290 Hydrostatics. 



temperature is sufficiently reduced ; whereas air and the gases 

 are found, with few exceptions, to preserve always their elastic 

 form in the state of the greatest compression and lowest tempera- 

 ture to which they have hitherto been reduced.! 



401. Although we are unable to assign the magnitude of the 

 elementary parts of fluid bodies, we cannot doubt that these parts 

 are material, and that the general laws of equilibrium and mo- 

 tion, already established, are applicable to them as well as to sol- 

 ids. But as this law of equilibrium is not the only one required, 

 some other is to be sought on which the equilibrium depends. 



402. As an equilibrium consists in destroying all the forces 

 employed, and as we do not know how the parts of a fluid trans- 

 mit their forces among themselves, it is only by having recourse 

 to experiment, that we are able to establish our first principles. 

 We begin, therefore, by stating what is most clearly and cer- 

 tainly known upon this subject. 



Pressure of Fluids. 



403. L?t ABCD be a canal or tube, composed of three 

 branches AB, BC, CD, of equal diameters. Let us suppose 

 that a heavy fluid is poured into the branch AB ; it will pass 

 through the branch 5Cinto the branch CD ; and when we cease 

 pouring, the surface of the fluid in the two branches will be in 

 the same horizontal line, whatever be the inclination of the 

 branch BC. This is a fact abundantly established and univer- 

 sally admitted. We proceed to make known the consequences 

 to be deduced from it. 



404. If through any point E, taken at pleasure, we imagine 

 a horizontal line EF to pass, it is evident that the weight of the 

 fluid KBCF contributes nothing to the support of the columns 

 AE, DF ; and that consequently the equilibrium would still be 

 preserved, if the fluid contained in EBCF were suddenly de- 

 prived of its gravity. This fluid, therefore, is to be regarded 



t See note on the condensation of gases into liquids. 



