hypothesis there are several fatal objections, as was subsequently demonstrated by D'Alembert, of which it will be sufficient to mention that the very existence of a spherical vortex is a mechanical impossibility. And yet such was the weight of the authority of its author, and the ingenuity with which it was defended by himself and his followers, that, as was mentioned above, it not only was received with general favor but for more than half a century it was accepted by most men of science without questioning and continued to be maintained by some, even after Newton had announced and demonstrated the law of gravitation. It is a notable illustration of the tenacity of error when once it becomes firmly fixed and widespread, that for some years after the publication of 'The Principia,' a Latin translation from the French of 'The Physics of Rohault'—a work entirely Cartesian—continued to be the text-book in Philosophy at the University of Cambridge—Newton himself being at the time Lucasian Professor of Mathematics. We have the authority of Play fair for the statement (which, indeed, has been called in question by Sir David Brewster, in his 'Life of Newton,' though so far as we have been able to see, without any sufficient reason) that the doctrines of 'The Principia' were introduced into the regular course of instruction at Cambridge by strategem. Dr. Samuel Clarke, a zealous advocate of the Newtonian Philosophy, prepared a new and more elegant translation of Rohault, with copious notes, in which the doctrines of 'The Principia' were explained and defended, and it was by this work, more directly than by the lectures of Newton himself, that Cartesianism was finally driven from the University.
Whilst Kepler's speculations as to the cause of the motions of heavenly bodies were soon supplanted by the hypothesis of Descartes, his more just views in regard to terrestrial gravity commended themselves to the scientific world and speedily passed into universal and abiding favor. In the memorable work of Galileo on the true system of the universe—completed the very year after Kepler's death, and published two years after; a work which, aside from its own merit, 'The Holy Inquisition,' by the persecution of its author, has made immortal—we find the doctrine of Kepler, on the subject of gravity, distinctly stated and elaborately defended. The Inquisition had power to imprison Galileo and commit copies of his work to the flames, but the truth it contained could not be burnt or bound. The earth 'still moved,' and matter continued to attract matter, unawed by the terrors of the Inquisition. The truth, once distinctly apprehended and announced, was never again to be lost, but was destined to grow in importance and be extended in its application far beyond the conceptions even of the great prophets of nature who were the first to proclaim it. The doctrine of Kepler on the subject of gravity may be regarded as.
