394 



NA TURE 



[February 22, 1900 



contend with, the revolution of the apparatus is rendered 

 easy in the extreme, and that a speed and steadiness of 

 revolution is obtained that was impossible with the older 

 forms of apparatus. 



Having devised an apparatus capable of such rapidity 

 of revolution, M. Bourdelles was led to the conclusion 

 that by reducing the number of sides in a revolving 

 apparatus, and so allowing of an increased size, it would 

 be possible, with the rapidly-revolving mechanism, to 

 produce flashes of great power, following one another at 

 as short intervals as had been done with the old many- 

 sided apparatus, and hence arose the feux-iclairs^ or 

 lightning-flash lights, now so generally employed. 



This system, it will thus be seen, makes use of dioptric 

 panels of the greatest possible amplitude, which are re- 

 volved at a speed limited only by the duration of flash 



Fig. 2. — Feu-p'clai: 



. win apparatus. 



necessary to give to the eye of the mariner the full per- 

 ception of the light emanating therefrom. In practice 

 this was found to be about i/io of a second for lighthouse 

 purposes. 



The first mercury-float feu-eclair light which was 

 established was that at Senetose, in the Island of Corsica, 

 in the year 1890. 



As a further advance in lighthouse apparatus, the twin 

 mercury-float feu-eclair may be mentioned. Fig. 2 is 

 a drawing of this apparatus. Here, instead of the super- 

 posed biform, triform or quadraform apparatus pre- 

 viously used, the two apparatus are placed side by side, 

 and are so set that the flashes from one apparatus are 



NO. 1582, VOL. 61] 



parallel to those from the other, so that at sea the beams 

 are in effect one. 



Following upon the single and twin feux-Mairs of M, 

 Bourdelles come the spindle-eclipser apparatus of the 

 writer. In this system only one— or at most two— diop- 

 tric lenses or panels are used in conjunction with an 

 eclipsing device which periodically obscures and discloses 

 the light. Figs. 3 and 4 are drawings of a single panel- 

 spindle eclipser. The action of this form of apparatus 

 is best explained by an example. 



Suppose a group-flashing light is required, each group 

 having two flashes ; all that is required is to so design 

 the mechanism of the eclipser that it will eclipse the 

 light after two complete all-round flashes, remain closed 

 for the length of time desired for the long dark period 

 between the groups, and then open just long enough to 

 allow the two flashes to be seen once more, and so on 

 ad infinitum. 



In* place of only one panel two can be used ; but here 

 it is necessary to have the eclipser in two halves, each 



Fig. 3. — Spindle eclipsing apparatus. (Section.) 



of which is operated separately, so as to obscure in rota- 

 tion the light from one panel and then the next. 



From what has been said, it is clear that with only one, 

 or at most two, simple dioptric panels and an eclipse it 

 is possible to produce all manner of group-flashing 

 characteristics which in the past demanded the splitting 

 up of the large panels into sections, from each of which 

 a beam emanated. In the new system a complete panel, 

 and that of the greatest possible amplitude, i.e. 180 in 

 altitude, and azimuth can be employed, and consequently 

 the most powerful flash is obtainable from this apparatus. 

 As the apparatus do not need to be of large size, the 

 method of mounting them upon upper and lower spindles 

 has been employed merely to render their construction 

 as simple as possible. 



In addition to the improvements mentioned above, which 

 deal with the actual lighthouse apparatus as a whole, there 



