OF SOLIDS AND LIQUIDS. 235 



%rie question concerning its cause ; ch using to 

 propose it by way of a question, because I am 

 not yet satisfied with it for want of experi- 

 ments." He, therefore, proposes (Optics, Quae- 

 ry 21.) to account for the gravitation of the 

 planets towards the sun, " By means of an 

 elastic fluid surrounding the sun (and in like 

 manner surrounding every other body,) suppo-^ 

 sing this medium to increase in density, as it 

 passes at greater distance from the sun, cau- 

 sing thereby the gravity of these greater bodies 

 towards each other, and of their parts towards 

 the bodies; every body endeavouring to go 

 from the denser parts of the medium towards 

 the rarer. For if this medium be rarer within 

 the sun's body, than at its surface ; and rarer 

 there, than at the hundredth part of an inch 

 from its body ; and rarer there, than at the 

 orbit of Saturn ; I see no reason why the in* 

 crease of density should stop any where, and 

 not rather be continued at all distances from 

 the sun to Saturn, and beyond. And though 

 this increase of density may, at great distances, 

 be exceeding slow, yet if the elastic force of this 

 medium be exceeding great, it may suffice to 

 impel bodies from the denser parts of the me- 

 dium towards the rarer, with all that power 

 which we call gravity." 



I shall make an extract also from Mr. 

 Coffc's Preface to the Translation of Sir I. 



