EXPERIMENTS ON THE QUAQUAVERSUS PRESSURE OF FLUIDS. 155 



EXAMPLE. The diameter of the moveable cover is 16 inches, and 

 that of the communicating tube one inch ; then, supposing that the 

 machine in the first instance is brought to a state of equilibrium, 

 and that a load of 1211 Ibs. is applied on the cover, in addition to 

 that which produces the equipoise ; to what height above the first level 

 will the water ascend in the communicating tube? 



Proceeding according to the rule, we obtain 



.7854 (D 8 + <P) = .7854 (16* + I 2 ) = 201 .8478 divisor ; 



consequently, by division it is 



And exactly after the manner of these two examples, may any 

 other case be calculated ; but in applying the principles to the 

 determination of weights, mercury ought to be employed in preference 

 to water, as it exerts an equal influence in less space, and besides, it 

 is not subject to a change of density by putrefaction and the like. 



4. EXPERIMENTS ILLUSTRATING THE QUAQUAVERSUS PRESSURE OF 

 INCOMPRESSIBLE FLUIDS. 



Before we conclude our inquiries on fluid pressure, it may be both 

 interesting and instructive to the readers of this work, to describe a 

 few select experiments, by which the equal distribution of pressure, 

 among the particles of an incompressible fluid is beautifully and 

 rigorously demonstrated, and its equal propagation in all directions, 

 placed beyond the possibility of the smallest doubt. 



Allied to the preceding subject, is the following, by which is exhi- 

 bited a very surprising effect of the equilibrium of incompressible 

 fluids, but which, for the sake of convenience, we shall suppose to be 

 water, since that is more easily obtained in small or large quantities, 

 than any other fluid whatever. 



EXPERIMENT 1. Let A BCD represent an upright section of a square 

 or cylindrical vessel, closed at top with a cover of 

 which A D is a section ; make a hole in the top at E, 

 and fix a tube FE therein of any convenient dia- 

 meter at pleasure, but small in comparison of the 

 diameter of the vessel. Let the tube be closely 

 fixed in the cover with pitch, or some other glutin- 

 ous matter, so as to be rendered air and water-tight 

 all round the orifice, and suppose its length or 

 height to be twelve or fifteen inches according to 

 circumstances ; then, fill the vessel with water by some holes made 



