United States, as developed in the report of the Light-house Board recently communicated to Congress, ask leave to report : That the subject has attracted occasional attention for some years, although your committee believe it never received a thorough investigation until the Light-house Board was appointed by the Secretary of the Treasury in May, 1851, under authority given by Congress. In January, 1838, the Senate called on the Treasury Department for a copy of a communication made by Messrs. E. & G . W. Blunt, relative to the light-houses of the United States, and also for a copy of the report in reply to that communication, made by Mr. Pleasanton, the Fifth Auditor of the Treasury, he being in charge of the whole light-house establishment. In the communica- 235 tion of Messrs. Blunt, they expressed the opinion that our establish- ment was badly managed, and was greatly inferior to the similar establishments of France and Great Britain. In his reply, Mr. Pleasanton undertook to show that this opinion was not well founded, and that the charges accompanying it were frivolous, unimportant, or groundless. Messrs. Blunt rejoined, with a view to prove that their statements were correct. In their first communication, Messrs. Blunt took occasion to state that the French light-houses were supe- rior to the English, the former being provided with lenses instead of parabolic reflectors. In May, 1838, the Committee on Commerce of the Senate reported upon the expediency of introducing the dioptric apparatus for illu- minating light-houses into the United States, and upon the expedi- ency of improving the organization of our light-house system. In that report it is stated that the Navy Board was required at the pre- vious session of Congress to examine the sites of a large number of new light-houses authorized at that session, and inquire into the facts concerning them. The act of Congress provided that in cases where objections were found to exist the erection of the buildings should be suspended. Under this provision the Navy Board arrested the erec- tion of no less than thirty-one of the houses proposed. The committee further stated that while our light-house system (if system it could be called) had, probably, most of the time, been conducted with reasonable care and satisfaction to the public in most respects, both the French and English had, by scientific research and improvement, perfected theirs to a considerably higher degree. The French took the lead, under Fresnel, who brought the lenticular apparatus into use. The committee were satisfied, with the evi- dence before them, that this apparatus was the best known, but to test the matter practically, they recommended that two sets of the first class and one of the second should be imported and put up at proper points to try their merits by actual experiment. Captain W. H. Swift, of the United States Topographical Engi- neers, stated, in 1842, that he had never seen upon our coast a light which approached, even in a remote degree, the brilliancy exhibited by certain English lights Avhich he referred to. FresnePs apparatus he considered superior to the English, and both immeasurably supe- rior to our own. 236 In 1845, two officers of the navy, viz: Lieutenants Jenkins and Bache, were sent to Europe by the then Secretary of the Treasury, to obtain information concerning the light-house establishments there. In the report of these officers, on their return, they denounced our lights as inferior to. all they- had seen abroad; recommended strongly the adoption of the French apparatus, and the appointment of a board of officers to devise some new plan of light-house management. A committee of the Franklin Institute, of Philadelphia, in May, 1849, stated that they were strongly impressed with the great excel- lence of the Fresnel system, a system which had then been estab- lished, as they said, in nearly three hundred places in Europe, where it was gradually superseding the old lights, whilst in no instance had it been abandoned after it had been once established. The recent Light-house Board consisted of Commodore Shubrick and Commander Du Pont, of the Navy, General Totten, of the Engi- neers, Colonel Kearney, of the Topographical Engineers, and Pro- fessor Bache, Superintendent of the Coast Survey, as members, with Lieutenant Jenkins, of the Navy, as Secretary. Their report sets forth, among other things, that in 1825, the French government adopted definitively what is called the French system of illumination, and that in 1834, a new impulse was given in England and Scotland to light-house improvement by letters from Sir David Brewster, and by the action of a committee of the House of Commons. Although, say the Board, the lens met with much favor in England, and has been gradually getting into use, until nearly one-half the seacoast lights have been changed since 1837, still Scotland has introduced a larger number in proportion to extent of coast. Following out these improvements, another committee on light-houses was raised by the House of Commons in 1845, and the result, among other alleged benefits, has been the introduction of a large number of lens appa- ratus, not only into Great Britain but into many of the Colonies. The Board, however, have been unable to discover that any steps have been taken in this country to keep pace with the light-house improvements of France and Great Britain, except the placing a lens apparatus at the Highlands of Navesink, an improved reflector apparatus in the Boston light-house, a lens of the second class at Sankaty Head, Nan tucket, and the lights authorized by law to be constructed, under the direction of the Topographical Bureau, at 237 Brandy wine Shoal, Carysfort Reef, and Sand Key. The law required that the lenticular apparatus placed at Navesink, and the improved reflector apparatus at Boston should be tested by full and satisfactory experiment, as to their merits, in comparison with the other appa- ratus in use. But the Board have never heard the result, nor that any such experiment was ever made. The Board, after examining the subject committed to them with the patience and zeal its importance demanded, arrived at a great number of conclusions set forth with remarkable particularity in their report. They condemn most emphatically our whole system. They distinctly declare, that in their judgment the light-houses, light-ves- sels, beacons, and buoys, and their accessories, in the United States, are not as efficient as they ought to be, and not so much so as those of France and Great Britain. That our light-house establishment does not compare favorably in point of economy with theirs. That the towers and buildings are not constructed, in general, of the best materials, nor with proper accommodations. That the lanterns, as a general rule, are of improper dimensions, constructed of ill-adapted materials, without scientific skill, and are in many instances not suited to the use designed. That there is no systematic plan of con- struction, illumination, and superintendence. That the illuminating apparatus is of a description now nearly obsolete where the best of that kind was employed before the introduction of the French lenses. That the seacoast reflector lights are in general too low, and are deficient in power and range. That the attendance is deficient. That the lights are not properly classified, nor well distinguished from each other. That there is not in useful effect a single first class light on the coast. That the lights at Navesink and Sankaty Head, Nantucket, are the best. That the Fresnel lens is greatly superior to any other mode of light-house illumination. That there is no proper system of distributing supplies to light-houses, and no system in the management of the light-house establishment. That the light-keepers in many instances are not competent. That the mode of repairs is not efficient or reliable. That the floating lights are comparatively useless for want of efficient lamps and reflectors. That the light-vessels are not well adapted to the service, and are not properly distinguished either by day or by night. That the buoys 238 are defective and the moorings insufficient. And that there is no proper system of beaconage or buoyage. These are but a few of the conclusions of the Board. Yet these are quite enough, if well founded, to show that the condition of the whole light-house establishment is such as to demand thorough renovation and reform. It is not to be endured that the lives of our seamen, and of the passengers often embarked with them, should ever be put in peril for Avant of the best protection in approaching our ports, or proceeding along our coast, that it is in the power of skill, science and systematic management to give. Upon no consideration whatever ought the United States to be second to any country under heaven in affording all possible security to the vast interests of commerce and navigation, upon which so much of national prosperity depends. For the correctness of the positions taken by the Light-house Board, and the sufficiency of the evidence on which they are based, it seems to your committee that the high character, elevated stand- ing, and eminent attainments of the members of the Board furnish an ample guarantee. If corroborative testimony Avere needed, more than enough, in the opinion of your committee, may be found in the various documents referred to in this report. Still it is due to Mr. Pleasanton to state, that in his reply to the report of the Light-house Board, he considers he has shoAvn that our lights are satisfactory to the captains of ships and pilots generally; that our light-house estab- lishment is managed more economically than that of Great Britain; that our light-ships are superior to the British; and that the French lenses are more expensive, without shoAving a better light "than the reflectors. It thus appears that the parties stand in direct opposition to each other. Both cannot be right. Your committee, after duly considering the question, cannot avoid the conclusion that Mr. Pleas- anton is far more likely to be in error than the Light-house Board. By way of remedy for the evils they specify, the Board recom- mend among other things the absolute adoption of the Fresnel ap- paratus for all new lights and all lights requiring renovation, modi- tied in special cases by Stevenson's apparatus. They also recommend the organization of a permanent Light-house Board for the construc- tion, repair, management, and superintendence of the light-houses, light-vessels, beacons, and buoys, of the United States. They pro- pose that this Board be composed of the Secretary of the Treasury, 239 as President, two officers of the Navy, of high rank, one officer of Engineers, one officer of Topographical Engineers, and two civilians of high scientific attainments, as members, with an officer of the Navy and an officer of Engineers as secretaries ; the officers, civil, military, and naval, to serve without additional salary. Your committee cannot doubt that the organization of a Light- house Board of this description would secure, beyond question, the selection of proper sites for light-houses along our shores, with due regard to the wants of commerce. They are satisfied it would also render quite certain the proper construction of the light towers and buildings, as well as the use of the best illuminating apparatus. They are convinced, too, it would ensure far greater efficiency, econ- omy, and systematic management throughout the whole light-house establishment, than is practicable under the superintendence of an auditor of the Treasury Department. A board of skilful, scientific men, combining the variety of qualification required, is obviously preferable for these purposes, to a disbursing officer, not supposed to be very highly endued with engineering, nautical, or optical knowledge. The fact stated by the Committee on Commerce of the Senate, in 1838, that the Navy Board stopped the erection of thirty- one new light-houses in one year, for sufficient reasons, indicates very clearly the necessity of a proper light-house organization at all times, even if no stress be laid upon the conclusions of the recent able Light-house Board. This necessity is certainly not lessened by the further facts that the present superintendent has omitted to test the merits of the Fresnel apparatus, as virtually directed by the act of Congress of 1838, and that he still strenuously opposes the more frequent selection of that apparatus for the use of our light-houses, in the face of a w r eight of testimony in its favor, which to your committee appears irresistible. This course plainly discovers a steadfast determination on his part against reform and improvement, far removed, as your committee think, from the true spirit which should actuate the head of so important an establishment. In any view your committee are able to take of the subject, the proposed change seems highly expedient. They therefore recommend the adoption of the accompanying resolution. All which is respectfully submitted. GEO. CURTIS, LEOPOLD BIERWIRTH, [ Committee. JAMES W. PHILLIPS, 240 Resolved, That the Chamber of Commerce of the City of New York cordially approves of the recommendation of the Light-house Board, contained in their report of 30th of January last, that a per- manent board be organized, to be charged by law with the entire management of the light-house establishment of the United States ; and that the Chamber sincerely hopes that Congress will carry that recommendation into effect. At a meeting of the Chamber of Commerce at New York, held on the 4th May, 1852, the preceding report and resolution were approved, and ordered to be printed and sent to the Senate and House of Representatives as the sense of the Chamber. MOSES H. GRINNELL, President. M. MAURY, Secretary. ROYAL INSTITUTION OF GREAT BRITAIN. WEEKLY EVENING MEETING. FRIDAY MARCH 9, 1860. The Lord Wensleydale, Vice President, in the Chair. Professor Faraday, D. C. L. F. R. S. On Light-house Illumination The Electric Light. The use of light to guide the mariner as he approaches land, or passes through intricate channels, has, with the advance of society, and its ever increasing interests, caused such a necessity for means more and more perfect, as to tax to the utmost the powers both of the philosopher and the practical man, in the development of the prin- ciples concerned, and their efficient application. Formerly the means were simple enough; and if the light of a lanthorn or torch was not sufficient to point out a position, a fire had to be made in their place. As the system became developed, it soon appeared that power could be obtained, not merely by increasing the light but by directing the issuing rays: and this was in many cases a more powerful and useful means than enlarging the combustion leading to the diminution of the volume of the former with, at the same time, an increase in its intensity. Direction was obtained, either by the use of lenses de- pendent altogether upon refraction, or of reflectors dependent upon metallic reflexion; and some ancient specimens of both were shown. In modern times the principle of total reflexion has also been em- ployed, which involves the use of glass, and depends both upon re- fraction and reflexion. In all these appliances much light is lost: if metal be used for reflexion, a certain proportion is absorbed by the face of the metal; if glass be used for refraction, light is lost at all the surfaces where the ray passes between the air and the glass; and also in some degree by absorption in the body of the glass itself. There is, of course, no power of actually increasing the whole amount of light, by any optical arrangement associated with it. The light which issues forth into space must have a certain amount of divergence. The divergence in the vertical direction must be enough to cover the sea from the horizon, to within a certain mod- erate distance from the shore, so that all ships within that distance may have a view of their luminous guide. If it have less, it may es- cape observation where it ought to be seen; if it have more, light is thrown away which ought to be directed within the useful degree of divergence; or if the horizontal divergence be considered, it may be necessary so to construct the optical apparatus, that the light within an angle of 60 or 45 shall be compressed into a beam diverging only 15, that it may give in the distance a bright flash having a certain duration instead of a continuous light or into one diverging only 5 or 6, which, though of far shorter duration, has greatly increased intensity and penetrating power in hazy weather. The amount of divergence depends in a large degree upon the bulk of the source of light, and cannot be made less than a certain amount, with the flame of a given size. If the flame of an Argand lamp f th of an inch wide, and 1| inch high, be placed in the focus of an ordinary Trinity House parabolic reflector, it will supply a beam having about 15 diverg- ence; if we wish to increase the effect of brightness, we cannot prop- erly do it by enlarging the lamp flame; for though lamps are made for the dioptric arrangement of Fresnel, which have as many as four wicks, flames 3 inches wide, and burn like intense furnaces, yet if one be put into the lamp place of the reflector referred to, its eifect would chiefly be to give a beam of wider divergence; and if to cor- rect this, the reflector were made with a greater focal distance, then it must be altogether of a much larger size. The same general result occurs with the dioptric apparatus; and here, where the four- wicked lamps are used, they are placed at times nearly 40 inches distant from 18 242 the lens, occasioning the necessity of a very large, though very fine, glass apparatus. On the other hand, if the light could be compressed, the necessity for such large apparatus would cease, and it might be reduced from the size of a room to the size of a hat; and here it is that we seek ir* the electric spark, and such like concentrated sources of light, for aid in illumination. It is very true, that by adding lamp to lamp, each with its reflector, upon one face or direction, power can be gained ; and in some of the revolving lights, ten lamps and reflectors unite to- give the required flash. But then not more than three of these faces can be placed in the whole circle; and if a fixed light be required in all directions round the light-house nothing better has been yet es- tablished than the four-wicked Fresnel lamp in the centre of its diop- tric and catadioptric apparatus. Now the electric light can be raised up easily to an equality with the oil lamp, and if then substituted for the latter, will give all the effect of the latter; or by expenditure of money it can be raised to a five or tenfold power, or more, and will then give five or tenfold effect. This can be done, not merely with- out increase of the volume of the light, but whilst the light shall have a volume scarcely the 2000th part of that of the oil flame. Hence, the extraordinary assistance we may expect to obtain of di- minishing the size of the optical apparatus and perfecting that part of the apparatus. Many compressed intense lights have been submitted to the Trinity House ; and that corporation has shown its great desire to advance all such objects and improve the lighting of the coast, by spending, upon various occasions, much money and much time for this end. It is manifest that the use of a light-house must be never failing, its service ever sure ; and that the latter cannot be interfered with by the introduction of any plan, or proposition, or apparatus, w r hich has not been developed to the fullest possible extent, as to the amount of light produced the expense of such light, the wear and tear of the apparatus employed, the steadiness of the light for 16 hours, its lia- bility to extinction, the amount of necessary night care, the number of attendants, the nature of probable accidents, its fitness for secluded places, and other contingent circumstances, which can as well be as- certained out of a light-house as in it. The electric spark which has been placed in the South Foreland High Light, by Professor Holmes, 243 to do duty for the six winter months, had to go through all this pre- paratory education before it could be allowed this practical trial. It is not obtained from frictional electricity, or from voltaic electricity, but from magnetic action. The first spark (and even magnetic elec- tricity as a whole) was obtained 28 years ago. (Faraday, Philosoph- ical Transactions, 1832, p. 32.) If an iron core be surrounded by wire, and then moved in the right direction near the poles of a magnet, a current of electricity passes, or tends to pass, through it. Many powerful magnets are therefore arranged on a wheel, that ^hey may be associated very near to another wheel, on which are fixed many helices with their cores, like that described. Again, a third wheel consists of magnets arranged like the first; next to this is another wheel of the helices, and next to this again a fifth wheel, carrying magnets. All the magnet .wheels are fixed to one axle, and all the helix wheels are held immovable in their place. The wires of the helices are conjoined and connected with a commutator, which, as the magnet-wheels are moved round, gathers the various electric cur- rents produced in the helices, and sends them up through two insu- lated wires in one common stream of electricity into the light-house lanthorn. So it will be seen that nothing more is required to pro- duce electricity than to revolve the magnet-wheels. There are two magneto-electric machines at the South Foreland, each being put in motion by a two-horse power steam-engine ; and, excepting wear and tear, the whole consumption of material to produce the light is the coke and water required to raise steam for the engines, and carbon points for the lamp in the lanthorn. The lamp is a delicate arrangement of machinery, holding the two carbons between which the electric light exists, and regulating their adjustment; so that whilst they gradually consume away, the place of the light shall not be altered. The electric wires end in the two bars of a small railway, and upon these the lamp stands. When the car- bons of a lamp are nearly gone, that lamp is lifted off and another instantly pushed into its place. The machines and lamp have done their duty during the past six mouths in a real and practical manner. The light has never gone out, through any deficiency or cause in the engine and machine house; and when it has become extinguished in the lanthorn, a single touch of the keeper's hand has set it shining as bright as ever. The light shown up and down the channel, and across 244 into France, with a power far surpassing that of any other fixed light within sight, or anywhere existent. The experiment has been a good one. There is still the matter of expense and some other circumstances to be considered; but it is the hope and desire of the Trinity House, and all interested in the subject, that it should ultimately justify its full adoption. [M. P.] THE LIGHT DUES LEVIED ON THE SHIPPING OF THE UNITED STATES IN GREAT BRITAIN. CORRESPONDENCE RESPECTING THE LIGHT DUES LEVIED ON AMERICAN SHIPPING IN THE UNITED KINGDOM. No. 1. Mr. Lawrence to Viscount Palmerston. (Received January 2, 1851.) UNITED STATES LEGATION, 138 PICCADILLY, December 31, 1850. The undersigned, Envoy Extraordinary and Minister Plenipoten- tiary of the United States of America, has the honor, under instruc- tions from his government, to invite the attention of Viscount Palmerston, her Majesty's Principal Secretary of State for Foreign Affairs, to the subject of the light dues exacted of the mercantile marine of the United States entering the ports of the United King- dom. It is nearly two years since her Majesty's government determined to respond to the invitation of the United States, made to the world many years ago, and recommend Parliament to repeal the prohibitory navigation laws of the kingdom ; and the commerce of the two nations has been conducted for now just one year on the reciprocal basis established in accordance with such recommendation. The United States ask Great Britain to carry out this principle; to estab- lish reciprocity in fact as well as in name, to do justice to the com- merce of the United States. The light-houses, floating-lights, buoys, and beacons on the whole sea and lake-coast, and rivers of the United States, were con- structed and are maintained by the federal government, an annual appropriation being made by Congress for these objects. No light 245 dues of any kind are levied, either on vessels of the United States or on ships of foreign nations. In the year 1792 there were but 10 lights in the Union. In the year 1848 there were 270 light-houses, 30 floating lights, and 1,000 buoys, besides numerous fixed beacons. There are probably at this time, including those under construction on the Pacific coast, more than 300 light-houses, with a propor- tionate number of floating lights, buoys, &c., all of which are given to the use of the world by the United States without tax or charge. The commerce of the United States is not met with a correspond- ing liberality in the ports of the United Kingdom. The reciprocity intended to be established by the navigation law of last year, and so much to be wished for between the two greatest commercial nations of the globe, will not be realized if American tonnage continues sub- jected to onerous light dues in Great Britain, while British vessels enjoy without pay the lights, GO s* 1 * 5> 2 53 8 ^ _S8-g !!i ||| L ^ s IN" i. *J o ...*-i ^ v s^ ^ i > v ^o !-8*1' <^ II r^ S S ^ Si I II * t! '"^^ 9 a * > AO| am jo a^ea^ i(OBa joj pas^qajnd no aqj jo uojced jad jsoo a^ejaA asnoi[ jqSii aijj jo aon -uaVJiBiu pu )joddns am joj papaadxa ^unouiB [BOX sjaaraaBjnq?ip uo snoissmiinoo joj sjuapusj -uijaiina oj pjvd sjunomy uo be aoiAjas uoo^iq paB Xonq joj pa -puodxa 5,mt! JB;O -?q8ij jo '-oig ';jod -dns '-.i;i:ii.9rji jaacu -asjjjSApB ojiqnd japan Jappiq %saM.o\ aqi jo aa. tpa joj pampjna no am jo UOJIB3 aad a}t!J a^BJaA juauiqsitqBjsa asnoq-iqStt aqj jo aous -uajuiBui puB vioddns ai[) aoj papuadxa junouis IBJOJ, siuanwsjnqsp no suojssitnmoo joj gjuapuaj -uuadns 04 piBd s^unoray i c ' -aatAjas uoaBaq i pue konq joj pa ' 3 -puadxa VJIB I<>I jo '-05? '^joddns 'sJiBd.u joj pa -puadxa ^OIB IBJOJ siassaA-iq3}iJO pjBoq no iq3j| jad 2 ! o : So SS 2 S S 8 -}qai[ jo jaqran^ TO * TT o o o -jadns jo suois -moo PUB 'BU,pads -U( '83IJBIB8 'SJIBd -aj 'saijddns joj pa -puadxa .,mB IKJOJ j -jqati jad isoo jtjnu i\ >*\ 111331 i | I |i I.I 1 I s 267 TABLE C. (ATLANTIC, GULF, AND LAKE COASTS.) Exhibiting the amounts appropriated, by Congress in special appropriation- bills, reported from the Committees on Commerce and in the general appro- priation bills for light-houses at neio localities, rebuilding old light-houses, light-vessels for new localities, and rebuilding light-vessels, occupying old stations ivhich required rebuilding, Sfc., for the Jive years ^18471852^ imme- diately preceding the organization of the Light-house Board. Date of approval of appropri- ation bills. Amountappropria- ted for new light- houses and re- building old ones. Amount appropria- ted for new light- vessels and re- building old ones. Amount appro- priated for fog bells, &c. Total. March 3, 1847 $521,250 00 $25,000 00 $546,250 00 August 12 and 14, 1848. March 3 1849 252,091 90 191 441 37 64,000 00 35 407 00 $750 00 750 00 316,841 90 227,598 37 September 28, 1850 March 3, 1851 422,590 00 314,432 39 8,000 00 42,500 00 5,500 00 250 00 436,090 00 357, 182 39 August 31, 1852 495 200 00 130,200 00 32,500 00 657,900 00 2,197,005 66 305,107 00 39,750 00 2,541,862 66 THORNTON A. JENKINS, W. B. FRANKLIN, W. B. SHUBRICK, Chairman. Secretaries. TREASURY DEPARTMENT, Office Light-house Board, March 13, 1858. 268 TABLE D. (ATLANTIC, GULF, LAKE, AND PACIFIC COAST.) Exhibiting the amounts of special appropriations made b i/ Congress for erect- ing light-houses at new localities, rebuilding old ones, building light-vessels for new localities, fyc., and for buoys, beacons, and fog bells for new localities, and restoring those destroyed, for the five years f 1852 to 1857^ immediately succeeding the organization of the Light-house Board. iijjs 14 if* m Date of approval appropriation of Q.V a~o 51 il l|. Irs l> u . fill Total. jij] lit ||J! 111! March 3, 1853. $276,250 00 $28,000 00 $6,000 00 $43, 160 00 $353,410 00 August 3, 1854. 1,210,338 00 33,500 00 19,600 00 239,640 00 1,503,078 00 March 3 1855 245 000 00 245 000 00 Aug. 18, 1856. 1,054,514 15 42,597 54 800 00 113,474 00 1,211,385 69 March 3,1857. 231.83881 -40,105 62 52, 112 60 324,057 03 3,017,940 96 144,203 16 26,400 00 448,386 60 3,636,930 72 To repair damages and supply losses occasioned by ice caused by storm of January 19, 1857. THORNTON A. JENKINS, W. B. FRANKLIN, W. B. SHUBRICK, Chairman. > Secretaries. TREASURY DEPARTMENT, Office Light-house Board, March 13, 1858. TABLE E. Exhibiting the amounts of special appropriations which were available on Jan- uary 1, 1858, and of those which have reverted, or will revert, to the surplus fund, under the administration of the Light-house Board. Balance on account of light-houses $1,356,200 63 Balance on account of buoys and beacons 30,407 28 Amount carried to surplus fund 369,597 90 Total. 1,756,205 81 W. B. SHUBRICK, Chairman. THORNTON A. JENKINS, ) . W. B. FRANKLIN, } Secretaries. TREASURY DEPARTMENT, Office Light-house Board, March 13, 1858. 269 > I IS ses and buo to Jamtary nd a im th I I < CO i i 1 'otal amount expend- ed for commissions of superintendents. ! ! ! 2 ! ,!!_(! i l i O 1 1 1 CO 1 B HUBRICK, C C" 111 1 GQ 11 i O ifl O - iO (M 1 O5 i-l Tj< (M O5 fea o * 5 3 lit S co ^ o i 1 "5 i CO t> CM >b o S o^ 1 I-. O tP r- r oo" 1?1 i^ 1 H 1 W. o CO g.ii i-H T^ C 3 il 1 iif. CO PQ ^ S *$ K ^J ft} ^j ^^ ^ ^) i n If 11 1!!4 c^ IM 3 00 3 S t 1 ih ^3 "o f5s5 |ss^ M 1 I'S, -< ^ a ^^i ^ % 0) jlji ^< O5 t o HO ^ 1 llsl i 00 S O S 8 ^ b 3."*- "H ^ r^ ^ g ) S w | 2 1 i 5 -~" > % 1 * ^ I 1 %> B. ill f 1 W Q Is > 5J S w bO bo *l * c g % ^ t& s>^4 i 1 O r^. r , EH "^ t^ p! 1 I 1 S S O 1 1 271 iiv s i g )U3m3gt)j3ApB oi(qnd J aapun 'japptq ISBMOI aqj jo .ii!3X qo3 joj pasKipjnd |io aqi jo uoipj2 J3d jso j aSiuaAy s i j juaiui(si(C|tnsa asnoq 9 g S 1 -iqH aqi jo aaiHsuamiBra pin: uixldtis 01(1 JOJ pa -puadxa IUIUHUB p3)oj 3duj3Ay i | 1 1 s]uaiBSs.mqsip no enois -simuioa joj Eiuapua^uijad g g D n B i -ns 0) pttid s}utioui aUeaaAV S o i a & a.ijAJas uoacaq put; Xonq joj papuadjca lunoum a3BJ3Ay 1 i s jo ''ay ')joddns *sjidaj 1 2 joj popuadxa ;nnom aBejaAy 00 g S s 8ia883A-]u8n jo pjnoq no % i ?H3it aad jsoo i^nuuB aSejaAy i i -8A-)q3ii jo jaqiunu a3ej3Ay 9 1 g qaua jo EJivdaj pun }jod -dns joj isoo innuo a3BjaAy 1 1 -saA-?q3n jo jaqmnu aSsjaAy 1 s A g}napu3^ui.i3dns jo snots -siuiiuoo put; 'suopoadsui M 8 3 S.ii.nqiii 'sjtedaj 'sanddns joj papuadxa ?unouiB a3uaaAy i i si ;q3ij Jad ;SOD inaus aScjaAy 1 i H 1 1-1 3 S1'l!t J J8fininu a3ej3AY 1 i f i I : 1 ^ I s 1 i s ij r 1 i - .s'S 1 I ^ . . 2^ * < 1 i g I iS la ^^' I s fi 3 . 272 ST. CHERON, (SEINE & OISE,) May 7, 1861. SIR : I was about leaving Paris, some three weeks ago, to locate myself in the country, where I pass the best part of the year, when I received the Report on Finances of the United States of 1858, as well as the very obliging letter with which you transmitted the doc- ument. I was then suffering from an attack of pleurisy, and my con- valescence was retarded by several accidents. This circumstance, joined to the many embarrassments inseparable from a change of residence, will be my excuse fgr not having earlier expressed my lively thanks. So soon as I was sufficiently restored to health I perused the important documents which you sent me, being attracted particularly by the chapters in relation to the light-house service. The prodigious development of this service within so short a time, under the Light-house Board, has truly astonished me. My old ex- perience, in fact, enables me the better to appreciate how much energy and activity were necessary to bring to this degree of perfec- tion the light-house service of such a vast expanse of coast as well on the Pacific as on the Atlantic without mentioning the task of succeeding in establishing, against hostile prejudices, the adoption of a new system. Much is due to you, sir, and to your honorable co- laborateurs, for having created in so short a time this magnificent and combined establishment, and you should congratulate yourself that, thanks to your activity, the Union, ivherein is strength, and which I find now so fatally compromised by the blindest passions, has not been overthrown before the accomplishment of your philanthropic work. I hope, however, that reason will yet triumph over these retrograde ideas, and that Providence will listen to the prayers of all generous hearts by maintaining the most admirable political struc- ture which has ever been erected by the genius of liberty. Excuse, dear sir, this digression upon the seething volcano of your national politics, and be pleased to accept the renewed assurance of my high esteem, as well as of my sentiments of great devotion. LEONOR FRESNEL. To Com' r THORNTON A. JENKINS, U. S. Navy, Secretary of the Light-house Board, Washington city, U. S. A. FINIS. UNIVERSITY OF CALIFORNIA LIBRARY Los Angeles i U.S. Light-house 377 board - U53p Papers on the com- parative merits of the catoptric and diop^ trie or cat^dioptric TC 377 U58p 000737759 1 jagHfl in /* > u