Page:Scientific Memoirs, Vol. 1 (1837).djvu/537

Rh have reckoned, in another series of experiments, the time which elapsed in developing 10 bubbles of air. The following is the table:

It is necessary to remark, that there was also a very feeble development 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 was 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 very difficult to translate into forces the deviation of the needle, these tables will not tend to confirm the law of Mr. Faraday: they only show that the deviation of the needle follows the same course as the development of the gas. I shall repeat the experiments, 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 interpolation of convenient application. The experiments cited are not sufficiently 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 exact, 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 surpasses 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