THE LIGHT OF THE STABS. 179 



method consisting in estimating in " steps " or 

 " grades" the difference in brilliance between the 

 variable, or suspected variable, and other stars 

 which are selected for comparison, and which 

 are of various degrees of brilliance, so that they 

 may be available for comparison with the vari- 

 able throughout its fluctuations. Argelander's 

 " steps " are tenths of a magnitude, and Gore 

 describes the method of observation as follows : 

 "If we call a and b the comparison stars, and v 

 the variable, a being brighter than b, and if v 

 is judged to be midway in brightness between a 

 and 6, we write a5v5b. If v is slightly nearer to 

 6, we write av4b. We may also write a3v7b, 

 or a7v3b, the sum of the steps being always 

 ten." 



This method, described in 1844, led to many 

 discoveries at Bonn in the following twenty 

 years by Argelander and his assistants Schmidt 

 and Schonfeld. At this time Eduard Heis 

 (1806-1877), at Minister, who also ranks as one 

 of the founders of meteoric astronomy, while 

 engaged on the construction of his great atlas, 

 attentively determined the change of magnitude 

 of stars visible to the naked eye ; and by means 

 of the naked eye, the opera-glass, and a small 

 telescope, he amassed a large number of observa- 

 tions. At the same time two English observers, 



