652 POPULAR SCIENCE MONTHLY. 



one time supposed to be the case with one of the stars of Ursa Major. 

 This suspected variation has not, however, been confirmed, and it 

 does not seem likely that any such changes take place in the color 

 of stars not otherwise variable. 



POSSIBLE SECULAR VARIATIONS IN THE BRILLIANCY OF STARS. 



All the variations we have hitherto considered take place with such 

 rapidity that they can be observed by comparisons embracing but a short 

 interval of time — a few days or months at the outside. A somewhat 

 different question of great importance is still left open. May not 

 individual stars be subject to a secular variation of brilliancy, meaning 

 by this term a change which would not be sensible in the course 

 of only one generation of men, but admitting of being brought out by 

 a comparison of the brightness of the stars at widely distant epochs? 

 Is it certain that, in the case of stars which we do not recognize as 

 variable, no change has taken place since the time of Hipparchus and 

 Ptolemy? This question has been investigated by C. S. Pierce and 

 others. The conclusion reached is that no real evidence of any change 

 can be gathered. The discrepancies are no greater than might arise 

 from errors of estimates. 



There is, however, an analogous question which is of great interest 

 and has been much discussed in recent times. In several ancient 

 writings the color of Sirius is described as red. This fact would, at 

 first sight, appear to afford very strong evidence that, within historic 

 times, the color of the brightest star in the heavens has actually 

 changed from red to a bluish white. 



Two recent writers have examined the evidence on this subject 

 most exhaustively and reached opposite conclusions. The first of 

 these was Dr. T. J. J. See, who collated a great number of cases in 

 which Sirius was mentioned by ancient writers as red or fiery, and 

 thus concluded that the evidence was in favor of a red color in former 

 times. Shortly afterwards, Schiaparelli examined the evidence with 

 equal care and thoroughness and reached an opposite conclusion, show- 

 ing that the terms used by the ancient authors, which might have 

 indicated redness of color, were susceptible of other interpretations; 

 they might mean fiery, blazing, etc., as well as red in color, and 

 were therefore probably suggested by the extraordinary brightness of 

 Sirius and the strangeness with which it twinkled when near the 

 horizon. In this position a star not only twinkles, but changes its 

 color rapidly. This change is not sensible in the case of a faint star, 

 but if one watches Sirius when on the horizon, it will be seen that it 

 not only changes in appearance, but seems to blaze forth in different 

 colors. 



It seems to the writer that this conclusion of Schiaparelli is the 



