

Mr. J. Prideaux on the Theory of Voltaic Action. 211 



by parity of reasoning, light should be contained in both heat 

 and the voltaic fluid, unless it also be indefinitely contained 

 in the wire ; and heat may be indefinitely continued by fric- 

 tion, where its source is yet more obscure. 



c) That common electricity passed through a water tube is 

 deprived of its power of deflagration, or of even affecting 

 Mr. Harris's delicate air-electrometer*, more effectually than 

 voltaic electricity is by passing through charcoal, which may 

 be thus proved : — 



A pair of Ley den jars, connected in both coatings, were 

 set on an insulating stool ; their outer and inner coatings com- 

 municating respectively with two balls, set at \ inch apart. 

 Between the outer coating and its ball, Harris's thermotest 

 was interposed. The prime conductor being put in commu- 

 nication with the inner coating, the outer having of course a 

 communication with the ground, the machine was turned 

 until the jars discharged themselves through the balls. The 

 thermotest rose 12°, or 1*2 inch; and so repeatedly, at the 

 64-th turn of the machine, with a smart explosion at each dis- 

 charge. 



A glass tube, about 7 inches long and f calibre, filled with 

 water, and wired through a cork at each end, was now inter- 

 posed between the inner coating and its ball. The discharge 

 now took place with a sharp hissing sound, a blue spark, and 

 no effect whatever on the thermotest, although it required 70 

 or more turns of the machine to make the spark pass ; and 

 very little electricity was left in the jars. 



The water tube was next placed between the prime con- 

 ductor and the inner coating, a similar one being made to 

 communicate between the outer coating and the ground; — thus 

 the jars were charged both inside and out through the water 

 tubes; and if, in the case just quoted, the inaction on the ther- 

 motest was caused by abstraction of caloric in passing through 

 the water, that caloric being now abstracted in charging the 

 jars, no heat could be produced in their discharge. But on 

 discharging them through the metallic circuit, as at first, the 

 thermotest rose in the same manner; and on repeating ami 

 varying the experiment, the same effect was always produced 

 by any given number of turns of the machine thrown on tiie 

 jars, whether charged through water or metal, provided they 

 were discharged through metal ; and the effect was uniformly 



null when the discharge took place through water. 



° ° ;197U i 



* To avoid circumlocution or ambiguity in the frequent repetition of the 

 words * electrometer," " galvanometer," &c, I shall take the liberty of 

 distinguishing Mr. Harris's instrument by the term " thermotest" ; and the 

 galvanometer of Professor dimming by the name " ma^netest." 



2 K 2 



