Variably Coupled Vibrations. 



Length of lath pendulum = 100 ^ cms. 



Length of gravity pendulum = 68*5 cms 



303 



Fio-s. 1-32 (Pis. VI. & VII.) are photographic repro- 

 ductions of traces obtained for the motion of the lower bob 

 under various conditions. 



Figs. 1-16 (PL VI.) are traces obtained when the upper 

 bob was struck, the coupling ranging from 5 per cent, 

 to 65 per cent. The first figures, i. e. those for the smaller 

 couplings, show very well the phenomenon of beats and the 

 slow surging to and fro of the energy of the bobs. The 

 series shows in a marked manner the effect of a progressive 

 tio"htenino- of the coupling until, in fig. 14, the case of the 

 note and its octave (frequencies p : q = 2 : 1) has been reached 

 very nearly. It will be seen that a coupling intermediate 

 between that of fig. 14 (58 per cent ) and that of fig. 1 5 

 (62 per cent.) would give the ratio p:q = 2:l. By com- 

 parison with the table in Section III., it will be seen that 



