It so chanced that my first experience of the thing was almost equally startling, so unexpected was it and so exceedingly sharp was the definition at the time. It was in an autumn early twilight, through air almost perfectly still, as the light went out of the sky and the markings on the planet began to come forth that the Phison of a sudden showed in duplicate to me, clear-cut upon the disk, its twin lines like the rails of a railway track traversing Aeria. Not more vivid do those of our transcontinental tracks appear as one sees them stretching off into the distance upon our Western plains. More impressive was the sight from the fact that I was not looking for it. It simply suddenly stood forth, this strange parallelism of pencil lines. My surprise matched the wonder of the sight.
Since then I have witnessed it several hundred times, but never with more absolute certainty than at that first fortunate revelation. To this distinctness is due the amazement it then aroused. Not simply because of its surpassing novelty, but for the insistence with which it proclaimed itself was the effect to be ascribed. Less well seen, doubt had robbed it of its full surprise. It requires as a rule steady definition for its initial unmistakable showing, if one would be instantly convinced. Except for such it is not usually easy to the unpracticed, though often discernible to the expert after it has once been seen. But that it is real no one who had had a good view of the sight could doubt; still less after the experience had been repeated over and over again.
What appears to take place is this: where previously a single pencil-like line joined two well-known points upon the disk, twin lines, the one the replica of the other, stand forth in its stead. The two lines of the pair are but a short distance apart, are of the same size, of the same length, and absolutely equidistant throughout their course. It is as if a second line had in some way been mysteriously added to the first since the latter was last seen some weeks before. This in a word is the phenomenon, technically called the gemination of the canals, which has since its discovery called forth so much comment. It is not in reality quite as simple or as sudden as it seems, but this was the way in which the phenomenon was first seen and in which it still continues to be criticised.