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VI. Repulsion and Rotation produced by Alternating Electric Currents. 
By G. T. Walker, B.A., B.Sc., Fellow of Trinity College, Cambridge. 
Communicated by Professor J. J. Thomson. 
Received November 5,—Read December 10, 1891. 
In the ‘Electrical World/ May, 1887, p. 258, or the ‘Electrical Engineer’ (New 
York), June, 1887, p. 211, “ Novel Phenomena of Alternating Currents,” may be seen 
an account of some experiments by Professor Elihu Thomson on the mechanical 
force between conductors in which alternating currents are circulating. 
In the case of a ring of metal in the presence of an electromagnet, in the coils of 
which an alternating current is passing, a force of repulsion is experienced by the 
ring, and this may be accounted for in the words of Professor Thomson as follows :— 
“ It may be stated as certainly true that were the induced currents in the closed 
conductor unaffected by any self-induction, the only phenomena exhibited would be 
alternate equal attractions and repulsions, because currents would be induced in 
opposite directions to that of the primary current when the latter current was 
changing from zero to maximum positive or negative current, so producing repulsion; 
and would be induced in the same direction when changing from maximum positive 
or negative to zero, so producing attractions.” 
This may be illustrated by fig. 1. Here the strong line represents the primary and 
Fig. 1. 
the thin line the secondary, while of the dotted line any ordinate is the product 
of the ordinates of the lines representing the intensities of the currents and, hence, 
represents the mechanical force of attraction or repulsion. 
2.7.92 
