314 M. Becquerel on the Electric effects of Contact 



temperature, and the electric effect immediately became in- 

 verse. 



Gold and diver comport themselves nearly in the same man- 

 ner in their contact with iron, and there is no other difference 

 but in the temperature at which the increments of the electro- 

 dynamic force cease to be proportional to the increments of 

 temperature. 



The manner in which Iron comports itself in its contact with 

 the different metals when the temperature is raised, is in ma- 

 nifest contradiction with the electro-chemical theory, which ad- 

 mits that the electrical effects of contact increase continually 

 with the rise of temperature, till the combination operates. 



Platinum, in its contact with copper, gold, silver, lead, zinc, 

 palladium, does not comport itself in the same manner as iron. 

 At first it is always negative, whatever be the temperature, 

 which proves that the electric current increases in intensity with 

 the elevation of temperature ; but the manner in which this 

 increase takes place, is not such as might have been supposed. 

 Experiment proves, as may be seen in the table p. 312, that, 

 from zero to 350°, for equal increments of temperatui'e, the dif- 

 ferences between the successive increments of the electro-dyna- 

 mic force are sensibly in an arithmetical ratio. 



Palladium follows the same law, for, from zero to 350°, there 

 is a constant ratio between the equal increments of temperature 

 and the increments of intensity. 



Copper and Zinc do not oppose the ordinary law. The elec- 

 trical intensities increase with the temperature, and the differ- 

 ences between the increments are in arithmetical progression. 

 With tin, lead, silver, these increments are sensibly equal, but 

 as they are feeble, there may exist between them differences 

 which the apparatus cannot recognise. 



Diminutions of temperature produce effects analogous to 

 those which I have obtained by an increase of it. I take a 

 closed circuit of two wires, one of copper, and another of pla- 

 tina, and I put one of the joints into melting ice, and the other 

 into a mixture of snow and diluted sulphuric acid. The fol- 

 lowing were the results :— 



