86 Mr. J. Aitken on some Experiments on 



gravitation; this tension varies at different points, being nothing 

 at the lowest point and increasing to a maximum at the highest 

 point of the chain : and there is also the tension produced by 

 putting and keeping the chain in motion; this tension is greatest 

 at the part of the chain approaching the driving pulley, and 

 least at the part just leaving it. 



Description of Apparatus. 



Before proceeding to the experiments, it will be necessary 

 for me briefly to describe the apparatus used. As chains were 

 used in almost all the experiments, the object of the apparatus 

 was simply to communicate in different ways motion to these 

 chains ; the apparatus was therefore of the simplest description 

 possible, and is represented to scale in figs. 1 to 5, PL IY. 

 Fig. 1 is a general view of the principal part of the apparatus. 

 A short steel spindle, a, running in a tube, is mounted hori- 

 zontally on the triangular supports b b at a convenient height 

 for making the experiments ; on one end of the shaft, a, is an 

 arrangement, c, for fixing on the different sizes and shapes of 

 pulleys shown in fig. 2. On the other end of the shaft is the 

 small brass pulley d, 1|- inch in diameter ; e is the driving-wheel 

 made of wood, 2 feet in diameter, having a groove for a driving- 

 cord cut in its circumference. The driving-wheel, e, is fitted to 

 the end of a horizontal axle running in the bearings, // ; the 

 bearings are cast in one piece with the plate g, which is held 

 firmly to the sole-plate h by means of the two screws i i, w T hich 

 pass through longitudinal openings in the plate g to admit of 

 the wheel being moved in a longitudinal direction for the 

 purpose of adjusting it to the proper distance from the pulley 

 d to keep the driving-cord k tight*. The driving-wheel is 

 driven by means of the handle I ; and motion is communicated 

 to the small spindle a by means of the cord k. The driving- 

 wheel is easily unmounted from its axle ; and the triangular 

 supports are fixed to the sole-plate by means of two long bolts 

 passing through both supports and clamping them firmly to the 

 sole-plate. The tube carrying the spindle a being also held 

 by screws to the supports b b, the whole apparatus is easily 

 unmounted for packing away. 



The chain, n, to be experimented on is hung over the pulley 

 A fitted to c on the end of the spindle a, and the pulley put 

 into rapid motion by means of the handle I. As the small 

 shaft makes about 13 revolutions for one of the driving-wheel, 



* If a small india-rubber band, such as those sold by stationers, is stretched 

 over the grove in the pulley d, the friction between the cord and the pulley 

 is very greatly increased, and the tightness of the cord becomes a matter of 

 less importance. 



