a close
conjunction gave Mr. James Nasmyth the rare opportunity of watching
Venus and Mercury for several hours side by side in the field of his
reflector; when the former appeared to him like clean silver, the latter
as dull as lead or zinc.[875] Yet the light _incident_ upon Mercury is,
on an average, three and a half times as strong as the light reaching
Venus. Thus, the reflective power of Venus must be singularly strong.
And we find, accordingly, from a combination of Zoellner's with Mueller's
results, that its albedo is but little inferior to that of new-fallen
snow; in other words, it gives back 77 per cent. of the luminous rays
impinging upon it.

This extraordinary brilliancy would be intelligible were it permissible
to suppose that we see nothing of the planet but a dense canopy of
clouds. But the hypothesis is discountenanced by the Flagstaff
observations, and is irreconcilable with the visibility of mountainous
elevations, and permanent surface-markings. To Mr. Lowell these were so
distinct and unchanging as to furnish data for a chart of the Cytherean
globe, and the peculiar arrangement of divergent shading exhibited in it
cannot off-hand be set down as unreal, in view of Perrotin's earlier
discernment of analogous linear traces. Gruithuisen's "snow-caps,"[876]
however--it is safe to say--do not exist as such; although shining
regions near the poles form a well-attested trait of the strange
Cytherean landscape.

The "secondary," or "ashen light," of Venus was first noticed by
Riccioli in 1643; it was seen by Derham about 1715, by Kirch in 1721, by
Schroeter and Harding in 1806;[877] and the reality of the appearance has
since been authenticated by numerous and trustworthy observations. It is
precisely similar to that of the "old moon in the new moon's arms"; and
Zenger, who witnessed it with unusual distinctness, January 8,
1883,[878] supposes it due to the same cause--namely, to the faint gleam
of reflected earth-light from the night-side of the planet. When we
remember, however, that "full earth-light" on Venus, at its nearest, has
little more than 1/12000 its intensity on the moon, we see at once that
the explanation is inadequate. Nor can Professor Safarik's,[879] by
phosphorescence of the warm and teeming oceans with which Zoellner[880]
regarded the globe of Venus as mainly covered, be seriously entertained.
Vogel's suggestion is more plausible. He and O. Lohse, at Bothkamp,
November 3 to 11, 1871, s