Page:The Solar System - Six Lectures - Lowell.djvu/74



up by other hands, and the impetus he gave the matter has resulted in a knowledge of Mars which has quite revolutionized even the conception he bequeathed of the planet.

Before proceeding to post-Schiaparellian work, it may interest you to know how the phenomena in question have been detected, and what they look like when seen.

Contrary to what the layman thinks, the size of the instrument is the least important factor in the process. As in most things, the man is the essential machine; and next in desirability to the presence of man is the absence of atmosphere. In good air, with fair attention, the canals are not very difficult objects. Indeed, the surprise is that they were not detected long ago. Under suitable atmospheric conditions a four-inch glass will show them perfectly. Steady air is one essential; steady study another.

In appearance they are unlike any other phenomena presented in the heavens. Pale pencil lines, deepening on occasion to India ink, seem to cobweb the continents. Their tone depends on the seeing, in the first place, and on the season, in the second. Their width is invariable throughout, and their directness something striking. Measurable width they have not; it is only by