INTRODUCTION. XXXIX 



fluids, preserve a perfect equilibrium between both and to each 

 its own due proportion of the life-giving gas, either as an 

 elastic or a non-elastic fluid. And it is, perhaps, owing to this 

 circumstance operating through the principle of specific gra- 

 vities, that the barometer the prophet of the weather, indicates 

 the changes which diversify the climate of our earth. When 

 the atmosphere becomes surcharged with water it falls as rain, 

 and the weight and bulk of the mass being diminished, the 

 rising column of mercury presages serene and dry weather, as 

 previously the falling barometer had prognosticated wind and 

 rain. Our inquiries cease the moment we approach the limit, 

 which separates chemical analysis from the mechanics of fluids. 



From the time of Archimedes till the age of Pascal,* the 

 annals of scientific discovery present no improvement in hydro- 

 statics. Pascal has the merit of discovering the pressure of 

 the atmosphere, and his treatise on the Equilibrium of Liquids 

 raised hydrostatics to the dignity of a science. The midnight 

 of barbarism, that for a thousand years had brooded over the 

 discoveries of the Sicilian philosopher, and had concealed the 

 Commentary of Sextus Julius Frontinus on the Aqueducts of 

 Rome, fled before the genius of Pascal and the powers of 

 Newton's mind ; the former, in the most perspicuous and simple 

 manner, demonstrating and proving by experiments the laws of 

 fluid equilibrium ; and the latter expounding the oscillation of 

 waves, a subject the most refined in Hydrodynamic science, 

 which, from that time, counts among its votaries the engineers and 

 philosophers of Italy, France, Sweden, Germany, and Britain. 



It is proper here to state, that we believe in the compres- 

 sibility of water ; but we hold it true that for all general opera- 

 tions in the mechanics of fluids this compressibility is so 

 small as not to occasion any error in the numerous and varied 

 formulae, from which we have drawn practical rules for the 



* Pascal gave proof of his skill in hydrostatics, by the celebrated well which he 

 dug at Port Royal des Champs, about six miles from Versailles. The well still exists, 

 in the midst of the farm yard of Les Granges ; but its machinery, by which a child 

 of ten years old could with ease and safety draw up water, is now no more. On 

 one side of the farm yard is a hovel, in which that good man studied during his 

 visits to Port Royal- a place rendered famous also by the name of the devout 

 Arnauld D'Andilli. 



