INTRODUCTION. 



treated of in the fourth chapter; but in the fifth, the subject is 

 purely practical, and involves some of the most important prin- 

 ciples in the whole range of Hydrodynamics. The reader now 

 enters upon that remarkable and important principle, 



That any quantity of fluid, however small, may be 

 made to balance or hold in equilibrio any other quantity, 

 however great ; 



and is enabled thence to investigate the theory and expound 

 the construction of those mechanical contrivances known as 

 Bramah's hydrostatic press, the hydrostatic bellows, and weigh- 

 ing machine, which are all methods of balancing different 

 intensities of force, by applying the simple power of non- elastic 

 fluids to parts of an apparatus moving with different velocities : 

 and this is all the mechanical powers can effect. 



The Sixth Chapter, which treats of these hydrostatic engines, 

 their theory of construction and scientific description, com- 

 mences with a distinct proposition ; the first having proved suf- 

 ficient to resolve every problem connected with fluid pressure 

 upon rectilinear and curvilinear figures considered as independent 

 planes immersed in the fluids, together with the pressure of 

 fluids upon the interior surfaces of vessels containing the fluids 

 and belonging to the class of regular bodies, the second pro- 

 position, which the reader now enters upon, involves the prin- 

 ciple whereon depend the construction and appliancy of the 

 hydrostatic press, an engine very generally employed in practical 

 mechanics, and which should therefore be scientifically as it is 

 practically known. But the same proposition extends to the 

 investigation of the hydrostatic bellows, and furnishes the prin- 

 ciple of a particular machine by which goods may be weighed 

 as by the common balance. It may thence be inferred, that as 

 yet, science has but stepped on the threshold of fluids that are 

 heavy and liquid. How far this distinguishing property, the 

 power of transmitting pressure equally in all directions, may yet 

 carry mankind, it would be idle to conjecture. Enough, how- 

 ever, is here shown to satisfy the reader, that in expounding the 

 laws of the pressure and equilibrium of fluids, as well as those 

 of their motion and resistance, he will encounter principles of 

 great practical utility in the construction and use of machines, 



c2 



