Page:Popular Science Monthly Volume 59.djvu/488

478 and complete. The ordinary method of transition from widespread and plausible error to the truth is by slow and gradual progress, and the discovery of the law of gravitation, so far from being an exception to this rule, is but one of its most striking illustrations. Such an accident as that which the discovery of the law of gravitation is supposed to have been is of the kind which only happens to men of large knowledge, profound thought, and after intense and protracted mental effort. Simple as this law is known to be, and easily apprehended and even demonstrated by ordinary minds, it needed one endowed with the most gigantic intellect probably ever given to mortal—availing himself of the suggestions and the results of the labors of those who had preceded him in the same field of inquiry—to make the discovery.

In tracing the history of this discovery, from the epoch when by the previous discovery of all the necessary data it for the first time became possible, the first place in the order of time, and next to Newton in the order of merit, is undoubtedly due to Kepler. Possessing a singularly lively imagination—we might say, volatile fancy—combined with a love for the truth that amounted to a ruling passion, and a breadth of knowledge in his favorite science far in advance of any other man of his age, he was eminently fitted for the work which he so successfully performed of scientific discovery. Fertile in hypotheses—sometimes the most extravagant—he was indefatigable in his labors to test his hypotheses by the facts. Without the slightest pride of opinion, he seemed to take a satisfaction in exploding his own theories when they were false, that was only exceeded by his delight when successful in demonstrating their truth. Of the men who have contributed to the advancement of science, there are few to whom we are under greater obligation, or whose character as an investigator of nature is more worthy of admiration, than 'The Legislator of the Heavens'—the father of modern astronomy.

In the introduction to his memorable work on 'The Motions of Mars,' referred to above, he opposed the doctrine of Aristotle on the subject of terrestrial gravity, and in the course of the discussion uses the following remarkable language:

A mathematical point, whether the center of the universe, or not, has no power to move heavy bodies to approach it. Let philosophers prove, if they can, that natural things have any sympathy with that which is nothing.

The true theory of gravity is founded on the following axioms. Gravity is a mutual affection between cognate bodies toward union or conjunction, similar to the magnetic virtue. If we assume the earth to be the center of the world, heavy bodies are not carried toward its center in virtue of its quality of center of the world, but in virtue of its quality of center of a cognate round body; BO that wheresoever the earth may be placed, or whithersoever it may be carried by its animal faculty (alluding to a fanciful theory which we shall have occasion presently to notice) heavy bodies will always be carried toward it.