PLEASURES OF SCIENCE. 21 



disturb the order of the system, and to make the appearances depart 

 from the doctrine, are themselves subject to a certain fixed rule, and 

 can never go beyond a particular point, but must begin to lessen when 

 they have slowly reached that point, and then lessen until they reach 

 another point, when they begin again to increase; and so on, for ever. 

 Thus, the planets move in ovals, from gravity, the power that attracts 

 them, towards the sun, combined with the original impulse they re- 

 ceived forwards ; and the disturbing forces are continually varying the 

 course of the curves or ovals, making them bulge out in the middle, as 

 it were, on the sides, though in a very small proportion to the whole 

 length of the ellipse. The oval thus bulging, however, its length never 

 alters, only its breadth, and that breadth increases by a very small 

 quantity yearly and daily ; after a certain number of years it becomes 

 as great as it ever can be; then the alteration takes a contrary direc- 

 tion, and the curve gradually flattens as it had bulged ; till, in the same 

 number of years which it took to bulge, it becomes as flat as it ever 

 can be, and then it begins to bulge again, and so on for ever ; and so 

 of every other disturbance and irregularity in the system. What at 

 first appears to be some departure from the rule, when more fully ex- 

 amined, turns out to be only a consequence of it, or a result of a more 

 general arrangement springing from the principle of gravitation ; an 

 arrangement of which the rule itself, and the apparent or supposed 

 exception, form parts. 



The power of gravitation, which thus regulates the whole system of 

 the universe, is found to rule each member or branch of it separately. 

 Thus, it is demonstrated, that the tides of the ocean are caused by the 

 gravitation which attracts the water towards the sun and moon ; and 

 the figure both of our earth and of such of the other bodies as have a 

 spinning motion round their axis, is determined by gravitation ; they are 

 all flattened towards the ends of the axis they spin upon, and bulge out 

 towards the middle. 



The great discoverer of the principle on which all these truths rest, 

 Sir Isaac Newton, certainly by far the most extraordinary man that 

 ever lived, concluded by reasoning upon the nature of motion and 

 matter that this flattening must take place in our globe : every one 

 before his time. had believed the earth to be a perfect sphere or globe, 

 chiefly from observing the round shadow which it casts on the moon in 

 eclipses ; and it was many years after his death that the accuracy of his 

 opinion was proved by measurements on the earth's surface, and by the 

 different weight and attraction of bodies at the equator, where it 

 bulges, and at the poles, where it is flattened. The improved tele- 

 scopes have enabled us to ascertain the same fact with respect to the 

 planets Jupiter and Saturn. 



Beside unfolding the general laws which regulate the motions and 

 figures of the heavenly bodies forming our solar system, Astronomy 

 consists in calculations of the places, times, and eclipses of those 

 bodies, and their moons or satellites, (from a Latin word, signifying an 

 attendant ;) and in observations of the fixed stars, which are innumer- 

 able assemblages of bodies, not moving round the sun as our earth 

 and the other planets do, nor receiving the light they shine with from 

 his light ; but shining, as the sun and the comets do, with a light of 



