78 Things not generally Known. 



that the name of Barakesch, given by the Arabians to Sirius, 

 signifies th star of a thousand colours ; and Tycho Brahe, Kep- 

 ler, and others, attest to similar change of colour in twinkling. 

 Even soon after the invention of the telescope, Simon Marius 

 remarked that by removing the eye-piece of the telescope the 

 images of the stars exhibited rapid fluctuations of bright- 

 ness and colour. In 1814 Nicholson applied to the telescope 

 a smart vibration, which caused the image of the star to be 

 transformed into a curved line of light returning into itself, 

 and diversified by several colours ; each colour occupied about 

 a third of the whole length of the curve, and by applying ten 

 vibrations in a second, the light of Sirius in that time passed 

 through thirty changes of colour. Hence the stars in general 

 shine only by a portion of their light, the effect of twinkling 

 being to diminish their brightness. "This phenomenon M. Arago 

 explains by the principle of the interference of light. 



Ptolemy is said to have noted Sirius as a red star, though 

 it is now white. Sirius twinkles with red and blue light, and 

 Ptolemy's eyes, like those of several other persons, may have 

 been more sensitive to the red than to the blue rays. Sir David 

 Brewster's More Worlds than One, p. 235. 



Some of the double stars are of very different and dissimilar 

 colours ; and to the revolving planetary bodies which apparently 

 circulate around them, a day lightened by a red light is suc- 

 ceeded by, not a night, but a day equally brilliant, though illu- 

 minated only by a green light. 



DISTANCE OF THE NEAREST FIXED STAE FROM THE EARTH. 



Sir John Herschel wrote in 1833 : " What is the distance 

 of the nearest fixed star? What is the scale on which our 

 visible firmament is constructed ? And what proportion do its 

 dimensions bear to those of our own immediate system ? To this, 

 however, astronomy has hitherto proved unable to supply an 

 answer. All we know on this subject is negative." To these 

 questions, however, an answer can now be given. Slight 

 changes of position of some of the stars, called parallax, have 

 been distinctly observed and measured ; and among these stars 

 No. 61 Cygni of Flamstead's catalogue has a parallax of 5", and 

 that of a Centauri has a proper motion of 4" per annum. 



The same astronomer states that each second of parallax in- 

 dicates a distance of 20 billions of miles, or 3J years' journey of 

 light. Now the light sent to us by the sun, as compared with 

 that sent by Sirius and a Centauri, is a,bout 22 thousand mil- 

 lions to 1. " Hence, from the parallax assigned above to that 

 star, it is easy to conclude that its intrinsic splendour, as com- 

 pared with that of our sun at equal distances, is 2*3247, that 

 of the sun being unity. The light of Sirius is four times that 



