PEIRCE. — BEHAVIOR OF THE CORE OF AN ELECTROMAGNET. 139 



nate representing any given value of the current shows, in twentieths of 

 a second, the time required, under the given conditions, after the cir- 

 cuit is closed for the current to attain this value. It is easy to deter- 

 mine a series of such areas with the help of a good planimeter, and the 

 full curve of Figure 32 actually represents the growth of the current in 

 the case mentioned according to my measurements of the large dia- 

 gram of which Fig. 32 is a very much reduced copy : for this curve the 

 horizontal unit is one tenth of a second and the vertical unit is one 

 fifth of an ampere. This curve has the general form of most of the 



riGORE 32. 



The ordinates of the boundary of the shaded area represent 2 (dt/di) for 

 E = 2%, r — 20. P shows the tlieoretical form of the corresponding current 

 curve. 



current curves which one obtains with a transformer the core of which 

 is at the outset neutral, but it is evident that in any case where the 

 final value of the current is small enough the asymptote will be moved 

 so far to the left that the integrand curve will rise continually from 

 the beginning, without the maximum and minimum values, and the 

 current curve will have the everywhere convex shape that we find in 

 practice when we cause the current to grow by short steps in the man- 

 ner indicated by the curve U in Figure 4. 



Figure 33 shows building-up current curves (^4, b, c) for E= 26, 

 and r = 20, 40, and 60, respectively. The dotted curves B and C are 

 copies of b and c with ordinates so magnified that the curves have the 



