Vibrations : Both Masses and Periods Unequal. 45 



funnels the masses were in the ratio 19 : 1 and if: the lengths 

 were really 11: 16 (instead of 20:1 and 12:16 respec- 

 tively), the minimum value of p/q as calculated would be 

 in sensible agreement with that experimentally observed and 

 would occur for practically the same coupling as that in 

 actual use. Table IV. is calculated from the above data 

 and is found to agree fairly well with the observations. 



Table IV.— Masses 19 : 1, Lengths 11 : 16. 



Coupling 



=y- 



Bridle Droop 



— Li 



Frequency 

 Ratio 

 p:q. 



Short Pendulum Length. 



Per cent. 





 1-724 0-1 

 3301 0-2 

 4-758 0-3 

 6112 0-4 

 7-379 0-5 



1-21 

 1*155 



1-115 

 L086 

 1-072 

 1-076 



Figs. 21 and 22 show traces with 32 per cent, coupling, 

 which gives a ratio of p/q almost equal to 2 : 1 or a tone and 

 its octave. In fig. 21 the conditions of starting masked the 

 compound character of the vibrations, but this is clearly 

 revealed in fig. 22. 



Quenched Spark. — Fig. 52, p. 714 of Professor J. A. 

 Fleming's 'Principles of Electric Wave Telegraphy and 

 Telephony/ 2nd ed., shows " the electrical beats produced 

 in the primary and secondary circuits when a sustained 

 primary spark is used and the single periodic oscillations 

 in the secondary circuit when the Quenched Spark is 

 employed.'" The mechanical analogue of beats was obtained 

 on the double-cord pendulum (see figs. 1 and 2, Plate V., 

 Phil. Mag. October 1917). The damping was not so marked 

 as in Prof. Fleming's case, because our damping factor was 

 almost negligible. 



To produce the effect of the quenched spark the masses of 

 the bobs were equal and also their separate frequencies ; 

 further their coupling was 10 percent. One of the bobs 

 was drawn aside and the other allowed to hang in its 

 slightly displaced position. The bob was then freed and 

 its oscillations were quickly diminished by the transference 

 of its energy to the other pendulum, which in about six 

 vibrations had attained an amplitude equal to that with 

 which the other pendulum started. The first pendulum had;, 



