TO THE MOVEMENT OF MACHINES. 



525 



have reckoned, in another series of experiments, the time which elapsed 

 in developing 10 bubbles of air. The following is the table: 



It is necessaiy to remark, that there was also a very feeble develop- 

 ment of gas even at the surface of the zinc, which was taken into 

 account. But the quantity of gas measured was, I believe, less than 

 the quantity of gas developed ; for there was a secondary action, which 

 wsis manifested by the blackness of the plate of silver, and which we 

 must attribute to a metallic reduction of the oxides dissolved in the 

 acid. As it is veiy difficult to translate into forces the deviation of 

 the needle*, these tables will not tend to confirm the law of Mr. Fa- 

 raday : they only show that the deviation of the needle follows the 

 same course as the development of the gas. I shall repeat the expe- 

 riments, but reversing the process ; that is to say, the development of 

 gas will be taken for the most exact measure of the force of the 

 current, and the value of the degrees of the galvanometer wall be 

 deduced from it, either immediately, or by some formula of intei-po- 

 lation of convenient application. The experiments cited are not suf- 

 ficiently rigorous to form the elements of calculation. 



To return to the magnetic machine. We had succeeded in obtaining 

 an inversion of the direction of the current, both instantaneous and ex- 

 act, by the commutator described above in article 7, the effect of which is 

 not at all affected by the quickness of rotation. We had even succeeded 

 in obtaining, at least for some time, a tolerably constant voltaic apparatus. 

 In short, the means have been discovered of reducing the expense of 

 maintenance to a minimum, by preventing the direct action of the acid 

 upon the zinc, an action which cannot be turned to any use, and which, 

 as is known, greatly sui-passes that which serves to produce the 

 voltaic current. Thus the most important difficulties in the practical 

 application of electro-magnetism being overcome, it appeared to me 

 time to examine more closely the nature of the forces which I desired 

 to put in use, and principally to seek for the cause which limits a 



* Beccinercrs Treatise on Electricity and Magnetism, vol. ii. p. 20. 



