Nov. 1 8, 1886] 



NA TURE 



63 



Commissioners do not propose, at least in the meantime, to 

 make any general report or further observations in regard to 

 these experiments. — I am, &c., 



(Signed) J. M. Duncan 

 The Assistant Secretary, Harbour Department, 

 Board of Trade 



Rifort on Fart I. of Report by the Specid Commitlee of the 

 Elder Brethren on Lighthouse Illuminants, by T. and D. 

 Stevenson, Engineers, to the Northern Lighthouse Board 



On September 2 la-t, the Board remitted to us, for con- 

 sideratiun and report. Part I. of the Report of the Committee 

 of the Trinity Mouse, on the experiments at South Foreland, 

 and having perused the reports of the experiments, we now beg 

 to report as follows : — 



As the Board is aware, the object of these experiments was to 

 determine the relative merits of gas, oil, and electricity, as 

 lighthouse illuminants, especially as regards their penetrative 

 power in fog ; also to ascertain the merits of certain optical 

 arrangements, and test certain improved oil and gas burners 

 patented by Sir James Douglass and Mr. Wigham. We think 

 that these experiments embrace all the suggestions that were 

 brought under the notice of the Elder Brethren for trial by the 

 Board of Trade, and which led that Board to suggest that this 

 train of experiments shou'd be entered upon. 



We have had several opportunities of inspecting the various 

 kinds of apparatus, and also of witnessing the experiments, and 

 in our opinion these experiments have been of an exhaustive 

 character, and have been conducted with great cai-e, , and, we 

 believe, in a spirit of the most perfect fairness and impartiality 

 to all parties ; and we have further to express our concurrence in 

 the conclusions of the Comadttee as expressed in the following 

 terms : — 



" (l) That the electric light, as exhibited in the A experi- 

 mental tower at South Foreland, has proved to be the most 

 powerful light under all conditions of weather, and to have the 

 greatest penetrative power in fog. 



" (2) That for all practical purposes the gaslight, as ex- 

 emplified by Mr. Wigham's multiform system in B experimental 

 tower, and the oil light, as exemplified by the Trinity House 

 Douglass six-wick burners in multiform arrangement up to 

 triform in C experimental tower, when shown through revolving 

 lenses, are equal, light for light, in all conditions of weather ; 

 but that quadriform gas is a little better than triform oil. 



",(3) That when shown through fixed lenses, as arranged in 

 the experimental towers, the superiority of the superposed gas 

 light is unquestionable. The larger diameter of the gas flames 

 and the lights being much nearer to each other in the gas 

 lantern, give the beam a more compact and intense appearance 

 than that issuing from the more widely separated oil burners. 



" {4) That for lighthouse illumination with gas, the Douglass 

 patent gas-burners are much more efficient and economical than 

 the Wigham gas-burners. 



" (5) That for the ordinary necessities of lighthouse illumina- 

 tion, mineral oil is the most suitable and economical illuminant, 

 and that for salient headlands, important landfalls, and places 

 where a very powerful light is required, electricity offers the 

 greatest advantages." 



We may explain that so far back as 1S69 we had also occasion 

 to conduct a series of experiments at Edinburgh on certain large 

 burners patented by XI r. Wigham, and brought before the 

 Board, with the view of increasing the power of sea lights, and 

 again in 1870 a further series of experiments was carried out by 

 us, by the direction of the Board of Trade, on the merits of the 

 electric light, and certain important results were obtained during 

 these sets of experiments at Edinburgh. The general result of 

 the gas experiments then made was that the large 52-jet gas- 

 burner was in no way superior to the 4-wick oil-burners when 

 used in connection with the ordinary annular lens, as the 

 "greater portio'n of the 7-inch gas flame" was with that size of 

 lens necessarily ex-focal. The large burner was slightly superior, 

 liowever, when used in a fi.xed light apparatus. Our opinion, 

 which has been corroborated by the recent experiments, there- 

 fore, was that in order to bring out the full power of these large 

 llames, an apparatus of larger focal distance than usual must be 

 employed, and hence we designed the lens of 1,330""" radius, 

 which has recently been tried at the South Foreland with the 

 most satisfactory results. 



The electric light experiments made at Edinburgh in 1867- 

 1S69, showed that if the electric light beam was made to 



diverge artificially to the same extent as the 4-wick oil flame, 

 it was in no way superior in brilliancy, and pointed to the 

 advisability of adopting for the electric light the azimuthal 

 condensing system of Mr. Thomas Stevenson. This system has 

 been adopted for the electric light apparatus at the South Fore- 

 land experiments. The Edinburgh experiments further showed 

 that it was necessary in any test of the intrinsic merits of 

 electricity, gas, or oil, that the maximum condensation con- 

 sistent with the requirements of navigation for each should be 

 employed. At the South Foreland experiments, however, the 

 condensation of the electric light was only 30' int3 5^ that is 

 only 6 times, whereas the Isle of May apparatus which was 

 exhibited at the South Foreland, condensed 45" into 3°, that is 

 15 times. Had this or a still m.ore condensed light been used in 

 the experiments, the electric light would have shown even 

 greater superiority than it did. 



We shall aftervvards report as to what, in our opinion, is 

 the arrangement of optical apparatus best suited for each 

 illuminant. (Signed) T. and D. Stevenson 



Edinburgh, October 14, iS85 



OFFICIAL REPORT ON THE USE OF OIL AT 

 SEA FOR MODIFYING THE EFFECT OF 

 BREAKING WAVES ^ 



THE following Memorandum, dated June 16 last, on the use 

 of oil at sea for modifying the effect of breaking waves, has 

 recently been printed and circulated by the Admiralty : — 



" Many further practical experiments at sea have been m.ade 

 since the report by Capt. Chetwynd, R.N., to the Royal 

 National Lifeboat Institution, dated September 30, 1884, on 

 the use of oil for smoothing broken or troubled waters, which 

 reoort was communicated to Commanders-in-Chief in Admiralty 

 ^ 3206 



Circular Letter of December I, 1884, N.S. . 



S305 



" As these further experiences go to show that the use of oil, 

 under different circumstances, is of very extended and simple 

 application, my Lords Commissioners of the Admiralty consider 

 it desirable, in order that the facts may be generally known, to 

 re-issue the report above mentioned, together with such other 

 information as may serve for the guidance of officers, whose 

 atten'ion is hereby called to the fact that a very small quantity 

 of oil skilfully applied may prevent much damage both to ships 

 (especially the smaller classes) and to boats by modifying the 

 action of breaking seas. 



" The principal facts as to the use of oil are as follow : — 



"On free waves, i.e. waves in deep water, the effect is 

 greatest. 



"In a surf, or waves breaking on a bar, where a mass ot 

 liquid is iu actual motion in shallow water, the effect of the 

 oil is uncertain, as nothing can prevent the Larger waves from 

 breaking under such circumstances ; but even here it is of some 

 service. 



" The heaviest and thickest oils are the most effectual : re- 

 fined kerosene is of little use ; crude petroleum is serviceable 

 when nothing else is obtainable ; but all animal and vegetable 

 oils, such as waste oil from the engines, have great effect. 



"' A small quantity of oil suffices, if applied in such a manner 

 as to spread to windward. 



'■ It is useful in a ship or boat, both when runnmg, or lymg-to, 

 or in wearing. 



" No experiences are related of Us use when hoistmg a tjo.at 

 up in a seaway at sea, but it is highly probable that much time 

 and injury to the boat would be saved by its application on such 

 occasions. , , ,. .u 1 



" In cold water, the oil being thickened by the lower tem- 

 perature, and not being able to spread freely, will have its 

 effect much reduced. This will vary with the description of 



oil used. ...,-. 



"The best method of application in a ship at sea appears to- 

 be han'^in" over the side, in such a manner as to be in the water, 

 small caniTas bags capable of holding from one to two gallons of 

 oil, such bags being pricked with a sail needle to facilitate 

 leakage of the oil. 



"The position of these bags should vary with the circum- 

 stances. Running before the wind, they should be hung on 

 ' From ihe Board 0/ Trade Journal. 



