216 Mr. M. Donovan on the supposed Identity of the Agent 



powerful deflecting effects could have been produced by the cause 

 commonly assigned, when it is considered that the galvanometer 

 which suffered these deflections, when similarly connected with 

 a powerful electrical machine, proved insensible to its current. 

 In the experiments wherein fused caustic potash or heated metals 

 were touched with melted sulphur, there was not more than a 

 quarter of a grain of the latter, scarcely the half of which acted, 

 yet the needle sometimes whirled round four times*. 



It appears very difficult to comprehend these results, which 

 are but a few out of many obtained by me, unless it be admitted 

 that in the phenomena called voltaic, the agent cannot be iden- 

 tical with that which produces the effects of ordinary electricity. 

 By supposing that certain elementary forces, which constitute 

 the electric fluid, exist together in combination while that agent 

 is in its natural state of equilibrium ; and that according to the 

 circumstances under which it is excited into a state of activity, 

 the elements present themselves either in their natural state of 

 combination, or more or less altered in their ratio, and therefore 

 in their properties, the phsenomena receive an explanation, as I 

 think, less embarrassed with difficulties, but still it must be ad- 

 mitted with quite a sufficiency of them. 



We know that the electric fluid occasionally evinces variable 

 properties according to the mode of its generation ; and this 

 variation agrees with the notion of difference of ratio of the con- 

 stituent elements such as has been here assvimed. It may be 

 expedient to advert to a few of these differences of properties. 

 Water is an excellent conductor of the lowest intensities of com- 

 mon electricity ; but it is declared on all hands to be not a good 

 conductor of voltaic electricity, and Sir H. Davy says that to 

 such low intensities it is an absolute insulator. Common elec- 

 tricity is remarkable for the distance through which it strikes ; 

 a spark of fifteen inches long may easily be obtained from a 

 powerful electric machine ; but Mr. Gassiot found that a nine- 

 gallon Leyden battery, charged by a water battery of 1024 pairs 

 of plates, coidd only project a spark to a distance of 5 oVo^^ ^^ 

 an inch, and sometimes j-Q^g^ths. For a long time it was doubted 

 if voltaic electricity could project a spark at all through air, un- 

 less when the poles are gradually withdrawn from contact in a 

 vacuum. Voltaic electricity overcomes the most powerful che- 

 mical affinities ; none in fact can withstand its influence, although 

 it would merely cause gold leaves to diverge a little. But com- 

 mon electricity, possessing the highest dynamic powers, can only 

 overcome comparatively the weakest affinities. One is power- 

 fully magnetic ; the other very little so. One, in order to produce 

 its effects, invariably requires the operation of its two poles ; in 

 * The experiments of Cumming should also be considered. 



