OF HYDROSTATICS. 



121 



blows into the bellows through the pipe B, he will raise LECT. 

 himself upward upon the board and the smaller the ^^^ 



bore of the pipe is, the easier he will be able to raise How a 



, man may 



himself. And then, by clapping his finger upon the top raise him- 



of the pipe, he can 'support himself as long as 



pleases ; provided the bellows be air-tight, so as not to his breath. 



lose what is blown into it. 



Upon this principle of the upward pressure of fluids, How lead 



a piece of lead may be made to swim in water, by im- ^ e b ^ o 



mersing it to a proper depth, and keeping the water 8W im i n 



from getting above it. Let C D be a glass tube open water - 



throughout, and EFG a flat piece of 



lead, exactly fitted to the lower end of the 



tube, not to go within it, but for it to 



stand upon ; with a wet leather between 



the lead and the tube to make close work. 



Let this leaden bottom be half an inch 



thick, and held close to the tube by pul- 



ling the packthread I H L upward at L 

 with one hand, whilst the tube is held in 

 the other by the upper end C. In this 

 situation, let the tube be immersed in 

 water in the glass vessel A B, to the depth of six inches 

 below the surface of the water at K; end then, the 

 leaden bottom jEjPGwill be plunged to the depth of 

 somewhat more than eleven times its own thickness : 

 holding the tube at that depth, you may let go the thread 

 at L ; and the lead will not fall from the tube, but will 

 be kept to it by the upward pressure of the water below 

 it, occasioned by the height of the water at K above 

 the level of the lead. For as lead is 11.33 times as 

 heavy as its bulk of water, and is in this experiment 

 immersed to a depth somewhat more than 11.33 times 

 its thickness, and no water getting into the tube between 

 it and the lead, the column of water EabcG below the 

 lead is pressed upward against it by the water KDEGL 

 all around the tube ; which water being a little more 



