216 



fects would be, he thinks, to deny that action and reaction are 

 equal. The contact theory, according to him, assumes that a force 

 which is able to overcome powerful resistance, both chemical and 

 mechanical, can arise out of nothing : that, without any change in 

 the acting matter, or the consumption of any other force, an electric 

 current can be produced, which shall go on for ever against a con- 

 stant resistance, or only be stopped, as in the voltaic trough, by the 

 ruins which its exertion has heaped in its own course ; — this, the 

 author thinks, would be a creation of power, such as there is no 

 example of in nature ; and, as there is no difficulty in converting 

 electrical into mechanical force through the agency of magnetism, it 

 would, if truBy supply us at once with a per[3etual motion. Such a 

 conclusion he considers as a strong and sufficient proof that the 

 theory of contact is founded in error. 



In a postscript, the author states that he has since found a passage 

 in Dr. Roget's treatise on Galvanism, in the Library of Useful 

 Knowledge, published in January 1829, in which the same argu- 

 ment respecting the unphilosophical nature of the contact-theory is 

 strongly urged*. 



* " Were any further reasoning necessary to overthrow it, (namely, 

 the voltaic theory of contact) a forcible argument might be drawn from the 

 following consideration. If there could exist a power, having the property 

 ascribed to it by the hypothesis, namely, that of giving continual impulse 

 to a fluid in one constant direction, without being exhausted by its own 

 action, it would differ essentially from all the other known powers in na- 

 ture. All the powers and sources of motion with the operation of which 

 we are acquainted, when producing their peculiar effects, are expended in 

 the same proportion t^s those effects are produced ; and hence arises the 

 impossibility of obtaining by their agency a perpetual effect, or, in other 

 words, a perpetual motion. But the electro-motive force ascribed by Volta 

 to the metals when in contact, is a force which, as long as a free course is 

 allowed to the electricity it sets in motion, is never expended, and conti- 

 nues to be exerted with undiminished power, in the production of a never- 

 ceasing effect. Against the truth of such a supposition the probabilities 

 are all but infinite." § 113, p. 32. 



