62 



NA rURE 



[AW. 1 8, 1886 



get the necessary contrast, which is here between appearances at 

 consecutive times, instead of as in ordinary vision between 

 appearances in neighbouring direclions." 



Prof. Stolies writes, on various occasions: — "The diffused 

 light of a powerful lamp would be weak and perfectly steady, 

 and might thus escape notice, while a difl'used light, even thou;rh 

 no stronger, if almost momentary like lightning might be suffi- 

 cient to attract attention, and you could afford to throw great 

 chemical force into the formation of a flash which was to last 

 only, as it were, for a moment." "If there are to be any 

 more experiments, I think it would be well worth while to try 

 explosions." " The more I think of it the more disposed I am 

 Jo think that it would be worth while to try some experiments 

 with flashes, I mean with explosions. The plant would not beat 

 all costly ; in fact, it would hardly cost anything. The chemicals 

 would not cost very much. Preliminary experiments on a small 

 scale, which could be tried anywhere, would show what chemi- 

 cals were good to use in order to get a flash as bright as may 

 conveniently be. But when the actual experiments in fog are 

 tried, the quantity used should not be by any means very small. 

 It should be enough to make the quantity of light for the 

 moment much greater than what was kept up in your most 

 powerful burners ; but that would not require a very large 

 ■quantity." 



I should add that Prof. Stokes is aware that " flares " have 

 been tried and used, but is clearly of opinion that further trials 

 should be made in that direction. As to the great effect of 

 sudden illumination in attracting attention there can be no 

 doubt ; but I find it hard to believe that in a fog in which an 

 observer at a small distance was unconscious when the beam 

 from the electric arc, through such a lens as the Mew Island 

 lenses, passed quickly across him, any " flare " would be per- 

 ceptible at the same distance. I do not know whether the ex- 

 periment has been tried of combining a light-and-sound signal, by 

 pi icing the materials used to produce a flash together with a charge 

 of compressed gun-cotton in the he.ad of a rocket, and so firing 

 the rocket that it would explode at a fixed distance and bearing 

 from the station and at a moderate altitude. A rocket will go 

 through any fog, and might be used to give a lift seaward to the 

 light and sound. 



VI. — Cost of each System 



I have not the data which are necessary for forming an in- 

 dependent opinion upon the estimates furnished in the Trinity 

 House report. These estimates rest on unexceptionable authority ; 

 and I only venture to make any remarks on the subject because 

 I am not entirely satisfied with the position assigned to the 

 electric light. 



I gather from the reference to the photometric results of 

 Mr. Valentin that in a former estimate the cost was considered 

 in relation to the yield of light by each illuminant. And I think 

 that an estimate of what light can be had on any system for a 

 given expenditure, or what the cost is on any system of a desired 

 quantity of light, is needed to make the comparison of the 

 relative cost complete. For example, a comparison is made in 

 tire Report (Tables I. and II., pp. 62-63), between a "first order 

 oil-lighted tower for one six-wick burner only," and a "gas 

 station to show a quadriform light of four times 68-jet power." 

 The annual cost of maintenance, including interest on capital 

 outlay, is estimated at 724/. for the first, and 16S7/. for the 

 second. But the light from a six-wick burner sho.vn as a fixed 

 light is probably rather less than 7000 candles, while that from 

 the 68-jet quadriform is 35,000 candles. Thus, if such a quadri- 

 form were substituted for or adopted instead of the single light, 

 both the cost and the light would be largely increased, but the 

 increase of light would be more than double the increase of cost. 

 Comparing the two as revolving lights, the increase of light 

 would be one-third greater than the increase of cost. So in the 

 comparison between the cost of the electric light and the other 

 illuminants. The expense of annual maintenance, with interest 

 on capital outlay, is estimated as being one-seventh greater for 

 the electric light than for the quadriform 68-jet gas ; but if 

 the yield of light is taken into account, the figures appear very 

 differently. The electric light is ten times as powerful as the 

 quadriform. The actual cost of light, which is the commodity 

 produced, may be compared in the two cases by stating the cost 

 of maintaining for one year each 1000 candles intensity of light 

 in the beam sent forth. By the electric arc the cost is about I/. , 

 by the quadriform gas 8.'. los. 



As to the actual estimate of the cost of the electric light, I 



venture to suggest that some reduction maybe found practicable. 

 Two engines of 30 horse-power, at a cost of 1250/., seems a 

 very full provision for the unfailing maintenance of one arc 

 light. The actual horse-power absorbed by one of the De 

 Meritens machines is given by Prof. Adams as io'4. M. Allard 

 state-; the price of one of M. de Meritens' machines, tested and 

 recommended by him in 1S80, as 350/. Dynamo-machines are, 

 I believe, less costly. I think all that is needful and best of 

 machines, lamps, and cables, may now be obtainable for less th m 

 2154/. ; and the estimate of 1217/. a year for wages, clothing, 

 coke, oil, carbons, &c., and repairs and renewals, may perhaps 

 be found in excess of the necessary cost. M. Allard gives the 

 following details of the cost of the apparatus and expenses at 

 Grisnez : — 



Two steam-engines of from five to six horse-power ... 488 



Two magneto-electric machines 852 



Four lamps 240 



Total 1580 



Annual expenses 537 



He also furnishes an estimate, which I transcribe, of the 

 average cost of converting an oil lighthouse into an electric 

 lighthouse : — 



Engine-house, keepers' dwellings, water-supply, &c. ... 1600 

 Two steam engines, of from six to eight horse-power, 



with shafting and straps 640 



Two electric machines with cable;, &c 560 



Four lamps 240 



First order lantern with oblique framing 800 



Optical apparatus, two feet in diameter, with arrange- 

 ments for revolving light 520 



Sundries, packing, carriage, and setting up 240 



Contingencies 400 



Total 5000 



Add "First cost of an ordinary first order oil-lighted tower" 

 (T. H. Report, Part I., p. 75), less "Apparatus, lantern and 

 glass," viz. 4834/. ; and it would seem to follow that the first 

 cost of an electric light station need not exceed 10,000/. 



The rather large difference between this estimate and that of 

 1 7, 749^^. furnished by the Trinity House Committee has no doubt 

 already received the consideration of the Elder Brethren, who 

 have had the details of M. AUards scheme before them. 



In order to obtain some further information, I have in- 

 quired of a London firm of electric light contractors as to 

 the cost of such an installation, and have received the following 

 figures : — 



£ 



Two 30 horse-power t^./^z/t' engines ']qq 



Three lamps, necessary cable, and labour 400 



Two dynamos and spare armature to fit either ... 480 

 It will be seen that these figures are not very diff'erent from 

 those of M. AUard's estimate. 



In concluding this report I desire to thank the Elder 

 Brethren of the Trinity House, and es,5ecially the Members of 

 the Committee, for the kindness which has made the daty of 

 co-operating with them in this inquiry a continual pleasure. 

 March 9, 1886 A. Vernon H.ircourt 



Letter to the Board of Trade from the Commissioners of A'orthern 

 Lighthouses 

 Northern LiglUhoiise Board, 84, George Street, 

 KUinburgh, Dxember 10, 1885 



Sir, — I am directed by the Commissioners of Northern 

 Lighthouses to acknowledge the recipt of your letter of the 

 3rd instant, in which you request to know whether the Com- 

 missioners propose to make any general report or observations 

 relative to the recent Lighthouse Illuminants Experiments at 

 the South Foreland. 



In reply I am directed to state that in view of the very able 

 and exhaustive Report {Part I.) by the Committee of the Elder 

 Brethren on this subject, in the conclusions of which the Com- 

 missioners concur, and of the report by their engineers dated 

 October 14 last, which accompanied my letter to the Elder 

 Brethren of the following day, and copy of which is herewith 

 transmi'ted for the inforjiation of the Board of Trade, the 



