That elevations really may be found on Mars is evident from the fact that snow or hoar-frost often remains in patches near the pole and occasionally quite far therefrom, for instance on the large island Hellas (40° S. Lat.), while it disappears from the surroundings and sometimes from the pole itself (the south pole). Such a highland covered by ice exists near the south pole, and is shown near the upper edge of [Fig. 24]. In places where snow always remains, a feeble glacier formation may occur. Most investigators assume that mountains and plateaus exist on Mars, although of modest altitude (Campbell believes that he has observed peaks 3000 m. (9800 ft.) high). Lowell who diligently has looked for mountains at the edge of the illuminated part of Mars, has reached the conclusion that they, if present, cannot rise more than 600 to 900 m. (2000 to 3000 ft.) above the surrounding plains. It were indeed improbable that all inequalities of the Martian surface should have been removed in the process of disintegration, which although at work for enormous extensions of time, has long been extremely feeble and is unassisted by torrents of rain which might rapidly wash the products into the valleys. At present, it is mainly the sand carried by the desert wind that slowly reduces the roughnesses and in this process extensive highlands are hardly touched. But, without the assumption, in itself very unlikely, of a nearly level surface on Mars it becomes difficult to comprehend how the canals, if filled with pure water, can proceed in straight lines without reference to existing differences in altitude. Like the rivers on the Earth they ought to bend according to the topography, even if constructed by engineers.
When the canals freeze at the approach of winter, they invariably have been observed to disappear in company with the lakes or oases at their crossings. They are then all covered by the reddish-yellow dust carried by wind from the surroundings. When a canal is about to reappear it frequently first comes to sight as a dark streak evidently the result of moistened ferro-oxide. Occasionally a mist formation precedes the appearance of the canal. It is plain that the cold, misty air settles in the valleys, there as here, and gives up its moisture to the salts on their bottom and the canal is thus brought out as a dark line. Sometimes the vicinity also assumes a darker shade indicating the absorption of some moisture. On the sides of the canals the less hygroscopic salts are deposited. Possibly the green colour of the canals is partly a contrast-effect due to the red surrounding, possibly also the result of finely divided matter in the liquid. It is also conceivable that the cause is the reducing influence on the ferro-oxide of the sulphuric gases emerging from the fissures; an exceedingly small quantity accomplishes in this case large results. F. le Coultre describes the colour as being sometimes a dead black.
Something similar applies to the seas. When these freeze, especially in shallow places, yellowish-red dust from the continent settles on their surface and lends it hues between the original dark green and the light yellowish-red. When the ice subsequently melts this dust sinks in the water which latter resumes its dark green colour.
Chloride solutions, if concentrated, freeze at the following temperatures; that of calcium at -55° C. (-67° F.) that of magnesium at -44° C. (-48.2° F.) and that of sodium at -22° C. (-7.6° F.). If now, as we previously have seen, the mean temperature of Mars as a whole is about -40° C. (-40° F.), of the equatorial belt about -10° C. (+14° F.), and of the pole in the height of summer about 0° C. (32° F.), it is evident that a liquefaction of the ocean surface and of the canals, particularly where salts are deposited, very readily may take place. We should in this connection remember that the ice on Mars is stationary while on Earth it is in motion. The consequence is that sand and dust in the course of thousands of years have accumulated on the bottom of the shallow basins in the polar ice. These seas appear therefore dark in spite of their exceedingly small depth and the white salt and ice-crystals remaining undissolved are unable to display their light colour. Even in the “ocean,” Lowell was persuaded that he had observed canals (see [Fig. 23]), and it may be possible that cracks are in evidence there, particularly in the most shallow sections, as is the case in the Tyrrhenian sea north of Sicily. It is significant that Flammarion has reached the conclusion, which at first appears highly hazardous, that the freezing point of water is lower on Mars than on Earth. This is entirely correct, if we let water stand for salt solutions.
It is customary to point to the strictly uniform breadth and the rectilinear appearance of the canals as clear evidence of their being artificial, i. e., the work of engineers. The Italian astronomer Cerulli strongly objected to this conception. “In the exceedingly rare cases when both sides of the canal plainly may be seen,” states Schiaparelli, “I have observed curves and notches in the borders.” This occurred with the canals Euphrates and Triton in 1879, and with the Ganges in 1888. And it would seem obvious that watercourses produced in old furrows would not, as a rule, be of uniform breadth. Antoniadi, by his observations in the autumn of 1909 (see [Fig. 17a] and [24]), has confirmed this opinion, as has le Coultre, who found twice as many irregular canals as rectilinear ones. Antoniadi remarks that some canals appear to be collections of lakes strung out in a certain direction while others are narrow lines which bend and twist. “The complicated network of straight lines is probably illusory.” The spots on Mars, he continues, are very irregular, and “present by no means any geometrical form” (on which the belief largely is founded that they are the product of intelligent beings). “The appearance of the planet reminds one of that of the Moon (except that the latter is dead, i. e., unchangeable) or of a terrestrial landscape viewed from a balloon.”—“In a word, the ‘geometry’ of Mars is revealed as a pure illusion.” Exceedingly instructive is a comparison between the two maps of Mars drawn by Schiaparelli (1886) and by Antoniadi (1909) reproduced here and found at the end of the volume. While Schiaparelli as a rule represents the canals as narrow, straight, or slightly curved bands of uniform width, these formations on the Antoniadi chart frequently dissolve into a series of dark spots joined by less obscure sections (see for example the canals Nectar and Oeroe at the Sunlake). The same is true about several of the so-called “seas,” particularly the Tyrrhenian (Mare Tyrrhenum), and the Sunlake (Lacus Solis); also about the “Ocean-bays” such as the well-known Syrtis major which with the Sunlake form the most conspicuous objects on the surface of Mars. These maps are, moreover, of great interest because several canals and other features present on one are absent on the other and vice versa. In this way, we obtain a vivid conception of the remarkable changeableness of the Martian surface as contrasted with the exterior of the Earth. The latter, if viewed from Mars, would not have presented any noticeable change in historical time except for the seasonal variation of the snow fields. This peculiarity of Mars is only explained by the fact that the geographical features of that planet as a rule are surface formations of a slight depth and therefore subject to rapid transformations.
Frequently, large white spots suddenly appear, especially near the lakes, such as the spot at Lake Phœnix near the centre of Fig. 24 which represents Mars on October 6, 1909, according to Antoniadi. These white spots disappear as suddenly as they show forth. The white colour is probably due to a very thin snow or hoar-frost, which is easily condensed in the vicinity of the lakes but which as readily vanishes at the approach of a warm draft or of sunshine.
Occasionally, dark spots on Mars are described as dissolving under strong enlargement into dark and light squares giving the appearance of a chessboard. This reminds one of the bayirs in Turkestan (see [Fig. 9]).
The collections of lakes along the cracks on Mars which appear to us as “canals” are repeatedly filled up by sand and dried out. They are revived through new depressions along the dislocation fissures, corresponding to our earthquakes, when vapours of water and other gases pour forth and condense to lakes in the deepest pockets of the fissures. Canals are therefore created rather rapidly, sometimes over night, and vanish occasionally as suddenly. The most remarkable case of “new” canals was made known through a communication by Lowell. Two new canals, at the time the most conspicuous on the surface of Mars, were observed east of “Syrtis magna” on September 30, 1909, from Flagstaff observatory, when they also were photographed, which precludes an illusion. (On the other hand there was no sign of the great canal Amenthes, shown on the map [Fig. 17], a short distance to the left, i. e., east of Syrtis in the very section where the new canals were observed.) Also two new oases through which the new slightly curved canals passed were observed for the first time, as were also a few minor canals in the neighbourhood.
In 1913, the double canal Æthiops (see [map] at Long. 240°; the canal is there single) was rediscovered from the Lowell observatory after an absence of fifteen years.
These data make it evident that one or possibly several rather strong earthquakes took place east of Syrtis major just prior to September 30, 1909 with the two oases as centres of collapse. The fissures now made visible have probably existed before but filled with sand and have now reappeared as a result of the condensation of water vapour when it emerged into the cold Martian air.