CHAPTER VI. 



ABOUT WATER HYDROSTATICS AND HYDRAULICS LAW OF ARCHIMEDES 



THE BRAMAH PRESS THE SYPHON. 



AT present we will pass from Air to Water, from Pneumatics to Hydrostatics 

 and Hydraulics. We must remember that Hydrostatics and Hydraulics are 

 very different. The former treats of the weight and pressure of liquids when 

 they are at rest, the latter treats of them in motion. We will now speak of the 

 properties of Liquids, of which Water may be taken as the most familiar 

 example. 



We have already seen that Matter exists in the form of Solids, Liquids, 

 and Gases, and of course Water is one form of Matter. It occupies a certain 

 space, is slightly compressible ; it possesses weight, and exercises force when 

 in motion. It is a fluid, but also a liquid. There are fluids not liquid, such 

 as air or steam, to take equally familiar examples. These are elastic fluids 

 and compressible, while water is inelastic, and termed incompressible. 



The chemical composition of water will be considered hereafter, but at 

 present we may state that water is composed of oxygen and hydrogen, and 

 proportions of eight of the former to one of the latter by weight ; in volume 

 the hydrogen is as two to one. 



From these facts, as regards water, we learn that volume and weight are 

 very different things, that equal , volumes of various things may have 

 different weights, and that volume (or bulk) by no means indicates weight 

 Equal volumes of feathers and sand will weigh very differently. 



[The old " catch " question of the " difference in weight between a pound of lead and a 

 pound of feathers " here comes to the mind. The answer generally given is that " feathers 

 make the heavier ' pound/ because they are weighed by avoirdupois, and lead by troy weight." 

 This is an error. They are both weighed in the same way, and pound for pound are the same 

 weight, though different in volume^ 



Fluids in equilibrium have all their particles at the same distance from 

 the contre of the earth, and although within small distances liquids appear 

 perfectly level (in a direct line), they must, as the sea does, conform to the 

 shape of the earth, though in small levels the space is too limited to admit of 

 any deviation from the plane at right angle to the direction of gravity. 



Liquids always fall to a perfectly level surface, and water will seek to 

 find its original level, whether it be in one side of a bent tube, in a watering 

 pot and its spout, or as a fountain. The surface of the water will be on the 

 same level in the arms of a bent tube, and the fountain will rise to a height 



