HALL. — THERMAL AND ELECTRICAL EFFECTS IN SOFT IRON. 611 



efficient of thermal conductivity. In what immediately follows the 

 subscript h will refer to the high temperature cross-section, which was 

 at one time a and another time e, while the subscript / will refer to the 

 low temperature section, which was at first e and later a. 



We must now take account of the fact that a part of the excess of 

 gh over gi is due to the lateral escape of heat from the main bars be- 

 tween the h and the / cross-sections. From the data, given in the last 

 column of the table above a curve is plotted from which may be found 

 the difference of temperature of the main bars at any section between 



h and /. Then, with the use of the data already given concerning 

 lateral flows, the amount of heat escaping laterally from each one of 

 the 16 linear centimeters of each bar between the k and / cross-sec- 

 tions is found. The total lateral outflow as thus found, from each bar, 

 is 0.0369, let us say 0.037, calorie per second. Taking first a tenta- 

 tive value of the thermal conductivity at f^, 203.7°, and replacing this 

 value later by one obtained by use of the data we are now dealing 

 with, proceeding, in other words, by a method of approximation, we 

 find that the gradient of temperature at t^ needed to carry through the 

 k cross-section this amount of heat is 0.346, or 0.35. This we must 

 subtract from gu in order to find just how much of the latter gradient 

 is necessary to transmit the amount of heat that passes through the 

 / cross- section. But before this subtraction is made we raise the value 

 of gt, from 5.90-f-, to 5.91, in order to make due allowance for the 

 fact of expansion in the main bars. We thus get 5.91—0.35 = 5.56 

 as the value of g^, which is to be compared with 5.26, the value 

 of gi. Accordingly, if k stands for thermal conductivity, and if / 



