122 FERGUSON'S LECTURES. 



than 11.33 times as high as the lead is thick, is suffi- 

 cient to balance and support the lead at the depth K E 

 If a little water be poured into the tube upon the lead, 

 it will increase the weight upon the column of water 

 under the lead, and cause the lead to fall from the tube 

 to the bottom of the glass vessel, where it will lie in the 

 situation bd. Or, if the tube be raised a little in the 

 water, the lead will fall by its own weight, which will 

 then be too great for the pressure of the water around 

 the tube upon the column of water below it. 

 How light L gt two pieces of wood be planed quite flat, so as no 

 wood may wa ter may get in between them when they are put to- 

 to lie at gether : let one of the pieces, as b d, be cemented to the 



bottom of the vessel A B (P- 121 >) and the oth er piece 

 be laid flat and close upon it, and held down to it by a 

 stick, whilst water is poured into the vessel ; then re- 

 move the stick, and the upper piece of wood will not 

 rise from the lower one : for, as the upper one is press- 

 ed down both by its own weight and the weight of all 

 the water over it, whilst the contrary pressure of the wa- 

 ter is kept off by the wood under it, it will lie as still as 

 a stone would do in its place. But if it be raised ever 

 so little at any edge, some water will then get under it ; 

 which being acted upon by the water above, will im- 

 mediately press it upward ; and as it is lighter than its 

 bulk of water, it will rise, and float upon the surface of 

 the water. 



All fluids weigh just as much in their own element as 

 they do in open air. To prove this by experiment, let 

 as much shot be put into a phial, as, when corked, will 

 make it sink in water : and being thus charged, let it be 

 weighed, first in air, and then in water, and the weights 

 in both cases written down. Then, as the phial hangs 

 suspended in water, and counterpoised, pull out the cork, 

 that wafer may run into it, and it will descend, and pull 

 down that end of the beam. This done, put as much 

 weight into the opposite scale as will restore the equi- 



