196 Historical Sketch of Electro-magnetism. [Sept. 



in your Annals in vol. xvi. of the First Series. It is full of 

 important matter, and contains, in few words, the results of a 

 great number of observations ; and, with his second paper, com- 

 prises a very large part of the J'acts that are as yet known relat- 

 ing to this subject. It is necessary, for the sake of connection, 

 in this account, that I state much of what has been described 

 in those papers, though nothing that I shall say will at all super- 

 sede the necessity of reading them, to those who wish to gain a 

 knowledge on the subject. 



Upon the excitation of the voltaic apparatus by the proper 

 arrangement of its plates and fluid, it is known that certain 

 powers are given to its poles or extremities which enable them, 

 when attached to an electrometer to show by their divergence a 

 certain tension of electricity ; or when connected together by 

 fluids, wires, or other conducting substances, to decompose or 

 heat them. These effects have been known for several years, 

 and are generally attributed to electricity produced by the appa- 

 ratus ; the effects of tension belonging to the insulated state of 

 the poles ; those of decomposition and heating to their connected 

 state. 



When the two poles of such a battery or apparatus are con- 

 nected by conductors of electricity, the battery is discharged ; 

 that is, the tension of the electricity at the poles is lessened, and 

 that according as the conducting power of the substance is more 

 or less. Good conductors, as the metals, discharge it entirely 

 and instantly ; bad conductors, with more or less difficulty ; but 

 as the instrument has within itself the power of renewing its 

 first state of tension on the removal of the conducting medium, 

 and that in a very short space of time, it is evident that the 

 connecting substance is continually performing the same office 

 during the whole time of its contact that it did at the first 

 moment, and this whether it be a good or a bad conductor ; and 

 it is also evident that it must be in a different state in this situa- 

 tion than when separated from the apparatus. It is important at 

 present rather to consider the action of a good conductor in dis- 

 charging the battery, as the phenomena to be considered are in 

 that case more energetic. A metallic wire, therefore, may be 

 used to connect the two poles; it will discharge a powerful 

 apparatus; and consequently whatever takes place in the con- 

 necting medium is here compressed into a very small place. 

 Those who consider electricity as a fluid, or as two fluids, con- 

 ceive that a current or currents of electricity are passing through 

 the wire during the whole time it forms the connection between 

 the poles of an active apparatus. There are many arguments in 

 favour of the materiality of electricity, and but few against it ; 

 but still it is only a supposition; and it will be as well to remember, 

 while pursuing the subject of electro-magnetism, that we have no 

 proof of the materiality of electricity, or of the existence of any 

 current through the wire. 



