INTRODUCTION. Iti 



fluids, in which we no longer consider each distinct particTe that is capable of 

 separate motion, but where we attend to the effect of an infinite number of 

 particles, constituting a liquid or aeriform aggregate. The general theory of 

 such motions will be premised, under the heads hydrostatics, or the affections 

 of liquids at rest, pneumatostatics, or the properties of clastic fluids at rest; 

 and hydraulics, or the theory of fluids in motion. The practical application 

 of this theory to hydraulic and pneumatic machines is of very considerable 

 importance, and is as interesting to the philosopher as it is necessary to the 

 engineer. The employment of the force of water and wind to the best ad- 

 vantage, the draining of lands and mhies, the supply of water for domestic 

 convenience, the manoeuvres of seamanship, the construction of the steam 

 engine, are all dependent upon hydrodynamical principles, and are often con- 

 sidered as comprehended in the science of hydraulics. Harmonies and optics, 

 the remaining parts of this division, are more insulated : the doctrine of 

 sound, the theory of music,, and the construction of musical instruments, are 

 as pleasing to the intellect in theory, as they are gratifying to the senses in 

 practice; but the science of optics is not less interesting, and at the same 

 time far more useful; the instruments which it furnishes are of almost indis- 

 pensable necessity to the navigator, to tire naturalist, to the physiologist, and 

 evert to the man of business or pleasure. It is perhaps in this science that 

 many persons of the greatest genius have been the most happily employed. 

 The reasons for which it is classed as a division of hydrodynamics will be ex- 

 plained hereafter. 



The contemplation of the particular phenomena of nature, as they are dis- 

 played in the universe at large, contributes perhaps less to the perfection of 

 any of the arts, which are immediately subservient to profit or convenience,, 

 than the study of mechanics and hydrodynamics. But the dignity and mag'^ 

 niiicence of some of these phenomena, and the beauty and variety of others, 

 render them highly interesting to the philosophical mind, at the same tinle 

 that some of them are of the utmost importance in their application to the 

 purposes of life. In ail these respects the science of astronomy holds the first 

 rank ; its uses in assisting navigation, and in regulating chronology, are be- 

 yond all calculation. Geography, and hydrography, or the particular histories 

 of the earth and sea, are immediately connected with astronomy. The discus- 

 iion of the properties of matter in general, and of the alterations of tempera-- 



