THE EARTH. 1.33 



wiil be great, in proportion as the arm filled with water is talL 

 We may, therefore, generally conclude, that the bottom of every 

 vessel is pressed by a force, in proportion to the height of the 

 water in that vessel. For instance, if the vessel filled with 

 water be forty feet high, the bottom of that vessel will sustain such 

 a pressure as would raise the same water forty feet high, which 

 IS very great. From hence we see how extremely apt our pipe?, 

 that convey water to the city, are to burst; for descending from a 

 hill of more than forty feet high, they are pressed by the water 

 contained in them, with a force equal to what would raise it to 

 m.ore than forty feet high ; and that this is sometimes able to 

 burst a wooden pipe, we can have no room to doubt of. 



Still recurring to our pipe, let us suppose one of its arms ten 

 times as thick as the other ; this will produce no effect whatso- 

 ever upon the obstacle below, which we .supposed hindering its rise 

 m the other arm ; because, how thick soever the pipe may be, 

 its contents would only rise to its own level ; and it will, there- 

 fore, press the obstacle with a force equal thereto. We may, 

 therefore, imiversally conclude, that the bott.im of any vessel is 

 pressed by its water, not as it is broad or narrow, but in propor- 

 tion as it is high. Thus the water contained in a vessel not 

 thicker than my finger, presses its bottom as forcibly as the 

 water contained in a hogshead of an equal height ; and, if we 

 made holes in the bottoms of both, the water would burst out 

 as forceful from the one as the other. Hence we may, with 

 great ease, burst a hogshead vrith a single quart of water ; and 

 it has been often done. We have only,' for this, to place a 

 hogshead on one end, filled with water : we then bore a hole in 

 its top, into which we plant a narrow tin pipe, of about thirty feet 

 high : by poiuing a quart of water into this, at the top, as it 

 continues to rise higher in the pipe, it will press more forcibly 

 on the bottom and sides of the hogshead below, and at last 

 burst it- 

 Still returning to our simple instrument of demonstration. 

 If we suppose the obstacle at the bottom of the pipe to be move- 

 able, so as that the force of the water can push it up into the 

 other arm ; such a body as quicksilver, for instance. Now, it 

 is evident, that the weight of water weighing down upon this 



2 NoUet's Lectures. 



