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.