OBJECTS, PLEASURES, AND ADVANTAGES OF SCIENCE. si 



Now, this is one of the most important truths in the whole compass of science ; for it does so happen 

 that the force with which bodies fall towards the earth, or what is called their gravity, the power that draws 

 or attracts them towards the earth, varies with the distance from the Earth's centre, exactly in the 

 proportion of the squares, lessening as the distance increases : at two diameters from the Earth's centre, it 

 is four times less than at one ; at three diameters, nine times less ; and so forth. It goes on lessening, 

 but never Li destroyed, even at the greatest distances to which we can reach by our observations, and there 

 can be no doubt of its extending indefinitely beyond. But, by astronomical observations made upon the 

 motion of the heavenly bodies, upon that of the moon for instance, it is proved that her movement is 

 slower and quicker at different parts of her course, in the same manner as a body's motion on the earth 

 would be slower and quicker, according to its distance from the point it was drawn towards, provided it 

 was drawn by a force acting in the proportion to the squares of the distance, which we have frequently 

 mentioned ; and the proportion of the time to the distance is also observed to agree with the rule above 

 referred to. Therefore, she is shown to be attracted towards the Earth by a force that varies according to 

 the same proportion in which gravity varies ; and she must consequently move in an ellipse round the Earth, 

 which ia placed in a point nearer the one end than the other of that curve. In like manner, it is shown 

 that the Earth moves round the Sun in the same curve line, and is drawn towards the sun by a similar 

 force ; and that all the other planets in their courses, at various distances, follow the same rule, moving in 

 el'ip^es, and drawn towards the Sun by the same kind of power. Three of them have moons like the 

 Earth, only more numerous, for Jupiter has four, Saturn seven, and Uerschel six, so very distant, that we 

 cannot see them without the help of glasses ; but all those moons move round their principal planets, as 

 ours does round the Earth, in ovals or ellipses ; while the planets, with their moons, move in their ovals 

 round the Sun, like our own Earth with its moon. 



But this power, which draws them all towards the sun, and regulates their path and their motion 

 round him, and which draws the moons towards the principal planets, and regulates their motion and 

 path round those planets, is the name with the gravity by which bodies fall towards the earth, being 

 attracted by it. Therefore, the whole of the heavenly bodies are kept in their places, and wheel round 

 the sun, by the same influence or power that makes a stone fall to the ground. 



It is usual to call the sun, and the planets which with their moons move round him (eight in 

 number, including Neptune, lately discovered ; and besides these, are the asteroids), the Sular System, because 

 tlii-y are a class of the heavenly bodies far apart from the innumerable fixed stars, and BO near each 

 other as to exert a perceptible influence on one another, and thus to be connected together. 



The Cornell belong to the same system, according to this manner of viewing the subject. They are 

 bodies which move in elliptical paths, but far longer and narrower than the curves in which the earth and 

 the other planets and their moons roll. Our curves are not much less round than circles ; the paths 

 of the comets are long and narrow, so as, in many places, to be more nearly straight lines than circles. 

 They differ from the planets and their moons in another respect ; they do not depend on the sun for the 

 light they give, as our moon plainly does, being dark when the earth comes between her and the sun ; and 

 as the other planets do, those of them that are nearer the sun than we are, being dark when they come 

 between us and him, appearing to pass across his surface. But the comets give light always of themselves, 

 being apparently vast bodies heated red-hot by coming in their course far nearer the sun than the nearest j 

 of the planets ever do. Their motion, when near the sun, is much more rapid than that of the planets ; j 

 they both approach him much nearer, retreat from him to much greater distances, and take much longer j 

 time in going round him, than any of the planets do. Yet even these comets are subject to the same 

 great law of gravitation which regulates the motions of the planets. Their year, the time they take to 

 revolve, is in some cases 75, in others 135, in others 800 of our yean ; their distance is a hundred timeb 

 our distance when farthest off*, and not a hundred and sixtieth of our distance when nearest the suu; j 

 -Aiftest motion is above twelve times swifter than ours, although ours is a hundred and forty 



swifter than a cannon-ball's ; yet their path ia a curve of the same kind with ours, though longer 

 and flatter, differing in its formation only as one oval differs from another by the string you draw it with 

 having the ends fixed at two points more distant from each other: consequently the sun, being in one 

 of those points, is much nearer the end of the path the comet moves in, than he is near the end of our 

 path. Their motion, too, follows the same rule, being swifter the nearer the sun : the attraction of 

 the sun for them varies according to the squares of the distances, being four times less at twice the 

 distance, nine times less at thrice, and so on ; and the proportion between the times of revolving and the 

 distances is exactly the same, in the case of those remote bodies, as in that of the moon and the earth. 

 One law prevails over all, and regulates their motions as well as our own ; it is the gravity of the comets 

 towards the sun, and they, like our own earth and moon, wheel round him in boundless space, drawn by 

 the same force, acting by the same rule, which makes a stone fall when dropped from the hand. 



The more full and accurate our observations are upon those heavenly bodies, the better we find all 

 their motions agreeing with thin great doctrine ; although, no doubt, many things are to be taken into 

 the account besides the force that draws them to the different centres. Thus, while the moon is drawn 



