LECTURE V. 



EXPERIMENTAL PHILOSOPHY. 



HYDRAULICS. 



HYDROSTATICS, we have seen, is that science 

 which relates to the weight and pressure of fluids ; 

 the science of hydraulics teaches us what respects 

 the motion of fluids, and the means of raising 

 them by pumps, and conducting them by pipes 

 or aqueducts from one station to another. This 

 branch of science is, also, called Hydrodynamics. 



It was laid down as a principle, in the preced- 

 ing lecture, that of all waters which communicate 

 with each other, the surface will be level, or, in 

 common language, that water will rise to its level, 

 or to the same height as its source. The reason 

 of this was not fully assigned then, because it was 

 not necessary ; it was observed, that fluids press 

 equally on all sides; but another reason which 

 partly operates to produce the level surface of 

 water is the pressure of another fluid, that is, the 

 air or atmosphere, which, as it bears equally on all 

 points of the earth's surface, must equally press 

 the source from which water is derived and the 

 orifice of the tube or pipe in which it rises, as 

 was evidenced in the three united tubes, which 

 were exhibited as explanatory of this fact. 



That a reservoir of water, less than S3 feet in 



