But now it must be stated that no less eminent an authority than Schiaparelli holds that Venus, as well as Mercury, makes but a single turn on its axis in the course of a revolution about the sun, and, consequently, is a two-faced world, one side staring eternally at the sun and the other side wearing the black mask of endless night.

Schiaparelli made this announcement concerning Venus but a few weeks after publishing his discovery of Mercury’s peculiar rotation.  He himself appears to be equally confident in both cases of the correctness of his conclusions and the certainty of his observation.  As with Mercury, several other observers have corroborated him, and particularly Percival Lowell in this country.  Mr. Lowell, indeed, seems unwilling to admit that any doubt can be entertained.  Nevertheless, very grave doubt is entertained, and that by many, and probably by the majority, of the leading professional astronomers and observers.  In fact, some observers of great ability, equipped with powerful instruments, have directly contradicted the results of Schiaparelli and his supporters.

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.  In the case of Mercury the markings, while not easily seen, appear to be sufficiently distinct to afford confidence in the result of observations based upon them, but Venus’s markings have been represented in so many different ways that it seems advisable to await more light before accepting any extraordinary, and in itself improbable, conclusion based upon them.