1863.] 653 



resistances at and 100C. The formula, however, expresses the 

 fact that the absolute difference between and 100 C. in the 

 resistance of an alloy is equal to the absolute difference between 

 and 100 in the calculated resistance of the alloy. 

 Formula 2 may also be written 



r ioo r 100 ~ V ~~ r o* 

 which, if correct, leads to the expression 



that is, the absolute difference between the observed and calculated 

 resistances of an alloy at any temperature equals the absolute 

 difference between the observed and calculated resistances at C. ; 

 or, in other words, 



r r' t =& constant ........ (3) 



After giving various examples to show the correctness of the above, 

 we prove that from the expression 



r f r' t =& constant (3) 



we may deduce the formula for the correction of resistance or con- 

 ducting-power for temperature of an alloy as soon as we know its 

 composition and its resistance at any temperature ; for, as r' 

 r' 0<5 , and r' t may be calculated with the help of the formula given 

 for the correction of conducting-power for temperature for most of 

 the pure metals, if the constant rtr't be determined, then 



%o =r 'ioo+ constant > 

 r f =r' t + constant, 



V =7 *'o + C0nstant 5 



and from these terms the formula for the correction of resistance or 

 conducting-power for temperature may be calculated, which in most 

 cases will be found very near the truth. 



In the second part we show by a few experiments that most alloys 

 of three metals will probably be governed by the same law with 

 respect to the influence of temperature on their conducting-power as 

 alloys of two metals. 



In the third part we deduce 



P:P'::M JOOO :M' 1000 ....... (4) 



(where P and P' represent the observed and calculated percentage 



