Physiological Effects and Spark of common Electricity, 259 



observed. But the quantities were so small, that on working 

 the machine for half an hour I could not obtain at either pole 

 a bubble of gas larger than a small grain of sand. If the con- 

 clusion which I have drawn (377.) relating to the amount of 

 chemical action be correct, this ought to be the case. 



331. I have been the more anxious to assign the true value 

 of this experiment as a test of electro-chemical action, because 

 I shall have occasion to refer to it in cases of supposed che- 

 mical action by magneto-electric and other electric currents 

 (336. 346.) and elsewhere. But, independent of it, there can- 

 not be now a doubt that Dr. Wollaston was right in his ge- 

 neral conclusion; and that voltaic and common electricity 

 have powers of chemical decomposition, alike in their nature, 

 and governed by the same law of arrangement. 



332. iv. Physiological Effects. — The power of the common 

 electric current to shock and convulse the animal system, and 

 when weak to affect the tongue and the eyes, may be consi- 

 dered as the same with the similar power of voltaic electricity, 

 account being taken of the intensity of the one electricity and 

 duration of the other. When a wet thread was interposed in 

 the course of the current of common electricity from the bat- 

 tery (291.) charged by eight or ten revolutions of the machine 

 in good action (290.), and the discharge made by platina 

 spatulas through the tongue or the gums, the effect upon the 

 tongue and eyes was exactly that of a feeble voltaic circuit. 



333. v. Spark. — The beautiful flash of light attending the 

 discharge of common electricity is well known. It rivals in 

 brilliancy, if it does not even very much surpass, the light 

 from the discharge of voltaic electricity; but it endures for an 

 instant only, and is attended by a sharp noise like that of a 

 small explosion. Still no difficulty can arise in recognising it 

 to be the same spark as that from the voltaic battery, especially 

 under certain circumstances. The eye cannot distinguish the 

 difference between a voltaic and a common electricity spark, 

 if they be taken between amalgamated surfaces of metal, at 

 intervals only, and through the same distance of air. 



334. When the battery (291.) was discharged through a 

 wet string placed in some part of the circuit away from the 

 place where the spark was to pass, the spark was yellowish, 

 flamy, having a duration sensibly longer than if the water had 

 not been interposed, was about three fourths of an inch in 

 length, was accompanied by little or no noise, and whilst 

 losing part of its usual character had approximated in some 

 degree to the voltaic spark. When the electricity retarded 

 by water was discharged between pieces of charcoal, it was 

 exceedingly luminous and bright upon both surfaces of the 



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