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of Edinburgh , Session 1875 - 76 . 
the chain begins to fall; but at this point its fall may be stopped, 
or the chain may be made to rise again by destroying the tension 
at the lower part of the chain. If we cause the chain, instead of 
meeting the platform at an acute angle, to strike it as near as pos- 
sible at right angles, then the motion of the chain where it strikes 
the platform is partly destroyed, and the chain again rises and may 
be kept balanced for a long time resting on the platform, and only 
touching the driving wheel at one point. The reason for this being, 
that if we partially stop the motion of the links by causing them 
to strike the platform, or if we alter the direction of their motion 
by causing them to strike the platform, then there will be less 
tension in the lower part of the chain than in the upper, as the 
tension in the lower part will be only that due to partially changing 
the direction of the motion of the links. The centrifugal force of the 
upper part of the chain will be therefore unbalanced, and will cause 
the chain to rise and keep its elevated position against the force of 
gravitation. If a quick upward motion is given to the platform, 
the chain may be thrown up in the air, and again dropped on the 
platform like a solid body. 
The next experiments are to show that centrifugal force may 
produce sufficient rigidity to cause a chain to run along a platform 
like a wheel. A short endless chain was put over a pulley which 
was driven at a great velocity; the chain was then dropped on the 
I platform, along which it ran for some distance. It is not necessary 
that the chains form circular loops to do this. The loop may be 
tall and narrow, and will, while running along, keep the longer 
axis of the curve in its original upright position. Nor need the 
chain be heavy. A watch-guard was hung over a pulley about eight 
inches diameter; it then formed a loop about eight inches broad 
by about two feet high. When thrown off the pulley it glided 
along the platform for some distance. The chains were also 
dropped on an inclined polished surface, on which they remained 
standing in rapid motion for some time. 
All these experiments only illustrate the balance of the centri- 
fugal force, and the tension when the motion is all in one plane. 
The next experiment is to illustrate this balance when the motion 
takes place in different planes. This is easily illustrated by means 
of a circular disc of paper, or any other flexible material. If we 
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