138 HEkSCHEL AND HIS WORK 



the motion was of one star round a companion star, or 

 round some far greater and immensely more distant sun. 



The conclusion which Herschel arrived at was that 

 the whole solar system was at that time moving to- 

 wards the constellation Hercules in the northern sky, 

 and that the star " X Herculis is possibly as well chosen 

 as any we can fix upon in that part of the heavens " 

 for the point we are moving towards. He modified 

 this view in 1804 on receiving more correct measure- 

 ments from the Astronomer - Royal : " It will be 

 necessary to mention that I have no longer supposed 

 the solar motion to be directed towards X Herculis. 

 A point at no very great distance from this star 

 has been chosen." As the direction of the tangent to 

 the sun's orbit is constantly changing, this change 

 of direction from age to age is unavoidable. He 

 did not attempt to estimate precisely the rate of 

 motion, but, " in a general way," he considered that 

 it "cannot certainly be less than that which the 

 earth has in her annual orbit." At the same time 

 he expected that future astronomers would assist him 

 in determining the direction of the solar motion ; and 

 he added that he had " begun a series of observations 

 upon several zones of double stars," with the view 

 of establishing or overturning his hypothesis. His 

 estimate of the rate of the sun's motion may not 

 be correct. Probably it is only from five to nine 

 miles a second, or less than half what he made it : 

 but science has accepted his view of the point, to 

 which the solar system has, for an hundred years, 

 been advancing. Recently a Lyrse (Vega) has been 

 claimed as the point we are now making for. 



In the years that followed his first papers on The 



