¥2 PHYSICS, 
~ 
in fig. 5, it will balance two pounds in the scale; and so for any other © 
number of pounds, because, if the distance of the small weight from 
the fulerum be three, four, or five times greater than the distance of the 
other weight, that weight must be three, four, or five times greater than 
the weight at the longer end. 
* II.—The Wheel and Axle. 
This machine, although apparently very different from the lever, is in 
reality constructed on the same principle. In fig. 8, we see an arrangement 
by which a small weight, P, balances a much greater one, W. Now, if we 
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Fig. 9. 
take a section of this machine (fig. 9), we see at once how it acts like a 
lever. Although the machine might be turned round, yet, in every 
position, the weights act at right angles to the diameters of the wheel and 
of the axle ; and as the machine is perfectly rigid, it is easily seen that it 
is simply a lever, with F, the centre of the axle, for its fulerum, and 
having on one side half the diameter of the wheel, and on the other 
half the diameter of the axle. If the half-diameter, FA, were six 
times greater than the half-diameter FB, the weight, P, would 
balance a weight six times greater than itself. 
What has been said applies to the machine 
in a state of equilibrium; for practical pur- 
poses, however, the weight on the wheel is not 
used, the axle being turned by a winch, H 
(fig. 8). The strength of a man pressing 
\—\ round the handle, acts like the weight on the 
circumference of the wheel. 
Fig 10 The capstan, used on board ships for heaving 
og the anchor, is on the same principle (fig. 10). 
The fulcrum is the centre of the machine; the short end of the lever, - 
with the heavier weight, is half the diameter of the part round which the 

