crease of
visual power, as happens in the observation of double stars, and it is
not the canal itself splitting in two longitudinally. Here is what is
seen: To the right or left of a pre-existing line, without any change in
the course and position of that line, one sees another line produce
itself, equal and parallel to the first, at a distance generally varying
from six to twelve degrees--i.e., from 350 to 700 kilometres (217 to 434
miles); even closer ones seem to be produced, but the telescope is not
powerful enough to distinguish them with certainty. Their tint appears
to be a quite deep reddish brown. The parallelism is sometimes
rigorously exact. There is nothing analogous in terrestrial geography.
Everything indicates that here there is an organization special to the
planet Mars, probably connected with the course of its seasons."[1]

[Footnote 1: L'Astronomie, vol. i, 1882, pp. 217 _et seq._]

Schiaparelli adds that he took every precaution to avoid the least
suspicion of illusion. "I am absolutely sure," he says, "of what I have
observed."

I have quoted his statement, especially about the duplication of the
canals, at so much length, both on account of its intrinsic interest and
because it has many times been argued that this particular phenomenon
must be illusory even though the canals are real.

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 inva