4 



PROCEEDINGS OF THE AMERICAN ACADEMY 



Table I. gives the equivalent diameters of stars of various magni- 

 tudes, assuming ^ = 1. 



TABLE I. — Equivalent Diameters of Stars of Various Magnitudes. 



The diameters corresponding to the intermediate magnitudes may 

 be found from Table II., which gives the diameters for every tenth of 

 a magnitude from 0.0 to 4.9. 



TABLE IL — Equivalent Diameters op Stars for each Tenth of a 



Magnitude. 



When the magnitude is increased by five, the diameter will be re- 

 duced ten times, and the decimal point should accordingly be moved 

 one place to the left. Thus, if a star of the 3.5 magnitude has a 

 diameter of 0".003, one of the 8.5 magnitude will have a diameter 

 of 0".0003 and one of the 13.5 magnitude, 0".00003. The diameter 

 of Sirius would be that corresponding to — 1.5 magnitudes, or 0".03, 

 were it not that I is probably greater than 1 owing to the blue color 

 of the star, and the diameter consequently less. 



Should future measurements render some other value of aS' more 

 probable. Tables I. and II. can still be used, merely changing s by the 

 same amount that S is altered. 



The smallest star that can be seen in the 15-inch telescope of the 

 Harvard College Observatory has a magnitude of about 15.5, and a 

 corresponding equivalent diameter of 0."000012. 



