Phenomena of Voltaic Electricity, 1 65 



posing a galvanometer instead, heating the points e as the 

 needle would swing one way, and removing the heat during 

 the time of its return (302.), feeble deflections were soon ob- 

 tained: thus also proving the current through heated air; but 

 the instrument used was not so sensible under the circum- 

 stances as chemical action. 



274. These effects, not hitherto known or expected under 

 this form, are only cases of the discharge which takes place 

 through air between the charcoal terminations of the poles of 

 a powerful battery, when they are gradually separated after 

 contact. Here the passage is through heated air exactly as 

 with common electricity, and Sir H. Davy has recorded that 

 with the original battery of the Royal Institution this discharge 

 passed through at least four inches of air*. In the exhausted 

 receiver the electricity would strike through nearly half an 

 inch of space, and the combined effects of rarefaction and heat 

 was such upon the inclosed air as to enable it to conduct the 

 electricity through a space of six or seven inches. 



275. The instantaneous charge of a Leyden battery by the 

 poles of a voltaic apparatus is another proof of the tension, 

 and also the quantity, of electricity evolved by the latter. Sir 

 H. Davy saysf, " When the two conductors from the ends of 

 the combination were connected with a Leyden battery, one 

 with the internal, the other with the external coating, the bat- 

 tery instantly became charged, and on removing the wires 

 and making the proper connexions, either a shock or a spark 

 could be perceived: and the least possible time of contact 

 was sufficient to renew the charge to its full intensity." 



276. In motion, i. Evolution of [Heat. — The evolution of 

 heat in wires and fluids by the voltaic current is matter of ge- 

 neral notoriety. 



277. h. Magnetism. — No fact is better known to philoso- 

 phers than the power of the voltaic current to deflect the 

 magnetic needle, and to make magnets according to certain 

 laws ; and no effect can be more distinctive of an electrical 

 current. 



278. iii. Chemical decomposition.— The chemical powers of 

 the voltaic current, and their subjection to certain laws, are 

 also perfectly well known. 



279. iv. Physiological Effects. — The power of the voltaic 

 current, when strong, to shock and convulse the whole animal 

 system, and when weak to affect the tongue and the eyes, is 

 very characteristic. 



280. v. Spark The brilliant star of light produced by the 



"* ■ Elements of Chemical Philosophy, p. 153. f Ibid. p. 154. 



