een [delta] Cassiopeiae and
[alpha] Persei.

Not very far off is the wonderful variable Algol, now due east, and
about 58 deg. above the horizon. The variability of this celebrated object
was doubtless discovered in very ancient times, since the name Al-gol,
or "the Demon" seems to point to a knowledge of the peculiarity of this
"slowly winking eye." To Goodricke, however, is due the rediscovery of
Algol's variability. The period of variation is 2d. 20h. 48m.; during
2h. 14m. Algol appears of the second magnitude; the remaining 6-3/4
hours are occupied by the gradual decline of the star to the fourth
magnitude, and its equally gradual return to the second. It will be
found easy to watch the variations of this singular object, though, of
course, many of the minima are attained in the daytime. The following
may help the observer:--

On October 8th, 1867, at about half-past eleven in the evening, I
noticed that Algol had reached its minimum of brilliancy. Hence the next
minimum was attained at about a quarter-past eight on the evening of
October 11th; the next at about five on the evening of October 14th,
and so on. Now, if this process be carried on, it will be found that the
next evening minimum occurred at about 10h. (_circiter_) on the evening
of October 31st, the next at about 11h. 30m. on the evening of November
20th. Thus at whatever hour any minimum occurs, another occurs _six
weeks and a day later_, at about the same hour. This would be exact
enough if the period of variation were _exactly_ 2d. 20m. 48s., but the
period is nearly a minute greater, and as there are fifteen periods in
six weeks and a day, it results that there is a difference of about 13m.
in the time at which the successive recurrences at nearly the same hour
take place. Hence we are able to draw up the two following Tables, which
will suffice to give all the minima conveniently observable during the
next two years. Starting from a minimum at about 11h. 45m. on November
20th, 1867, and noticing that the next 43-day period (with the 13m.
added) gives us an observation at midnight on January 2nd, 1868, and
that successive periods would make the hour later yet, we take the
minimum next after that of January 2nd, viz. that of January 5th, 1868,
8h. 48m., and taking 43-day periods (with 13m. added to each), we get
the series--

h. m.
Jan. 5, 1868, 8 45 P.M.
Feb. 17, ----, 8 58 ----
Mar. 31, ----, 9 11 ----
May 13,