Lessons in elementary physics / by Balfour Stewart.

  • Balfour Stewart
Date:
1895
Catalogue details

Licence: Public Domain Mark

Credit: Lessons in elementary physics / by Balfour Stewart. Source: Wellcome Collection.

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    caused by the contact of two heterogeneous metals, while he was wrong in imagining that work can be done by the voltaic arrangement without the consumption of some such fuel as zinc. Thus there is probably a sort of electric irritation kept up at the point where the two heterogeneous metals come into contact ; and when the battery is at work, this irritation proves a kind of predisposing cause, in virtue of which the potential energy of the fuel zinc is converted into an electric current in the first instance, and after that most frequently into heat. Perhaps it is wrong to suppose that the electrical irri- tation is entirely confined to the points of contact of the heterogeneous metals, and that nothing is due to the nature of the liquid. The points of contact of the heterogeneous metals must, however, be regarded as the chief source of electrical separation. 383. Thomson’s Crucial Experi- ment.—The important experiment made by Thomson was of the follow- ing nature ;— Let m denote a metallic needle, movable round the point m in the plane of the paper, and let c and = denote two semicircular rings—the one (c) of copper, and the other of zinc, both being soldered together ; then if m be charged with positive electricity it will turn from the zinc to the copper, and if charged with negative electricity it will turn from the copper to the zinc. Phis behaviour may be explained by supposing that in conse- quence of the contact of the two metals, copper and zinc, the copper becomes negatively and the zinc positively electrified. Therefore in a zinc and copper battery this electrical irritation, which IS kept up at the junction of the two metals, will cause a current of positive electricity to flow /hrotif^h the liquid from the zinc to the copper. J. J. Thomson has shown that when a rod of glass is united to one of sealing-wax their surface of contact becomes the seat of a permanent electrical separation in virtue of whicli tlie glass will be found to be charged with positive and the wax with negative electricity months after the two have been united together. The electrical separation caused by the contact of heterogeneous bodies is thus seen to be associated with non- U I)
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