AND THE ATMOSPHERE. 217 



has undergone, from the cube, to the form of a 

 bottle, diminishes its weight in proportion to 

 tiie increased quantity of water which it has 

 displaced ; the excess of density contained by 

 the copper, over the water in which it is im- 

 mersed, will, nevertheless, cause the bottle to 

 sink. The pressure downward which is thus 

 produced, is not the pressure from the increased 

 density of the water in the bottle above that 

 which is external to it, both are of the same 

 nature: the difference altogether depends on 

 the difference which exists between the pres- 

 sure from the copper, overcoming the resist- 

 ance of the water. The denser body immersed 

 in the rarer one. If to the top of this bottle of 

 water, thus sinking in water, a bladder full of 

 air is tied to the neck of it, instead of the bottle 

 of water sinking as before, it will be found to 

 float, and to rise^on the surface the reason is 

 obvious ; the rarity of the air in the bladder, 

 together with the density of the copper, are 

 not equal to the density of the water alone, in. 

 which the bottle is placed : when a bottle of 

 water sinks in water, and a bottle of air swims 

 in it, it is not that water gravitates in water ; 

 but that the solid substance of which the 

 bottle is composed, is denser than the water 

 in which it is immersed ; and when a bottle of 

 air floats in water, it is because the air which 

 that bottle contains, added to the weight of the 



