ould be
regarded as corresponding to the maximum and not the minimum stage of
sun-spot activity. According to this view, the star is to be regarded as
possessing an extensive atmosphere of hydrogen, which, during the
maximum, is upheaved into enormous prominences, and the brilliance of
the light from these prominences suffices to swamp the photospheric
light, so that in the spectrum the hydrogen lines appear bright instead
of dark.

It is not possible to suppose that Mira can be the center of a system of
habitable planets, no matter what we may think of the more constant
stars in that regard, because its radiation manifestly increases more
than six hundred fold, and then falls off again to an equal extent once
in every ten or eleven months. I have met people who can not believe
that the Almighty would make a sun and then allow its energies "to go to
waste," by not supplying it with a family of worlds. But I imagine that
if they had to live within the precincts of Mira Ceti they would cry out
for exemption from their own law of stellar utility.

The most beautiful double star in Cetus is gamma, magnitudes three and
seven, distance 3", p. 288 deg.; hues, straw-color and blue. The leading
star alpha, of magnitude two and a half, has a distant blue companion
three magnitudes fainter, and between them are two minute stars, the
southernmost of which is a double, magnitudes both eleven, distance 10",
p. 225 deg..

The variable S ranges between magnitudes seven and twelve in a somewhat
irregular period of about eleven months, while R ranges between the
seventh and the thirteenth magnitudes in a period of one hundred and
sixty-seven days.

[Illustration: MAP NO. 21.]

The constellation Eridanus, represented in map No. 21, contains a few
fine double stars, one of the most interesting of which is 12, a rather
close binary. The magnitudes are four and eight, distance 2", p. 327 deg..
We shall take the five-inch for this, and a steady atmosphere and sharp
seeing will be necessary on account of the wide difference in the
brightness of the component stars. Amateurs frequently fail to make due
allowance for the effect of such difference. When the limit of
separating power for a telescope of a particular aperture is set at 1"
or 2", as the case may be, it is assumed that the stars composing the
doubles on which the test is made shall be of nearly the same magnitude,
or at least that they shall not differ by more than one or two
m