Rigidity produced by Centrifugal Force. 89 



the chain to the groove in the pulley ; also an arrangement for 

 fixing an india-rubber pulley in a position to press the chain 

 against the pulley A : they were held in position by being 

 clamped to the supports b b. 



Description of Experiments. 



I. If a long endless elastic band or cord is hung over the 

 pulley fixed to the end of the spindle a, fig. 1, PL IV., and 

 motion is gradually communicated to the band, the elastic band 

 is seen to grow in length, the lower end of the loop getting 

 further and further from the pulley, the loop keeping, however, 

 much the same shape it had while at rest. This elongation 

 becomes very marked if the band is loaded : if, for instance, 

 we use an endless india-rubber band to which are cemented by 

 means of india-rubber solution a number of pieces of lead. 

 This band, if put in motion (taking care to keep the pieces of 

 lead on the inside of the loop to prevent them being torn off 

 by the centrifugal force), can be easily drawn out to double 

 its original length. 



II. If in place of an elastic band we hang an endless chain 

 over the pulley and put it in motion, we already know that 

 the motion so communicated to the chain has but little ten- 

 dency to alter the form of the loop in which the chain hangs. 

 In fig. 3, PI. III., is represented the change produced by the 

 motion in the shape of the loop : the full lines show the form 

 while at rest ; the dotted lines represent the shape when in 

 motion. It will be observed that the change is not great ; and 

 this is the case even when the velocity is great. Later on I 

 shall show how the motion produces this change of shape. The 

 motion will of course produce a tension in the chain similar to 

 that produced in the india-rubber band ; but the chain, being 

 much less elastic, is not elongated to any perceptible extent. 

 If we now attempt to alter the form of the loop in which the 

 chain hangs, we shall find that the motion has communicated 

 new properties to the chain : it now resists any effort made to 

 alter its shape ; and after we remove the disturbing force gravi- 

 tation can only very slowly restore it to its original form. The 

 chain now conducts itself something like a rigid body. When 

 struck near its lowest part, it looks like a bar of lead ; it be- 

 comes indented at the point struck, and very slowly loses the 

 impression of the blow. 



It has been customary to call this property which the chain 

 has acquired in virtue of its motion by the name of rigidity. 

 There are, however, reasons which have induced me slightly 

 to differ from the ideas generally received on this subject; and 

 it is with the greatest diffidence that I here venture to state 



