268 



SCIENCE 



[Vol. XVI. No. 406 



way, particularly if the flame be turned up rapidly under a 

 sudden fog. 



The electric- light apparatus far exceeded the others in the 

 amount of light it gave out. Even in fog and haze it sur- 

 passed them; for, although the highly refrangible rays were 

 rapidly dispersed, yet the remaining beam was not more cut 

 down than that from gas or oil, and still maintained its 

 superiority. This great power partly results from the small- 

 ness of the luminous area. The high condensation is ob- 

 tained at the expense of the angular opening of the trans- 

 mitted beam, which is less than with the taller flames of gas 

 and oil. In practice the upper portion of the full beam 

 must reach the horizon, as seen from the lantern of the 

 lighthouse, while the lower portion must strike the sea at a 

 moderate distance from its foot. It does not appear whether 

 the electric beam employed would have fulfilled both these 

 conditions. If it would not, — and the necessity of adjusting 

 the carbons in certain cases to bring the full beam on to the 

 observers suggests that it would not, — a deduction must be 

 made from its value. Electric lights are practically reserved 

 for revolving lights, the chief object of which is to guide the 

 mariner from long distances. Fixed lights do not need the 

 same far reaching brilliancy, and it was abundantly proved 

 that for these the gas-burners surpassed the oil-burners em- 

 ployed. Further, gas yields itself with special facility to 

 conferring on a fixed light a distinctive character by means 

 of intermittence. 



All the points of difl'erence that we have noted are clearly 

 set forth in the reports, and little difi'erence of opinion exists 

 concerning them. But the advocates of gas claimed for it a 

 special quality; namely, that of difl'usiug a warning glow 

 through a fog at a distance beyond which the light could be 

 actually seen itself. Sir George Stokes and his colleagues 

 do not profess themselves able to decide whether the extea- 

 sion of distance at which warning will be conveyed by the 

 glow from a gas or other light is such as to be of practical 

 importance. They, however, make some general remarks 

 on the subject, pointing out that the glow or burr is mainly 

 produced by light which has been diffracted, and retains an 

 approximation to its primitive direction. It is deflected from 

 its course by an angle which is not by any means very small, 

 and therefore it cannot matter much whether the regular 

 light from which it originally came was concentrated by the 

 lens within a more or less small angle. The fog illumi- 

 nating power must depend mainly on the quantity of light 

 sent out from the source, while the fog penetrating power 

 depends on the concentration of the beam. It follows that 

 the fog illuminating power of the electric light will be much 

 smaller, in proportion to its power for direct penetration, 

 than would be the case with oil, and still more with gas. 

 Conversely, the glow from gas will extend farther beyond 

 the limits of direct penetration of the beam than will the 

 glow frx)m oil, and still more than the glow from electric 

 light. In light fog the direct light would probably be seen 

 first; and, even if it were not, the slight extension of dis- 

 tance resulting from the glow would be of little value. But 

 if the fog were comparatively thick, the ship must approach 

 nearer to the lighthouse, where the illumination of the fog 

 would be stronger, and the luminosity would be seen well 

 before the actual light. This would be rendered more dis- 

 tinguishable from a thinning of the fog if the light was 



rapidly extinguished and relighted. In the second part of 

 the report Sir Leopold McClintock speaks of "a striking, 

 thrilling effect, which at once caught the eye," produced by 

 cutting off the gas every few seconds. No opportunities, 

 however, occurred for properly estimating the value of this 

 effect, and it could not be taken into consideration in sum- 

 ming up the results of the experiments. 



In reviewing the conclusions of the Trinity House com- 

 mittee. Sir George and his colleagues do not propose any 

 serious modifications as to the first four points. (1) They 

 consider the experiments established the superiority of the 

 electric light, as exhibited at the South Foreland, under all 

 conditions of weather. (2) They indorse the statement made 

 as to the relative efficiency of gas and oil for revolving lights. 

 (3) With the flxed lenses they attribute the superiority of 

 gas chiefly to the fact, that, as the light is condensed by the 

 optical apparatus in vertical planes only, the inferiority of 

 the oil-light, as regards the initial quantity emitted, is not 

 compensated for, as with anniilar lenses, by its superior con- 

 densation arising from the smaller width of the flame. (4) 

 While admitting that the photometric measurements estab- 

 lish the superiority of tlie Douglass over the Wigham burners, 

 as regards economy and efficiency arising from greater con- 

 centration of light, they state they have no information as to 

 whether the employment of glass chimneys forms any serious 

 drawbacks. It was the fifth recommendation of the original 

 report that was most strenuously objected to by the advocates 

 of gas, since it practically rejected that illuminant. It is 

 now somewhat modified in form, and the use of gas is re- 

 ferj-ed to, although scarcely recommended. We are now 

 told, (5) " Though gas possesses undoubted advantages over 

 oil in some respects, such as facility in increasing the power 

 on the sudden occurrence of a fog, absence of the necessity 

 of trimming, power of making instantaneous transition from 

 light to darkness, and conversely, we do not think these ad- 

 vantages sufficient to outweigh the advantages which mineral 

 oil possesses for ordinary employment on account of its sim- 

 plicity and economy. We think, too, that for specially im- 

 portant sea-lights the experiments show that electricity offers 

 the greatest advantages. At the same time, we see no rea- 

 son for confining the choice to these two alternatives; nor 

 does it appear that the words of the report so confine it. There 

 may be special reasons in particular cases for giving the 

 preference to gas, and it seems even desirable that mariners 

 should have the opportunity of witnessing the effects of differ- 

 ent systems, which would thereby be subjected to the test of 

 long continued practical experience." As to the latter part, 

 mariners have long had the opportunity of witnessing the 

 effects of diffei-ent systems, for several splendid gaslights are 

 to be seen on the Irish coast, while there are electi-ic lights 

 on different parts of the coasts of Britain. Oil-lights, of 

 course, are common enough. 



It is not altogether to be wondered at that the Trinity 

 House is disinclined to adopt gas in the present impoverished 

 state of the Mercantile Marine Fund. In the days when 

 that fund was overflowing they could have done so with 

 ease, but now they have only a limited sum to spend on 

 lighting our coasts, and therefore have to make it go as far 

 as possible. Tlie addition of a gas-making plant to a light- 

 house means a considerable initial expense, and possibly an 

 increase of working charges. During foggy weather the 



