392 



Dr. W. Huggins on the Motions of [June 13, 



scope shows to be moving from the earth (Sirius, Betelgeux, Rigeh Procyon) 

 are situated in a part of the heavens opposite to Hercules, towards which the 

 sun is advancing, while the stars in the neighbourhood of this region, as 

 Arcturus, Vega, a Cygni, show a motion of approach. There are in the 

 stars already observed exceptions to this general statement ; and there are 

 some other considerations which appear to show that the sun's motion in 

 space is not the only or even, in all cases, as it may be found, the chief 

 cause of the observed proper motions of the stars*. 



There can be little doubt but that in the observed stellar movements we 

 have to do with two other independent motions — namely, a movement 

 common to certain groups of stars, and also a motion peculiar to each 

 star. 



Mr. Proctor has brought to light strong evidence in favour of the drift of 

 stars in groups having a community of motion by his graphical investi- 

 gation of the proper motions of all the stars in the catalogues of Mr. 

 Main and Mr. Stonef . The probability of the stars being collected into 

 systems was early suggested by Michell and the elder Herschelt. One of 

 the most remarkable instances pointed out by Mr. Proctor are the stars 

 /3, y, £, £ of the Great Bear, which have a community of proper motions §, 

 while a and rj of the same constellation have a proper motion in the oppo- 

 site direction. Now, the spectroscopic observations show that the stars /3, 



* As the velocities assigned to the stars are, for reasons already stated, provisional 

 only, I feel some hesitation in drawing from them the obvious conclusions which they 

 would suggest. The velocities given in the Tables for those stars which are moving 

 in direction in accordance with the sun's motion towards Hercules do not bear to each 

 other the relation which they should have if they were mainly produced by the sun's 

 motion. Even for these stars, therefore, we must look elsewhere for the cause to which 

 they are chiefly due. 



t See " Preliminary Paper on certain Drifting Motions of the Stars," Proc. Roy. 

 Soc. vol. xviii. p. 169. 



I Sir William Herschel writes : — " Mr. Michell's admirable idea of the stars being 

 collected into systems appears to be extremely well founded, and is every day more con- 

 firmed by observations, though this does not take away the probability of many stars 



being still as it were solitary, or, if I may use the expression, intersystematical 



A star, or sun such as ours, may have a proper motion within its own system of stars, 

 while at the same time the whole starry system to which it belongs may have another 

 proper motion totally different in quantity and direction." Herschel further says, 

 " And should there be found in any particular part of the heavens a concurrence of 

 proper motions of quite a different direction, we shall then begin to form some conjec- 

 tures which stars may possibly belong to ours, and which to other systems." — Phil. 

 Trans. 1783, pp. 276, 277. 



§ Mr. Proctor, speaking of these stars, says : — "Their drift is, I think, most signifi- 

 cant. If, in truth, the parallelism and equality of motion are to be regarded as acci- 

 dental, the coincidence is one of most remarkable character. But such an interpretation 

 can hardly be looked upon as admissible when we remember that the peculiarity is only 

 one of a series of instances, some of which are scarcely less striking." — Other Worlds 

 than Ours, p. 269. See paper in Proc. Roy. Soc. vol. xviii. p. 170. 



