MUTUAL CHANGES COMMON TO ALL MATTER 



61 



volume in the liquid during the experiment. With the con- 

 ditions described there is no alteration, as the measurement of 

 the total volume would show. We may consider a portion of 

 the water to act as an incompressible body, which is depressed 

 atone end by the added water, while at the other end it succeeds 

 in raising a certain quantity. The relation of the quantity of 

 water raised to the quantity depressed depends upon the 

 sectional areas of the columns, and consequently upon the 

 vertical displacements. It may be of value to note that the 

 sectional areas of the columns in this experiment correspond 

 with the arms of the lever. 



44. The Internal Stress of Liquids. The preceding obser- 

 vations having shown some conditions of equilibrium of liquids 

 afc rest, the internal state of such liquids remains to be inves- 

 tigated. 



It may be noticed, in the first place, that in a given 

 column of liquid the pressure increases with the depth, just 

 as in the case of a solid. 

 The pressure at the 

 bottom of the regular- 

 liquid column AB (No. 

 1, fig. 19) varies directly 

 with the linear height 

 A B, just as in the case 

 of a homogeneous solid 

 of similar shape. The 

 bottom of the vessel supports the quantity 

 of matter in the vessel just as if it were 

 a solid rod receiving no support from 

 the sides. The stress between the matter 

 and the earth -is the same whether it is 

 solid or liquid matter. With the arrange- 

 ment here shown (No. 2, fig. 19) of a 

 string passing over a pulley A and through 

 a hole in the ground and greased plate P, 

 fitting against the ground edges of the 

 vessel v, the varying quantities of liquid added to v will be 

 found to be balanced by proportional quantities of matter at 



(i) 



^m v 



