108 HYDROSTATICS. 



under more water. A simple experiment, how- 

 ever, will confute this idea. 



Suspend from a balance an empty phial, corked, 

 and loaded so as to sink in water, and counterpoise 

 it by an equal weight in the opposite scale, when 

 it is immersed in the water ; then pull out the 

 cork, and the water will rush in and fill the phial, 

 but the equilibrium of the balance will be de- 

 stroyed; and it will require as much weight to 

 restore the equilibrium, as the real weight of the 

 water in the phial ; thus proving, that the water 

 in the phial lost none of its weight by being sur- 

 rounded by a fluid of the same kind. 



Though fluids are subject to the same laws of 

 gravity with solids, yet their want of cohesion oc- 

 casions some peculiarities. 



The parts of a solid are so connected together, 

 as to form but one and the same whole ; and their 

 effort is, as it were, concentrated in a single point, 

 called the centre of gravity. This is not the case 

 with fluids. Their parts gravitate independently 

 of each other. And hence it is, that the surface 

 of a fluid contained in an open vessel is always 

 level, or parallel to the horizon. 



Fluids have this remarkable property, that they 

 press not only in common with solids perpendicu- 

 larly, but also upwards, sideways, and in every 

 direction, equally. 



To confirm this by experiment, take a glass tube 

 open at both ends, and, stopping one end with 

 your finger, immerge the other in water. The 

 water will be prevented from rising far in the tube 

 by the air which is contained in it ; but if you take 

 away your finger from the upper end, the air within 

 the tube will be suffered to escape, and the water 



