INTRODUCTION. XXIX 



matter immersed in the sea to a given depth, as being likely to 

 suggest some easy and accurate methods of determining the depth 

 of the ocean, when it is so profound as to preclude the appli- 

 cation of the methods npw in use. The next fact claiming our 

 attention here, is the result we obtain by putting fluids of dif- 

 ferent densities into bended tubes, when the perpendicular alti- 

 tudes of these fluids above their common surface will vary 

 inversely as their specific gravity ; for we herein settle at once 

 the grand problem in our domestic policy what is the best 

 method by which large towns and cities, or in fact any place, 

 can be supplied with water from a distance. But this is not all 

 another result is, the construction of the hydrostatic quadrant, 

 for finding the altitude of the heavenly bodies, when from haze 

 or atmospheric obscurity, the horizon is rendered indistinct or 

 invisible. We trust our investigation of this beautiful principle 

 of the pressure of fluids of variable density, will in some mea- 

 sure facilitate the construction of the hydrostatic quadrant an 

 instrument but as yet in its infancy. 



The Eighth Chapter is one of vast utility in constructive me- 

 chanics, when it is necessary to investigate the pressure of fluids 

 on dykes and embankments, a subject interesting and im- 

 portant in the doctrine of Hydraulic Architecture, and peculiarly 

 applicable to the inland navigation and the maritime accommoda- 

 tion of a country situated like Great Britain, every where inter- 

 sected by canals, and seamed in all the sinuosities of her coast 

 by the tides and waves of the restless and turbulent commercial 

 ocean. Moreover, this subject is particularly applicable to the 

 great works now in progress, as rail-roads, docks, harbours, and 

 basins. The brevity of this chapter is compensated by the unity 

 it confers on separate and distinct portions of fluid pressure 

 and support : and the exact formulae it affords to practical men 

 in estimating expense, while their undertakings are executed with 

 systematic regard to permanent durability. 



The Ninth Chapter treats of floatation, and the determina- 

 tion of the specific gravities of bodies immersed in fluids, com- 

 prehending therein some of the most interesting and important 

 principles of Hydrodynamic Science. There are two general 

 propositions embraced by this department of the philosophy of 

 fluids : viz. 



