DRIFTING OF THE STARS. 231 



Septentriones. Moreover, as the stars belonging to this particular 

 type are certainly in many cases, and probably in all, very large orbs ' 

 (referring here to real magnitude, not to apparent brilliancy), the in- 

 ference seemed fairly deducible that the drifting five stars are not 

 nearer than Alpha, and therefore (since we have seen that it is unlikely 

 that all the Septentriones lie at nearly the same distance) the inference 

 would be that the drifting stars lie much farther away than the rest. 



It remained, however, that the crucial test of motion-measurement 

 should be applied. 



In the middle of May last I received a letter from Dr. Huggins an- 

 nouncing that the five are all receding from the earth. In all, the hy- 

 drogen line called F is " strong and broad." In the spectrum of Alpha 

 the line F is "not very strong " (so faint, indeed, Dr. Huggins afterward 

 informed me, that he preferred to determine the star's motion by one 

 of the lines due to magnesium in the star's atmosphere). He found 

 that Alpha is approaching. As to Eta, Dr. Huggins remarked that 

 the line at F is " not so strong or so broad " as in the spectrum of 

 " the five." He was uncertain as to the direction of motion, and men- 

 tioned that " the star was to be observed again." He subsequently 

 found that this star is receding. But, whereas all the five are receding 

 at the enormous rate of thirty miles per second, Eta's recession was 

 so much smaller that, as we have seen, Dr. Huggins was unable to 

 satisfy himself at a single observation that the star was receding at alL 



It will be seen that my anticipations were more than fulfilled. 

 The community of recessional motion was accompanied by evidence 

 which might very well have been wanting viz., by the discovery that 

 neither Eta nor Alpha shared in the motion. Moreover, the physical 

 association between the five stars was yet further evidenced by the 

 close resemblance found to exist between the spectra of the five stars. 

 Dr. Huggins remarked in his letter : " My expectation had nothing to 

 do with the above results. At the moment, I thought Alpha was in- 

 cluded in the group, and was therefore a little disappointed when I 

 found Beta going the opposite way." 



We have at length, then, evidence, which admits of no question 

 so obviously conclusive is it to show not only that star-drift is a re- 

 ality, but that subordinate systems exist within the sidereal system. 

 We moreover recognize an unquestionable instance of a characteristic 

 peculiarity of structure in a certain part of the heavens. For, though 

 star-drift exists elsewhere, yet every instance of star-drift is quite dis- 

 tinct in character the drift in Cancer unlike that in Ursa, and both 

 these drifts unlike the drifts in Taurus, and equally unlike the drift in 

 Aries or Leo. Much more, indeed, is contained in the fact now placed 



1 Sirius demonstrably gives out much more light than our sun, and according to the 

 best determinations of his distance he must (if his surface is of equal intrinsic lustre) 

 be from 2,000 to 8,000 times larger than the sun. Vega, Altair, and Rigel, are also cer- 

 tainly larger and may be very much larger than our sun. 



