106 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



values of the strength of the current for ordinates, will have the 

 general form of the line U in Figure 4, though, if the core be so large 

 that the building up time at each stage is long, the diagram will be 

 much drawn out horizontally. The curve which shows the march of 

 the current when the electromotive force is applied directly to the coil 

 without the intervention of the rheostat will resemble line V in the 

 same figure. The exact forms of these curves depend, of course, upon 



SECONDS. 



PlGUliE 3. 



If / centimeters parallel to the horizontal axis represent one second, and an 

 ordinate m centimeters long one ampere, A • 10* • r/hn (where A is the area, 

 in square centimeters, of CDGF) represents the change in the magnetic flux 

 through the circuit during the interval KL. 



the magnetic state of the core at the outset, and will be very different 

 if the iron has been thoroughly demagnetized before the observation 

 is made, or if it be strongly magnetized. Figure 5, which illustrates 

 this fact for some V curves, records some measurements made upon a 

 15 K.W. transformer {R) belonging to the Lawrence Scientific School. 

 In the case represented by each line the core was previously magne- 

 tized in one direction with the full strength of the current, and the 

 circuit was then broken and left open for a few seconds. With thft 



