G/O LECTURE LIV. 



between them, is found to heat the negative ball much more than the posi- 

 tive. We cannot, however, place much dependence on any circumstance 

 of this kind, for it is doubtful whether any current of the fluid, which we 

 can produce, possesses sufficient momentum to carry with it a body of sensible 

 magnitude. It is in fact of little consequence to the theory, whether the terms 

 positive and negative be correctly applied, provided that their sense remain 

 determined; and that, like positive and negative quantities in mathematics, 

 they be always understood of states which neutralise each other. The 

 original opinion of Dufay, of the existence of two distinct fluids, a vitreous 

 and a resinous electricity, has at present few advocates, although some have 

 thought such a supposition favoured by the phenomena of the galvanic de- 

 composition of water. 



When electricity is simply accumulated without motion, it does not appear 

 to have any effect, either mechanical, chemical, or physiological, by which 

 its presence can be discovered ; the acceleration of the pulse, and the ad- 

 vancement of the growth of plants, which have been sometimes attributed 

 to it, have not been confirmed by the most accurate experiments. An un- 

 interrupted current of electricity, through a'perfect conductor, would perhaps 

 be also in every respect imperceptible, since the best conductors appear to 

 be the least affected by it. Thus, if we place our hand on the conductor of 

 an electrical machine, the electricity will pass oft' continually through the 

 body, without exciting any sensation. A constant stream of galvanic elec- 

 tricity, passing through an iron wire is, however, .capable of exciting a 

 considerable degree of heat, and if it be transmitted through the hands of 

 the operator, it will produce a slight numbness, although in general some in- 

 terruption of the current is necessary in order to furnish an accumulation 

 sufficient to produce sensible effects; and such an interruption may even 

 increase the effect of a single spark or shock; thus, gunpowder is more readily 

 fired by the discharge of a battery passing through an interrupted circuit, 

 than through a series of perfect conductors. 



The most common effect of the motion of the electric fluid is the production 

 of light. Light is probably never occasioned by the passage of the fluid 

 through a perfect conductor; for when the discharge of a large battery renders 

 a small wire luminous, the fluid is not wholly confined to the wire, but 



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