Rigidity produced by Centrifugal Force. 95 



A variation of this experiment may be made by dropping 

 the chains when in rapid motion on an inclined metal or other 

 polished surface, where they will remain in rapid motion for 

 some time, gradually getting their form flattened by gravi- 

 tation. 



VI. The next experiments are best made with a long chain 

 forming a loop of JO or 12 feet, figs. 1 to 4, PL VI. The 

 chain is put in motion by means of the pulley H shown at 

 fig. 4, PL IV. 



A. Fig. 1, PL VI. If the chain is struck on the descending 

 side of the loop (at, say, the point B), then one part of the wave 

 so formed is carried rapidly with the motion of the chain 

 down the one side of the loop and up the other — so rapidly that 

 the eye cannot follow it. After the wave strikes the pulley 

 on the ascending side at C, it is reflected from it, and travels 

 slowly down the ascending side of the loop C D, gradually 

 becoming smaller and smaller, and dies out before reaching 

 the bottom D. The other part of the wave which was formed 

 when the chain was struck at B, slowly travels upwards 

 against the motion of the chain, till it meets the pulley, when 

 it is reflected, and very rapidly carried round by D to G, 

 where, like the first part of the wave, it is reflected and slowly 

 travels downwards. 



B. If we strike the chain on the ascending side at a point a 

 short distance below C, so as to form the wave shown in fig. 1, 

 PL VI., then the one part of the wave slowly travels down 

 the chain, while the other part is rapidly carried up to the 

 pulley, where it is reflected, and slowly travels down the chain ; 

 and as this reflected wave travels more rapidly than the wave 

 in front of it — on account of the greater tension on the chain, 

 due to gravity, at' the wave further up the chain — it overtakes 

 the first wave, and the two form one complete wave, and travel 

 to the bottom together. The successive positions and forms 

 of the waves are represented by the dotted lines in fig. 1. 



C. The next experiment illustrates the manner in which 

 gravitation acts on the moving chain. By means of the 

 movable pulleys E and F, fig. 3, PL IV., the chain is put into 

 the shape represented in fig. 2, PL VI., where H is the driving- 

 pulley and E and F are the two movable pulleys. The chain is 

 then put in rapid motion in this shape, in the direction shown 

 by the arrows. If now the pulleys E and F are suddenly 

 removed so that all the weight of the chain hangs from H, 

 the chain in falling passes through a series of forms somewhat 

 like those represented in the figure. The points most worthy 

 of notice in this experiment are : — 1st, the slowness of the 

 descent of the CO form ; 2nd, the peculiar balance of the chain : 



