1902.] The Dissipation of Energy by Electric Currents. 361 



Experiment. 



The rate at which energy is being dissipated by electric currents, 

 induced in the cylinder, has been obtained in the following manner.. 

 The horizontal radius in fig. 2 has been divided into ten equal parts, 

 and the cylinder is supposed to be cut by vertical planes 0, a, /?, y . . .. 

 passing through the points of intersection, the plane containing the 

 axis of the cylinder. The circles 1, 2', 4 show the paths traversed by 

 the longitudinal sides of the exploring coils during rotation of the 

 cylinder. In the plane a, let 9, 6 V 6 2 be the angles which the plane of 

 the exploring coils makes with the horizontal when the coils 1, 2', 4 

 have respectively one of their longitudinal sides in the plane a. Three 

 paths of induced electric currents in the plane oc are now assumed. 

 No. 1 is taken to be the rectangle having its two sides, which are 

 parallel to the longitudinal axis, equal to and coinciding with the sides 

 of the coil, and its two other sides the straight lines necessary to- 

 complete the rectangle in the plane a. Similarly with regard to coils. 

 2' and 4. Each path is assumed to have a cross-sectional area of 

 1 sq. cm. throughout its longitudinal length, and this area multiplied 

 by the sine of the angle which the plane of the coil makes with the 

 horizontal, throughout the remaining portion of its length. The 

 electric resistance of each path has been calculated in ohms. Fig. 3 : 



^ O 40 60 120 160 200 240 280 320 . 560 400' 



Time in Seconds. 



Fig. 3. 



gives a set of curves obtained with 360 seconds periodic time, and 

 maximum average induction 19,900 C.G.S. units per square centimetre 

 for No. 4 coil. The curves give the electromotive forces in volts per 

 turn for coils 1, 2', and 4 respectively. The electromotive force of 

 No. 1 coil at angles 6 on each side of the point 0, where the curve 



