idi 



The Pendulum. 



The pendulum as our time marker, and its importance in 

 relation to timepieces, is sufficient excuse for making some simple 

 lessons with it as the subject. 



Suspend a small weight from a convenient place by a strong 

 thread, thirty-nine inches long, the length counted from the 

 point where the thread is attached to the qenter of the weight. 

 Have the pupils determine how many times in a minute this 

 pendulum vibrates. If it does not vibrate sixty times in a 

 minute, correct the length till this is its rate. Keep this pendu- 

 lum as the time keeper for the succeeding experiments. 



Have them make other pendulums of the same length, some 

 ■with much heavier weights and some with lighter weights, and" 

 determine if there are differences in the rate. 



Have the pupils constract a pendulum long enough to vibrate 

 once in two seconds, and one short enough to vibrate twice in a 

 second. Let them measure and compare these with the seconds 

 pendulum. Do the same for pendulums vibrating once in three 

 seconds and three times in a second. A liigh ceiling, a window 

 or a tree will give an opportunity for hanging a long pendulum. 



The use of the pendulum as a time instrument can now be 

 explained. The importance of accurate and uniform time in 

 business and in railroad and otlier travel, etc., may be seen. 

 On ]Mt. Hamilton <ivery day at noon a jjendulum in a fine clock 

 stationed there is connected by electric wires with most Western 

 Union Telegraph Offices on the Pacific Coast. In any one of 

 these offices at noon any one can hear the telegraph instrument 

 beating in unison with the pendulum on Mt. Hamilton. Thus 

 all timepieces might be kept in accurate accord with this one. 



In other parts of the United States there are centers from whicli 



