332 Prowe's Life of Copernicus. Oct.
suffice to make plain the entire structure of the world — the entire mazy round of the starry dance ! ' [1]
It was reserved for Kepler to banish from astronomy these anomalous survivals of an earlier time. No subtle conspiracy of circular motions could abide the touch of the Ithuriel-spear of his genius. The first of his three ' Laws ' declared that the planets revolve in ellipses, of which the sun occupies one focus ; the second showed their velocity to depend upon the position occupied in those ellipses ; the third pointed out the existence of a determinate relation between the mean or average velocity of each, and its mean distance from the sun. The geometrical plan of the solar system was thus completed ; it remained to show that these beautiful and harmonious relations had a physical cause. This, the eminent work of Newton, was prepared and facilitated by the efforts of Galileo. The Tuscan astronomer's detection of the phases of Venus removed a formidable objection to the new views of which he was the enthusiastic champion, and his discovery of the satellites of Jupiter offered an exquisite illustration of their truth; but still more effective in securing their irrevocable adoption were his investigations into the nature of motion, and the clear and sound mechanical ideas thereby attained. All these partial researches — the laborious reform of Copernicus, the eager yet patient divinations of Kepler, the bold inductions of Galileo — were embraced and perfected in the sublime generalisation of Newton. By the conception of one universal force ruling the movements of the heavenly bodies, yet no other than that familiar power of gravity by which our globe clasps its constituting particles together, and asserts its right of property over every object on its surface, the human mind attained its highest triumph over the material universe. The working of the machine was at last laid bare, and its motive power — however unfathomable in its secret springs — was brought within the range of exact calculation. It might, in this limited sense, be said that the How ? as to the arrangements of the solar system was answered by Copernicus and Kepler, the Why ? by Newton. And in this answer was the fullest justification of the profound intuitions, the intrepid confidence, and the earnest reasonings of the Frauenburg astronomer.
- ↑ Concluding words of the ' Commentariolus,' Prowe, Th. ii. p. 292.
