Lastly, by treating the exhausted battery as an accumulator, that is to say, by passing a current through it in the opposite direction, we restore the various products to their original condition; the copper absorbs oxygen, and the alkali is restored, while the zinc is deposited; but the spongy state of the deposited zinc necessitates its being submitted to a process, or to its being received upon a mercury support. Again, the oxide of copper which we employ, being a waste product of brazing and plate works, unless it be reduced, loses nothing of its value by its reduction in the battery; the depolarization may therefore be considered as costing scarcely anything. The oxide of copper battery is a durable and valuable battery, which by its special properties seems likely to replace advantageously in a great number of applications the batteries at present in use. * * * * * FARCOT'S SIX HORSE POWER STEAM ENGINE. This horizontal steam engine, recently constructed by Mr. E.D. Farcot for actuating a Cance dynamo-electric machine, consists of a cast iron bed frame, A, upon which are mounted all the parts. The two jacketed, cylinders, B and C, of different diameters, each contains a simple-acting piston. The two pistons are connected by one rod in common, which is fixed at its extremity to a cross-head, D, running in slides, E and F, and is connected with the connecting rod, G. The head of the latter is provided with a bearing of large diameter which embraces the journal of the driving shaft, H. The steam enters the valve-box through the orifice, J, which is provided with a throttle-valve, L, that is connected with a governor placed upon the large cylinder. The steam, as shown in Fig. 2 (which represents the piston at one end of its travel), is first admitted against the right surface of the small piston, which it causes to effect an entire stroke corresponding to a half-revolution of the fly-wheel. The stroke completed, the slide-valve, actuated by an eccentric keyed to the driving shaft, returns backward and puts the cylinders, B and C, in communication. The steam then expands and drives the large piston to the right, so as to effect the second half of the fly-wheel's revolution. The exhaust occurs through the valve chamber, which, at each stroke, puts the large cylinder in connection with the eduction port, M.