220 PROCEEDINGS OP THE AMERICAN ACADEMY. 



iron wire in an oscillating circuit might be eciuivaleiit to a copper 

 wire of greater length, owing to the higher self-induction of iron. He 

 based his opinion upon the known fact that for slowly oscillating cur- 

 rents the self-induction of iron is eight or ten times greater than that 

 of a copper wire of the same dimensions. 



He says : " I therefore expected that short iron wires would pro- 

 duce equilibrium with longer copper wires. This expectation was 

 not confirmed ; the branches remained in equilibrium when the 

 copper wire was replaced by an iron wire of equal length. If the 

 theory of the observations here given is correct, this can only mean 

 that the magnetism of iron is quite unable to follow oscillations so 

 rapid as those with which we are here concerned, and that it there- 

 fore is without effect." * 



The rate of oscillation here used was approximately one hundred 

 million per second, and the diameter of the wires was two millimeters. 



In the same paper, he gives another experiment of like tenor. 

 He brought the primary and secondary into resonance, and then in 

 one instance he surrounded one side of the rectangular secondary by 

 an iron tube, and in a second instance he replaced this side by an 

 iron Arire of the same diameter as the copper wire. In each case he 

 found the secondary still in resonance with the primary, and was con- 

 firmed in his former conclusion. The secondary employed was a 

 rectangle 180 cm. long and 75 cm. wide, and only a length of 75 cm. 

 out of the total length of 510 cm. was changed. The diameter of the 

 wires was 2 mm., and the spark micrometer was used to test for 

 resonance. 



In a later paper t on the " Finite Velocity of Electromagnetic 

 Actions," he compares the rate of propagation along copper wires 

 of various diameters, and also the rate of propagation along copper 

 wires with that along iron wires. 



He says : " If we replace tlie copper wire previously used (diam. 

 1 mm.) by a thicker or a thinner copper wire, or by a wire of an- 

 other metal, the nodal points are found to remain in the same posi- 

 tions. Thus the rate of propagation in all such wires is the same, 

 and we are justified in speaking of it as a definite velocity. Even 

 iron wires are no exceptions to this general rule ; hence the magnetic 

 properties of the iron are not called into play by such rapid disturb- 

 ances." t (100,000,000 reversals per second.) 



* Electric Waves, p. 36. J Electric Waves, p. 113. 



t Poggendorff, Annalen, XXXIV. 551. 1888. 



