LETTER VI.

OF THE DISCOVERIES OF KEPLER AND GALILEO.

DISTINGUISHED above other creatures, by the faculty of reason, and the superiority of his nature, man is still the slave of prejudice and opinion, prone to error, and subject to continual delusion. Truth and science advance by slow degrees; one age destroys the labours of another, whilst conjecture and hypothesis supply the place of argument and demonstration. Nature performs her operations constantly before our eyes, and has furnished us with the means of tracing their causes and connections; but the mind, debased by indolence, or bewildered by superstition, regards these astonishing scenes with indifference, and considers all attempts to investigate their causes, as the effects of a presumptuous and daring impiety.

From the time of Pythagoras to the sixteenth century, when the true system of the world was again revived by Copernicus, the vulgar opinion of the motion of the heavens, and the immobility of the earth, was generally received; and time, instead of discovering its fallacy, served only to strengthen and confirm it. To the authority of men of acknowledged reputation for their learning and talents, the example of ages was added; and thus error was transmitted from one generation to another, with additional prevalence. Plato and Aristotle were referred to as the arbiters of every dispute, from whose authority there was no appeal ;

and when reason and argument failed, the aid of religion was called in to their support.

To dissent from the opinions of Aristotle, or those which his ignorant interpreters had given him, was looked upon as a heresy that called for the loudest anathemas of the church. And so venerable and sacred were those doctrines held, that whoever presumed to controvert them, was considered as an impious innovator, that attempted to remove the land-marks both of faith and reason. To his opinions, in all religious controversies, both parties appealed; from these the Papist supported all his absurdities, and the Protestant drew arguments for their refutation.

Error being thus established by time, superstition and prejudice, the face of nature was covered with a veil of awful obscurity, and the progress of useful knowledge effectually prevented. The highest ambition of some of the most eminent men of the age, was to prove the truth of that by sophistical arguments, which reason and science affirmed to be false. But such fantastical opinions could not always prevail; time will constantly be found to produce some lovers of truth, who will penetrate through clouds of error to attain it. After a long night of the most profound darkness, Copernicus again revived the true system of Pythagoras and his followers, and showed it to be the only one which is agreeable to reason and observation.

But the greatest champion of useful learning that had hitherto appeared in the world, was Sir Francis Bacon, Lord Verulam, who by his superior know

ledge and eminent abilities, overthrew the establishment of ignorance and error, and convinced the infatuated world, that opinions supported by the authority of Aristotle and antiquity, were not infallible. By clear incontrovertible arguments, supported by reason and science, he refuted their errors, and showed that the only method of obtaining a true knowledge in philosophy was by observation and mechanical experiments.

It was now that men began to discern truth from falsehood, and, disregarding hypothesis and conjecture, to investigate the works of nature from their effects and appearances. Matter and motion were observed to constitute the principal phænomena of the visible world; and as the properties and affections of these are the subject of mechanics, that science grew into esteem, and was assiduously cultivated by the most eminent mathematicians in Europe.

By applying mathematical reasoning to mechanical experiments, Sir Isaac Newton established the truth of the ancient Pythagorean system; and upon this foundation raised the superstructure of that philosophy, which, whilst all other systems sink into ruins, and little more than their inventors names are remembered, will remain for ever firm and unshaken for being once demonstrated to be true, it must eternally remain so, as nothing can alter it but the utter subversion of the laws of nature, and the constitution of things.

The method of admitting nothing into philosophy, unconfirmed by experiment or demonstration,

required too great a perseverance for the flighty imagination of those, who, contenting themselves with the semblance of truth, expatiated in the wilds of fiction. For a work of this kind, the genius and industry of a Newton was alone, sufficient, who chose rather to acquire a little true knowledge of nature from practical investigation, than to aim at a general comprehension of all her operations, upon the weak foundation of probability and conjecture.

But in order that the genius of this extraordinary man may appear in its true light, it will be necessary to give you some account of the labours of those, who, since the time of Copernicus, had been preparing the way, and laying the foundation. for his discoveries and pursuits; which information is the more necessary, as many persons, who have but a slight acquaintance with the progress of astronomical learning, are apt to entertain very erroneous opinions upon the subject. As the labours of many are attributed to one Hercules, so, by a like exaggeration, Sir Isaac Newton is said to be the author of all the discoveries and improvements which have ever been made in this science. But as his merit is too great to stand in need of such extravagant additions, it will be proper to divest him of this false glory, by ascribing to him that only to which he has an undoubted claim.

The first founder of modern astronomy was Kepler; and if it be the privilege of genius to change received ideas, and to announce truths which had never before been discovered, he may justly be considered as one of the greatest men

that had yet appeared in the world. Hipparchus, Ptolemy, Tycho Brahe, and even Copernicus himself, were indebted for a great part of their knowledge to the Egyptians, Chaldeans, and Indians, who were their masters in this science: but Kepler, by his own talents and industry, has made discoveries, of which no traces are to be found in all the annals of antiquity.

This philosopher was born at Wiel, in the province of Wirtemberg in Germany, on the 27th of December, 1571, and was one of the most zealous partizans of the Copernican system that had hitherto appeared. In 1596 he published a large work upon the proportions and dimensions of the orbits of the planets, which coming into the hands of Tycho Brahe, he advised him to apply himself to observation, before he attempted to discover the laws of nature; and assured him, if he would do this, he would find more truth in his hypothesis than in that of Copernicus. He perceived the genius of Kepler, and wished for nothing more earnestly than to have him for his disciple.

I shall not enter into a detail of the reasons which are given by Kepler for arranging the planets according to the order of the five regular bodies, nor of the mysterious harmony which he finds between celestial and sublunary things. He was a man of a warm imagination, which led him into many absurdities; and it was the folly of that age, to mix sacred things with those which have no connection with them. He tells us in his Mysterium Cosmographicum, that he looked upon three grand things

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