concerned in the Phenomena of ordinary Electricity, S^c. 217 



the case of the other, one is sufficient. The magneto-electric 

 machine, if connected with the galvanometer by means of stout 

 copper wires, long enough to place the needle out of reach of 

 the powerful influence of the combined magnets of the machine, 

 will cause no small deflection when the coils are made to revolve 

 rapidly. But if, removing the galvanometer, the same arrange- 

 ment be connected with the insulated gold leaves of a difi'erential 

 electrometer, the effect on them is barely observable. Here then 

 we have an electric fluid in operation quite diff'erent from ordi- 

 nary electricity, on account of its much greater effect on the 

 galvanometer, and its trifling influence on the electrometer j 

 while the current resembles that of a voltaic series, on account of 

 its chemical and deflective powers, although no chemical action 

 is concerned in its production. Yet the deflective power of 

 magneto-electricity is far weaker than the electricity in many 

 cases produced by a single voltaic combination in which chemi- 

 cal action is taking place, and which nevertheless would not be 

 capable of producing decomposition of water, although magneto- 

 electricity does it with such facility. M. Lame observes that 

 thermo-electric cun-ents are distinguished from voltaic and 

 magneto-electric curi'ents by their being much more difficultly 

 transmissible through liquids *. It is also worthy of notice, that 

 no power of common electricity passed through the coil of the 

 electro-magnetic apparatus is capable of giving a shock, although 

 the electricity of a pair of zinc and copper plates of an inch 

 square, or even a pair of zinc, and copper wires, is adequate to 

 that effect e^en in a violent degree. 



So dififerent and independent of each other are the electric 

 and voltaic agents, that the voltaic spark may be taken through 

 the electric, each retaining its characteristic appearance. And 

 if a fine platinum wire be made red-hot by means of a voltaic 

 battery, a current of common electricity may be passed through 

 it, and drawn from any particular part of the wire in its own 

 proper form of sparks. The aura electrica produced will cool the 

 wire when sparks are not taken ; but when they are drawn, the 

 wire on each side of that spot will be as much incandescent as ever. 



Not the least remarkable difference of properties between the 

 electricity evolved Ijy a voltaic combination and that by a fric- 

 tional machine, is the facility with which the latter is conducted 

 by all metals, and the obstruction which is experienced by the 

 former in passing through some. An easy mode of observing 

 this difficulty of conduction, is by means of an electro-magnetic 

 apparatus of the construction at present used for medical pur- 

 poses. If the triad, consisting of one platinized silver plate and 

 two zinc plates, be connected with the coil by twelve feet of 

 * Cours de Physique de I'Ecole Polytechnique, iii. 286, 



