APPLICATIONS OF THE ELECTRIC LIGHT. 277 



even at a high cost. There were, however, only two points 

 of light. (See Les Mondes, tome /., page 691, and tome //, 

 pp. 221 and 278). 



The electric lighting of the slate quarries at Angers has 

 lately been provided for in a permanent manner by Lorain. 

 For this purpose a Gramme machine of the pattern described 

 on page 75, and two Serrin regulators, have been used. The 

 large subterranean gallery thus lighted up is no less than 

 100 metres in length, with a width varying from 15 to 50 

 metres, and a height of 60 metres. The whole of it walls, 

 vaulted roof, and floor is black, yet in spite of the absence 

 of reflection from its surfaces, it is illuminated almost as well 

 as it would be in broad daylight under a clear sky, and with 

 great satisfaction to the workmen and advantage to the 

 Company. 



A speed of 800 turns per minute would appear to be 

 sufficient for obtaining a splendid light with the Gramme 

 used, if the regulator had been placed near it ; but on account 

 of the depth of the quarry the regulator was about 350 metres 

 from the source of electricity. In order to obtain a good 

 light and a regular working of the apparatus, it was requisite 

 to give the machines a mean and nearly constant velocity of 

 I > 1 35 revolutions per minute. Conducting wires of a greater 

 diameter are about to be used, and this will allow of such a 

 reduction of the velocity that the electro magnets will not 

 become heated beyond 50. 



The machines have been running simultaneously and con- 

 tinuously day and night since they were put up, eight months 

 ago. With regard to duration and continuity, this experiment 

 is the most conclusive that has hitherto been made with the 

 Gramme machine, which has victoriously stood this severe 

 test. (See the journal La Lumiere ekctrique for i5th May, 

 1879.) 



The employment of the electric light for the illumination 

 of works carried on at night was one of the first useful appli- 

 cations of this method of lighting, and, dating from the works 



