INTRODUCTION. 



BRIEF SKETCH OF THE MOST NECESSARY PRIN- 

 CIPLES OF NEWTON'S NATURAL PHILOSOPHY, 

 WHICH ARE REQUIRED FOR THE UNDER- 

 STANDING OF WHAT FOLLOWS. 1 



Six planets, of which three have companions Mercury, 

 Venus, the Earth with its moon, Mars, Jupiter with four 

 satellites, and Saturn with five describe circles around 



1 This short introduction, which may perhaps be unnecessary for 

 most readers, I have thought it desirable to draw up for those who 

 may not be sufficiently acquainted with Newton's principles, in order 

 that it may prepare them to understand the following theory. [It 

 need hardly be said 'that Kant here gives an account of the 

 elements of the Solar System, only in so far as known at the time 

 when he wrote (1755). The great discoveries made since then have 

 to be kept in mind, especially in their important bearing on the 

 proof of his theory. The great planet Uranus was discovered by Sir 

 W. Herschel in 1781, twenty-six years after the publication of 

 Kant's essay. The first asteroid, or minor planet Ceres, was dis- 

 covered by Piazzi of Palermo, on the first day of the nineteenth 

 century, and some four hundred more have been discovered since. 

 The still more remarkable discovery of Neptune, on the basis of the 

 calculations of Adams and Leverrier, was made in 1846. Mr Hall 

 of Washington discovered, on nth and I7th August, 1877, that Mars 

 has two moons. Tr.] 



