62 SIXTEENTH CENTURY. PT. in. 



most remarkable among hundreds of men who have added 

 to the general stock of knowledge. A detailed account of 

 all the steps by which the different sciences progressed would 

 fill many large volumes, and would only be confusing except 

 to those who already know a great deal about the subject. 

 In this book we can only throw a rapid glance over the last 

 four centuries of modern science, and try to understand such 

 new discoveries as ought to be familiar to every educated 

 person. It is, therefore, very important to bear in mind 

 that when we come to a great man who discovers or lays 

 down new laws, there have always been a number of less- 

 known observers who have collected the facts and ideas from 

 which he has formed his conclusions, although to mention 

 all these men would only fill the pages with a string of use- 

 less names. 



It is also necessary to explain why the plan is adopted 

 of giving new discoveries in the order in which they occurred. 

 Each separate science would no doubt have been easier to 

 follow, if the account of it had been carried on without any 

 break if, for example, Astronomy had been spoken of first, 

 then Optics, then Mechanics, and so on. But this arrange- 

 ment would not show the gradual way in which our know- 

 ledge has grown from century to century, nor how the work 

 done in one science has often helped to bring out new 

 truths in another. Therefore, although by following the 

 order of dates we shall be forced sometimes to pass abruptly 

 from one subject to another, this is, I believe, the best 

 method of teaching the ' History ' of Modern Science. 



Copernican Theory of the Universe, 1473-1543. 

 It was stated (p. 32) that about A.D. 100 Ptolemy formed a 

 ' System of the Universe ' which supposed our little earth to 

 be the centre of all the heavenly bodies ; and the sun, 

 together with all the stars and planet?, to move round us 



