NEWS FROM THE STARS. 
387 
analysis of the probabilities in favour of and against the theory 
that the concurrence of apparent motion was merely accidental, 
I came to the conclusion that the five large stars and the two 
smaller ones form a true drifting set. I found, on a moderate 
computation, that the odds were upwards of half a million to 
one against the concurrence being accidental ; and since I had 
recognised other instances of concurrence not less striking, I 
felt that it was morally certain that these stars belong to one 
star-family. 
The reader will perhaps not be surprised to learn, however, 
that before publishing this conclusion I submitted it (in July, 
1869) to one who was, of all men, the best able to pronounce upon 
its significance — the late Sir John Herschel. I have the letter 
(dated August 1, 1869) which he sent in reply before me as I write. 
The part relating to my discovery runs as follows : — u The 
considerations you adduce relative to the proper motions of the 
stars are exceedingly curious and interesting. Of late years 
catalogues have gone into much detail, and with such accuracy 
that these motions are of course much better known to us than 
some twenty or thirty years ago. The community of proper 
motion over large regions (of which you give a picture in Ge- 
mini and Cancer) is most remarkable, and the coincidence of 
proper motion in Beta, Gamma, Delta, Epsilon, and Zeta Ursss 
Majoris most striking. Your promised paper on this subject 
cannot fail to be highly interesting.” '* 
In a letter written on May 11, 1870, and referring not to 
another letter of mine, but to my “ Other Worlds,” Sir John 
Herschel remarked, 66 the cases of star-drift such as that in Ursa 
Major are very striking, and richly merit further careful ex- 
amination.” 
My first public expression of opinion respecting the star-drift 
in Ursa Major was conveyed in the following terms : — “ If these 
five stars indeed form a system (and I can see no other reason- 
able explanation of so singular a community of motion), the 
mind is lost in contemplating the immensity of the periods 
* He proceeds as follows (the passage is removed from the main text as 
relating to a different branch of the subject) : — u I cannot say that I am at 
all surprised at its being found that the average proper motions of stars of 
small magnitudes is not less than those of large, considering (as I have al- 
ways done) that the range of individual magnitude (i.e. lustre) must be so 
enormous that multitudes of very minute stars may in fact be our very near 
neighbours,” Compare my paper on u The Sun’s Journey through Space,” 
above referred to, which paper also deals with the point touched on in the 
next sentence of Sir John Herschel’s letter : — ({ Your remark on the conclu- 
sion I have been led to draw relative to the small effect of the correction 
due to the sun’s proper motion, will require to be very carefully considered, 
and I shall of course give it every attention.” 
c c 2 
