﻿Energy of the Amperian Molecule. 



477 



so as to alternately heat and cool the iron if the effect looked 

 for existed. In this way fifteen readings were obtained 

 between every pair of reversals. It was found, however, that 

 a small inductive effect on the galvanometer- circuit occurred 

 at each reversal, and could not be quite got rid of. The 

 needle always kicked from 05 to 1 and oscillated. On the 

 other hand, it so happened that the period of oscillation of the 

 needle was almost exactly 60 seconds. We therefore divided 

 the fifteen readings into five groups of three ; and taking the 

 mean of each three we assumed it to represent the average 

 position of the needle during one minute. Five reliable 

 readings were thus obtained at intervals of 0*5, 1*5, 2*5, 3'5, 

 4*5 minutes after each reversal of the B current. Nine such 

 reversals formed a "' set." At the end of a set the connexions 

 of the galvanometer were reversed, to eliminate a possible 

 direct magnetic effect on the needle of the galvanometer, and 

 the set was repeated. Two such sets thus constituted a com- 

 plete experiment. 



In the following table the mean values of the differences 

 between the readings in the strong and in the weak field, 

 taken at 0'5, 1*5, 2'5, &c. minutes after alteration of the 

 field, are given for the four sets of two complete experi- 

 ments. The final mean values of these differences are thus 

 each dependent on 108 separate readings of the galvanometer. 



Table I. 



Time in minutes after al- ] 

 leration of field between [■ 

 the values 2717 and 2883. J 



05 



-0-64 

 -0-43 



-0-30 

 -0-38 



1-5 



-0-47 

 -0-24 



-0-33 

 -0-18 



2-5 



-0-42 

 -0-30 



-0-36 



-0-28 



35 



-0-38 

 -0-16 



-011 



+0-07 



45 



-0-33 

 -031 



-0-10 

 -0-08 



-021 



-,-, , T J Set 1 



^P*- L \Set2 





E*pt. n.{ s^ 2 ::::::::::::::: 





Final mean differences 



-0-44 



-031 



-0-34 



-015 



The effect of commutating the galvanometer upon the sign 

 of the differences has been allowed for in the table by reversing 

 the signs of Set 2 in each experiment. The — sign to every 

 difference except one means that, except in that case, the 

 cross-wires stood more to the left of zero when the pile was 

 in the strong field than when it was in the weak one. 



To determine the thermal meaning of this fact, we next 

 sent a small mcmentary current through the copper-wire coil 

 mentioned above as being upon the other end of the pile. The 

 galvanometer was connected as for Set 1. A motion of the 



