Forces of some Metallic Alloys in Contact with Copper. 41 



Experiment 28, on the 29th Feb. — To ascertain the value of 

 /3, deflections were taken with two different intensities of the 

 current. We obtained : — 



With 5= tan 19 53 the deflection 27*15, 

 „ s=tan 7 45 „ 12*80, 



whence /3= 5*600. This experiment gave the thermoelectric 

 force =103*37. 



Experiment 29, on March 6. — With s= tan 20° 13' the de- 

 flection in the air-thermometer was 22*35. Thermoelectric force 

 = 84*27. 



Experiment 30, March 9. — Deflection =19*08 when s =tan 

 19° 35'. Thermoelectric force =74-61. 



The following Table makes evident the constant diminution 

 of both forces. The first column gives the day of the experi- 

 ment ; the second contains the values of a which have been cal- 

 culated, with the value of /3=5*6, from Exp. 26-30. The re- 

 duced deflections of the thermoelectric current are given in the 

 third column ; the fourth is obtained by division of the numbers 

 in the third column by those in the second. 





Electromotive 

 force. 



Thermoelectric 

 force. 



Ratio. 



February 28. 



„ ' 28. 



n 29. 



March 6. 



9. 



124-85 



109-42 



98-81 



80-51 



7011 



120-24 

 113-39 

 103-37 



84-27 

 74-61 



096 

 103 

 105 

 105 

 1-06 



Consequently both forces diminish in nearly the same propor- 

 tion. The alteration proceeded most quickly directly after the 

 casting, the diminution being already sensible after a few hours. 

 It might be supposed that the galvanic current (which, it is well 

 known, calls forth both temporary and permanent changes in the 

 conducting-wire) is the cause of the phenomenon here observed. 

 That this is not the case, however, is shown by the experiments 

 with the wires first cast, in which the change had taken place 

 although they had lain several weeks unused, as well as Experi- 

 ments 26-30, in which one of the pairs of wires had not been 

 exposed to the influence of any stronger current than the ther- 

 moelectric current produced by the cooling of the place of sol- 

 dering. It must also be remarked that the diminution of the 

 electromotive force cannot be ascribed to any change of structure 

 of the copper wire, because this had been drawn a very long time 

 before the experiments. 



