312 TENTH ANNUAL REPORT OF 



been carried on relative to the two hypotheses, as to the origin or 

 cause of the development of the electricity in the galvanic apparatus, 

 viz : whether it is due to the contact of tlie metals or to the chemical 

 action of the acid on one of them. But it must be evident to those 

 who have paid attention to the history of this branch of science that 

 justice cannot be done to this interesting discussion in a few i)ages of 

 this report, and that the author has merely given a brief sketch of 

 only one of the hypotheses ; but since this is comparatively little 

 known, except in Germany, it will be acceptable to the English 

 reader.] 



This discussion has been carried on with no little warmth ; but the 

 history of science shows that when a theory is properly established, 

 controversy in reference to it ceases. If any one, at this time, should 

 assert that the earth does not revolve about the sun, astronomers 

 would give themselves little trouble to refute the objection which 

 might be urged against the received theory. Drieberg recently 

 attacked the physical theory of the pressure of the air, but his opin- 

 ions have not produced the least excitement among physicists. Op- 

 position provokes discussion only when theories have not risen above 

 mere hypothesis, and this is partly the case with reference to tho 

 source oi' the electricity of the galvanic circuit. 



The matter in dispute is not fully ripe for decision, and we can 

 only expect a perfect solution of the difficulty when we are better 

 informed of the nature of electricity itself. In Euler's time the 

 theory of the vibrations of light was advocated wath much ability, 

 yet this distinguished mathematician was unable to render it gen- 

 erally acceptable, and it was only by the discovery of new facts, par- 

 ticularly those of polarization, that the theory received that form 

 which silenced opposition. The exi)lanatiun of the origin of the elec- 

 tricity of the pile must rest on the theory of the molecular constitu- 

 tion of matter in relation to the ethereal medium, tlie existence of 

 which we are obliged to admit in order to generalize the facts of 

 light, heat, and other emanations from the sun. The establishment 

 of a general theory of this kind which will give definite conceptions 

 of the relation of known phenomena, and lead us to infer the exist- 

 ence of facts of which we have as yet no idea, is one of the most im- 

 portant objects of science, and even the attempts which have been 

 made to arrive at a general view of this kind have been fruitful in new 

 and interesting results. 



The materials, however^ for the full establishment of such a theory 

 do not at present exist, and consequently we cannot expect more than 

 approximations to a generalization of the character required. 



§1. Brief sketch of the theories. — Volta found that when a slip of 

 zinc and one of copper were soldered end to end, the one exhibited 

 signs of plus, and the other of negative electricity. He therefore con- 

 cluded that the electricity was due to the contact of the two metals, 

 and that the acid of the circuit only ])erformed the office of a con- 

 ductor. This view was at first generally adopted, but as the phe- 

 nomena came to be more minutely studied, it was found insufficient 

 to explain them, and Wollaston, Davy, and others, adopted the hypo- 

 thesis that the electricity was due to the chemical action of the acid 



