Forced Vibrations Experimentally Illustrated. 173 



III. Illustrative Experiments. 



In fig. 1 is shown an experimental arrangement that was 

 found convenient when exact quantitative work was not the 

 aim but rather a lecture demonstration of the general features 

 involved was required. 



Kff. 1. 



LP 



^H 



Forced Vibration Apparatus with Differing Forces. 



The tightly stretched cord AB is drawn down to a peak 

 at C by the weight of the driving pendulum CD about 

 60 cm. long with bob of iron about 6 cm. diameter. The 

 responding systems are pendulums of graduated lengths and 

 with very light bobs so that their free vibrations are quickly 

 damped. These pendulums should be placed fairly near to 

 the driver and the point A kept far from them, so that their 

 points of suspension all have approximately the same motion 

 Irom the vibrations of the heavy bob D. The bobs of these 

 responding pendulums may be — 



(a) of solid cork about 2*3 cm. long, 1*2 cm. diameter, and 



0*4 gm. mass. 



(b) of hollow paper cones, semi-vertical angle 20°, of mass 



0-2 gm. 



(c) of paper cones, semi-vertical angle 45°, of mass 0'3 gm. 



(d) of blown-glass spheres in imitation of pearls, diameter 



6 mm. 

 The attachments to the cord AC may be made by passing the 

 cotton suspension through it with a needle and leaving 

 the end free. They are then sufficiently held by friction and 



