HYDROSTATICS, 17 
proportional to the area of that surface. Suppose the box B to be filled 
with water, and to have a number of openings of the same size, as a 
| 
and 6, with pistons or plugs exactly fitting 
them; and, for greater simplicity, suppose 
the water to be without weight, so that we 
may consider merely pressure arising from the 
forcing down of the plug. If the piston at a 
be pressed in with a certain force—say, equal 
to a weight of one pound—this pressure will 
be transmitted to all parts of the vessel (because 
the particles of the liquid could not be at rest unless there was an equal 
‘pressure throughout), and thus to the piston at b. And since the piston is 
of the same size as that ut a, the pressure on it is the same as the 
reaction of the water on the piston at a; in other words, there is a 
pressure of one pound on it. The pressure on the two, then, is two 
pounds, and both being equal in size, the area of the two is twice that 
of one of them. If there were a large piston, c—say, four times as large 
as a—the pressure on it would be four pounds. If a piston, one square 
inch in area, were pressed into a vessel full of water with a force of one 
pound, and if the area of one of the sides of the vessel were one foot, 
then the pressure of the water on that side would be 144 pounds. 
On this principle there has been constructed a very useful and 
powerful machine, named the Hydraulic Press, which is also called 
Bramah’s Press, from the name of the inventor. The figure (19) shews 
the essential parts of the machine H « a 
is a force-pump by which water is At 
forced from the tank T, through the 
tube G, to F, the cavity of a strong 
eylinder, E. D is a piston which passes 
water-tight through the top of E, and is 
pressed upward by the pressure communi- 
cated to the water by the piston of the 
force-pump H. On the top of D isa plate, = 
on which are placed the articles to be 4 
pressed, C; and the rising of the plate, 
caused by D being forced upward by the 
water, presses these against another plate, 
AA. Itis very easy to calculate the pressure 
communicated to D ; for, according to the 
law stated above, the pressure caused by the piston of H is to the pressure 
on D as the area of the piston is to the area of the end of D. If the area 
of the end of D were 1000 times greater than that of the piston of H, 
and the piston of H were pressed down with a force of 500 pounds, 
B 








Fig. 18. 



MLA 
Fig. 19. 
