Iviii 



INTRODUCTION TO HYDROSTATICS. 

 Fig. 4. 



the rest, it is only the column of particles immediately above the orifice 

 that can weigh upon and press out the liquid. 



In a cubical vessel, the pressure downwards will be double the lateral 

 pressure on one side, for every particle at the bottom of the vessel is 

 pressed upon by a column of the whole depth of the fluid, whilst the 

 lateral pressure diminishes equably from the bottom upwards to the sur- 

 face, where the particles have no pressure. 



The pressure of fluids upwards, though it seems in direct opposition 

 to gravity, is also a consequence of their pressure downwards. When, 

 for example, water is poured into a tea-pot, the water rises in the spout 

 to a level with that in the pot. The particles of water at the bottom 

 of the pot are pressed upon by the particles above them ; to this 

 pressure they will yield, if there is any mode of making way for the su- 

 perior particles, and as they cannot descend, they will change their direc- 

 tion and rise in the spout. 



Suppose the tea-pot to be filled with columns of particles of water 

 similar to that described in Jig. 5, the particle 1 at the bottom will be 



Fig. 5. 



Fig. 6. 



pressed laterally by the particle 2, 

 and by this pressure be forced into 

 the spout, where, meeting with the 

 particle 3, it presses it upwards, and 

 this pressure will be continued from 

 3 to 4, from 4 to 5, and so on, till the 

 water in the spout has risen to a level 

 with that in the pot. 



You may also reverse the experi- 

 ment by pouring water into the spout, and you will find 

 that the water will rise in the pot to a level with that in 

 the spout, for the pressure of the small quantity of water 

 in the spout will force up and support the larger quantity 

 in the pot. But this will be better exemplified byjtfg. 6, 

 in which a goblet is filled by means of a narrow tube. In 

 the pressure upwards, as well as that laterally, the force 

 results entirely from the height, and is quite independent 

 of the horizontal dimensions of the fluid. The tube, how- 

 ever, could never be filled by pouring water into the goblet, 

 because the water in the goblet cannot force that in the tube 

 above its own level, and as the end of the tube is considera- 

 bly highest, if water be poured into the goblet after it is full, 

 it will run over instead of rising in the tube above the level. 



