ACOUSTICS AND GRAVITATION. 



57 



and 84. They may reenforce or annul each other. I fancy that the first 

 displacement is of the form 83, which on subsidence immediately breaks 

 up into harmonics of the form 84. 



In table i (which was obtained primarily from the waves, but also 

 holds for the lines) group-periods from i second to 10 seconds or more 

 were observed. The periods change continuously in the lapse of time, as 

 well as (discontinuously) in different instruments. Exceptionally long 

 group-periods (20 seconds) were found in- an old unipolar telephone. 



TABLE i. 



Period G of recurrence of group waves or lines at any part of the field. Objective, T=o. 32 

 sec. Inductor, r= 0.08 sec. andr =0.01 sec. Resistance i,ooo+R. 



* 3 groups in field, t 6 groups in field. ** Near coincidence. 



The group-periods 6", here found, are of secondary interest and follow 

 from the fact that the objective (T) and induction (r) periods are not 

 quite in the ratio n of two small whole numbers. Thus if T = r(N+i/x), 

 the group period would be G = xT. But as the mercury interrupter is 

 damped, x will be variable under incidental conditions, so that G varies in 

 the lapse of time. 



