'SUN'S MOVEMENT THROUGH SPACE 137 



between the two men, and Glasgow seems to have 

 become a favourite place of summer pilgrimage to 

 Herschel. It was clear that he was favoured by the 

 flowing tide of scientific thought. He took it at the 

 flood : he even guided it into the channels along 

 which it has since flowed in an ever increasing 

 volume. It " is an arduous task," he said of this quest 

 after our solar system's movement in space, " which we 

 must not hope to see accomplished in a little time ; but 

 we are not to be discouraged from the attempt. Let 

 us, at all events, endeavour to lay a good foundation 

 for those who are to come after us." And this 

 good foundation, by precept and example, he did lay. 



With the boldness of a man who had confidence 

 in himself and his instruments, he wrote : " I think 

 we are no more authorised to suppose the sun at 

 rest than we should be to deny the diurnal motion 

 of the earth, except in this respect, that the proofs 

 of the latter are very numerous, whereas the former 

 rests only on a few, though capital testimonies." He 

 founded this conclusion on a discussion of the motions 

 observed in seven of the principal fixed stars. But 

 in support of his view he also quoted a table of the 

 proper motions of twelve stars in fifty years given 

 by Lalande, motion in the two directions known to 

 astronomers as right ascension and declination, cor- 

 responding to longitude and latitude on the earth. 

 Twenty-seven motions altogether had to be accounted 

 for. On the hypothesis of a general movement of 

 the solar system through space, twenty-two out of 

 these twenty-seven movements were explained. The 

 five exceptions he " resolved into the real proper 

 motion of the stars." He did not then know whether 



