156 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



about one third of a millimeter thick. The exciting coil consists of 

 1394 turns of well insulated copper wire. 



Figure 3. The ordinates of the boundary of the shaded area represent 

 10 4 o,(:T) for E = 10, r = 1, and n = 100. The curve OPQ, shows the 

 theoretical form of the corresponding current curve. 



TABLE III. 



