408 



PROCEEDINGS OP THE AMERICAN ACADEMY 



Admirable material is thus furnished for a comparison of the re- 

 sults of photographic and eye observations of this region. The pho- 

 tographs of the stars which are common to F and to tlie catalogue 

 of Professor Bond (Annals, V. 270) were first compared by a method 

 closely resembling that adopted by Argelander for the study of varia- 

 ble stars. Table I. gives the stars which were selected for standards, 

 with which the others are to be compared. Each star in the photo- 

 gra[)h was then compared with two of these, — one a little brighter, the 

 other a little fainter. Tlic differences were estimated in grades. Tiie 

 sum of the two ditferences gave a measure of the interval between 

 the two comparison stars. It frequently happened that no difference 

 in brightness was perceptible between the star to be measured and 

 one of the comparison stars. The number of measures of star inter- 

 vals between the comparison stars is therefore less than the number 

 of stars compared. In Table I. the successive columns give for each 

 comparison star a designation, and the number and magnitude in the 

 Bond catalogue. The next column gives the photographic magnitude, 

 found by a process which will be detailed below. This is followed by 

 the number of comparisons between each star and that following it, 

 and the mean value of this difference in grades. The last column 

 gives the assumed brightness in grades, and equals the number of 

 grades by which each star is fainter than the first on the list. 



TAP,LE I. 



The light of each star measured was next reduced to grades by the 

 assumed light in grades of the comparison stars. Two values were 

 found, — one derived from the brighter, the other from the fainter 

 comparison star. In 50 cases the results agreed exactly, in 11 cases 



