564 PROCEEDINGS OF THE AMERICAN ACADEMY. 



points respectively. Accordingly the points touched hy the ice after 

 the stretching were probably not in all cases just the same as the points 

 touched before the stretching. Nevertheless, it will be seen that the 

 curve C 4 of Figure 7, which corresponds to the observations after 

 stretching, agrees very closely in the main with the curve C 3 obtained 

 before the stretching. 



The next curve, C 5 , is made from data obtained by touching points 

 25.5, 26. 6, 27.7, etc. ; that is, points intermediate between those which 

 gave C 4 . The differences between these two curves are such as might 

 have been expected. 



C 6 is a composite of C 4 and C 5 . 



So much for the curves of Figure 7, representative of the behavior of 

 wire No. 1. The curves of Figure 8 show the behavior of wire No. 2, 

 taken from the same piece as No. 1. C x in Figure 8 is for the state 

 before annealing; it shows a somewhat smaller range of electromotive 

 force than the corresponding curve of Figure 7, with about the same 

 number of changes of sign. C 2 is for the state just after annealing. As 

 with wire No. 1, annealing has increased the range of electromotive force 

 and diminished the number of changes of sign. C 3 is the curve obtained 

 after brightening the surface of the annealed wire. It differs very little 

 indeed from C 2 . C 4 is from the data obtained after permanently stretch- 

 ing the wire 10 per cent, a 50 cm. piece becoming 55 cm., as with No. 1. 

 Here, again, the effect of stretching is very slight. Finally, C 5 shows 

 what was found after reannealing the stretched wire. This annealing, 

 like those previously mentioned, has profoundly changed the character 

 of the representative curve ; and here the increase in range of electro- 

 motive force has been very great. The maximum electromotive force 

 indicated by C 6 is about 65 X 10 -8 volt. 



Such thermo-electric heterogeneity as these tests reveal would be 

 found in a wire made by joining together at their ends pieces of german- 

 silver wire from 1 cm. to 6 cm. long, but averaging about 2.5 cm., 

 these pieces varying through some little range of chemical composition 

 or of hardness and each piece having within itself minor differences of 

 composition or of hardness. 



Direct experiment with a german-silver and copper couple, similar 

 to those already described in diameter and condition of wire, showed 

 that, when one junction of such a couple is touched with a sharp edge of 

 ice, the temperature of the room being near 18° C, the thermo-electromo- 

 tive force developed is about 284 X 10 -6 volt, about 450 times the maxi- 

 mum indicated by the curve C 6 in Figure 8. As the room temperature 



