best atmospheric conditions, to a broad black band visible at the first glance.
To all these characteristics must be added, of course, the extraordinary occurrence of the gemination or doubling of the canals. It is natural to suppose that, in such cases, what would be seen would be the apparition of a new canal along side of an old one. That, in fact, is what Schiaparelli described as occurring during his earlier observations; but, during the opposition just passed (1888), he discovered that this was not a general rule, and that it may happen that neither of the new canals, when a doubling takes place, may coincide with the old one. "The identity," he adds, "in the general direction and situation is then merely approximative; every trace of the former canal disappears, giving place to two new lines." Both the width and the distance apart of the twin canals vary in successive seasons.
It would carry us far beyond the limits of space available for this article to enter into a more minute account of Schiaparelli's observation of the many anomalies and changes of appearance which the canals present at different seasons and under varying circumstances. Enough has been said to indicate that it would be impossible to make a map which should show the precise appearance of the surface of Mars at any fixed period, and at the same time contain a representation of all the phenomena which are, from time to time, to be seen there. And it should be said, because this is a matter that has been misunderstood, that Schiaparelli
| Ordinary Appearance. | Appearance in April. 1888. | |
| Changes in the Aspect of Libya. | ||
does not intend his maps to be taken as portraitures of the planet, but simply as sketches showing details of whose existence there is no doubt whatever, but all of which can not be, or have not been, seen simultaneously.
And now there remain yet other remarkable circumstances to be mentioned in order to complete the picture of the surface of Mars,
