so found by the same observer to be a
variable. It may be of interest to the reader to know that Goodricke was
deaf and dumb, and that he died in 1786 at the early age of twenty-one
years!

It was not, however, until the close of the nineteenth century that much
attention was paid to variable stars. Now several hundreds of these are
known, thanks chiefly to the observations of, amongst others, Professor
S.C. Chandler of Boston, U.S.A., Mr. John Ellard Gore of Dublin, and Dr.
A.W. Roberts of South Africa. This branch of astronomy has not, indeed,
attracted as much popular attention as it deserves, no doubt because the
nature of the work required does not call for the glamour of an
observatory or a large telescope.

The chief discoveries with regard to variable stars have been made by
the naked eye, or with a small binocular. The amount of variation is
estimated by a comparison with other stars. As in many other branches of
astronomy, photography is now employed in this quest with marked
success; and lately many variable stars have been found to exist in
clusters and nebulae.

It was at one time considered that a variable star was in all
probability a body, a portion of whose surface had been relatively
darkened in some manner akin to that in which sun spots mar the face of
the sun; and that when its axial rotation brought the less illuminated
portions in turn towards us, we witnessed a consequent diminution in the
star's general brightness. Herschel, indeed, inclined to this
explanation, for his belief was that all the stars bore spots like those
of the sun. It appears preferably thought nowadays that disturbances
take place periodically in the atmosphere or surroundings of certain
stars, perhaps through the escape of imprisoned gases, and that this may
be a fruitful cause of changes of brilliancy. The theory in question
will, however, apparently account for only one class of variable star,
namely, that of which Mira Ceti is the best-known example. The scale on
which it varies in brightness is very great, for it changes from the
second to the ninth magnitude. For the other leading type of variable
star, Algol, of which mention has already been made, is the best
instance. The shortness of the period in which the changes of brightness
in such stars go their round, is the chief characteristic of this latter
class. The period of Algol is a little under three days. This star when
at its brightest is of about the second mag