OF ARTS AND SCIENCES. 



21 



has the advantage of eliminating an error in estimating its brightness, 

 but does not give a good determituition of tlie light curve. Dr. Schon- 

 feld observed Algol, according to liie method of Argelander, from l8-'>9 

 to the present time, and has given the results up to 1870, in the 

 Sec/isti>iddreissi(/ster Jahreshericht des Mannheimer VWeins fur Natur- 

 kunde, p. 70. He has not published his comparisons, but has given his 

 resulting light curves, which will be nia<le the basis of the following 

 discussion. We must first reduce his grades to ab.solute measure?, 

 which is done in Table VII. The successive columns give the name 

 of the comparison stars, the light in grades adopted by Schcinfeld, the 

 logarithm of the light as measured by Seidel {Resultate photometrischer 

 Messungen^ Miinchen, 1862), the logarithms of the light as measured 

 by Wolff {Photometrische Beohachtangen an Fixsternen, Leipzig, 1877), 

 after subtracting 0.232 to eliminate the constant difference between 

 his measures and those of Seidel. The next column gives the differ- 

 ence between the measures of Seidel and Wolff, and shows that on the 

 average they differ only .040, or a tenth of a magnitude. If L denotes 

 the logarithm of the light, and g the corresponding number of grades, 

 we may assume L =z a -\- gh. This is only equivalent to admitting 

 Fechuer's law or assuming that Schonfeld's grades correspond to equal 

 ratios of light. A solution by least squares gives a = 8.446 and 

 b = 0.025, or L = 8.446 -\- 0.025 g. The sixth column gives the 

 value of L computed by this formula for the various values of g 

 assumed by Schonfeld. The last two columns give the errors of 

 Seidel and Wolff, assuming the estimates of Schonfeld to be exact. 

 The average value of these differences is but little more than a tenth 

 of a magnitude. Apparently, c Aurigce was estimated by Schonfeld 

 about three tenths of a magnitude too bright, and 8 Persei about two 

 tenths too faint. Omitting these stars the errors would be reduced 

 about one half. 



TABLE VII. — Comparison Stars for /3 Petrsei. 



