Enough has been said to show that the Cartesian universe was based on crude atomism. Its mode of construction, moreover, evinced a total disregard of mechanical principles. Yet some acquaintance with the laws of motion was by that time easily within reach. The first of the three, at any rate, had been unmistakably enounced by Galileo in 1632, and Descartes himself strongly championed its validity. Yet he thought it necessary, in order to keep the planets moving, to immerse them in one great self-gyrating vortex centred on the sun, each being further provided with a similar subordinate whirlpool for the maintenance of its domestic system. Comets were left in a singularly anomalous position. They circulated freely on the whole, their exemption from planetary restrictions being tacitly recognized; nevertheless, they took advantage of every encountered swirl to help themselves on towards their destination. Among the fables of pseudo-science Delambre declared that, had the choice been offered to him, he would have preferred the solid spheres of Aristotle to the _tourbillons_ of Descartes. 'The spheres,' he added,[2] 'have proved helpful both for the construction of planetariums representing in a general way the celestial movements, and for their calculation by approximate rules deduced from them; but the system of vortices has never served any purpose whatsoever, whether mechanical or computative.' Its vogue had, nevertheless, been brilliant and sustained. Advanced thinkers in the time of Louis Quatorze piqued themselves upon being Cartesians. The vortical hypothesis was novel--it seemed daring; and though it might not be true, it had plausibility enough for fashionable currency. Nor did it deserve the unmitigated contempt with which it was treated by Delambre. A glance at the skies makes us pause before condemning it to scornful oblivion. Just two centuries after its promulgation the first spiral nebula was identified in Canes Venatici. That the heavens swarm with analogous objects is certain, and their status as partially developed systems is visible in every line of their conformation. Our own planetary world may, or may not, have traversed the stage they so copiously illustrate; but in any case they prove beyond question that vortices variously conditioned are prevalent among the forms assumed by cosmic masses advancing towards an orderly arrangement.