43.0 



Dr. S. Bidwell. On the Changes of [Apr. 11, 



Nickel. — Since the effect of magnetisation upon a nickel rod or wire 

 is to shorten it, while, if the " correction " be admissible, iron is always 

 lengthened by magnetisation, it was to be expected from analogy that 

 the effects upon thermoelectric power would be opposite in iron and 

 in nickel. In iron the thermoelectric power of the magnetised with 

 respect to the unmagnetised metal is positive ; in nickel, therefore, it 

 should be negative. This view, though in accordance with what is 

 generally accepted as the fact, is, however, at variance with the results 

 of all my experiments. 



Five different samples of nickel were used, curves for four of these 

 (L), (M), (N), (0), being given in fig. 7. 















i 



200 









(N) 



(0) 





cted cut 



150 



IOO 











(m) 





Corn 



50 





>o 4< 



>o 6< 



)0 8< 



fO IG 



OO 12 



oo 14 

 Magnetic 



00 16 



Field. 









(I) 





























(h> 









i50'E d 

 100=0 



5°&§ 



Fi&. 7. — Curves (L) and. (M) show changes of thermoelectric force for pure nickel ; 

 (N") and (O) the same for impure nickel. Curves (£) and. (I) give changes of 

 length, and correspond to (L) and (O) ; (m) shows mechanical compression ; 

 the dotted curve (n) is (k) inverted and plotted to the scale of ordinates 

 in the right-hand margin. 



Curve (L) relates to a piece of thick wire 2*95 mm. in diameter, 

 bought of Messrs. Johnson and Matthey as pure. The retraction 

 curve* for another piece of the same wire is that marked (k). 



Curve (M) was given by a wire 0*65 mm. in diameter; this was also 

 supplied by Messrs. Johnson and Matthey, and described as being 

 " as pure as conveniently possible." 



Curve (N) shows the result of an experiment with a sample of wire 

 supplied by Messrs. J. J. Griffin and Sons, which did not purport to be 

 pure and probably contains a considerable proportion of iron. 



* ' Phil. Trans.,' vol. 179, p. 228, fig. 6, 1888. 



