The reader may ask: "Why so readily accept Schiaparelli's conclusions
with regard to Mercury while rejecting them in the case of Venus?"
The reply is twofold. In the first place the markings on Venus, although
Mr. Lowell sketched them with perfect confidence in 1896, are, by the
almost unanimous testimony of those who have searched for them with
telescopes, both large and small, extremely difficult to see,
indistinct in outline, and perhaps evanescent in character. The sketches
of no two observers agree, and often they are remarkably unlike. The
fact has already been mentioned that Mr. Lowell noticed a kind of veil
partially obscuring the markings, and which he ascribed, no doubt
correctly, to the planet's atmosphere. But he thinks that,
notwithstanding the atmospheric veil, the markings noted by him were
unquestionably permanent features of the planet's real surface.
Inasmuch, however, as his drawings represent things entirely different
from what others have seen, there seems to be weight in the suggestion
that the radiating bands and shadings noticed by him were in some manner
illusory, and perhaps of atmospheric origin.
If the markings were evidently of a permanent nature and attached to the
solid shell of the planet, and if they were of sufficient distinctness
to be seen in substantially the same form by all observers armed with
competent instruments, then whatever conclusion was drawn from their
apparent motion as to the period of the planet's rotation would have to
be accepted.
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