94 Mr. J. Aitken on some Experiments on 



wheel is performing the part of a pump, and the loose chain 

 on the platform the part of the water supply. The different 

 parts of the jet, however, in this case are rigidly connected 

 and all moving at the same velocity, which causes the curve 

 of the chain to differ from that of the water jet. 



V. The chains in the previous experiments were, to a 

 certain, degree, rigid. If we give the platform a quick up- 

 ward motion, the chain rises from the platform like a rigid 

 body, and again falls on it, getting its form but little put out 

 of shape by the treatment — because when it falls on the 

 platform, although it gets slightly flattened, yet it tends to 

 bend so as to cause the links to strike the platform more 

 nearly at right angles, and therefore tends to cause the upper 

 part of the chain to rise again, till the chain is pulled upwards 

 and into such a shape as to reduce the angle at which the links 

 meet the platform, the chain thus again regaining its form 

 of equilibrium. This quasi-rigidity communicated to the chains 

 by the motion is so great, that when thrown off the pulley in 

 rapid motion they run along the ground like wheels. The 

 simplest way of making this experiment is to hang the chain 

 over a pulley which has a flange on one side only, such as 

 that shown at B, fig. 2, PI. IV. After sufficient velocity has 

 been communicated to the chain, it is easily slipped over the 

 edge of the pulley and dropped on a platform, along which it 

 will run for some distance. The platform ought to be movable, 

 and should be brought as near the lower part of the chain as 

 possible, as the chain gets put out of shape if it falls far. It is 

 also an advantage to put some rough or ridged surface on the 

 platform where the chain drops on it, as it enables the chain 

 to get up a longitudinal motion quickly. 



The chains for this experiment may be short, so that when 

 hung over the pulley they form nearly circular loops ; or they 

 may be long, so as to form long loops. These long loops do not 

 run along like a solid body, but always keep the longer axis 

 of their figure vertical, as shown at D, rig. 6, PLY. As they 

 move along they gradually lose their velocity, and get flattened 

 down and put out of shape. For this experiment we may use 

 light or heavy chains. Chains weighing from 6 to 8 oz. per 

 yard do very well ; but any weight of chain may be used. A 

 common watch-guard, for instance, if hung over an 8-inch 

 pulley so as to form a loop 8 inches by about 2 feet, and driven 

 at a great velocity, will, when dropped off the pulley, glide 

 along looking like a polished wire hoop. It is not simply the 

 " rigidity " which enables these chain- wheels to keep their 

 shape and elevated position ; the explanation given in ex- 

 periment IV. D also applies to them. 



