698 Mr. S. C. Laws on the Change of Resistance of Metals 



From his experiments, Patterson"*, using the same for- 

 mula, found X 



for cadmium = 4*1 x 10 " 6 

 and for zinc = 2*3 x 10~ ? . 



The difference in these numbers is a consequence rather of 

 the different values assumed for v and ejm than of any 



OT 



differences in the values found for — . 



r 



For, working with fields varying between 17,000 and 



1 Br 

 29,000 c.G.s. units, Patterson found for cadmium ^^ — = 



28*2 X 10 " ]3 , while my experiments for fields between 8000 

 and 13,000 give 26'5 x 10 13 : in the case of zinc both sets of 

 experiments give the value 8*7 X 10~ 13 for this quantity f. 



The mean of the values obtained by Grunmach $ with 

 fields varying from 8000 to 16,000 C.G.s. units are 27*3 and 

 11*0 respectively. 



1 Sr 



H 



r 



The experiments with graphite indicate that here 



varies approximately inversely as the absolute temperature, 

 so that the same formula for this quantity shows that \ is 

 approximately independent of temperature. The same result 

 is again arrived at by considering the effect of temperature 

 on resistance ; for, since the resistance is practically inde- 

 pendent of temperature, the equation 



1 1 e 2 X 

 - = 5 n — - 

 p Z m v 



makes X independent of temperature, provided that here, as 

 in the case of metals, n is proportional to *s/6, that is, if the 

 specific heat of electricity is not abnormally large in the case 

 of graphite §. 



Actually, the resistance of graphite decreases somewhat 

 with rise of temperature so that X should increase slightly at 

 higher temperatures. The experiments here described point 

 to the same conclusion, for these indicate that the change in 



— is rather less than is required by the inverse first power 



* Patterson, he. cit. p. 655. 



t By an obvious slip the values given by Patterson are 282 and 87 

 respectively, he. cit. p. 652. 



X Grunmach, he, cit. p. 170, 



§ This point has been recently verified in some experiments, as yet 

 unpublished. 



