CHAPTER IX.—S CYGNI. 
131 
The mean light-curve was derived from observations as far as 1905 March 
24. It shows a steady and rapid decline, with a well-defined minimum, a halt 
in the rise at about 12th magnitude, and a maximum about as sharp as the mini¬ 
mum. The halt in the rise is referred to by Townley as a double maximum, 
but nothing is shown of it in the mean light-curve published in the Harvard 
Annals S 7 , Plate hi. In the light-curve, fig. 26, this halt is shown before the 
maxima of epochs 32, 33, 34, 40, and 45. At the other maxima the observations 
are too few to furnish evidence. 
Later Note. —It was possible to observe the minimum, epoch 46, in the 
fall of 1905, in better conditions than any previous one. Advantage was taken 
of an unusually clear night, November 18, to secure photometer measures of the 
faint comparison star d with the result, 15.48 and 15.73, on the Harvard and 
Potsdam scales, respectively. The variable was then i6£ (corresponding to i6f 
on the Potsdam scale), the faintest ever observed. 
The difference in scale is very noticeable in Table 79; as compared with 
mine, the Harvard and H. M. Parkhurst scales are respectively 15 and 16 
per cent more extended. The reasons for this discordance are not clear, but 
it should be noted that the measures of the faint stars in the Harvard list all 
depend on the single star a (=C of Table 70, color GW), too slender a basis 
it would seem, especially as the meridian photometer measures in Volume 44 
of the Annals depend on three zones, one of which was interrupted and the other 
two stopped by clouds. It may also be said that the stars x and y were used 
with the 6-inch, which would make the limit of that instrument about 13.7 if 
the Harvard scale is accepted. Taking everything into account, it seems probable 
that the truth lies between the two scales. 
