----, 9 24 ----
June 25, ----, 9 37 ----
Aug. 7, ----, 9 50 ----
Sept. 19, ----, 10 3 ----
Nov. 1 ----, 10 16 ----
Dec. 14, ----, 10 29 ----
Jan. 26, 1869, 10 42 ----
Mar. 10, ----, 10 25 ----
Mar. 13, ----, 7 43 ----[7]
Apr. 25, ----, 7 56 ----
June 7, ----, 8 9 ----
July 20, ----, 8 22 ----
Sept. 1, ----, 8 35 ----
Oct. 14, ----, 8 48 ----
Nov. 26, ----, 9 1 ----
Jan. 8, 1870, 9 14 ----
Feb. 20, ----, 9 27 ----

From the minimum at about 10 P.M. on October 31st, 1867, we get in like
manner the series--

h. m.
Dec. 13, 1867, 10 13 P.M.
Jan. 25, 1868, 10 26 ----
Mar. 8, ----, 10 39 ----
Apr. 20, ----, 10 52 ----
June 2, ----, 11 5 ----
June 5, ----, 7 53 ----[8]
July 18, ----, 8 6 ----
Aug. 30, ----, 8 19 ----
Oct. 12, ----, 8 32 ----
Nov. 24, ----, 8 45 ----
Jan. 6, 1869, 8 58 ----
Feb. 18, ----, 9 11 ----
Apr. 2, ----, 9 24 ----
May 15, ----, 9 37 ----
June 27, ----, 9 50 ----
Aug. 9, ----, 10 3 ----
Sept. 21, ----, 10 16 ----
Nov. 3, ----, 10 29 ----
Dec. 16, ----, 10 42 ----
Jan. 28, 1870, 10 55 ----

From one or other of these tables every observable minimum can be
obtained. Thus, suppose the observer wants to look for a minimum during
the last fortnight in August, 1868. The first table gives him no
information, the latter gives him a minimum at 8h. 19m. P.M. on August
30; hence of course there is a minimum at 11h. 31m. P.M. on August 27;
and there are no other conveniently observable minima during the
fortnight in question.

The cause of the remarkable variation in this star's brilliancy has been
assigned by some astronomers to the presence of an opaque secondary,
which transits Algol at regular intervals; others have adopted the view
that Algol is a luminous secondary, revolving around an opaque primary.
Of these views the former seems the most natural and satisfactory. It
points to a secondary whose mass bears a far greater proportion to that
of the primary, than the mass even of Jupiter bears to the sun; the
shortness of the period is also remarkable. It may be noticed that
observation points to a gradual diminution in the period of Algol's
variation, and the diminution seems to be proceeding more and more
rapidly. Hence (assuming the existence of a dark secondary) we must
suppose that either it travels in a resisting medi