118 THEORY OF CONSTRUCTION AND SCIENTIFIC DESCRIPTION 



When the forces on the pistons, are to one another, respec- 

 tively as the areas of the apertures or spaces which they 

 occupy. 



And it is obvious, that the same thing will take place, whatever 

 may be the number of the pistons pressed. 



Hence it appears, that by taking the areas of the pistons E and F, 

 in a proper ratio to one another, we can, by means of an incompres- 

 sible fluid, produce an enormous compression, and that too by the 

 application of a very small force. 



Put P zz the force or pressure on the piston E, 

 A=z the area of the orifice which it occupies, 

 p zz the pressure on the piston F, and 

 a zz the area of the orifice or space to which it is fitted. 



Then, according to the principle announced in the foregoing pro- 

 position and demonstrated above, we shall obtain 



a : A ::p : P. 



But because, by the principles of mensuration, the areas of different 

 circles are to one another as the squares of their diameters ; if there- 

 fore, we substitute d? and D 2 respectively for a and A in the above 

 analogy, we shall have 



d* : D 9 : : p : P, 



and from this, by making the product of the mean terms equal to the 

 product of the extremes, we get 



p^ ^d\ (88). 



122. This is the principle upon which depends the construction and 

 use of that very powerful instrument, the Hydrostatic Press, first 

 brought into notice about the year 1796, by Joseph Bramah, Esq., 

 of Pimlico, London ; who announced it to the world as the discovery 

 of a new mechanical power. 



In this however, he was mistaken, for although the principle upon 

 which it depends may be said to constitute a seventh mechanical 

 power, yet the principle announced in Proposition II. was not new 

 to philosophers at the time when Mr. Bramah applied it to the 

 construction of his presses, it having long been familiarly known 

 under the designation of the Hydrostatic Paradox ; and besides, 

 the celebrated Pascal obscurely hinted at its application to mecha- 

 nical purposes, but did not pursue the idea far enough to produce 

 any thing useful, or to entitle him to the full merit of the discovery. 



The improvement introduced by Mr. Bramah, consisted in the 

 application of the common forcing pump to the injection of water, 



