LETTER IV.

OF THE SYSTEMS OF PTOLEMY, TYCHO BRAHE, AND. COPERNICUS.

Or all the gifts and benefits which the Author of nature has so plentifully bestowed upon mankind, those which consist in the improvement of the -mind by arts and sciences are the most estimable. And, independently of the practical advantages which society derives from the cultivation of them, they afford us more pure and unalloyed pleasures than any of the gratifications of sense can possibly.

bestow.

The unbounded view of nature, which I have laid open in my last letter, and the wonderful operations of the Deity in every part of this stupendous fabric, will not only ennoble the mind and strengthen the understanding, but it is likewise calculated to answer a still more important purpose, that of laying a sure foundation for natural religion, and leading us, in the most satisfactory manner, to a knowledge of the great Author and Governor of the universe.

To study nature, is to search into the works of the creation; where every step must lead us to form more exalted ideas of the Divine Being who prevails throughout, directs and animates the whole. From the microscopic animalcule, which is indiscernible to the unassisted eye, to the great and immeasurable luminaries of heaven, he is every where present. And whilst we perceive his wisdom and

power thus equally displayed in the motions and operations of the greatest and subtilest parts of the creation, we cannot but be excited and animated to correspond with the general harmony.

What sublime ideas of this great Being, do we obtain from contemplating the vast diversity of his works, which the cursory survey we have taken of them, imperfect as it is, affords us; and how is the mind enlarged and captivated by the astonishing scenes, and agreeable reflections, which these enquiries continually present to our view. That part of nature, which is the immediate object of the senses is very imperfect, and but of small extent; but by the assistance of art, and the help of our reason, it is enlarged till it loses itself in an infinity on either hand. The immensity of things on one side, and their minuteness on the other, carry them equally out of our reach, and conceal from us the greater and more noble part of physical operations. As magnitude of every sort, abstractedly considered, is capable of being increased to infinity, and is also divisible without end; so we find that, in nature, the limits of the greatest and least dimensions of things are placed at an immense distance from each other. We can per

ceive no bounds to the vast expanse in which natural causes operate, and are no less at a loss when we endeavour to trace things to their elements, and to discover the limits which conclude the subdivisions of matter.

The objects which we commonly call great. vanish, when we contemplate the vast body of the

earth; the terraqueous globe itself is soon lost in the solar system; in some parts it is seen only as a distant star; and in others it is unknown, or visible only at certain times, by vigilant observers, assisted, perhaps, by instruments like our telescopes. The sun himself dwindles into a star; Saturn's vast orbit, and the orbits of all the comets, crowd into a point, when viewed from numberless places between the earth and the nearest fixed stars: other suns give light to illuminate other systems, where our sun's rays are unperceived; but these also are swallowed up in the immeasurable expanse. Even all the systems of the stars, which sparkle in the clearest sky, must possess but a small part of that space over which such systems are dispersed; since more stars are discovered in one constellation, by the telescope, than the naked eye perceives in the whole heavens.

And after we have risen thus high, and left all definite measures so far behind us, we find ourselves no nearer to a term or limit; for all this is nothing to what may be displayed in the infinite expanse, beyond the remotest stars that have ever been discovered.

In like manner, if we descend in the scale of nature, towards the other limit, we find a like gradation from minute objects to others inconceivably more subtile; and are led as far below sensible measures, as we were before carried above them, by similar steps, which soon become lost in equal obscurity. From microscopic observations that discover animals, thousands of which

would scarcely form a particle discernible to the naked eye; from the propagation, nourishment and growth of those animals; from the subtilty of the effluvia of bodies, which retain their particular properties after the utmost degree of rarefaction; from many astonishing experiments of the chemists; and especially from the inconceivable minuteness of the particles of light, which find a passage through the pores of transparent bodies in all directions, it appears, that the sub-divisions of the parts of bodies descend by a number of steps or gradations that surpasses all imagination, and that nature is inexhaustible on every side, the two extremes of great and small being equally removed from our comprehension.

Nor is it in the magnitude of bodies only that this endless gradation is to be observed. Of motions, some are performed in moments of time, and others are finished in very long periods; some are too slow, and others too swift to be perceived by us. So that wherever we turn ourselves, we are lost in an endless labyrinth; and find fresh reasons, at every step, to adore and venerate that Being, whose works are so various and hard to be comprehended.

But it is now time to leave these pleasing digressions, and to give you some account of the different opinions of philosophers, concerning the situation of the heavenly bodies, or the place which they possess in the universe; in which enquiry you will not be surprized to find, that they are no less various and contradictory, than those relating

to the figure and motion of the earth, as mentioned in a former letter. For mankind must have made considerable advances in astronomy, before they could so far disengage themselves from the prejudices of sense and popular opinion, as to believe in a doctrine so sublime and remote from vulgar apprehension, as that which the moderns have now firmly established.

The beginnings of sciences, as well as of other things, are uncertain and obscured with fables; we collect, however, from several testimonies, that the true doctrine of the planetary motions was known in the world from the most early ages, and taught by some of the greatest and wisest men of antiquity. That admirable philosopher Pythagoras, who flourished near five hundred years before Christ, was undoubtedly acquainted with this doctrine. But, from the accounts of his disciples and followers, it is evident, that it was not the result of his own observations; but that he had received hints of it from some more enlightened nations, who had made greater advances in the science.

It is most probable, indeed, that the doctrine was transplanted by him from the east, in which part of the world he spent two and twenty years, and scrupled not to comply with all the customs peculiar to the eastern nations, in order to obtain free access to their priests and magi, to whom almost all knowledge of arts and sciences was then confined. And as he was a man of extraordinary qualities, and had an insatiable thirst for knowledge, so he seems to have been the most success