( 208 ) 



point o/ inflection — — =0. the temperature of the point of proporttonoihty 



dr r . dr 



— = — and the temperature of the minimum — = 0. It is clear that 



the situation of these points, and the correspondence 1 ) and difference 

 of their situation and of the coefficient of variability of the resist- 

 ance with the temperature in general for different metals of different 

 classes must furnish important data for the theory of electrons. 



The investigation of these points is only possible by the aid of 

 liquid hydrogen. Only in some cases — and even then the purity 

 of the metal is open to doubt — the point of inflection, whose " 

 existence was indicated by Dewar, was found high enough to be 

 ascertained without measurements for hydrogen temperatures. For 

 metals in the purest and normal state the point of proportionality lies 

 probably still below the temperatures which are to be reached with 

 liquid hydrogen. It is true that Dewar derived from his measurements 

 at two hydrogen temperatures that it was surpassed for some of 

 his metal wires. Our measurements, however, point to this that as 

 a metal is brought to a purer and more normal state, the point of 

 proportionality is found to be lower. The metal wire which came 

 nearest to this ideal state, was one of our gold wires. Even at the 

 lowest temperature the point of proportionality was not yet reached 

 for that wire. Probably Dewar's wires were further removed from 

 this ideal state. 



With the low situation which we find for the point of proportionality 

 measurements at two hydrogen temperatures do not suffice, but we 

 have made determinations at at least three hydrogen temperatures, 

 because they were necessary to determine the probable situation of the 



d*r 



point of proportionality by the aid of—. Until we have reached the pro- 

 portional point, we need not discuss the question of the minimum point. 

 In the inquiry into the properties of the metals in the ideal state 

 we must know first of all in how far the metal is in this state, 

 and else how we can derive what would be found in this state. 

 The influence of small deviations in the nature of the metals on 

 the change of the resistance with the temperature, becomes so ex- 

 ceedingly great for the hydrogen temperatures, that a special investi- 

 gation is necessary for them. Here two things have to be paid 

 attention to: to small amounts of admixture, and to differences in 



') In this respect something is to be derived from the formulae given by us in 

 this and in the preceding communications. 



