244 



SCIENCEi 



[Vol. I., Ko. 9. 



odd numbers in the opposite ; and it would 

 appear at first sight that these coils could not 

 be connected together in series without the 

 one set of currents neutralizing the other. 



But, b}' connecting the ar- 

 mature coils together in 

 the manner shown in Fig. 

 27 it will be seen, that al- 

 though the currents gen- 

 erated in consecutive coils 

 are opposite in direction 

 to one another, yet their 

 combined current transmitted to the collecting- 

 apparatus is in the same direction. 



In the early part of this article, attention was 

 drawn to the distinction between the luminous 

 and geographical range ; and, in all the instal- 

 lations described, regard has onlj' been paid 

 to the increase of the former, the latter being 

 neglected. This is readily explained by the 

 necessit3- there was of giving a unit to the new 

 system of lighting the French coasts. There 

 is, however, a poiiit which it will be important 

 to consider, and which may serve to augment 

 the efficiencj* of the system. In daj's of heavy 

 fog, when the luminous range is considerably 

 diminished, this diminution would be much less 

 if the geographical range could be increased. 



A rather ipportant step has been made in 

 this direction bj' the use of speciallj' constructed 

 optical appa- 

 ^^ ^ ratus. This 



apparatus is 

 furnished on 

 the upper 

 part with a 

 series of an- 

 nular lenses, 

 whose effect is to project above the light a beam 

 of vertical rays extending to a great height. 

 This beam illumines either the clouds, or the 

 vapor which fills the atmosphere, and is even 

 visible in clear weather, because the air con- 

 tains enough particles, both solid and vapor- 

 ous, to allow the phenomenon of diffusion to 

 be produced. These luminous rays thus pro- 

 jected are visible to quite a distance even in 



foggy nights, and the geographical range is 

 notablj' increased. 



The first application of this sj'stem, which 

 has not yet been adopted in France, is about 

 to be made in the Sea of Azof. The ships 

 which cross this sea in the direction of Berdi- 

 ansk are guided to their point of arrival by a 

 light, which, in the actual state of its installa- 

 tion, could not be seen sufficientl}- far ; and it 

 was decided to apply the system mentioned 

 above. The apparatus recently constructed 

 by Messrs. Sautter and Lemonnier will shortlj^ 

 be installed, and then the efficacy of the sj-s- 

 teni can be judged. 



The example thus given by the French light- 

 house board has alreadj- been followed by other 

 nations. The Ottoman government has studied 

 a plan of electric lighting for the coasts of 

 Turkey-. In England an appropi'iation has 

 been asked to establish, in 1881, about sixtj- 

 electric lights ; and a similar request will be 

 made for the establishment of a hundred lights 

 in 1882. 



On account of the time which the complete 

 execution of the project for lighting the French 

 coasts will take, it may be that the experience 

 obtained with the first lights will show some 

 modifications to be made to the adopted plan, 

 and that the lights last made maj' not have 

 entirelj- the same dimensions and characteristics 

 as those first built. 



In fact, some criticisms have ])eeu made bj" 

 foreign engineers, especially on the diameter 

 of 0.6 met. of the optical apparatus, — a di- 

 ameter which these engineers consider rela- 

 tivel}' too small. The faults ascribed to optical 

 , apparatus of small diameter are those of heat-' 

 ing too readily on account of the proximity 

 of the luminous foyer, and also that of being 

 more quickl}- covered with carbon-dust. We 

 do not, however, believe that there is much 

 to fear from this with apparatus 0.6 met. in 

 diameter ; since, for the last twentj- years, the 

 lights of la H^ve have worked well with appa- 

 ratus 0.3 met. in diameter. The probabilities 

 are, that future modifications will onlj- be 

 changes in detail, which will not affect the 

 general project. 



The above shows the means France has taken 

 to light her coasts, and is a most emphatic 

 recognition of the value of the electric light 

 for that purpose. 



The arc-light, however, has two defects 

 which have uot been mentioned, — one, a lack 

 of fixit3^ ; the other, a deficiencj' in the red 

 and yellow rays of the spectrum. This lack 

 of fixit}- is partly- due to the carbons not being 

 homogeneous, and partl}^ to faults in the regu- 



