THE GREAT STAR MAP 443 



the bifurcation must be proved independently for these remoter 

 stars, since there is apparently a breach of continuit3^ 



But another reason has been suggested also. In a most 

 interesting lecture on the Milky Way, delivered to the British 

 Association at its South African meeting,^ Mr. A. R. Hinks of 

 Cambridge developed the idea that the Milky Way was made 

 up of a number of independent star-clouds or clusters. If 

 these are in relative motion, as they presumably are, there 

 will be occasions on which one cloud meets another. The 

 stars in each being widely scattered, one will pass through 

 the other freely, without much risk of collision between any 

 of the members. This supposition would explain all the main 

 facts as we know them at present ; but we cannot say how far 

 it will fit in with facts to be discovered in the future, when 

 we have compared plates taken at greater intervals, and begin 

 to learn something of the movements of the more distant stars. 



By the kindness of Mr. Eddington (Chief Assistant at the 

 Royal Observatory, Greenwich) I am enabled to reproduce 

 two diagrams which show the very latest piece of evidence in 

 favour of the existence of these two star-drifts. It should first 

 be premised that since a series of parallel lines, such as the 

 parallel edges of a box, appear to us to converge to a point 

 (the " vanishing-point " of perspective), so a cluster of stars 

 moving in parallel paths, like a flock of migrating birds, would 

 seem to us to have movements converging to a definite point 

 in the heavens. A beautiful instance of such convergence 

 among some stars in the constellation Taurus was detected 

 a couple of years ago by Prof. Boss of Albany, N.Y. He 

 had suspected its existence for nearly twenty years, but the 

 knowledge of the stellar motions was too inaccurate to convert 

 his suspicion into certainty. This has only come with the 

 completion of a vast research on the movements of the stars 

 which he has conducted with infinite patience : removing one 

 source of error after another by a laborious series of approxi- 

 mations until at last he was able to produce a catalogue of 

 movements freed, as far as possible, from all discernible 

 systematic errors. Incidentally he got values for the motions 

 of the Taurus cluster sufficiently accurate to make it clear 

 that they were apparently converging to a point. With this 

 clue and the help of spectroscopic observations he was able 

 ' See an abstract in Proc, Camb. Phil. Soc. vol. xiii. Pt. IV. 



