CHAPTER II.—T ANDROMEDA. 
19 
Table 10 collects the magnitude results for each night from Table 8 and forms 
the means. The magnitudes for the separate nights are expressed in the Harvard 
system, and followed by the column “J Mag.” giving the residuals from the 
mean of three nights. The columns of means give the magnitude in both systems, 
and lastly the means of the separate residuals. 
Table 11 gives the comparisons of the variable by Argelander’s method 
(including a few photometric and photographic), the resulting photometric magni¬ 
tudes of the variable, and a comparison with the mean light-curve. The Central 
Time (6 hours west of Greenwich) is given in the third column to the nearest hour, 
but as the records were usually made to the nearest quarter hour, the decimal 
of the Julian day in the fourth column is carried farther and sometimes differs 
by one or two hundredths from the hour in column three. In the fifth column, 
“Aperture,” 6 stands for the 6J-inch Brashear reflector (clear aperture equivalent 
to 6.2 inches = 15 cm.), 3 for the same with diaphragm, 12 and 40 for the Yerkes 
refractors (30 and 102 cm. respectively), 24 for the 60 cm. reflector. 
The comparisons in the seventh column, unless otherwise stated, were made 
by Argelander’s method, the comparison stars being denoted by letters, v stand¬ 
ing for the variable. The stars compared were brought equally distant from the 
center of the field and the head turned till the line joining the eyes was parallel 
to that joining the stars. Then by glancing from one star to the other the interval 
in steps was estimated. In the records the brighter star is given first; civ is read 
“ c is one step brighter than the variable;” 64-57;, 6 is four or five steps brighter 
than the variable. When the variable was not seen the limiting magnitude is 
usually estimated from the faintest comparison star visible, for example “limit 
4<e” means that the limit of visibility is four steps fainter than e. 
The reductions in columns 8, 9, and 10 were made as follows: (1) The light 
scale was formed in the usual manner from all the step intervals in column 7, 
with the results given in the fifth column of Table 7. (2) Each comparison in 
the seventh column then gives the brightness of the variable in steps, column 8. 
For example, on the first date, since b= 39.0 steps, the comparison 64-57; gives 34.5 
for the brightness of the variable. (3) To form the mean step values for the 
ninth column, if the estimated interval is greater than two or three steps the results 
are weighted inversely as the interval. (4) To obtain the corresponding photometric 
magnitudes given in the tenth column in the Harvard system, recourse is had 
to the “Magnitude-Curve” (fig. 4). Using the data in Table 7, for the stars 
measured with the photometer, the step values are platted as ordinates and 
the magnitudes as abscissae. (5) A smooth curve is drawn through the platted 
points, giving from the step values in the ninth column the magnitudes in the 
tenth. The step values of the stars not measured are entered in crosses on the 
magnitude-curve, and the resulting magnitudes are given in Table 7, eighth and 
ninth columns. 
