LESSONS IN PHYSICS. 35 



of a pail or barrel filled with water, as well as through holes in 

 the bottom. And the fact that objects float on liquids, shows 

 that they press upward ; hence, it seems clear that liquids press in 

 all directions downward, sidewise and upward. Careful experi- 

 ments show that in a body of water, at rest, pressure is equal in 

 all these directions. The rigid mountain seeks its level as eagerly 

 as a body of water but the mobility of the water enables it to 

 find its level more easily and quickly than the mountain can. 

 Every body of liquid when at rest has a level surface, that is, 

 every part of the surface is equally distant from the center of the 

 earth, arid this is true however irregular the body of water may 

 be. If a tube or pipe, even miles in length, be connected with a 

 pond, lake, or other body of water, it becomes a part of the 

 pond or lake and the water rises to the same level in the pipe as 

 in the pond. This accounts for many springs and artesian wells, 

 and on this principal many cities and towns are supplied with 

 water from ponds or lakes, often miles away among the hills 

 above them, the main pipe being divided and subdivided into 

 thousands of service pipes in each of which the water rises to any 

 level not above the level of the reservoir. In practice it will not 

 rise quite as high as the source, on account of friction in pipes. 

 The liquid water weighs about 62% pounds or 1,000 ounces per 

 cubic foot, or about .577 of an ounce per cubic inch. Water is 

 heavy and when urged down a steep slope by the force of gravity 

 exhibits a terrific power; even when the slope is only moderately 

 steep its destructive power is immense, as shown in the case of 

 the disaster from the breaking of the dam at Johnstown, Penn- 

 sylvania, and as manifested everywhere in the work of torrents 

 and rivers. This force is sometimes utilized in placer mining, by 

 bringing the water down a steep slope in pipes, using it to move 

 soil, gravel and rocks, much as a garden hose is sometimes used 

 for cleaning walks, etc. It is also used for driving various kinds 

 of machinery. 



The fact that liquids press upwards may be shown as follows : 

 Suspend a solid, as a stone, by a wire from one end of a scale 

 beam, so that it hangs near the bottom of a pail or tub. After 



