62 



ELEMENTS OF LABORATORY WORK 



the other end (B) of the string. If the two portions of the 

 string are vertical, or at the same angle with the vertical, equal 

 quantities of matter at each end counterpoise that is, the plate 

 and the liquid will be equal to the quantity of matter at B. 

 There is, therefore, no vertical support to the liquid from the 

 sides of the vessel. 



If we now immerse a thin plate in a liquid, and weigh it 

 while immersed, as if its density were being ascertained, it will 

 be found that it is counterpoised by the same quantity of 

 matter at all depths. 



The next observation is that the pressure at the bottom of 

 a vessel depends in no way upon the shape of the vessel, or the 



Fig. 19. 



quantity of liquid contained in it, but merely upon the linear 

 vertical distance between the lower and upper surfaces of the 

 liquid, and also, as we should expect, upon the area of the 

 lower surface. Vessels of the shapes shown above (Nos. 3 and 4, 

 fig. 19), together with the pulley and ground-glass plate, are 

 sufficient to demonstrate this. 



The following facts are therefore clear : 



1. That the vertical sides of the vessel (No. 1) do not sup- 

 port the liquid in the meaning of reducing the stress between 

 the earth and the liquid. 



2. That the sides of the vessel (No. 3) do reduce the stress 

 to the extent that the bottom of the vessel only requires 



