One of the most significant facts that came out in the early
observations was the evident connection between the appearance of the
canals and the seasonal changes on Mars. It was about the time of the
spring equinox, when the white polar caps had begun to melt, that
Schiaparelli first noticed the phenomenon of duplication. As the season
advanced the doubling of the canals increased in frequency and the lines
became more distinct. In the meantime the polar caps were becoming
smaller. Broadly speaking, Schiaparelli's observation showed that the
doubling of the canals occurred principally a little after the spring
equinox and a little before the autumn equinox; that the phenomenon
disappeared in large part at the epoch of the winter solstice, and
disappeared altogether at the epoch of the summer solstice. Moreover, he
observed that many of the canals, without regard to duplication, were
invisible at times, and reappeared gradually; faint, scarcely visible
lines and shadows, deepened and became more distinct until they were
clearly and sharply defined, and these changes, likewise, were evidently
seasonal.
The invariable connection of the canals at their terminations with the
regions called seas, the fact that as the polar caps disappeared the
sealike expanses surrounding the polar regions deepened in color, and
other similar considerations soon led to the suggestion that there
existed on Mars a wonderful system of water circulation, whereby the
melting of the polar snows, as summer passed alternately from one
hemisphere to the other, served to reenforce the supply of water in the
seas, and, through the seas, in the canals traversing the broad
expanses of dry land that occupy the equatorial regions of the planet.
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