Rigidity produced by Centrifugal Force. 103 



pulley C (fig. 2, PI. IV.) and driven at the same velocity, the 

 loop of the chain with the longest links opens out and tends 

 to take up the circular form, the smaller links keeping near 

 the form the chain had while at rest. In the long-link chain 

 there is no reverse curve, while it is well-marked in the short- 

 linked one. 



XL An elastic cord in rapid motion also tends to assume 

 the circular form, because the internal strains in the quickly 

 curved parts tend to open them out in the same manner as if 

 the cord were at rest. An elastic cord, when in motion, does 

 not take the reverse curve like a chain, because its tendency 

 to do so is resisted by the strain in the material. 



XII. In all these experiments gravitation acted on the 

 chains, so that, whatever form we might give them, gravita- 

 tion soon restored them to their original form of stability. 

 An attempt was therefore made to get quit of the disturbing 

 effects of gravitation, as it was thought that the action of the 

 other forces might be more conveniently studied if its effects 

 were removed. The problem, however, is an extremely diffi- 

 cult one, and has quite baffled all my attempts. Many me- 

 thods suggested themselves for accomplishing this end ; some 

 of them were tried ; but none of thorn was successful. The 

 next experiment shows the plan which was found most suc- 

 cessful, namely suspension. The chain n (fig. 5, PL VII.) is 

 suspended by a number of fine cords d d to a circular metal 

 disk e. The disk e rotates freely about a vertical axis, and is 

 placed at a considerable distance above the chain ?z, so that 

 the cords d d may be as long as possible. The disk is also 

 capable of being moved in any direction horizontally. In 

 the experiment this was done by hanging it by means of a 

 long wire. Motion was communicated to the chain by means 

 of the apparatus shown at fig. 5, PL IV., the chain being 

 passed round the horizontal driving-pulley i and pressed 

 against it by means of the elastic pulley r. 



Let me here briefly refer to the imperfections of this arrange- 

 ment, as the results are modified by these imperfections. 

 First, the effects of gravitation are by no means balanced by 

 this arrangement, as may at once be seen by the position of 

 the cords. This imperfection may, however, be reduced by 

 making the cords long, and by arranging the point of suspen- 

 sion so that it can be moved in every direction, so that the centre 

 of suspension may always be kept vertically over the centre of 

 gravity of the chain. Second, the method of imparting 

 motion to the chain is very imperfect. The chain ought to 

 be perfectly free at all points, whereas this method compels 

 the chain always to pass between the two pulleys. And, third, 



