HYDROSTATICS. Ill 



quantity of water, how small soever, will sustain 

 any weight, however large. 



The same may be shown thus : let A G B D re- 

 present a hollow cylinder of wood, which nearly 

 fills the cavity. In the cylinder, suppose a little 

 water, whose surface is g b (Plate 8. fig. 5.); then, 

 if the wooden cylinder be put into the hollow one, 

 the water will rise between the surfaces to a and d t 

 and the wood will be sustained floating. The 

 nearer the wooden cylinder approaches to the size 

 of the cavity, the less water is necessary for the 

 experiment. 



The hydrostatic bellows is perhaps the best ma- 

 chine for demonstrating the upward pressure of 

 fluids. It consists of two thick oval boards (Plate 8. 

 fig. 6.) each about 16 inches broad, and 18 inches 

 long, covered with leather, to open and shut like a 

 common bellows, but without valves ; only a pipe 

 about three feet high is fixed into the bellows. 

 Let some water be poured into the pipe ; it will 

 run into the bellows, and separate the boards a 

 little : then lay three weights, each weighing 100 

 pounds, upon the upper board, and pour more 

 water into the pipe, which will run into the 

 bellows, and raise up the board with all the weights 

 upon it; and if the pipe be kept full until the 

 weights are raised as high as the leather which 

 covers the bellows will allow them, the water will 

 remain in the pipe, and support all the weights, 

 even though it should weigh no more than a 

 quarter of a pound, and they 300 pounds : nor 

 will their utmost weight cause the boards to de- 

 scend, and force the water out at the top of the 

 pipe. 



The reason of this will be made evident, by con- 



