Rigidity produced by Centrifugal Force. 87 



a velocity of from 40 to 70 feet per second may easily be com- 

 municated to the chains. 



The pulleys for fitting to the spindle a are of different forms 

 and sizes, and are shown to scale at A, B, C, D, fig. 2 ; their 

 uses will be pointed out in describing the experiments. 



Very light chains were used, as many experiments can be 

 made with light chains which would be dangerous or impossible 

 with heavy ones without more elaborate apparatus. The chains 

 were almost all machine-made, as the weight per unit of length 

 is much more uniform in machine- than in hand-made ones ; 

 their motion is therefore much more regular. They were 

 generally of the common figure-8 pattern, one half of the link 

 being at right angles to the other half. The chains of this kind 

 varied in weight from \\ oz. per j^ard to 10 oz. per yard ; other 

 kinds of chains were also used, amongst them the pin and flat- 

 link chain used for hanging windows. 



For guiding and altering the shapes of the curves of the 

 chains while in motion, wooden pulleys having grooves in their 

 circumference, and running freely on steel spindles fixed to 

 handles, were used. The shapes and sizes of these are shown at 

 E, F, fig. 3. In some cases the hollow india-rubber ball 

 shown at Gr, fig. 3, was found useful, not only for altering the 

 shapes of the curves of the chain, but also for other purposes, 

 which shall be described further on. The india-rubber ball 

 was mounted on a steel spindle, by passing a brass tube through 

 it, and fixing a circular brass plate to each end of the tube, and 

 cementing the ball to the end plates. The india-rubber ball did 

 very well at first ; but as the chains require to be kept well 

 oiled, the oil soon spoiled the india-rubber and made the ball 

 nearly useless. The following plan was then adopted : — A flange 

 about 2-inch diameter was fixed to the end of a short piece of 

 brass tube, and a loose flange and nut was screwed on the other 

 end ; disks of the required size were cut from sheet india-rubber, 

 and holes pierced in their centres ; the brass tube was passed 

 through the centres of a sufficient number of these disks ; the 

 loose flange was then put on, and the whole screwed tightly 

 up by means of the nut. This plan was adopted because the 

 india-rubber could be easily and quickly replaced if destroyed. 

 In place of india-rubber we may use disks of cloth. At first 

 sight the pulley so constructed does not look very promising ; 

 but after it is in use, the motion confers a quasi-elasticity upon 

 it which enables it to do its work remarkably well. 



For experiments with long chains the apparatus shown at 

 fig. 4 was used. It is simply a short steel spindle, to one end 

 of which a small pulley, a, is fixed, and to the other end the 

 wooden pulley H ; the spindle bearings are fixed to a piece of 



