26 Report of the Progress of the Sciei2ces hi France. 



Hydrostatics. The theory of the motion of fluids has been sub- 

 jected by Lagrange to the most rigorous analysis. 



1. The properties of the equilibrium of a free system of 

 bodies, relative to the motion of translation. 



2. The properties of equilibrium relativie to the movement of 

 rotation. 



Of Slat'ics. Lagrange has referred all the laws of static, or 

 of the tlieory of tlie etjuilibrium of solids, to three princi;>les ; 

 that of the lever, th:.r of the composition of forces, and that of 

 the virtual velocities. 



Of Marhhies They make u[) for the weakness of our or- 

 gans, and new machines are daily invented. The Voltaic pile 

 has been one of the most valuable discoveries of late years for 

 the advancement of science. 



Of IJydroslafics and Hydronamics. " Although we are ig- 

 norant," says M.Lagrange (tome i. p. 174), " of the interior 

 constitution of fluids, it cannot be doubted that the particles of 

 which they arc coini)0sed are material, and that for this reason 

 the general laws of equilibrium cannot suit them as tliey do 

 solid bodies. In fact, the general property of fluids, and the 

 only one which distins;uishes them from solid bodies, consists 

 in all their parts yielding to the smallest possible force and 

 moving with all possible facilitv." 



In order to conceive the cause of ihese phasnomena, we must 

 admit that each particle of matter has a peculiar force^ which 

 it never loses. 



From sal ammoiiiac for instance, wlien triturated with lime, 

 tlie volatile alkali is extricated with ail its usual vivacitv. 



From the sulphuric acid, when poured upon the same salt, 

 the marine acid is also extricated with force. 



The molecules of the ammonia and those of the marine acid 

 had each therefore a peculiar force which was in iiisu, like those 

 of a spring. 



The molecules of solids, on the contrary, are most frequently 

 nearly immovenble, because their peculiar forces are in 7n>i/, as 

 in the metals, stones, &c. Nevertheless they have sometimes 

 particular motions, like those of warm substances, sonorous 

 bodies, electric bodies, &;c. 



The molecules of fluids have a constant rotatrrv motion 

 around their axis or point of equilibrium, and they yield to the 

 least force. Whereas solids oppose all their vis inert ice in the 

 ratio of their masses. This is the cause of the differences ex- 

 hibited by solids and fluids in their motions. 



Fluids are divided into two classes : Ethereated fluids, which 

 Davy impro];erly calls impcnderatle fluids. Non-ethereated 



fluids. 



