37. They end by running into one or other of the polar caps.
38. Their look is geometrical to a degree, suggesting artificiality on its face.
39. Their appearance is singularly confirmed by their behaviour.
40. During the winter season of the part of the planet in which they find themselves, they are of exceedingly tenuous proportions, only just visible with care.
41. As the polar cap begins to melt in the spring, lines are seen running out of it, deeper in tint and more imposing in size than any elsewhere to be seen on the disk.
42. As time goes on, the lines that connect with them successively darken down the latitudes.
43. Until the darkening of the network crosses the equator into the planet’s other hemisphere.
44. The arctic or antartic canals, as the case may be, lighten at the same time, and gradually this lightening, too, follows the wave of darkening which preceded it down the disk in like manner.
45. Six months after the phenomenon thus disclosed at one cap, a regular wave proceeds from the other cap down the disk in the opposite direction. Thus in every Martian year two waves of darkening affect the canal system alternately from one cap and then the other, this rythmic oscillation in appearance being exactly timed to the planet’s seasons.
46. The oases undergo a similar regular transformation. From the merest pinpoints they develop into quite sizable round spots, and then in due season fade out again to what they were before.
Now, if one considers first the appearance of this network of lines and spots, and then its regular behaviour, he will note that its geometrism precludes its causation on such a scale by any natural process and, on the other hand, that such is preciseley the aspect which an artificial irrigating system, dependent upon the melting of the polar snows, would assume. Since water is only to be had at the time it is there unlocked, and since for any organic life it must be got, it would be by tapping the disintegrated cap, and only so, that it could be obtained. If Mars be inhabited, therefore, it is precisely such a curious system we should expect to