hich in an imperfect
instrument might cause such a result I do not undertake to make a
selection. It is certain that Venus's satellite has vanished with the
improvement of telescopes, while it is equally certain that even with
the best modern instruments illusions occasionally appear which deceive
even the scientific elect. Three years have passed since I heard the
eminent observer Otto Struve, of Pulkowa, give an elaborate account of a
companion to the star Procyon, describing the apparent brightness,
distance, and motions of this companion body, for the edification of the
Astronomer-Royal and many other observers. I had visited but a few
months before the Observatory at Washington, where, with a much more
powerful telescope, that companion to Procyon had been systematically
but fruitlessly sought for, and I entertained a very strong opinion,
notwithstanding the circumstantial nature of Struve's account and his
confidence (shared in unquestioningly by the observers present), that he
had been in some way deceived. But I could not then see, nor has any one
yet explained, how this could be. The fact, however, that he had been
deceived is now undoubted. Subsequent research has shown that the
Pulkowa telescope, though a very fine instrument, possesses the
undesirable quality of making a companion orb for all first-class stars
in the position where O. Struve and his assistant Lindenau saw the
supposed companion of Procyon.

I may as well point out, however, that theories so wild have recently
been broached respecting Venus, that far more interesting explanations
of the enigma than this optical one may be looked for presently. It has
been gravely suggested by Mr. Jos. Brett, the artist, that Venus has a
surface of metallic brilliancy, with a vitreous atmosphere,--which can
only be understood to signify a glass case. This stupendous theory has
had its origin in an observation of considerable interest which
astronomers (it is perhaps hardly necessary to say) explain somewhat
differently. When Venus has made her entry in part upon the sun's face
at the beginning of transit, there is seen all round the portion of her
disc which still remains outside the sun an arc of light so brilliant
that it records its photographic trace during the instantaneous exposure
required in solar photography. It is mathematically demonstrable that
this arc of light is precisely what _should_ be seen if Venus has an
atmosphere like our earth's. But mat