228 THE POPULAR SCIENCE MONTHLY. 



Making leisure, in the summer of 1869, for entering upon such an ex- 

 amination, I was led to several results, which not only confirmed the 

 above-mentioned theory, hut suggested relations which I had not hith- 

 erto thought of. Some of these resvdts are discussed in the article 

 called " Are there any Fixed Stars ? " already referred to ; others are 

 presented in an article called " Star-drift," in the Student for Octo- 

 ber, 1870. The special results on which Dr. Huggins's recent discov- 

 eries throw light, were first publicly announced in a paper read before 

 the Royal Society, on January 20, 1870. 



I had constructed a chart in which the proper motions of about 

 1,200 stars were pictured. To each star a minute arrow was affixed, 

 the length of the arrow indicating the rate at which the star is moving 

 on the celestial vault, while the direction in which the arrow pointed 

 shows the direction of the star's apparent motion. This being done, it 

 was possible to study the proper motions much more agreeably and 

 satisfactorily than when they were simply presented in catalogues. 

 And certain features, hitherto unrecognized, at once became apparent. 

 Among these was the peculiarity which I have denominated " Star- 

 drift ; " the fact, namely, that certain groups of stars are travelling in 

 a common direction. 1 This was indicated, in certain cases, in too sig- 

 nificant a manner to be regarded as due merely to chance distribution 

 in these stellar motions ; and I was able to select certain instances in 

 which I asserted that the drift was unmistakable and real. 



Among these instances was one of a very remarkable kind. The 

 "seven stars" of Ursa Major the Septentriones of the ancients are 

 known to all. For convenience of reference, let us suppose these seven 

 divided as when the group is compared to a wagon and horses. Thus, 

 there are four wagon-wheels and three horses. Now, if we take the 

 wagon-wheels in sequence round their quadrilateral (beginning with 

 one of the pair farthest from the horses), so as to finish with the one 

 which lies nearest to the horses, these are named by astronomers, in 

 that order, Alpha, Beta, Gamma, and Delta, of the Great Bear. Thus, 

 Alpha and Beta are the well-known pointers (Alpha nearest the pole), 

 and Delta is the faintest star of the Septentrion set. The three horses 

 are called in order Epsilon, Zeta, and Eta ; Ejisilon being nearest to 

 Delta. Now, when the proper motions of these seven stars had been 

 mapped, I found that, whereas Alpha and Eta are now moving much 

 as they woidd if the sun's motion were alone in question, the other five 

 are all moving at one and the same rate (on the star-sphere, that is) in 

 almost the exactly opposite direction. Moreover, a small star close by 



1 I include this among " features hitherto unrecognized," though Michell had already 

 noted the fact that the stars are arranged into systems. " We may conclude," he said, 

 " that the stars are really collected together in clusters in some places, where they form a 

 kind of systems ; while in others there are few or none of them, to whatever cause this 

 may be owing, whether to their mutual gravitation or to some other law or appointment 

 of the Creator." 



