W\B^«cp\K KOJiwv and its EffectsArP » •'-' •* -^^ 'WL 



at a considerable distance from the other pole {e. g. an inch and 

 a half), becomes charged with the electricity which corresponds 

 to that pole and the above-mentioned current; but it is charged 

 by radiation mei'ely, and not by sparks. In accordance with 

 these results, it was found that when a wire connected with the 

 earth was held at a short distance from one of the poles, and 

 sparks taken from it for some time, then, after the cessation of 

 the current, the whole induction coil was charged with that kind 

 of electricity which belonged to the other pole. 



The sparks which can be drawn from one of the poles of the 

 induction coil in its unconnected condition are of course stronger 

 when the other pole is connected with the earth, and apparently 

 always stronger at the negative than at the positive pole. 



When the two poles of the induction coil are brought so near 

 to one another that sparks pass between the two, the circuit may 

 be considered closed ; but this closing of the circuit differs from 

 that produced by a good conductor; in the latter, both currents 

 circulate; in the former, only the one which is produced by 

 breaking the inducing current. The stratum of air between the 

 poles, which may be compared to a filter, insomuch as it keeps 

 one current back, requires to be only very thin. A piece of dry 

 blotting-paper, when placed between two metallic plates connected 

 by wires with the poles of the induction coil, perfectly fulfils the 

 pui'pose of separating one-half of the electricity, and occasions a 

 current of constant direction, which, its discontinuity excepted, 

 possesses all the properties of a galvanic current of high inten- 

 sity, — is similar, in fact, to that of a very great number of veiy 

 small plates. 



The interruption by means of points serves, of course, the 

 same purpose ; and in many respects this purpose may be still 

 better eflfected by means of the electric egg, because in rarefied 

 air the discharge between the ends of the metallic conductors 

 takes place much more quietly than by the sudden springing of 

 sparks in air of the common density. The thinner and more 

 rarefied the stratum of air, the less the current will be weakened 

 by this interruption, although, perhaps, a part of the same may 

 always remain behind in the wire. 



The effects of the current when interrupted by a stratum of air, 

 and its difference from a perfectly closed current, are manifested 

 by the galvanometer. A definite deviation is now obtained which 

 depends upon the direction of the current. It is greater with a 

 thick than with a tldn induction wire, and it is also more conti- 

 nuous and regular when the current is interrujjted by discharges 

 iu a partial vacuum, than when it is broken by sparks in common 

 air. When wc consider the difficulty with which the deviation 

 of a magnetic needle is effected by frictional electricity, the faci- 



PldL Mag, S. 4. Vol. 10. xNo. G4. Aug. 1855. K 



