SO ELECTRICITY IN MOTION. 



diverging rays, shows that k is negative. The sparks, exhibited 

 by small balls, differently Htctrifi< -d, have also similar varieties irt 

 their forms, according to the nature of their charges. 



The production of heat by electricity frequently accompai 

 that of light, and appears to depend in some measure on the 

 circumstances. A fine wire may be fused and dissipted by the 

 discharge of a battery; and without being perfectly melted, it 

 may sometimes be shortened or lengthened, accordingly .1- it i 

 loose or stretched during the experiment. The more readily a 

 metal conducts, the shorter is the portion of it which the same 

 shock can destroy ; and it has sometimes been found, that a double 

 charge of a battery has been capable of melting a quadruple length 

 of wire of the same kind. 



The mechanical effects of electricity are probably in many cases 

 the consequences of the rarefaction produced by the heat which is 

 excited ; thus, the explosion attending the transmission of a shock 

 or spark through the air, may easily be supposed to be derived 

 from the expansion caused by heat ; and the destruction of a glass 

 tube, which contains a fluid in a capillary bore, when a spark is 

 caused to pass through it, is the natural consequence of the con. 

 version of some particles of the fluid into vapour. But when a 

 glass jar is perforated, this rarefaction cannot be supposed to be 

 adequate to the effect. It is remarkable that such a perforation 

 may be made by a very moderate discharge, when the glass is in 

 contact with oil or with sealing wax ; and no sufficient explanation 

 of this circumstance has yet been given. 



A strong current ol electricity, or a succession of shocks or 

 sparks, transmitted through a substance, by means of fine wires, 

 is capable of producing many chemical combinations and decom- 

 positions, some of which may be attributed merely to the heat 

 which it occasions, but others are wholly different. Of these the 

 moat remarkable is the production of oxygen and hydrogen gas 

 from common water, which are usually extricated at once, in such 

 quantities, as, when again combined, will reproduce the water 

 which lias disappeared; but in some cases the oxygen appears to 

 be disengaged most copiously at the positive wire, and the hydro- 

 gen at the negative. 



When the spark is received by the tongue, it has generally a 

 subacid taste ; and an explosion of any kind is usually accompa. 

 nied by a smell somewhat like that of sulphur, or rather of fired 



