ON RAISING AND REMOVING WEIGHTS. 157 



now draw the end of the lever upwards. In this direction, a strong man 

 can exert a force equivalent to twice his weight ; consequently the second 

 kind of lever possesses here a temporary advantage over the first ; although, 

 if the operation were continued, the workman would he more fatigued by 

 raising even the same weight hy this method, than if he could conveniently 

 apply his weight to a lever of the first kind : and for this purpose, cross 

 bars have sometimes been added to levers, in order to enable several work- 

 men to stand on them with advantage at once. A bent lever operates 

 precisely with the same power as a straight one, provided that the forces be 

 applied in a similar manner with respect to its arms : and in all cases, the 

 forces capable of balancing each other are inversely as the distances of the 

 points of action from the fulcrum. Some addition of force is necessary for 

 overcoming the equilibrium and producing motion, but the velocity of the 

 motion being seldom of much consequence, a small preponderance is usually 

 sufficient. 



The principal inconvenience of the lever is the short extent of its action : 

 this may, however, be obviated by means of the invention of Perrault, 

 in which two pins are fixed in the lever, at a short distance from each 

 other, sliding in two pairs of vertical grooves provided with ratchets, so that 

 when the long arm of the lever is pulled by means of a rope, the nearer pin 

 serves as a fulcrum, and the more distant one is elevated at the same time 

 with the weight, and is detained in its place by the click ; but when the 

 rope is slackened, the weight sinks a little, and raises the pin which first 

 served as a fulcrum, to a higher place in its groove. The same effects may 

 also be produced by catches or clicks resting upon ratchets on the opposite 

 sides of a single upright bar, which passes through a perforation in the 

 lever. There must, however, be a considerable loss of force from the con- 

 tinual intermission of the motion. (Plate XVII. Fig. 213.) 



An axis with a winch, that is, a lever bent at the end, is known from 

 the common machine for raising a bucket out of a well. A vertical or 

 upright axis with two or more levers inserted into it, becomes a capstan. 

 In these cases, if we wish to estimate the force with accuracy, we must add 

 to the radius of the axis half the thickness of the rope, when we compare 

 it with the arm of the lever. 



Sometimes the weight of a reservoir or bucket of water is employed for 

 raising another bucket, filled with coals or other materials, by means of a 

 rope or chain coiled round a cylinder or drum, or two drums of different 

 sizes. This machine is called a water whimsey : when the bucket of 

 water has reached the bottom, a valve is opened by striking against a pin, 

 and lets out the water. In a machine of this kind employed in the Duke 

 of Bridgwater's coal works, the water descends thirty yards and raises a 

 smaller quantity of coals from a depth of sixty. In such cases, supposing 

 the action to be single, and the stream of water to be unemployed during 

 the descent of the reservoir, a considerable preponderance may be advan- 

 tageously employed in giving velocity to the weights, provided that the 

 machinery be not liable to injury from their impulse. 



An erect axis or drum, turned by the force of horses walking in a circle, 

 is used for raising coals and other weights, and is called a gin, probably by 



