April 21, 1893.] 



SCIENCE. 



217 



lights, and their needs are not nearly satisfied. It was eloquently 

 said by the Secretary of State at the International Marine Con- 

 ference at Washington in 1889: "The spoken languages of the 

 world will continue to be many, but necessity commands that 

 the unspoken language of the sea shall be one." Thus the signal- 

 lighting of the sea-coasts and of the ships traversing the sea is a 

 work truly and emphatically international — a work which 

 neither in its magnitude nor its variety suggests any notion of 

 finality. For instance, the English Admiralty published in 1862 

 forty notices to mariners in relation to lights, buoys, dangers, 

 etc., in all the work. In 1892 its similar notices amounted to 

 over 600. 



The considerations of power or intensity and of distinctiveness 

 follow naturally on the numerical increase of lighthouses. The 

 early illuminating apparatus of Fresnel and his successors were 

 mainly confined to two forms, fixed and revolving, the latter 

 being approximately from six to eight times as powerful as the 

 former, the four-wick vegetable oil flame being the brightest 

 illuminant in botU. Subsequently composite lights of both fixed 

 and revolving sections were adopted, as well as more effective 

 flames. Next followed the important enhancement of revolving 

 apparatus by the holophotal system of Thomas Stevenson, who 

 also introduced the use of condensing prisms and of mirrors for 

 fixed lights, and who lastly, after many minor improvements, 

 suggested the maximum size of lens yet attained, called the hyper- 

 radial — a light particularly suited to great headlands and other 

 stations where ranges of visibility of thirty or forty miles are 

 necessary. The increase pari passti of the potency of lamps — 

 thanks chiefly to the unwearied and intelligent labors of Sir 

 James Douglass with petroleum, and of Mr. Wigham of Dublin 

 with gas — • has given due effect to these great developments of 

 dimension. The first-order revolving light shortly to be estab- 

 lished on Heceta Head, Oregon, the work of Messrs. Chance of 

 England, is an example of the holophotal system with twenty six 

 prisms of a radius of 930 millimetres. Mosquito Inlet, Florida, 

 erected in 1887, is an example of a hyper-radial fixed light of 

 1330 millimetres radius, with prisms, on the holophotal system. 

 This was constructed by Messrs. BarbieJ & Co. of Pai-is. Dondra 

 Head and Barberyn, Ceylon, are examples of hyper-radial revolv- 

 ing lights without prisms, and with lenses of 80° vertical angle. 

 These lights are the work of Messrs. Chance. 



Power or intensity of beam has also been attained by super- 

 posing one lens apparatus on another, increasing pro tanto the 

 total effectiveness of the light. Mr. Brown of Lewisham, Eng- 

 land, was the first (in 1859) to propose this arrangement of lenses, 

 and Mr. Wigham of Dublin the first (1872) to carry it out in some 

 fine Irish lights constructed by French makers. Messrs. Chance 

 have since constructed striking examples of the biform type for 

 Bishop Eock and Round Island, Scilly Isles, for the Bull Rock, 

 Ireland, and for the Eddystone, English Channel. 



A further method of intensifying lighthouse beams is the elec- 

 tric illuminant. Here the United States have not been backward 

 in following the example of Great Britain and France, though 

 the American use has been more conspicuous in buoys and 

 beacons than in sea-lights like the St. Catherines in England, the 

 Isle of May in Scotland, or the Cap Grisnez or Ushant in 

 France. 



It is, however, beginning to be understood that the electric 

 light in its present condition is not, save in a few cases, to be too 

 strongly recommended for lighthouse service. Its cost, when ap- 

 plied to large apparatus, both for instalment and for mainten- 

 ance is very considerable, and in thick weather its superiority of 

 penetration tothe rays of gas or oil lamps of the present imposing 

 dimensions is a much controverted point. It is, indeed, a mixed 

 question, for the lighthouse engineer and the financial secretary, 

 to be determined according to the nautical and economical con- 

 ditions of each station. Yet it must never be forgotten that the 

 true way of estimating the combined effectiveness and expense 

 of a light is to divide the units of first cost and annual mainten- 

 ance by the units of power or intensity. 



A more important consideration seems to be that of distinctive- 

 ness. The early French plan of making a portion of the appar- 

 tus of fixed optical sections and a portion of revolving optical 



sections has the obvious disability of inequality of range where 

 the light is white throughout or red throughout, so that a vessel 

 observing the flash at a certain distance can OBly see the fixed 

 beam at a much less distance, and can only know the true char- 

 acter of the light after an interval more or less prolonged. When 

 color is used for the revolving portion this difference is no doubt 

 much diminished, but it is still too great. A light wholly of re- 

 volving sections is preferable for all purposes in tbese days of 

 high speed and multiplied trafifio. And it is the revolving light 

 that affords a much greater number of characteristics than the 

 fixed. The group-flashing system in double and triple series by 

 optical combinations, first introduced by Dr. John Hopkinson 

 and Messrs. Chance in 1875, has been adopted all over the world; 

 and the gas group-flashing system of Mr. Wigham, of about the 

 same date, has been extensively used in Ireland. Combinations 

 of red and white flashing lights, where the former is rendered 

 as powerful as the latter by special optical contrivances, have 

 been repeatedly employed, especially by Messrs. Chance. 



A very valuable form of distinction largely adopted in modern 

 times, is the occulting light, that is, a flxed beam interrupted by 

 a short darkness instead of a long darkness interrupted by a short 

 flash as in a revolving light. The sharp contrast of dark and 

 light is thus substituted for the old fixed light, and this is par- 

 ticularly valuable for ports and harbors where shore and ship 

 lights are now so much more numerous and powerful than before. 

 A very simple form of clockwork, designed by the writer, gives 

 movement to the occulting screens for small lights and to the 

 vertically dropping screen which is preferable for sea lights where 

 the occulting system is accounted powerful enough for a sea- 

 light. In occulting lights care should be taken that the duration 

 of darkness should be suflScient to affect the eye sensibly, as. for 

 instance, two seconds at least. There is a growing tendency, 

 also, to make the flashes of revolving lights too short in duration 

 or too quick in recurrence. The difficulty of identifying a light 

 and of taking a bearing by it is thus much increased, and the 

 wear and tear of the mechanism for rotating the apparatus becomes 

 very serious despite the recent expedient of a mercury trough in 

 which the framework revolves. 



The most approved optical and mechanical arrangements for 

 our lighthouses would be of little avail if the aliment oil or gas, 

 which sustains the greater number of them, were of unsuitable 

 quality. As regards gas there need be no other provision than 

 that made for the town or harbor supply near the lighthouse, and 

 the only need is to use it with adequate pressure in an appro- 

 priate burner in single or multiple jets or rings. As regards oil, 

 the different vegetable varieties, the chief of which was colza, 

 have now nearly fallen into disuse, giving place to petroleum in 

 some of its many forms. The luminiferous properties of good 

 oil and good gas are almost equal, but the cost of petroleum is 

 not more than one-fourth that of vegetable oil, and not greater 

 than that of gas, while its extreme pliability and convenience 

 make it quite as valuable as gas. The lighthouse world is in- 

 debted to an American, Captain Doty, for first showing, twenty 

 years ago, how mineral oil could be used in a multiple-wick 

 burner, and it is indebted also to Americafor the largest and best 

 supplies of the oil itself. The only drawback has been the un- 

 doubted greater risk of fire and explosion, but even this has been 

 obviated by the introduction of the variety called "heavy min- 

 eral oil," which, having a flashingpoint of 240° to 270°, is almost 

 absolutely safe. It is now generally used in Europe. 



The improvement of burners fit for mineral illuminants has 

 proceeded, as I have said, well nigh to perfection in the hands of 

 the Trinity House of London and of their late engineer, Sir James 

 Douglass. His six-wick burner is of the power of about 900 

 candles consuming about ^ of a gallon per hour; his ten- wick 

 burner is of about 2,200 candles, consuming about Ij'j of a gal- 

 lon per hour. I believe that no form of the Doty or any other 

 oil-burner equals this. The pressure lamps of Messrs. Chance 

 used with such burners seem to secure the maximum of advan- 

 tage in the focus of any dioptric sea-light. Very much excellent 

 work, however, in the way of improvement of burners, has been 

 achieved by Major Heap and by Mr. Funck, bis assistant at Tomp- 

 kinsville. 



