A Pendulum is readily made with a musket ball, and a piece of silk. The length of a Pendulum is measured from the centre of the ball to the end of the loop on which it swings.
| { 1 Seconds | 39·14 | inches | |
| Length of Pendulums to vibrate | { ½ Seconds | 9·8 | ” |
| { ¼ Seconds | 2·45 | ” |
To find the length of a pendulum to make a given number of vibrations.
Rule.—As the square of the given number of vibrations is to the square of 60, so is the length of the standard (39·14 length for one second) to the length sought.
Or, multiply 39·14 by the square of the time required for the Pendulum to vibrate—viz., by the square of ½ = ¼, for ½ second; and by the square of 2 = 4 for two seconds.
To find the number of vibrations, the length of pendulum being given.
Rule.—Multiply 60 seconds by the square root of 39·14, divided by the length of the given pendulum.
Or say, As the given length is to the standard length, so is the square of 60 (its vibrations per minute) to the square of the number required.
PORTFIRES.