202 HISTORY OF SCIENCE. 



is heaped up from the earth, but the earth which is withdrawn from 

 the water. We may consider the earth as a mass floating in the globe 

 of water, and as its centre is nearer to the moon than are the waters 

 on the opposite side, it will be drawn away from these, which, being 

 thus left behind as it were, will be in the same relative situation to the 

 earth as if they were heaped up. By comparing the spring and neap 

 tides, Newton found that the attractive force which the moon exerts 

 acts upon the ocean is to that exerted by the sun as 448 to 100 ; and 

 that, while the former body produces a tide of 8 '6 feet, the latter pro- 

 duces one of i *9 feet high, and the two combined raise a tidal wave 

 of io| feet high. 



FIG. 87. BIRTHPLACE OF NEWTON. 



We have now briefly indicated the main points of the great disco- 

 veries and investigations of Newton in the fields of mathematical and 

 astronomical science. These last constitute collectively the system of 

 the world which was unfolded in the " Principia" The phenomena 

 of the heavens had for ages attracted the attention of men ; but it was 

 reserved for the illustrious English philosopher of the seventeenth cen- 

 tury to combine and explain them by one great and simple law. But 

 the materials for this, as for every great discovery, had been prepared 

 by the labour of men of science of all times. Newton turned to account 

 the geometry of Plato, and Euclid, and Apollonius ; he combined into 

 a few simple principles all the mechanical truths and dynamical laws 

 discovered by Archimedes, and Galileo, and Huyghens ; he developed 

 into a new and powerful calculus the mathematical investigations of 

 Wallis and Barrow ; he availed himself of the telescopic discoveries of. 

 Galileo ; and he explained the mysterious numerical relations which 

 the labours of Kepler had brought to light. 



The grand and simple principle of the system unfolded in the 



