10 THE OCEAN. [Book I. 



century, Copernicus published his cosmical theory, 

 maintaining that the earth rotates each day on its 

 axis, and revolves each year round the sun. 



Even then these views met with no ready accept- 

 ance. And after the publication of the theory of 

 Copernicus, one of the greatest of philosophers, Des- 

 cartes, was at great pains to explain how, when, in 

 describing his system of the world, he spoke of the 

 earth moving, he did so improperly, and only for the 

 sake of simplifying the explanation of an hypothesis : 

 and he argued that, even supposing his cosmical 

 hypothesis to be true, even then, speaking in a proper 

 sense, the earth did not really move. 



These men, with Kepler, Galileo and others, paved 

 the way for Newton, who, immediately after Descartes, 

 enforced the theory of the axial rotation and orbital 

 revolution of the earth with such clearness and pre- 

 cision that the belief in these motions gradually 

 extended until they at length became generally 

 accepted as incontrovertible facts. 



These two motions of the earth, re- discovered by 

 Copernicus — namely, the diurnal motion of rotation 

 on its axis, and the motion by which it is annually 

 revolved in its orbit round the sun, are the only 

 great movements of the earth of which we have, 

 even at the present day, a definite knowledge. But 

 besides these motions, a third great movement was, 

 towards the close of last century, pointed out by Sir 

 William Herschel, who showed that not only is the 



