256 



On Alternating Electric Currents. 



[Dec. 10, 



FIG. 1. 



ordinate represents the product of the ordinates of the other lines, 

 and hence represents the mechanical force of attraction or repulsion. 



In the case of self-induction causing a lag, shift, or retardation of 

 phase of the secondary current, there is a repulsion due to the sum- 

 inative effects of strong opposite currents for a lengthened period 

 against an attraction due to the summative effects of weak currents 

 of the same direction during a shortened period, the resultant effect 

 being a greatly- preponderating repulsion. 



The diagram for this is fig. *2. Professor Thomson has shown, 

 experimentally, that two circular coils, whose planes are perpendicular 



FIG. 2. 



to the line joining their centres, repel one another when an alternating 

 current traverses one of them, and that if they be placed with their 

 centres coincident and. planes making an acute angle, there will be a 

 couple tending to increase that angle. 



As these results have been used as means of measuring alternating 



