286 Galvanic Apparatus, Theory of Galvanism, 6^c, 



vouis the separation of caloric from the electricity which does not 

 radiate; this result seems consistent with my hypothesis, that the 

 fluid as extricated by Volta's pile is a compound of caloric and 

 electricity*; i)Ut not with the other hypothesis, which supposes 

 it to be electricity alone. The finest needle is competent to 

 discharge the product of the most powerful machine without de- 

 tiiment, if received gradually as generated by them. Platina 

 points, as small as those which were melted like wax in my ex- 

 periments, are used as tips to lightning rods without injury, 

 unless in sudden discharges produced under peculiar circum- 

 stances f. 



The foUowiiig experiment I conceive to be very unfavourable 

 to the idea that galvanic ignition arises from a current of elec- 

 tricity. 



A cylinder of lead of about a quarter of an inch diameter, and 

 about two inches long, was reduced to the thickness of a common 

 brass pin for about three cjuarters of an inch. When one end was 

 connected with one pole of the apparatus, the other remained 

 suspended by this filament; yet it was instantaneously fused by 

 contact with the other pole. As all the calorific fluid which acted 

 upon the suspended knob, must have passed through the filament 

 by which it hung, the fusion could not have resulted from a pure 

 electrical current, which would have dispersed the filament ere a 

 mass fifty times larger had been perceptibly affected. According 

 to my theory, caloric is not separated from the electricity until 



* According to the theory here alluded to, the galvanic fluid owes its 

 properties to caloric and electricity; the fcrmer predominating in propor- 

 tion to the size of the pairs, the latter in proportion to the number, being in 

 both cases excited by a powerful acid. Hence in batteries which combine 

 both qualifications sufficiently, as in all those intervening between Children's 

 large pairs of two feet eight inches by six feet, and the 2000 four-inch pairs 

 ot the Royal Institution, the phaenomena indicate the presence of both fluids. 

 In De Luc's column, where the size of the pairs is insignificant, and the 

 energy of interposed agents feeble, we see electricity evolved without any 

 appreciable quantity of caloric. In the calorimotor where we have size only, 

 the number being the lowest possible, we are scarcely able to detect the 

 presence of electricity. 



NA'hen the fluid contains enough electricity to give a projectile power 

 adequate to pass chrough a small space in the air, or through charcoal, which 

 impedes or arrests the caloric, and favours its propensity to radiate, this 

 principle heat is evolved. This accounts for the evolution of intense heat 

 under those circumstances which rarities the air, so that the length of the 

 jet from one pole to the other may be extended after its commencement. 

 Hence the portions of the circuit newest to the intervening charcoal, or 

 heated space, are alone injured ; and even non-conducting bodies, as quartz, 

 introduced into it are fused, and hence a very large wire may be melted by 

 the fluid, received through a small wire imperceptibly affected. 



See Silliman's Journal, No. G, Vol. 1. Thomson's Annals, Sept. 1810. 

 Tilloch's Philosophical Magazine, October 1S19» 



* See Adams's Electricity, On points. 



circum- 



