180 PROGRESS OF SCIENCE IN THE CENTURY. 



main chapters. First it passed through an ohserv- 

 ing-period lasting through thousands of years of 

 nightly study by watchers in the plains of the East 

 to its culmination in the discoveries of Copernicus 

 and Keppler. It then passed into a stage of analysis 

 and generalisation, when the genius of ISTewton 

 rationalised a huge mass of facts in the formula 

 of gravitation. ^' God said, Let Kewton be, and 

 there was light." It finally reached a stage of deduc- 

 tion, which, from a knowledge of the positions and 

 movements of the heavenly bodies, predicts their fu- 

 ture courses. This might also be called the evolu- 

 tionary period, since one of its dominant aims has 

 been to show how the solar and other systems have 

 come to be what they are. 



The Succession of Systems. — The Ptolemaic sys- 

 tem — ^which placed the earth immovable in the centre 

 of the universe — was superseded by the system of 

 Copernicus (1473-1543), which made the sun the 

 immovable centre. This again was reformed by 

 Keppler (1571-1630), who stated the famous laws 

 or descriptive formula? of the movements of the 

 planets in their orbits, but was impelled to call in 

 the service of guiding spirits to account for them. 

 Galileo Galilei (1564-1642) was the first to use for 

 systematic study the telescope which the Dutchman, 

 Hans Lippersheim, had invented, and in spite of his 

 revelation of some of the wonders of the heavens — 

 the broken surface of the moon, the countless stars 

 of the Milky Way, the satellites of Jupiter, and the 

 spots on the sun — was almost made a martyr for his 

 dogged adherence to Copernican doctrine. But we 

 must not do more than mention these great names, 

 which are separated by a long interval from the nine- 

 teenth century. 



