If the force of gravity had varied in any other inverse law, so that it should diminish as the distance increases, neither of these two conditions would have been answered.

One body indeed, projected in a proper direction and with a determinate velocity, might describe a circle about another body, and about the common center of gravity of the two bodies, whatever be the variation in the law of gravity at different distances. But the mutual action of several such bodies would immediately disturb the regularity of their motions. And however small the deviation might be at first, since there would be in the system itself no tendency to regain its original state, it is clear, that without a continual exertion of an external intelligent power, a series of changes would occur which would terminate in an entire subversion of the system.

Upon the system of nature, on the contrary, stability is impressed by the hand of God. Unwearied research and great sagacity have led men by degrees to measure and to weigh the planetary system: and at every fresh step, some new discovery has been made, which affords fresh grounds for astonishment at the power and wisdom of the Almighty. There was a period in the history of science, when men of the greatest intellect, the most

ardent enquirers into the works of nature, thought that the frame of the material system in which we are placed was not so accurately adjusted, but that it would, from time to time, require correction by the immediate interposition of the Creator's handb. Subsequent improvement in abstract science has shewn that this is not the case. The great machine of the solar system is so nicely balanced within itself, that it will continue to perform its majestic revolutions, until it shall seem good to the Almighty to cause it to cease to be. The paths which the planets trace out in their appointed courses undergo slight variations in magnitude and form and position; their motions are sometimes accelerated and sometimes retarded; but these changes are corrected by the very causes which produce them. There is a mean state about which the whole system oscillates. Reckoning from this state, all the

"While comets move in very eccentric orbs, in all manner of positions, blind fate could never make all the planets move one and the same way, in orbits concentric, some inconsiderable irregularities excepted, which may have risen from the mutual action of the comets and planets upon one another, and which will be apt to increase till this system wants a reformation." Newton's Optics, B. ill. Qu. 31. Bailly expresses this fact with great elegance and precision. "La nature est animee par des forces qui se combattent, par des agens qui tendent a se detruire.

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variations extend only to a certain limited degree. Having attained that point, they begin to decrease and pass to the opposite extreme: and after a lapse of a greater or less time regain their first position. Now this is far from being a mere speculative truth. It is a fact of exceeding importance to ourselves, as well as to the whole system in which we are placed.

1. The path which the earth describes about the sun is nearly circular. Suppose this to have been originally the form of the orbit, but that the mean distance could have varied in the lapse of ages. The result would, in process of time, have been fatal to all creatures animate and inanimate upon the face of the earth. The consequence might have been slow in its advance: but the evil day must have come: and might have been almost computed, if science could have attained in any degree its present perfection. Conceive, now, the misery of mankind, if they were conscious that such a fatal change was inevitably approaching. If the disturbing power were such as continually to increase the distance of the earth from the sun, in every succeeding year the seasons would

y a un équilibre, elle s'en écarte, et n'y revient que par des oscillations. Tout subsiste, tout dure dans l'ensemble, tout varie dans le détail. Voila la loi de la nature." Traitè de l'Astron. Indienne-Discours Preliminaire, p. xxxviii.

return more slowly. The fruits of the earth would gradually become insufficient for the sustenance of its inhabitants. The influence of the sun in diffusing light and heat would continually diminish. Cold, such as now benumbs the polar regions of the earth in their dreary winter, would by degrees bind up the rivers and the seas and all animated beings would eventually be destroyed.

A change equally fatal, but opposite in kind, would take place, if any planet continually approached the sun, although its orbit still retained a nearly circular form.

But against the possibility of any such change the law, which the Creator has given to the material world, effectually provides. The mean distance of each of the planets from the sun does indeed vary; but it varies by such a small quantity as to be quite insensible except by the most accurate observation. And even to this small variation the Creator has set bounds, which shall not be passed.

2. But although the mean distance of a planet may be secure from change; although,

d Allowing heat to be occasioned by the action of the solar rays upon the atmosphere, a change of distance would still cause a change of mean temperature, for the number of rays which were incident in a given time would vary.

e La Grange, Mem. of Berlin, 1776. Méc. Celeste, Part. I. Liv. II. ch. vii. No. 54. 61-ch. viii. No. 65. Woodhouse's Astron. vol. II. ch. xxi.

for instance, the earth from year to year may remain at the same average distance from the sun, it is possible to conceive that the form of its annual orbit may be changed. That the eccentricity, as it is called, may vary. That the oval, which it describes, though now a very round oval, may, at some subsequent period, become a very long oval; that the earth may therefore approach nearer and nearer to the sun at a particular part of each revolution, and finally fall into that central body. Such a change also would evidently be fatal to the creatures which are placed upon the earth, and to its fruits.

But the law imposed upon the force, which pervades and connects the universe, forbids such a change. Since the motions of all the bodies in the planetary system are in the same direction, the form of their orbits remains nearly unaltered: and the small change which does take place is, in this instance also, a periodical change.f

3. The regular succession of the seasons, and consequently the comfort and existence of all beings upon the surface of the earth, depends also upon the inclination of the earth's axis to the plane of its orbit continuing nearly invariable. In order to effect this, the axis of rotation must be a permanent axis. The points terminating

* Méc. Celeste, Part. I. Liv. II. ch. vii. No. 37. 61. Woodhouse's Astron. vol. 11. ch. xxiii.