88 Mr. J. Aitken on some Experiments on 



wood, c. The whole apparatus is firmly attached to a scaffolding., 

 or any other convenient place, by means of screw-nails passing 

 through c. The chain to be experimented on is hung over the 

 pulley H ; and an endless cord is passed over the pulley a and 

 carried clown to the driving-wheel of the apparatus shown in 

 fig. 1, which may be standing on a table or other convenient 

 place. 



For experiments with a horizontal chain, a slight addition 

 was made to the apparatus shown in fig. 1. These additions 

 are shown in fig. 5. As before, a is the steel spindle, having 

 the small brass pulley d fixed at one end, by which motion is 

 communicated to it ; to the other end is fixed a wooden pulley 

 c, having a groove in its circumference, in which is placed a 

 stretched india-rubber band of circular section ; on the top of 

 the pulley c rests the horizontal pulley i. Motion is communi- 

 cated to the horizontal pulley i by means of the pulley c. The 

 pulley i is supported in its position by means of the horizontal 

 bars e e (only one of which is shown in sketch), which are 

 clamped to the triangular supports b b by means of the screws 

 ff. The horizontal bars e e are held together at the end by 

 means of the cross-piece g, to which they are held by means 

 of the screws h h. To the cross-piece g is clamped, by means 

 of the screw /, the vertical bar of wood m ; to m is attached, by 

 means of the brass plate p, the tube o, in which runs the spindle 

 of the pulley i ; the brass plate p moves in m round the screw 

 q like a compass-joint. By this arrangement the pulley i may 

 be fixed in a horizontal position, or turned to any angle that 

 may be desired, by first turning p round the screw q, then 

 lowering the bar m till the pulley i rests on the pulley c. The 

 horizontal bars e e rest on pins, uuuu, driven into b b. The 

 bars e e can be moved on the pins uuu u to the right or 

 left, so as to cause the pulley c to act near the centre or the 

 circumference of the underside of the pulley i, so as to give 

 a quick or slow motion to the pulley i, as may be desired for 

 the experiment, r is an india-rubber ball mounted on a steel 

 spindle, and so arranged that it can be adjusted to press the 

 chain against the pulley i, at whatever angle the pulley i is put. 

 In order to increase the friction between the pulley i and the 

 chain, the pulley is covered with india-rubber. The pulley i is 

 pressed against the pulley c by means of a spiral spring at the 

 lower end of the spindle o ; the spindle o is carried down below 

 the horizontal bars e e for making experiments with apparatus 

 hung from it. As all the bolts are provided with thumb- 

 screws,the whole apparatus is easily and quickly taken to pieces. 



In addition to the apparatus shown in PI. IV., a simple ar- 

 rangement was placed below the pulley A, fig. 1, for guiding 



