602 
Transactions of the Uoyal Society of South Africa. 
is now determined by recording the time 20, 40, 60, 80, 100, etc., vibrations. 
Finally tv = tv — seconds. 
M 
This also enables students to determine the variation of t when the 
length of the vibrator is increased or decreased. (Tjj> for the pendulum used 
in the South African College Laboratory is 0*8 sees. Minimum for the 
above pendulum is 0*68 sees.) 
Applied Mathematics Laboratory, 
South African College, Cape Town. 
