218 Prof. S. P. Thompson on a Mode of 



Fig. 1. 



Reference to figure 2 will elucidate the phase relations. 

 In this figure the upper curve relates to fork A and the lower 

 to fork B. Positive values of the ordinates relate to positive 

 displacements in the sense of approach to the electromagnet. 



Fig. 2. 



When A has moved through J of its cycle of movements, 

 and the displacement is a negative maximum a u it makes 

 contact for B's electromagnet, which gives a momentary im- 



