PEIRCE. — ESTABLISHMENT OF CURRENT IN COIL. 



155 



bounds the shaded area was plotted on a large scale, one vertical unit 

 corresponding to 10 4 ft ( T) and one horizontal unit to a hundred T, 

 and the area X from T — 0, to T = T , for a number of different 

 values of T was measured with the aid of a good planimeter in terms of 

 the unit square of the figure. A few values of the areas X are shown 

 in Table III. These areas divided by a hundred express the time in 

 seconds to which T corresponds. The resultant curve, P Q, Figure 

 3, is the desired curve for growth of the current. 



Figure 2. Magnetization curve, OBA, for the electromagnet J which at 

 the outset is in a neutral state. Each horizontal division is 100 Ampere-turns 

 and each vertical division is 100,000 Maxwells. The ordinates of the dotted 

 curve represent the slopes of the magnetization curve, with each vertical 



division equal to 200 -. . - • 



M Ampere-turn 



Further Facts Regarding Electromagnet J. — We may add to 



the foregoing discussion, of the characteristics of the electromagnet J 

 the results of a series of hysteresis cycles obtained some years ago. 

 An outline of this magnet is shown in Figure 1. It weighs about 

 300 kilograms: the core has a square cross-section of 156 square 

 centimeters area, and was built from varnished sheets of soft iron 



