PEIRCE, — CHANGES IN INDUCTANCES OF ELECTRIC CIRCUITS. 



579 



mate value of the intensity (/) of magnetization depends very much 

 upon the manner in which the given exciting current is made to attain 

 its final strength. 



The experiments of Riicker ^ upon small solid iron toroids seem to 

 show that at moderate excitations there may be a difference of from 

 6 per cent to as much as 30 per cent in the final flux density due to 

 a given current, according as the current is applied suddenly or by 



Figure 35. 



many short steps, and, unlike some other observers, he found a very real 

 difference (7} — T^), though a smaller one than in the case of the solid 

 metal, for a toroid with core of fine iron wire (Blumendraht). In the 

 case of a large electromagnet with solid, closed core, weighing alto- 

 gether more than 1500 kilograms, Babbitt found, by a very ingenious 

 method of procedure, a difference of 17.4 per cent between the final 

 flux density in the iron caused by the sudden application of a given 

 current, and the growth from nothing of the same current in 56 steps. 

 The cross-section of this massive core is more than 450 square centi- 

 meters in its narrowest part, and eddy currents are so much in evidence 

 that quite two minutes are required for a " suddenly applied " current 

 to attain its steady value. 



Babbitt also carried out a long series of very accurate measurements 

 extended over several months, upon two small toroids of fine, carefully 

 annealed iron wire, and upon a toroid weighing more than 40 kilograms 

 made of very well softened iron wire about half a millimeter in diam- 

 eter. His results show conclusively that if one of these softened and 

 demagnetized cores has been first put through the cycle due to a 

 given excitation a considerable number of times to obliterate the effects 



'' Babbitt, These Proceedings, 46, 1911; Riicker, Inaugural Dissertation, 

 Halle- Wittenberg, 1905. 



