Page:The evolution of worlds - Lowell.djvu/111

Rh Thus when we reason upon them we see that the peculiar markings of the planet lose their oddity, becoming the very pattern and prototype of what we should expect to view. Interpreted, they present us the picture of a plight more pitiable even than that of Mercury. For the nearly perfect circularity of Venus' orbit prevents even that slight change from everlasting sameness which the libration of Mercury's affords. To Venus the Sun stands substantially stock-still in the sky,—a fact which must prove highly reassuring to Ptolemaic astronomers there, if there be any still surviving from her past. No day, no seasons, practically no year, diversifies existence or records the flight of time. Monotony eternalized,—such is Venus' lot.

What visual observations have thus discovered of the rotation time of Venus, with all that follows from it, the spectroscope at Flagstaff has confirmed. At Dr. Slipher's hands, spectrograms of the planet have told the same tale as the markings. It was with special reference to this point that the spectrograph there was constructed, and the first object to which it was directed was Venus.

The planet's rotation time was to be investigated by means of the motion it brought about in the line of sight. Visual observation, telescopically, reveals motion