One by one these carets stood out to view, punctuating the points where canals later were to show or terminating those that already existed. Strung thus with them at intervals was the whole coastline of the diaphragm, beginning with the Mare Icarium and stretching round through the Mare Tyrrhenum, Mare Cimmerium, Mare Sirenum, and Mare Erythraeum to the Mare Icarium again. As the planet got nearer to the earth their peculiar shape began to define itself, and it was again in the case of those giving origin to the Phison and Euphrates that the recognition came first. What had appeared earlier simply as a spot now stood out as two triangular notches, indenting the coast and giving exit at their apices, the eastern one to the Phison, the western to the Euphrates. These were the things, then, that had constituted the Portus Sigaeus of Schiaparelli.
Commonly the carets lie at the bottom of well-marked bays, as, for example, those terminating the Syrtis Minor and the Sinus Titanum. But frequently they are placed in the very midst of a long and otherwise unaccented coast, as is the case in mid-course of the Mare Cimmerium and the Mare Sirenum. Yet in no instance is the thing unassociated with a canal. In every case one or more canals leave the caret for their long traverse down the disk.
This is not their only canal connection. When the canals in the dark regions came to be discovered, each of them was found by me, as nearly as difficult observations would permit, to be associated with the caret upon its other side. Thus the lacing of the Mare Cimmerium and Sirenum used them as its reeving-points. Similarly those at the mouths of the Phison and Euphrates did duty likewise to the Maesolus and the Ion. In such manner the carets stood in dual relation to canals; subserving a purpose to the light-region canals on the one hand and to the dark-region ones on the other. In a way the caret, then, holds the same position toward the canals that do the spots in the light or dark regions. Like them it is a canal-distribution point. Unlike them, however, in shape it is triangular instead of round, and we are piqued to inquire to what cause it can owe its different contour. The answer seems to lie in the character of the locality, not simply in its complexion. For the spots in both the northern and the southern dark patches are as circular as those standing in the light, whether they lie in the centre or upon the edges of them. The edges of the northern patches, however, and the other sides of the southern ones do not present the clear-cut character of the northern coast of the diaphragm. Where they seem to be definitely bounded they are so by darker canals. This hints that their contours are not defined by antithesis of level, while that of the northern coast of the great diaphragm is. Difference of altitude is then concerned in their constitution; the canal system here falls to a lower level, and these triangular spots instead of round ones are the result. Topographic only, such explanation leads the way to a more teleologic one, and serves even on first acquaintance to stir curiosity to some satisfying cause.
Suggestive in several ways for its resemblance to the carets is another detail not far distant from the Portus Sigaei, the twin-forked Sabaeus Sinus. Curiously enough, this feature of Mars, which has been well known and recognized ever since the eagle-eyed Dawes detected it more than forty years ago, proves to be a sort of connecting link between the main markings and the details of more modern detection. The twin-forked Sabaeus Sinus, as its name implies, is of the form of a double bay; was considered to be one in fact so long as the maria were held to be seas. It straddles the point of land which, called the Fastigium Aryn, has been taken for the Greenwich of Martian longitudes. Each ‘bay’—not in truth a bay at all—indents the ochre in an acute triangle, from the tip of which many canals proceed like the rays of a fan from a holding hand. Both tips are darker than the main body of the dark mare from which they proceed. They thus recall in general character the carets. They further reproduce specifically the Portus Sigaei, for they give origin to two doubles, the Gihon and the Hiddekel, in exactly the same manner that the two nicks of the Portus Sigaei do to the Phison and Euphrates. Nor are their tips much farther apart than those of the Portus, five degrees measuring the spread of the one and four degrees that of the other respectively; the reason for their earlier discovery lying in their greater size. They thus perform the same office as the Portus Sigaeus, are quite comparable to it in width, and differ in shape only as a larger and more acute triangle differs from a smaller and blunter one. Undreamt of by Dawes and unheeded since, they were the first hint to the world of the duality which forms so strangely pervasive a feature of the canal system of the planet.
Thus the carets stand connected with the canals quite as intimately as the oases but in a significantly different manner. For, in addition to their intermediary standing between the light regions and the dark, their relation to the doubles is peculiar. An instance is offered by the double Euphrates and another by the Ganges. The Euphrates, as we saw in Chapter XVIII, leaves the Portus Sigaei at the south, one line leaving each caret centrally, so that each caret is concerned only with its own line and has no connection with its fellow. At their northern ends both lines have similarly each its own Lucus Ismenius. The like seems to be true of the Ganges. Similarly the twin Titan, have each its own. Such twin duty in the matter of doubles seems to be the rule with the carets, even more so than with the oases; and this is probably from the fact that the coastline is of more limited extent than the interior.
Altogether the carets offer to our inspection glosses in finer print upon the general text of the canals. Thought upon what they show takes us a step farther toward the solution of the strange riddle of this other world, a riddle which he who runs may not read, still less scout, and which only reasoning, without prejudice or partiality, can unravel.
CHAPTER XXII
THE CANALS PHOTOGRAPHED
Photography holds to-day a place of publicity in the exposition of the stars. Directed by Draper to the heavens thirty-four years ago, the camera recorded then the first picture ever taken of the moon. From this initial peering into celestial matters, practice has progressed until now the dry plate constitutes one of the most formidable engines in astronomic research. Not most effectively, however, in the field which might have been predicted. Beautiful as the lunar presentment was, as a presentiment of what was coming, it pointed astray. For it is not in lunar portrayal, superbly as its crater walls in crescent chiaroscuro or its crags that cast their tapering shadows athwart the dial of its plains stand out in the latest photographs of our satellite, that the camera’s greatest service has since been done. Impressive as they are, these pictorial triumphs are chiefly popular, and appeal on their face to layman and scientist alike. Not in the nearest to us of the orbs of heaven, but in the most remote has celestial photography’s most prolific field been found to lie. Its province has proved preëminently the stars, especially the farthest off, and that star-dust, the nebulæ, from out of which the stars are made. Reason for this explains at once its efficiency and its limitations.
Its rival, of course, is the eye. It is as regards the eye that its comparative merits or demerits stand to be judged. Now, thus viewed, its superiority in one respect is unquestionable; it simply states facts. But though it cannot misinform, it can color its facts by giving undue prominence to the effect of some rays and suppressing the evidence of others, so that its testimony is not, it must be remembered, always in accord with that of human vision. Speaking broadly, however, it is so little complicated a machine as to register its results with more precision than the retina. The evidence of the camera has thus one important advantage over other astronomic documents: it is impersonally trustworthy in what it states. Bias it has none, and its mistakes are few. Imperfections, indeed, affect it, but they are of purely physical occasion and may be eliminated or accounted for as well by another as by the photographer himself.