established, it
seems to be the only one yet put forth which can lay any claim to a
scientific basis. What gives most color to it is the extreme suddenness
with which the new stars, so far as has yet been observed, invariably
blaze forth. In almost every case it has been only two or three days
from the time that the existence of such an object became known until
it had attained nearly its full brightness. In fact, it would seem that
in the case of the star in Perseus, as in most other cases, the greater
part of the outburst took place within the space of twenty-four hours.
This suddenness and rapidity is exactly what would be the result of a
collision.

The most inexplicable feature of all is the rapid formation of a 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