(35) White spots are occasionally visible, lasting unchanged for weeks, in the tropic and temperate regions, showing that the climate is apparently cold,
(36) But at the same time proving that most of the surface has a temperature above the freezing-point.
(37) In winter the temperate zones are more or less covered by a whitish veil, which may be hoar-frost or may be cloud.
(38) A spring haze surrounds the north polar cap during the weeks that follow its most extensive melting.
(39) Otherwise the Martian sky is perfectly clear; like that of a dry and desert land.
The way in which these thirty-nine articles fit into one another to a mortised whole is striking enough at first sight, but becomes more and more impressive the more one considers it. For some are due to one kind of observation, some to another. In the taking they are unrelated; yet in the result they agree. Equally pregnant is the history of their acquisition. Most of them were detected as the outcome of observations at the opposition of 1894, and led to the theory which was published in the writer’s first book on the subject. Others are the result of the five oppositions that have since occurred. These have proved entirely corroborative of the previous ones and of the theory then deduced, and that in two distinct ways: first, by the accumulated evidence they have brought to the matter along the old lines; and, secondly, by what they have revealed in new directions. Of these thirty-nine articles of Martian scientific faith in observation or deduction, (9), (10), (21), (22), (25), (27), (28), (30), (33), (35), (36), and (38) are in whole or part new. That continued scrutiny is thus corroborative of the earlier results, both along the old and along new lines of investigation, warrants additional confidence in the conclusion.
Considering, now, these counts, we see that they make reasonably evident on Mars the presence of:—
1. Days and seasons substantially like our own;
2. An atmosphere containing water vapor, carbonic acid, and oxygen;
3. Water in great scarcity;