Page:The Solar System - Six Lectures - Lowell.djvu/47



Schiaparelli was the only one to see these markings till 1896, when the subject was taken up at Flagstaff. The planet was at the time coming out from inferior conjunction, and was at first no easy matter to find ; for in relative visibility Mercury behaves like the Moon. Size of disk does not begin to compensate for phase, as calculation would lead one to expect ; because obliquity of illumination greatly enfeebles its amount. The planet presented so faint a contrast with the sky that on one occasion an assistant, coming to look at it through the telescope, could not see it until its exact position was pointed out to him ; and I always picked it up myself by trailing it across the field, an object in motion being much more evident than one at rest, as every hunter knows. Nor could I at first make much out of it ; it was only a pretty little moon nearly lost in the vast blue sky. To my surprise, however, as it left elongation to return to the Sun, it grew brighter and brighter, and distinct dark markings came out upon its disk. The best views occurred when popular almanacs inform their readers : "Mercury invisible during the month." In the clear sky and steady air of Arizona and Mexico the markings were not especially difficult objects, though more difficult than the canals on Mars. They