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.

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    2d. The cold wire being sharpened to a point and plunged deliberately into the mercury to the bottom of the bath, the deflection was 19°. 3d. But when I touched the surface of the mercury with the very point of the cold wire, there was a deflec- tion of 60°. Having laid a plate of tinned iron upon the surface of some hot mercury, it was touched with the point of the cold wire. There was a strono- deflection of the needles in the opposite direction to what would have been the case had the mercury been touched and not the iron. The under surface of the iron was, therefore, act- ing as a hot face, and the parts round the point as a cold face, being temporarily chilled by the touch of the wire. These results explain the anomalies observed by some of those who investigated the course of thermo-electric currents by means of small metallic fragments. It would therefore seem that when wires of the same metal are used as electromotors, the quantity of electric- ity evolved depends on the quantity of caloric that can be communicated in a given time. Time, therefore, under these circumstances, must enter as an element of thermo- electric action. In the case of a single metal, the maxi- mum effect would be produced when the hot element is a mass and the cold one a point. And, lastly, that the quantities of electricity evolved in a pile of pairs are directly proportional to the number of the elements. In the first trials I made to determine the effect of in- creasing the number of pairs in a pile, the results ob- tained were contradictory; by operating, however, in the following way, the jjroposition was at last satisfactorily determined. 1st. The resistance to conduction was made nearly