GALVANISM. 



by its abandoning the first particle of 

 oxygen, which finds no other particle of 

 hydrogen to replace it, causes the oxygen 

 to appear at that point in the form of 

 gas. We have thus the two gases formed 

 at each end, not from the same indivi- 

 dual particle of water, but from the two 

 which happen at that moment to be in 

 contact with the wires. The production 

 of the two gases will take place at the 

 same instant in both places, each par- 

 ticle having only to move ore step, that 

 is, from one particle to the adjoining 

 one, instead of having to traverse the 

 whole extent of the line, and no current 

 will be perceptible in the fluid. If this 

 theory be correct, the operation of gra- 

 vity in favouring the descending current 

 of ihe heavier element, namely oxygen, 

 might be rendered sensible ; and that 

 this is actually the case appears by an 

 observation of Mr. Sylvester, that when 

 the wire giving out oxygen is placed at 

 a much lower level than that which 

 gives out hydrogen, the effect is sensibly 

 greater than when the positions are 

 reversed." 



(107.) Similar explanations of the 

 mode of transfer have been given by 

 Dr. Henry, and by Grotthus ; and from 

 the following passage in Sir H. Davy's 

 last paper on the subject,* it would 

 seem jthat he entertained views some- 

 what similar. " If it be supposed that 

 the fluid is divided into two zones, xli- 

 rectly opposite in their powers to the 

 poles of the battery, the virtual change 

 may be regarded as taking place in the 

 two extremities of these zones nearest 

 the neutral point ; so that by a series of 

 decompositions and recompositions, the 

 alkaline matters and hydrogen separate 

 at one side, and oxygen, pure, or in union, 

 at the other. In this way the electricity 

 may be regarded as the transporter of 

 the ponderable matters, which assume 

 their own peculiar characters at the mo- 

 ment when they arrive at the point of 

 rest." That visible motions are sometimes 

 produced in fluid conductors when 

 transmitting the electric current, has 

 been shown by Sir H. Davy, who no- 

 ticed the very singular convulsive agi- 

 tations into which mercury is thrown, 

 when placed within the circuit of a pow- 

 erful voltaic battery discharged through 

 water.f These motions, which are fre- 

 quently of a violent and capricious kind, 

 have also attracted the attention of Mr. 



Philosophical Transactions for 1826, p. 416, 417 

 t Elements of Chemical Philosophy, p. 172, 



Herschel, and he has made them the 

 subject of an interesting research, of 

 which an account is contained in the 

 Philosophical Transactions.* 



(108.) The following singular fact 

 has been noticed by Mr. Porrett : If a 

 vessel be divided by a membranous par- 

 tition into two compartments, of which 

 the one is filled with water, and the other 

 contains but a very small quantity, and if 

 the positive wire from a voltaic battery be 

 inserted into the former, and the nega- 

 tive wire into the latter, the water will 

 be impelled from the first compartment 

 into the second, through the partition, 

 and will at length rise to a higher level 

 in the latter than in the former.f Mr. 

 A. De la Rive, upon repeating these 

 experiments, arrived at the same result, 

 when he employed distilled or river 

 water, which has but a small conduct- 

 ing power; when, however, a saline 

 solution of sufficient strength was used, 

 no such effect of impulsion was per- 

 ceptible. But the reality of such an 

 effect under the above circumstances, is 

 sufficient to establish the existence of 

 a mechanical force derived from the 

 current of voltaic electricity. 



(109.) We have already had occasion 

 to observe that a theory, founded upon 

 totally different views of the sources of 

 galvanic power from those which have 

 now been stated, has been applied to the 

 explanation of the phenomena. As this, 

 which has been termed the electric 

 theory of galvanism, has been adopted 

 by several eminent philosophers, it 

 ought not to be considered as undeserv- 

 ing of notice in this place. 



(110.) It was conceived by Volta, the 

 original author of this theory, that the 

 primary source of the electricity liberated 

 during the action of a galvanic appa- 

 ratus, might be traced to the contact of 

 the dissimilar metals. He assumed as 

 a fundamental fact, that during the 

 whole time that these metals are in 

 contact, a certain force is in constant 

 operation, tending to effect a transfer of 

 electricity from the one metal to the 

 other. To this force he gave the name > 

 of electromotive force. When, for ex- 

 ample, zinc and copper are in contact, 

 the alleged operation of this force i's to 

 impel the electricity from the copper to 

 the zinc, so as to maintain in the latter 

 a positive state, when compared with 

 the former, which will, consequently, 



* For 1824, p. 163. 



t Thomson's Annals of Philosophy, viii. 74, 



