THE RENAISSANCE 119 



orbits, and similar complications appeared on every 

 side in mechanical problems. By Galileo's investiga- 

 tion, the whole position was reversed, and it was seen 

 that it was the destruction of motion or a change in 

 its direction which required the exertion of some 

 external applied force. Thus the planetary system 

 needed no vortices to keep it in motion, but some 

 cause was required to explain the continual deviation 

 of the planets from a straight course, as they swung 

 round the sun in their orbits. Never before had it 

 been possible even to formulate the problem correctly, 

 but now the way was open to a solution, and the man 

 was at hand. In 1642, the year of Galileo's death, 

 Isaac Newton was born. 



But, before we follow the consequences of Galileo's 



labours, and deal with Newton's supreme achievement, 



Gilbert of we must pass in review other trains of 



Colchester, thought which went to make that new 

 intellectual world in which Newton dwelt. 



In the land of Newton the new method of experi- 

 ment, so well used by Galileo in Italy, was simultane- 

 ously and worthily put in action by William Gilbert 

 of Colchester (1540-1603), fellow of St John's College 

 in Cambridge, and sometime President of the College 

 of Physicians. In his book, De Magnete, Gilbert 

 collected all that was known about magnetism, and 

 added many new and valuable observations of his own. 



The mariner's compass is said to have been known 

 to the Chinese from early times. Descriptions of it 

 seem first to have appeared in European literature 

 about the twelfth century, coming probably from 

 Saracenic sources, though the references indicate that 



