Scientific memoirs : being experimental contributions to a knowledge of radiant energy / by John William Draper.

  • Draper, John William, 1811-1882.
Date:
1878
Catalogue details

Licence: Public Domain Mark

Credit: Scientific memoirs : being experimental contributions to a knowledge of radiant energy / by John William Draper. Source: Wellcome Collection.

    340/488 (page 336)
    2. When a current of electricity, flowing from the poles of a battery, is made to traverse a metallic sheet, the whole of it does not pass in a stiaight line from one pole to the other, but diffuses itself through the metal, di- verging from one point and converging to the other. The greater part of the current is found, however, to take the shortest route. 3. Combining, therefore, the foregoing observations (1, 2), we perceive that there are certain forms of con- struction w^hich will give to thermo-electric arrangements peculiar advantages. For example, the surfaces united by soldering must not be too mass- ive. Let A, Fig. 55, be a semi-ring of antimony, and B a semi-ring of bismuth; let them be soldered to- gether along the line C H, and at the point H let the temperature be raised: a current is immediately ex- cited ; but this does not pass around the rino; A B, inasmuch as it finds a shorter and readier channel through the metals, between H and d, circulating therefore as indicated by the arrows. Nor will the whole current pass round the ring until the temperature of the soldered surface has become unifoi-m. An obvious improvement in such a combination is shown at H in Fig. 56, which con- sists of the former arrangement cut out along the dotted lines: here the whole current so soon as it exists is forced to pass along the ring. And because the mass of metal has been diminished at the line of junction, such a pair will change its temperature very quickly. One of the best forms for a thermo- Pig.5T. electric couple is given in Fig. 57, where