380 POPULAR LECTURES AND ADDRESSES. 



distance is then ;i little farther increased, the watch 

 will often stop : if then a slight impulse round the 

 vertical axis is given to it to start it, it will com- 

 mence vibrating according to the first fundamental 



o o 



mode, with a largely losing rate. The other corre- 

 sponding result is obtained by commencing with 

 the points of support too far asunder for the 

 critical arrangement and bringing them gradually 

 together. 



Without exciting independent vibrations of the 

 chronometer or watch as a whole, and counting 

 them, it is easy to perceive whether the circum- 

 stances approach the critical condition, by apply- 

 ing the hand to steady the watch, and then ob- 

 serving the phenomena presented when it is left 

 to itself. If the upper points of support arc cither 

 much too wide apart or much too close together 

 for the critical arrangement, the watch-case will 

 not take any regular harmonic vibration, but will 

 make a slight (perhaps scarcely perceptible) jump 

 once every semi-period, or once every period of the 

 balance-wheel, according to the character of the 

 escapement. But if the upper points of support 



