OUTLINES OF NATURAL PHILOSOPHY. 



misphere opposite to the Sun, this attraction is to- 

 ward the point which has the Sun in its nadir. 



336. If the surface of the Earth be covered 

 by a fluid, the parts will move in obedience to 

 these forces ; those columns, where the Sun is 

 vertical, will be rendered lighter, and will be 

 lengthened, in order- to be in equilibria with 

 those at the distance of 90, which will of course 

 be shortened. 



The same thing exactly will happen in the opposite 

 hemisphere ; and if the waters on the Earth's sur- 

 face were at rest, the Ocean would form itself into 

 an oblong spheroid, with its longer axis passing 

 through the attracting body. When there are two 

 attracting bodies, their effects will most nearly co- 

 incide, when they are nearest to one another ; and 

 will be equal to .the sum of the two effects taken 

 separately. When they are 90 distant, the effect 

 produced will be the difference of the separate ef- 

 fects. This is NEWTON'S explanation of the tides. 

 He calculates the mean force by which the Sun 

 diminishes the force of gravity at the surface, as 

 equal to one 1 2868200 part of gravity. Hence he 

 deduces the longer axis, and the greatest rise of 

 the tide produced by the Sun at 9.2 inches. De 

 Systemate Mundi. Opera, torn. in. p. 212. A 

 different determination h given in the Principia, 

 lib. in. prop. 36. 



The 



