by Induction-currents. 259 



principal current induced, 177*26. The difference of these two 

 last numbers, or 11 -58, represents the lessened disengagement 

 of heat by the principal current when the latter induces a cur- 

 rent in another conducting wire. But the numbers 11*58 and 

 28-75 (obtained by the induced current) only represent the 

 disengagement of heat in the platinum wire, and give no account 

 of the disengagement in the other parts of the two circuits. 

 Hence by comparing these two numbers we cannot know whether 

 an induction of this kind really produces heat. But for the 

 same current the disengagement of heat is proportional to the 

 resistance of the circuit, and that not merely for metallic con- 

 ductors, but also for liquids. Hence, if we multiply 28-75 by 

 the resistance of the induced circuit, and 11'58 by the resist- 

 ance of the principal current, the first of these products will 

 represent the total heat disengaged in the induced current, 

 and the second the difference in the heat developed in the prin- 

 cipal circuit when the latter induces and when it does not. If 

 M is the resistance of the principal current, we find by experi- 

 ment that the resistance of the induced current is 04405 M. 

 These two quantities of heat may therefore be represented by 

 28-75 x 0-4405 M, and 11-58 M. The first gives 12*66 M, and 

 may be regarded as being quite equal to the second; from 

 which it follows that this kind of induction does not give rise to 

 a production of heat. 



Two other series of observations led to the same result; in the 

 first, the heat disengaged by the induced current was 12*36 M, 

 and the difference of the heat disengaged by the principal cur- 

 rent during induction and without induction was 13*21 M. In 

 the second series 9*52 M was obtained for the first arrangement, 

 and 9*63 M for the second. These results prove that when in- 

 duced currents are produced in a closed circuit by opening and 

 closing the principal inducing circuit, the induction gives rise neither 

 to an increase nor to a diminution of heat. The quantity of heat 

 developed by the induced current is equal to the lessened produc- 

 tion of heat which takes place in the principal current owing to 

 this induction. 



IV. 



In order, by bringing a secondary circuit near an inducing 

 current or by removing it away, to obtain an induced current 

 so strong that the heat which it disengaged could be measured, 

 a special apparatus was constructed. It consisted of a fixed coil 

 of copper wire covered by silk, the interior diameter of which 

 was 200 millims. In the inside of this was another, also covered 

 with silk, which by suitable mechanism could be made to rotate 

 rapidly about an axis in the plane of the first coil. The ends of 



