CHILDHOOD OF SCIENCE. 201 



and the cubes of the mean distances of the planets. That is, 

 taking, for instance, the earth's revolution about the sun as one 

 (year), and the distance from the sun as one (radius), the square 

 and cube of which are still one ; then, as the periodical time, say 

 of Saturn, is about 29|- years, one is to the square of 29J as one 

 is to the cube of Saturn's distance from the sun in radii of the 

 earth's orbit. The sum worked out gives 9|- radii for Saturn's 

 distance ; that is, Saturn should be 9^ times further from the sun 

 than the earth is. In this second trial, Kepler found to his infi- 

 nite satisfaction and delight that the rule would hold exactly true 

 in the case of all the planets. It was in reality a capital discov- 

 ery ; for it was the one column on which was constructed the 

 whole science of celestial mechanics. It was the foundation of 

 all of Newton's demonstrations ; for it gave the only absolute 

 proof of universal gravitation. It was the germ from which 

 have sprung more physical truths than from any other discovery 

 that has ever been made. Yet at the time when it was made I 

 can hardly conceive how it should have been regarded as more 

 than a curious relation, a freak of the Great Artificer. At least 

 so thought those who came after Kepler ; and seventy years 

 passed before the Principia of Newton gave to the world the 

 first sign of its true importance.. Yet Kepler, with a scientific 

 instinct, a sublime, inexplicable foresight, records the 8th of May, 

 1618, as the day of the most important discovery of his life and 

 of the age ; and he bursts forth in that ever memorable rhapsody : 

 " Nothing holds me. I will indulge in my sacred fury. I will 

 triumph over mankind by the honest confession that I have 

 stolen the golden vases of the Egyptians to build up a tabernacle 

 for my God far away from the confines of Egypt. If you for- 

 give me, I rejoice. If you are angry, I can bear it. The die is 

 cast ; the book is written, to be read either now or by posterity ; 

 I care not which. It may well wait a century for a reader, as 

 God has waited six thousand years for an observer." 



The last and the greatest name I have to mention is that of 

 Galileo the Florentine, who in the year 1600 and at the age of 

 36, had just commenced his eventful career as the first experi- 

 mental philosopher and the sturdy creed-questioner. Up to this 



