PEIRCE. — CHANGES IN INDUCTANCES OF ELECTRIC CIRCUITS. 583 



rheostat of resistance a* ; when the circuit was suddenly closed the 

 current grew to the tinal value corresponding to this resistance by the 

 curve OHD or MNC, as the case might be. When at the proper time 

 the rheostat resistance was suddenly shunted out of the circuit, the 

 current rose to the value OA by the curve DXU or the curve CZB. 

 If X had been shunted out at the start the current curve had the shape 

 accurately represented, when the starting point had been shifted j ust 



> 



.1— - 

 s 



N SECONDS. 



Figure 40. The current in one coil of the toroid DN which is in series 

 with a battery follows the line OKLZ or the line NSQ, according as another 

 coil on the same core is open or closed. When this last coil which has been 

 closed is suddenly opened while the battery current is rising, this changes 

 abruptly and follows exactly the upper part of the Una OKLZ. 



far enough to the right, by PDXU or QCZB. It was not possible to 

 detect any difference between the curves DXU and CZB and the upper 

 parts of the curves obtained with iv all the time out of circuit. This 

 figure was drawn by superposing several oscillograms, for it is very diffi- 

 cult after one curve has been taken upon the sensitized paper carried by 

 the revolving drum to start another curve some time afterwards at such 

 a point that it shall coincide with the upper part of the first one. This 

 feat has, however, just been accomplished in another case by Mr. John 

 Coulson, who made the records shown in Figures A and B, and has 

 helped me in most of the experimental work of this paper. Figure 38, 

 drawn from another photograph, shows the two curves which coincide 

 in A. The oscillograph was in circuit with the coil of a large toroid of 

 about 41 centimeters in diameter, the core of which is made of soft, 

 varnished iron wire about half a millimeter in diameter. Each record 

 shows a current curve obtained by applying the electromotive force 

 directly to the circuit, and the second part of a current diagram when 

 an extra resistance, at first in the circuit, was suddenly shunted out. 



