238 GRAVITY AND LEVITY 



them, and the rarified medium through which 

 they pass, than from any attracting power iu 

 the earth : if they fall in water, their motion is 

 retarded when they reach the solid matter of 

 the earth, it is altogether arrested ; they are 

 resisted by it more than they press it ; their 

 weight is actually, and absolutely, annihilated. 

 But if these effects arise from the relation which 

 exists between the quality of the medium, and 

 the matter by which they are surrounded, they 

 cannot arise from the attracting power of the 

 earth ; and, if they do not arise from the atr 

 tracting power of the earth, it must necessarily 

 follow, that gravity gravitation, or weight, is 

 a relative, and not a positive term. The 

 question then is, By what standard is this 

 relation to be measured? I answer, the 

 density which the same bulk of matter con- 

 tains, with relation to the rarity, of the 

 same bulk of matter which it displaces : it 

 is the density, or tenuity, of the medium, which 

 is displaced, with relation to the density, or 

 tenuity, of the body which displaces it, which 

 determines whether a body shall descend, or 

 ascend, or remain suspended ; and constitutes 

 the standard of measure. Gravitation, there- 

 fore, properly defined, is the pressure down- 

 wards which dense bodies produce, on such as 

 are rare; and levity is the pressure upwards 

 which rare bodies produce on such as ars 



