324 St. John — Wave lengths of Electricity on Iron Wires. 



For the iron wire circuit (diameter 01186 cm ) £=1258; 

 H = 430 ; R = 1-6T x 10 9 ; p = 36 X 10 7 whence R' = 403 X 10 9 . 

 L=34xl0 3 . 



The damping factor becomes e~ 6x 10 t approximately. 



The time required for the amplitude to fall to one half its 

 maximum value is t = 0-000,000,115 sec. On the basis of 

 115 xlO 6 alternations per second, the number of complete oscil- 

 lations during this time is 6*5. A like calculation for the cor- 

 responding copper circuit gives about 60 times as many. 



The following table shows the results when copper circuits 

 are compared in which wires of different diameters are used. 



3d Maximum. 

 Copper wire (diameter 0- 1201 cm ) 562-5 om 

 " " " 0- 0884 ) 553-5 



" " " 0-07836 ) 552-0 



" " " 0-03915 ) 534-0 



The half wave lengths calculated from this maximum are : 

 Copper (0-0120l cm ) 255'8 cm 

 (0- 0884 ) 252-2 

 " (0-07836 ) 251-6 

 " (0-03915 ) 244-8 



These are found bv dividing the total length of the circuit 

 by 5. 



535X2 = 1070 length of sides. 



30 " closed end. 



62X2= 124 equivalent of end capacities. 



1224 

 1224-h5 = 244-8 cm =half wave length. 



The range of wires suitable for the study of the phenomena 

 is rather limited. If the wires have a greater diameter than 

 l mm the difference between iron and copper is slight; while 

 with wires less than - 5 mm in diameter the damping is so great 

 that long wires cannot be used, and the advantage cannot be 

 taken of the cumulative effect. 



I wish to express my great obligations to Professor John 

 Trowbridge for the encouragement and suggestions that I have 

 received from him. 



Conclusions. 



1. The self-induction of iron circuits is greater than that of 

 similar copper circuits under very rapid electric oscillations 

 (115 xlO 6 reversals per second). The change in self-induction 

 varies from 34 to 4-3 per cent in the present investigation and 

 increases with decreasing diameters. 



