the purpose.[1477] A shimmer of F was suspected, and had
also been perceived by Mr. O. T. Sherman of Yale College. Still, the
effect was widely different from that of the characteristic blazing
spectrum of a temporary star, and prompted the surmise that here, too, a
variable might be under scrutiny. The star, however, was certainly so
far "new" that its rays, until their sudden accession of strength, were
too feeble to affect even our reinforced senses. Not one of the 1,283
small stars recorded in charts of the nebula could be identified with
it; and a photograph taken by Dr. Common, August 16, 1884, on which a
multitude of stars down to the fifteenth magnitude had imprinted
themselves, showed the uniform, soft gradation of nebulous light to be
absolutely unbroken by a stellar indication in the spot reserved for the
future occupation of the "Nova."[1478]

So far, then, the view that its relation to the nebula was a merely
optical one might be justified; but it became altogether untenable when
it was found that what was taken to be a chance coincidence had repeated
itself within living memory. On the 21st of May, 1860, M. Auwers
perceived at Koenigsberg a seventh magnitude star shining close to the
centre of a nebula in Scorpio, numbered 80 in Messier's Catalogue.[1479]
Three days earlier it certainly was not there, and three weeks later it
had vanished. The effect to Mr. Pogson (who independently discovered the
change, May 28)[1480] was as if the nebula had been _replaced_ by a
star, so entirely were its dim rays overpowered by the concentrated
blaze in their midst. Now, it is simply incredible that two outbursts of
so uncommon a character should have _accidentally_ occurred just on the
line of sight between us and the central portions of two nebulae; we
must, then, conclude that they showed _on_ these objects because they
took place _in_ them. The most favoured explanation is that they were
what might be called effects of overcrowding--that some of the numerous
small bodies, presumably composing the nebulae, jostled together, in
their intricate circlings, and obtained compensation in heat for their
sacrifice of motion. But this is scarcely more than a plausible
makeshift of perplexed thought. Mr. W. H. S. Monck, on the other hand,
has suggested that new stars appear when dark bodies are rendered
luminous by rushing through the gaseous fields of space,[1481] just as
meteors kindle in our atmosphere. The idea, which has b