THE EARTH. 159 



From this easy yielding of its parts to external 

 pressure, arises the art of determining the speci- 

 fic gravity of bodies by plunging them in water ; 

 with many other useful discoveries in that part 

 of natural philosophy called hydrostatics. The 

 laws of this science, which Archimedes began, 

 and Pascal, with some other of the moderns, have 

 much improved, rather belongs to experimental 

 than to natural history. However, I will take 

 leave to mention some of the most striking para- 

 doxes in this branch of science, which are as well 

 confirmed by experiment, as rendered universal 

 by theory. It would indeed be unpardonable, 

 while discoursing on the properties of water, to 

 omit giving some account of the manner in 

 which it sustains such immense bulks as we see 

 floating upon its soft and yielding surface ; how 

 some bodies that are known to sink at one time, 

 swim with ease, if their surface be enlarged; 

 how the heaviest body, even gold itself, may be 

 made to swim upon water ; and how the lightest, 

 such as cork, shall remain sunk at the bottom : 

 how the pouring in of a single quart of water 

 will burst a hogshead hooped with iron ; and 

 how it ascends in pipes from the valley, to travel 

 over the mountain : these are circumstances that 

 are at first surprising; but, upon a slight con- 

 sideration, lose their wonder. 



* In order to conceive the manner in which all 

 these wonders are effected, we must begin by 



* In the above sketch, the manner of demonstrating used by Monsieur 

 D'Alembert is made use of as the most obvious, and the most satisfactory. 

 Vide Essai sur, &c. 



47 



