24 OBJECTS, ADVANTAGES, AND 



rule must evidently hold for all proportions of the lengths of its beams. 

 If, then, the lever be 17 feet long, and the pivot, or fulcrum, (as it ig 

 called, from a Latin word signifying- support,') be a foot from one end, 

 an ounce placed on the other end will balance a pound placed on the 

 near end ; and the least additional weight, or the slightest push or 

 pressure on the far end, so loaded, will make the pound weight on the 

 other move upwards. If, instead of an ounce, we place upon the long 

 end the short end of a second beam or lever supported by a fulcrum, 

 one foot from it, and then place the long end of this second lever upon 

 the short end of a third lever, whose fulcrum is one foot from it ; and 

 if we put on the end of this third lever's long arm an ounce weight, 

 that ounce will move upwards a pound on the second lever's long arm, 

 and this moving upwards will cause the short arm to force downwards 

 16 pounds at the long end of the first lever, which will make the short 

 end of the first lever move upwards, though 256 pounds be laid on 

 it ; the same thing continuing, a pound on the long end of the third 

 lever will move a ton and three quarters at the short end of the first 

 lever ; that is, will balance it so that the slightest touch or pressure 

 with the finger, or a touch from a child's hand will move as much as 

 two horses can draw. The Lever is called on this account a mecha- 

 nical power ; and there are five other mechanical powers of which its 

 properties form the foundation ; indeed they may be resolved into 

 combinations of levers. Thus the wheel and axle is only a lever moving 

 round an axle, and always retaining the effect gained during- every 

 part of the motion, by means of a rope wound round the butt end of 

 the axle ; the spoke of the wheel being the long arm of the lever, 

 and the half diameter of the axle its short arm. By a combination of 

 levers, wheels, pullies, so great an increase of force is obtained, that, 

 but for the obstruction from friction, and the resistance of the air, 

 there could be no bounds to the effect of the smallest force thus mul- 

 tiplied ; and to this fundamental principle, Archimedes, one of the 

 most illustrious mathematicians of ancient times, referred, when he 

 boasted, that if he only had a pivot or fulcrum whereon, he might rest 

 his machinery, he could move the earth. Upon so simple a truth, 

 assisted by the aid derived from other means, rests the whole fabric of 

 mechanical power, whether for raising weights, or cleaving rocks, or 

 pumping up rivers from the bowels of the earth ; or, in short, perform- 

 ing any of those works to which human strength, even augmented by 

 the help of the animals whom Providence has subdued to our use, 

 would prove altogether inadequate. 



The application of Dynamics to the pressure and motions of fluids, 

 constitutes a science which receives different appellations according as 

 the fluids are heavy and liquid like water, or lig:ht and invisible like 

 air. In the former case it is called Hydrodynamics, from the Greek 

 words signifying water and power, or force ; in the latter Pneumatics, 

 from the Greek word signifying breath or air ; and Hydrodynamics is 

 divided into Hydrostatics, which treats of the weight and pressure of 

 liquids, from the Greek words for balancing of water, and Hydraulics, 

 which treat of their motion, from the Greek name for certain musical 

 instruments played with water in pipes. 



Ihe discoveries to which experiments, aided by mathematical reason- 



