314 Magneto-Electric Illumination. [July, 



of electric force by the mere turning of a wheel, is of 

 value outside the physical laboratory. It is available — 

 (1) for medical purposes ; (2) for telegraphy ; (3) for electro- 

 plating, gilding, &c; (4) for military purposes, signalling, 

 explosions, &c. ; (5) for chemical decompositions ; and (6) 

 for electric illumination. 



A large machine, which has lately been exhibited in 

 London, driven by a 23-horse-power engine, produced a 

 light equal to 8000 candles ; a copper wire about 1^ m.m. 

 in thickness, suspended between the poles, became instantly 

 red-hot with a revolution of little over 300 in a minute. 

 Larger machines are being made that will probably give a 

 light equal to 25,000 candles. 



This machine has lately been examined by the French 

 Societe d' Encouragement, and in accordance with the recom- 

 mendation of the reporter, Count du Moncel, a prize of 

 3000 francs has been awarded for it to M. Gramme; whilst 

 the manager of the " Alliance Company," M. Joseph Van 

 Malderen, who superintended its manufacture, has had 

 awarded to him a gold medal. In his report, Count du 

 Moncel says that a machine 1*25 metre in height, o*8 metre 

 long, and the same in width, driven by a 4-horse engine, 

 gave a light equal to 900 carcel lamps. It also heated to 

 redness two juxta-posed copper wires 12 metres long and 

 0*7 m.m. diameter, and fused an iron wire 2*5 metres long 

 and i*3 m.m. thick. 



The constancy of direction of the electric current gene- 

 rated by this machine is, however, not of so great an im- 

 portance for the electric light as for other purposes for 

 which it may be used. Indeed, the electric light is by many 

 electricians thought to be superior when produced by a 

 magneto-electric machine of the old form without any com- 

 mutator. The alternate reversal of the currents of electricity 

 produces no flickering or irregularity in the arc of light, as 

 they occur far too quickly to be appreciated by the eye, 

 whilst the rapid reversal of the direction causes the carbons 

 to wear away with great regularity, thus enabling the point 

 of light to be kept more easily in the focus. 



For the electro-deposition of metals — copper, silver, &c, 

 constancy of direction of current is indispensable, and here 

 the experiments show a marked superiority of the Gramme 

 machine over other magneto-electric machines. 



In the galvanoplastic works of M. Christofle, of Paris, 

 where experiments have been going on for more than a year, 

 it is found that the best machine hitherto known, when moved 

 with a velocity of 2400 revolutions per minute, only deposits 



