CHAPTERS ON THE STARS. 239 



the imaginary star just mentioned, the number expressing its magnitude 

 being — 1.4. 



This suggests what we may regard as one of the capital questions in 

 celestial photometry. There being no limit to the extent of the scale, 

 what would be the stellar magnitude of the sun as we see it when ex- 

 pressed this way on the photometric scale? Such a number is readily 

 derivable when we know the ratio between the light of the sun and 

 that of a star of known magnitude. Many attempts have been made 

 by observers to obtain this ratio; but the problem is one of great 

 difficulty, and the results have been extremely discordant. Amongst 

 them there are three which seem less liable to error than others; those 

 of Wollaston, Bond and Zollner. Their results for the stellar magni- 

 tude of the sun are as follow: 



Wollaston —26.6 



Bond —25.8 



Zollner —26.6 



Of these, Zollner's seems to be the best, and may, therefore, in 

 taking the mean, be entitled to double weight. The result will then be: 



Stellar magnitude of sun — 26.4 



From this number may be readily computed the ratio of sunlight 

 to that of a star of any given magnitude. We thus find: 

 The sun gives us: 



10,000,000,000, the light of Sirius. 

 91,000,000,000, the light of a star of magnitude 1. 

 9,100,000,000,000, the light of one of magnitude 6. 



The square roots of these numbers show the number of times we 

 should increase the actual distance of the sun in order that it might 

 shine as a star of the corresponding magnitude. These numbers and 

 the corresponding parallax are as follows: 



These parallaxes are those that the sun would have if placed at such 

 a distance as to shine with the brightness indicated in the first column. 

 They are generally larger than those of stars of the corresponding mag- 

 nitudes, from which we conclude that the sun is smaller than the 

 brighter of the stars. 



