140 EXPERIMENTS ON CENTRIFUGAL FORCE. 



on, wliich serve for fixing the ring to the axis, as shown in fig. 

 99, B. Thevse lijbtle .tubes, 4 mm long, l mm wide, are made by heat- 

 ing a small sheet of brass, 8 mm long, and 4 mm broad, and bending it 

 after cooling round a wire l nim thick ; the flat pliers are used for 

 pressing the brass close to the wire. The spindle passes through two 

 holes, which are bored through the two crossbars of the frame, just 

 wide enough to litthe spindle moderately tight. The spindle is about 

 16 or 17 cm long ; l cm from its lower end a horizontal hole, l mm wide, 

 is drilled through it, and a pin, 2 cm long, made of wire, with a small 

 ear at one end, is pushed through the two tubes and the hole in the 

 spindle. The ear should just fit round a wire peg driven into the 

 crossbar ; this will ensure that frame, ring, and spindle rotate 

 together. For the peg, drive a wire-pin into the crossbar. 



The flattening of a globe may be more beautifull) 

 shown by a drop of oil, suspended in a liquid, as in art. 3 

 If a circular disc of metal with a wire through the 

 centre of it be placed within such a drop, and made t( 

 rotate, adhesion causes the oil to participate in th( 

 rotation ; it flattens out even on applying a moderate 

 speed, and if the velocity increases the oil leaves the 

 disc altogether and forms a circular ring surrounding 

 the disc; if at this moment the rotation is stopped, th< 

 oil contracts again to a globe round the disc, and th< 

 experiment may be repeated. 



Cut a circular disc of thin brass, 12 mm in diameter, punch a hoi 

 in the centre, and solder it to a straight piece of wire from 2 to 4 m 

 thick, and about 20 cm long, about l cm distant from one end. Pas 

 the wire througha glass tube 15 cm long, just wide enough to allow th 

 free motion of the wire, but not wider. Fix upon the end of the wir 

 which projects from the glass-tube a small cork about 6 mm thicl 

 Pass one end of a piece of india-rubber tubing, 4 cm long, over th 

 cork, and the other end over the lower extremity of the shaft of th 

 whirling- table, so as to connect them, but not too stiffly. Raise th 

 apparatus above your table, by means of little boxes, stools, etc., sothf 

 the disc upon the wire be a few centimetres above the table. Moistc 

 the disc, and the wire about l cm above and below the disc, well wit 

 oil ; clamp the glass tube, in a perfectly vertical position, and so as to I 

 in one straight line with the shaft, into the retort- stand, allowin 



