nebula around this star. In the first photographs of the latter,
the appearance presented is simply that of an ordinary star. But,
in the course of three or four months, the delicate photographs
taken at the Lick Observatory showed that a nebulous light
surrounded the star, and was continually growing larger and
larger. At first sight, there would seem to be nothing
extraordinary in this fact. Great masses of intensely hot vapor,
shining by their own light, would naturally be thrown out from the
star. Or, if the star had originally been surrounded by a very
rare nebulous fog or vapor, the latter would be seen by the
brilliant light emitted by the star. On this was based an
explanation offered by Kapteyn, which at first seemed very
plausible. It was that the sudden wave of light thrown out by the
star when it burst forth caused the illumination of the
surrounding vapor, which, though really at rest, would seem to
expand with the velocity of light, as the illumination reached
more and more distant regions of the nebula. This result may be
made the subject of exact calculation. The velocity of light is
such as would make a circuit of the earth more than seven times in
a second. It would, therefore, go out from the star at the rate of
a million of miles in between five and six seconds. In the lapse
of one of our days, the light would have filled a sphere around
the star having a diameter more than one hundred and fifty times
the distance of the sun from the earth, and more than five times
the dimensions of the whole solar system. Continuing its course
and enlarging its sphere day after day, the sight presented to us
would have been that of a gradually expanding nebulous mass--a
globe of faint light continually increasing in size with the
velocity of light.