30 
invisible with telescopes of ordinary power for more than the 
half of its entire period. 
Mr. G. Knott, F.K.A.S., of the Woodcroft Observatory, 
Cuckfield, Sussex, has kindly favoured me with a copy of his 
observations of S Delphini, made during the present year, 
and of the light-curve laid down from them. He has obtained 
for the date of maximum August 1 i, 1805 — magnitude, 8*8. 
Considering the nature of the observations, and the form of 
the light-curve at its maximum, this result agrees very fairly 
with that derived from my own observations. It will how- 
ever be seen that there is a slight difference in our modes 
of drawing a curve through the points laid down ; Mr. Knott 
evidently regarding apparent irregularities as being principally 
owing to errors of observation, while, on the other hand, I 
have regarded them as being mainly due to actual changes in 
the brightness of the star. Treating his observations pre- 
cisely as I have treated my own, I do in fact, obtain the 
same date of maximum, August 9, 1865. 
The colour of S Delphini is decidedly <f reddish,” and my 
observations seem to indicate that this colour becomes sensibly 
more intense as the star approaches its minimum. The 
difference of O’ 1 between my own and Mr. Knott’s estimations 
of magnitude at the last maximum is doubtless due to the 
colour of the star, and to the fact that while my observations 
have been made with a telescope of five inches aperture, Mr. 
Knott’s have been made with one having an aperture of 
seven and one-third inches. 
Erratum. — Page 20, last paragraph, for ajpion ononis , read apion ononidis. 
