﻿434 Prof. Lyle and Mr. Baldwin on Propagation of 



dynamometer measured the phase-difference of the currents 

 induced in two short solenoids placed at various distances 

 apart on the rod. This was equal to the phase-differenco of 

 the two resultant fluxes at the points, provided the time- 

 constants of the circuits of the two solenoids were negligible. 



The "velocity" deduced varied from 232,300 cm./sec. 

 for 64 steel wires each 1*8 mm. diam., to 4410 cm./sec. for 

 a steel rod 12 mm. diam., a result which indicates the great 

 influence of eddy currents. He found that the "velocity " 

 was not directly influenced by the character of the iron of 

 the rod 



The amplitude ¥ x of the resultant flux at different points 

 he found to be given by the formula 



F, = F «-^, 



where X is to a first approximation a constant depending on 

 the material of the bar, but independent of the area of its 

 cross-section. 



The values he found for X when a?, the distance from the 

 centre of the magnetizing solenoid, is in centimetres, were 



•1027, -1017, -1007 for soft iron, 

 •148 for hard iron, 



•1451, -1616, -1637 for steel. 



One frequency only was used. 



Trouton * attempted to obtain stationary flux-waves by the 

 interference of two trains of waves travelling in opposite 

 directions round a ring of iron wires, the two trains being- 

 produced by an alternating current of known frequency 

 circulating in a short solenoid looped on the ring. He 

 concluded, however, that the effects which he observed 

 were not due to interference but to some peculiarity of 

 the ring. 



Zenneck f, assuming the permeability fi and the leakage 

 coefficient \= — d¥/¥dx constants, where F is the flux at cc, 

 obtained from theory expressions for the flux- waves at 

 different points along iron cylinders in terms of the initial 

 flux where #=0, and to verify his theoretical conclusions 

 used a Braun tube to determine the relative amplitudes and 

 phases of the flux oscillations at any two points. 



For thick wires (some millimetres in diameter) he found 

 that the " velocity " and the leakage coefficient X increased 

 with frequency, while for wires less than 1 mm. in diam. 



* F. T. Trouton, ' Nature,' vol. xlv. p. 42 (1891). 

 t J. Zenneck, Ann. der Phys. vol. ix. p. 497 (1902), and vol. x. p. 845 

 (1903). 



