100 Mr. J. Aitken on some Experiments on 



curious reverse curve in the chain, caused by it curving further 

 round than seems necessary, and then requiring to be unbent 

 again. These two alterations in the shape of the loop look as 

 if the motion had conferred a certain degree of rigidity on 

 the chain, which enabled it to resist bending at the entrance to 

 the curve, and also to resist unbending at the other side. 

 There are also alterations in the shape of the loop near the 

 driving-pulley. It will be also noticed that the chain does 

 not now hang in the same position as when at rest ; its centre 

 of gravity is evidently a little to one side of its position 

 of rest. This is caused by the manner in which motion is 

 imparted to the chain ; the tension on the ascending side 

 of the chain is greater than on the other side, thus causing 

 the centre of gravity to move to the one side. 



VIII. The alterations in the curvature of the chain produced 

 by the motion have hitherto been supposed to be due to the 

 friction of the links pivoting on each other, under the great 

 tension produced in the chains by the centrifugal force. That 

 this is not the full explanation, however — though it may, 

 in part, explain the flattening of the loop at the entrance to 

 the curve — is easily proved by taking two precisely similar 

 chains, and passing one of them through a flame, so as to dry 

 and oxidize its surface, and oiling the other chain. The only 

 difference between the two chains now is, that there is more 

 friction in the one than in the other when in motion. If we 

 now hang these two chains over the double pulley C, fig. 2, 

 PL IV., the two gooves in which are of exactly the same 

 diameter, so as to drive the two chains at the same velocity, 

 we shall thus get what the effect due to friction is. We find 

 that the oiled chain has the reverse curve well marked, while 

 there is no reverse curve in the other chain, the effect of the 

 friction being to make the loop open out and take up a form 

 approaching a circle. Further, if we cause both of the chains 

 to take up the same curvature at the bottom part of their paths, 

 which we can easily do by passing them over a small pulley 

 or a glass rod, we shall then find that the reverse curve is 

 notably least where the friction is greatest. 



The alterations in the curvature of the chain when in motion 

 are in all probability almost entirely due to the change of mo- 

 tion which takes place in the links when moving in a path of 

 varying curvature. For instance, when a link is descending the 

 flat part of its path (a, fig. 3, PI. III.), its motion is almost 

 simply one of translation ; whereas, when moving round the 

 curved parts, such as b, it has a motion of rotation as well as a 

 motion of translation. The result of this is, the links resist the 

 force tending to increase their rate of rotation when passing from 



