530 



PROCEEDINGS OP THE AMERICAN ACADEMY. 



inflection, and had become everywhere convex upward. With a voltage 

 of only 6 and the low resistance primary of the transformer as exciting 

 coil, the building-up time was an extremely short fraction of a second, 

 and the building-up curve looked like a very straight, and nearly vertical, 

 sign of integration. 



If a number of equal coils of wire of a given size, each of resistance r, 

 be wound together uniformly about a wooden ring so as to have equal 

 self-inductances, and if a storage battery of small internal resistance be 

 made to send a current through (say) n of the coils in series, the induc- 

 tance of the circuit will be nearly proportional to ri 2 and the time-constant 



Figure 13. 



which is independent of the applied electromotive force and therefore 

 of the current, will be nearly proportional to n. If the core of the ring 

 be made of iron, the problem will, of course, be complicated in many 

 ways, but in this connection Figure 12 is interesting; curves 3, 2, and 1 

 show the manner of growth of a current in coils of about 85, 170, and 

 340 turns about the core of the transformer just mentioned, in terms 

 of its final value. The electromotive force was in reality the same 

 for all three cases, and the currents were 6 amperes, 3 amperes, and 

 1.5 amperes. 



