62 



SCIENTIFIC RECREATIONS. 



a body of as irregular form as we please; a stone, for example. A" thread 

 is attached to the stone, and it is then placed in a glass of water full up to 

 the brim. The water overflows ; a volume of the liquid equal to that of the 

 stone runs over. The glass thus partially emptied is then dried, and placed 

 on the scale of a balance, beneath which we suspend the stone ; equilibrium 

 is established by placing some pieces of lead in the other scale. We then 

 take a vase full of water, into which we plunge the stone suspended from 

 the scale, supporting the vase by means of bricks. The equilibrium is now 

 broken; to re-establish it, it is necessary to fill up with water the glass 



Fig. 64. Demonstration of the upward pressure of liquids. 



placed on the scale; that is to say, we put back in the glass the weight of a 

 volume of water precisely equal to that of the stone. 



If it is desired to investigate the principles relating to connected vessels, 

 springs of water, artesian wells, etc., two funnels, connected by means of an 

 india-rubber tube of certain length, will serve for the demonstration ; and by 

 placing the first funnel at a higher level, and pouring in water abundantly, 

 we shall see that it overflows from the second. 



A disc of cardboard and a lamp-glass will be all that is required to 

 show the upward pressure of liquids. I apply to the opening of the lamp- 

 glass a round piece of cardboard, which I hold in place by means of a string; 

 the tube thus closed I plunge into a vessel filled with' water. The piece of 

 cardboard is held by the pressure of the water upwards. To separate it 



