158 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



first of these cycles are given in Table IV. The next diagram, Figure 

 5, show's the slopes of the curve corresponding to Table IV, as a 

 function of the strength of the exciting current. 



From equation (4) it will be seen that the march of current on 

 reversal of e. m. f. may be obtained. If the slope for any point of 

 the flux curve is multiplied by n 2 /l0 8 (E-ri), the result is the value of 

 dt/di, for the reversed current curve, when the constant voltage E is 

 applied to the exciting coil and reversed, where the coil consists of n 

 turns of wire with resistance r ohms. Figure 5 exhibits dt/di for E = 

 19.5, r = 15, and n = 1394. 



Figure 5. 



If now the area X, underneath the curve, Figure 7, from z = to 

 x — i, for a number of different values of i, be measured in terms of 

 the unit square of the figure; this area expresses the time required 

 for the reverse current to attain the strength i. Table V contains a 

 few values of X which were measured with a planimeter, and from 

 which the desired reverse current curve, shown in Figure 7, was 

 plotted. 



