40 SIR ISAAC NEWTON. 



tained that the weight of the same body would be 

 twenty-three times greater at the surface of the 

 sun than at the surface of the earth, and that the 

 density of the earth was four times greater than 

 that of the sun. He found the true figure of the 

 earth ; he explained the phenomena of the tides. 



Of the " Principia," Sir David Brewster says, in 

 his able life of Sir Isaac Newton, it is "a work 

 which will be memorable not only in the annals of 

 one science or of one country, but which will form 

 an epoch in the history of the world, and will ever 

 be regarded as the brightest page in the records 

 of human reason, a work, may we not add, which 

 would be read with delight in every planet of our 

 system, in every system of the universe. What 

 a glorious privilege was it to have been the author 

 of the ' Principia ' ! 



" There was but one earth upon whose form, and 

 tides, and movements, the philosopher could exer- 

 cise his genius, one moon whose perturbations 

 and inequalities and actions he could study, one 

 sun whose controlling force and apparent motions 

 he could calculate and determine, one system of 

 planets whose mutual disturbances could tax his 

 highest reason, one system of comets whose 

 eccentric paths he could explore and rectify, 

 and one universe of stars to whose binary and 

 multiple combinations he could extend the law of 

 terrestrial gravity. 



"To have been the chosen sage summoned to 

 the study of that earth, these systems, and that 



