HOLMAN. — THERMO-ELECTRIC FORMULA. 193 



Investigations on Light and Heat, made and published wholly oe in part with 

 Appeoprution prom the Rumfoed Fund. 



X. 



CONTRIBUTIONS FROM THE PHYSICAL LABORATORY OF THE 

 MASSACHUSETTS INSTITUTE OF TECHNOLOGY. 



XLIV. —THERMO-ELECTRIC INTERPOLATION 

 FORMULA. 



By Silas W. Holman. 



Presented November 13, 1895. 



In this paper are collected the several well known types of for- 

 mulae for expressing the thermal electro-motive force of a couple as a 

 function of the temperature of its junctions. Two new formuke are 

 also proposed. All then are tested against the most reliable experi- 

 mental data upon the subject, and their relative merits discussed. 



The Existing Formula. 



Consider a simple closed electric circuit composed of two different 

 metals, each homogeneous in matter and temper, the metals beino- in 

 contact at two points. For simplicity, assume the metals to be in 

 the form of wires joined at their ends. Let one junction be at a tem- 

 perature of /i°, the other of c°, on the ordinary centigrade scale. Let 

 2^e be employed as a suggestive symbol to denote the resultant elec- 

 tro-motive force in the circuit, induction being excluded from consid- 

 eration. Then 2*e is a function of h and c which involves constants 

 dependent upon the nature of the metals, and which may be repre- 

 sented by 



The discovery of the natural expression for / (h, c) is not only of 

 scientific importance, but is urgently needed in the development of 

 the art of pyroraetry. At present even a satisfactory empirical 

 formula for interpolation is lacking, the best still being probably that 

 of Avenarius and Tait. 



VOL. XXXI. {y. s. xxiiT.) 13 



