L. MECHANICS AND ENGINEERING. 531 



ity and ease of movement, with a small consumption of ether 

 or alcohol. 9 C\ 3Iarch, 1873, 43. 



THE GRAMME MAGNETO-ELECTEIC MACHIXE. 



The prize of 3000 francs oifered by the Societe d'Encour- 

 agement of Paris for an apparatus giving an electric current 

 constant in direction and intensity, the electromotive force 

 and the resistance of which should be comparable to that of 

 a nitric-acid battery of sixty to eighty cells of the ordinary 

 size, and which should be superior, both in economy and 

 Iiealthfulness, to any thus far produced, has just been award- 

 ed tcr the magneto-electric machine invented by M. Gramme. 

 This apparatus, therefore, merits a brief description. It con- 

 sists of a horseshoe magnet, between the poles of which re- 

 volves a ring of iron, lying in the same vertical plane with 

 the magnet itself This ring is entire, and is wound with 

 covered wire in sections, the ends of which terminate in rods 

 arransjed about the transverse axis on which the rinse turns. 

 Upon the ends of these rods, as the ring rotates, press suc- 

 cessively two copper disks, one on each side of the axle, which 

 serve as the electrodes. The current developed by the rota- 

 tion, due entirely, as Gangain has proved, to the motion of 

 the helices, is continuous and uniform in direction. By using 

 electro-magnets instead of permanent ones, and by adopting 

 Ladd's principle of re-enforcement, the power of the machine 

 has been vastly increased. A machine of this sort, in daily 

 use for electro-plating in the establishment of M.Christolfe,in 

 Paris, weighs 460 kilogrammes, of which 135 kilogrammes 

 are the weight of wire on the permanent magnets, and 40 

 kiloorrammes that on the movable ones. About one-horse 

 power is required to give it its normal velocity of 300 turns 

 a minute. With this velocity, the current is equal in inten- 

 sity to that of two Bunsen cells of the ordinary size, and in 

 quantity to 32 such cells. It will deposit 600 grammes of 

 silver per hour. With this velocity, the temperature of the 

 armature never exceeds 112 Fahr., and with 275 turns a 

 minute, no heating takes place. A Wilde machine, much 

 larger in size, and making 2400 revolutions per minute, de- 

 posited only 510 grammes of silver per hour. For the elec- 

 tric light, the Gramme machine is somewhat varied, so as to 

 increase proportionately its intensity. The one tested by the 



