Through the works of Schiaparelli, Flammarion, and Lowell the vivid interest of the general public has been directed toward our neighbour planet Mars. Several investigators, Flammarion and Lowell among them, assert with full confidence that Mars has intelligent inhabitants, who have built and maintain the curious “canals,” which, it is stated, could not have been created except by intelligent beings far superior to man.

Air, water, and sunshine exist there, says Flammarion in his well-known great work, La PlanÈte Mars (1902, page 515). “It appears incongruous to us to condemn a world like Mars, where all the conditions for life exist, to such a fate” (to be a dry desert). No doubt sentiment and the desired result play a part in all such deductions, as indeed the words chosen by Flammarion would indicate.

As contrasted to the Earth, Mars is, on the other hand, considerably further removed from the Sun, whose radiation therefore on Mars possesses only 43 per cent. of its intensity on Earth. Judging by this fact, the mean temperature of Mars should fall far below that of the Earth and considerably below the freezing point of water and under such conditions it is hard to imagine a vegetation near the poles of Mars as Lowell does in his volume, Mars as the Abode of Life (1909), or even in the neighbourhood of the canals anywhere on the surface of the planet as assumed by Flammarion.

With such ideas in vogue we can well understand that the astronomers would point their lately extremely sharpened instruments toward our ruby-coloured neighbour in the sky when, in 1909, it passed very close to the earth under conditions particularly favourable to accurate observations, more so in fact than they had been during the seventeen preceding years.

Numerous astro-physicists, among them the world’s foremost representatives of their discipline, have repeatedly turned their spectroscopes toward Mars in order to ascertain whether water vapour was present there or not. In the spectrum of the Sun we find several so-called “rain-bands” due to the fact that the light before it reaches the apparatus has passed through the moisture of the air. The more humid the air the more strongly developed these rain-bands are. If we direct the instrument first on the Moon, which lacks an atmosphere and therefore also moisture, and then on Mars, which for the sake of simplicity we assume standing close to the Moon-disk, a difference should appear in the spectra of these two bodies, provided moisture is present in the atmosphere of Mars. The rain-bands ought to be more pronounced in sunlight that has passed the atmosphere of Mars (passed it twice as the light is reflected by the surface of the planet) than in light reflected from the naked Moon. The bands appear of course in both spectra as the light on its final stage to the spectroscope passes the atmosphere of the Earth, which never is free from moisture. In this manner Huggins and Janssen, scientists of world-wide fame, believed that they had demonstrated the presence of water vapour on Mars. Campbell, on the other hand, the prominent director of the Lick Observatory, made similar investigations of the planet in 1894, and so did a French astronomer, Marchand, in 1896 and 1898, both under unusually favourable circumstances as the former installed his instrument 1283 m. (5200 ft.) and the latter 2860 m. (9370 ft.) above sea level, but neither found any indication of moisture in the atmosphere of Mars.

It is evident that the observations would be far more accurate if we could eliminate the moisture from the atmosphere of the Earth, in which case no rain-bands would appear in the spectrum of the Moon. It would then be unnecessary to compare the two spectra; we would only have to determine whether rain-bands were present in the spectrum of Mars or not. We can never entirely avoid the water vapour of the air, but its influence may be greatly reduced by making our observations from high mountains or in desert climates where the air is comparatively dry, that is free from water vapour. Investigations undertaken where the air is dry deserve therefore more confidence than those handicapped by greater humidity. The observations by Campbell and Marchand fall in the former category, and it would, therefore, appear that the presence of water vapour on Mars to any extent worth mentioning is highly doubtful.

In later trials, Campbell and Keeler have employed an improved method, using photographs of the spectra on sensitive plates, but neither has succeeded in discovering any water vapour in the atmosphere of Mars.

Obviously photography offers a great advantage over direct ocular observation. The two pictures may be placed side by side and very accurate measurements may be made at leisure. We may also choose the moments for exposure when the two stellar bodies stand equally high over the horizon so that the sunlight reflected from them traverses equal distances in the humid atmosphere of the earth.

It now devolved upon Lowell to test his theories by means of the magnificent resources at his disposal in Flagstaff observatory in the desert of Arizona 2200 m. (7200 ft.) above sea level. In the months of January and February the dew-point there is about -7°C. (+19.4°F.) i.e., each cubic meter (1.3 cu. yds.) of air contains 2.8 grammes (43.25 grains) of water vapour while saturated air at zero temperature (32°F.) holds nearly twice this amount or 4.8 grammes (74 grains) per cubic meter (1.3 cu. yds.). Slipher, working in this observatory, pushed the sensitiveness of his plates to the utmost then obtainable, and photographed the spectrum of Mars in January and February, 1908. He found that the most important rain-band always was more prominent in the spectrum of Mars than in the spectrum of the Moon photographed later during the same night. Peculiarly enough, it was only the rain-band designated “A,” and located in the red spectral field, that was of a marked difference in the two spectra. Other bands gave no indication of the presence of water vapour on Mars. This result did not directly contradict the conclusions reached by Campbell and Keeler, also by means of photography; they had investigated other bands than “A.” The “A”-line might therefore possibly be more sensitive to water vapour than the others.

Slipher’s discovery was considered so valuable that it must be employed to the limit. The well-known physicist Very was therefore called in consultation; he made careful measurements of the intensity of the “A”-lines on the various plates and calculated that the atmosphere of Mars contained 1.75 times as much water vapour as that of the Earth at the point of observation. If we desire to determine the proportion of water vapour in the air at the surface of Mars from this statement we may figure in the following manner. The amount of water vapour in a vertical column of air one square meter (1.2 sq. yds.) in section is, according to Hann, 2500 times the amount in a cubic meter (1.3 cu. yds.) at the surface of the earth. At the time of the observation, the latter amount was 2.29 grammes (35.4 grains); on each square meter (1.2 sq. yds.) of the ground rested therefore 5725 grammes (12 lbs. 11 oz.) of water vapour. That the quantity of water is not larger, although the depth of the atmosphere far exceeds 2500 m. (1.5 miles), is due to the fact that the temperature rapidly decreases with distance from the ground. On Mars, the temperature ought not to fall so quickly with change in height because the intensity of gravity there is 2.68 times smaller than on the Earth. The temperature drops there 2.68 times slower with ascent in the atmosphere, and a column of air on Mars one square meter (1.2 sq. yds.) in section should therefore contain 6680 times as much water vapour as a cubic meter (1.3 cu. yds.) at its surface. As Mars did not stand in zenith, the distance traversed by the light-ray in the atmosphere was greater—in fact 1.43 times greater than if such had been the case. A column of air in the direction of the light-ray, one square meter (1.2 sq. yds.) in section contained therefore 8175 grammes (18 lbs. 3 oz.) water vapour. In the atmosphere of Mars which the light passed in a vertical direction there was, if we are to believe Very, 1.75 times as much, or 14,300 grammes (31 lbs. 8 oz.) and in a cubic meter (1.3 cu. yds.) at the surface of the planet, consequently 6680 times less, or 2.14 grammes (33.1 grains). The corresponding dew-point is then, according to this determination, -10.3°C. (+13.5° F.). It is agreed upon that a desert climate prevails on Mars. It might at the time of the observation conform to the extremely dry climate at Salt Lake City in the height of summer when the humidity there is only 31 per cent. of saturation. Under such conditions saturated air at noon in the equatorial belt on Mars should contain 7 grammes (108 grains) per cubic meter (1.3 cu. yds.) corresponding to a temperature of 5.3°C. (41.5°F.).

It must be admitted that this was not very encouraging to Lowell. If the temperature in the middle of the day, when the sunlight falls perpendicularly on the surface of the planet, rises only to about 5°C. (41°F.), the mean temperature for twenty-four hours, even in the midst of the summer, must in this entirely clear, light air be far below freezing and vegetation on Mars is therefore not very well conceivable. In spite of this, Lowell saw in Slipher’s measurements a confirmation of his theory that Mars is the abode of an intelligent race that utilizes, in their wrestle with existence, a verdant vegetation pushed even into the polar regions.

Campbell, however, went one step further than Slipher. In August and September, 1909, Mars occupied a position in the sky particularly favourable to observations. Campbell decided to benefit thereby. With the support of a rich patron of science, a Mr. Crocker, who on several occasions has made magnificent contributions toward astronomical research, Campbell equipped an expedition to Mount Whitney in California, 4425 m. (14,502 ft.) high and the loftiest peak in the United States. He was accompanied by an able scientific staff, the most prominent of which were Dr. Abbot, head of the observatory belonging to the Smithsonian Institution, and a well-known German astronomer, Albrecht. The members of the expedition were affected by mountain sickness and suffered many severe hardships when the wind was high, reaching about 25 m. per sec. (56 miles per hour), and at the same time cold, falling below zero (freezing) during the night. The barometric pressure was only 447 mm. (17.6 inches). During the nights, when the observations were made, the water content of the air fell to between 0.5 and 0.9 grammes (7.7 grains to 13.9 grains) per cubic meter (1.3 cu. yd.) or 2.5 to 4 times less than Slipher had to contend with. The spectra of the Moon and of Mars were photographed in close succession, two exposures being made in each case. The band “A” was plainly visible on several plates. No indication of greater prominence of this band in the spectrum of Mars could be found. Other rain-bands were also investigated with the same result. Neither were the characteristic bands of oxygen stronger in the spectrum of Mars, than in that of the Moon. Slipher believed that he had discerned a difference, although of a hair’s breadth, which would indicate the presence of oxygen in the atmosphere of Mars. The conclusion itself is not improbable, but the amount of oxygen there is in any case considerably smaller than in the Earth’s atmosphere.

Several statements by Campbell, as well as Slipher’s observations, indicate that a difference ought to have appeared between the spectrum of Mars and that of the Moon if the water content in Mars’ atmosphere had been the same as in the Earth’s at the time of the observation. This content, as stated before, was about 3 times smaller on Mount Whitney than at Flagstaff. At the latter place, the measurements gave 1.75 as the ratio of water vapour on Mars to that on the Earth. The amount of water vapour with the Sun in zenith on Mars should therefore, according to Campbell’s observations, only reach 0.4 gramme (6.1 grains) per cubic meter (1.3 cu. yds.) corresponding to a dew-point of -28°C. (-18.4°F.) or to an actual temperature of -17°C. (+1.4°F.) allowing also for a desert climate with only 31 per cent. saturation. This temperature is probably higher than the mean for a summer day as the observations were made at noon on Mars.

It must now be evident that we should consider Mars as unfit to harbour living beings. There is possibly a slight amount of oxygen in the thin air but the extremely low temperature and the scant supply of water vapour form insurmountable obstacles to the subsistence of even the simplest forms of life in the equatorial regions on Mars. The temperature difference between day and night must be enormous on account of the desert climate. Even if life could develop during the day, which has nearly the same duration as with us—Lowell fixed it at 24 hours, 37 minutes, 22.6 seconds—and during which the temperature possibly might rise above the freezing point, it would nevertheless be destroyed without mercy by the bitter frost at night.

Campbell has offered an explanation of the indications of water vapour on Mars, apparent on Slipher’s photographs. An analysis of the latter’s observations shows that the Moon was photographed about four hours later in the night than was Mars. On all occasions except one, clouds appeared in the sky. This indicates the presence of moisture in the air, so that the humidity should change with the temperature which latter rapidly falls in the course of the night. Campbell, himself, found during the clear nights, when he made his observations, that the humidity in the hours of the night up to midnight falls to a fraction—a half or a third—of its original value an hour or so after sunset. This rapid temperature drop is probably confined to the strata immediately above the observation point but the moisture is strongly concentrated downward so that this change in humidity undoubtedly should have been taken into account. Or better, observations should be avoided in the beginning of the night and the Moon and Mars photographed as soon after each other as possible, precautions taken by Campbell but not by Slipher. That the latter found less traces of water on the lunar photos than on the martian ones is, therefore, probably due to the fact that the former were taken about midnight but the latter not long after sunset, when the atmosphere contained much more water vapour. Thus, we learn how a small slip, more obvious to the meteorologist than to the astronomer, may spoil a labour otherwise done with extraordinary care.

To Campbell’s critique Very answered by the suggestion that the meteorological conditions during the Mount Whitney observations should have been exceptionally unfavourable. The entire south-west of the United States and the north of Mexico were visited at that time by cloudy weather and heavy downpours. Very contends that this humidity should partly have extended to the high strata above Mount Whitney and therefore rendered the calculation of the moisture content of the air entirely unreliable.

Simultaneously (August, 1910) new measurements were published of Slipher’s photo-plates from February, 1908, which Very had examined. The result was now that the rain-band “A” was 2.5 times more pronounced in the spectrum of Mars than in that of the Moon. Furthermore, the oxygen absorption-band “B” was 1.5 times stronger for Mars than for the Moon. Great quantities of water vapour and oxygen should, therefore, undoubtedly exist in the atmosphere of Mars.

In the meantime Campbell had not been idle. The difficulty with the older measurements consisted in the fact that the absorption line of water vapour in the atmosphere of Mars occupies the identical place of the line due to vapour in the Earth’s atmosphere. There exists, however, a method, as already pointed out by Campbell in 1896, of separating the two, which method is available when Mars either approaches or departs from the Earth with sufficient velocity. The latter could be determined both from the known motions of the two planets and from the displacement of certain spectral lines of the Sun. These two determinations were in almost perfect agreement; for instance January 26–27, 1910, astronomical calculations gave a relative velocity of 19.1 km. (11.86 miles) per second and spectroscopical measurements 19.2 km. (11.93 miles) per second, while on February 3–4 the relative velocity was 18.1 km. (11.24 miles) a difference of 1 km. (.62 miles) per second. This trial shows the accuracy of the method. Among the absorption lines of water vapour and of oxygen there was, however, none due to the atmosphere of Mars. Campbell assumes that such lines would certainly have been visible if they had been only one-fifth as strong as the so-called tellurian lines. The advantage of this method is evidently that the “martian” and the “tellurian” lines lie close beside each other on the same plate so that differences in sensitiveness, exposure, and atmospheric conditions are entirely eliminated.

From these and the following data we may calculate water content and temperature of the atmosphere on Mars anew: water vapour at the point of observation was 1.9 grammes (29.3 grains) per cubic meter (1.3 cu. yds.), zenith-distance of Mars 55° and incident as well as reflected sun-rays formed an angle of 70° with the surface of Mars; hence, the amount of moisture at the surface was only 0.12 gramme (1.85 grains) per cubic meter (1.3 cu. yds.), corresponding to -38°C. (-36.4° F.) for saturated air and to -27°C. (-16.6° F.) for air of 31 per cent. saturation. Oxygen content per cubic meter (1.3 cu. yds.) at the surface of Mars would be only a sixteenth part of corresponding numerical value on the Earth. This determination is more accurate than any of the previous ones and reduces the temperature another 10°C. (18°F.) below the lowest value derived earlier in this chapter. We should remember, however, that, during the trial of September, 1909, the sun stood practically in zenith on Mars, while in January and February, 1910, we are concerned with a point where sunrise had occurred about four and a half hours previously. The latter observation should give a value close to, but slightly above, the mean diurnal temperature on Mars.

No determination comparable in precision with this one by Campbell appears to have been made. We must therefore recognize it as conclusive.

We may easily calculate the surface temperature of a planet from the intensity of the solar radiation received, or insolation, provided the surrounding vapour shell contains no heat retarding gas. The most important gases of this kind are water vapour, which, as we just have seen, is very sparse in the atmosphere of Mars, and carbon dioxide, of which there probably also, for reasons stated below, is only a scant supply in the martian gas shell. Such calculations were first performed by Christiansen of Copenhagen, who assumed 2.5 calories as the solar constant on Earth, i.e., the amount of energy received through insolation per minute by each square centimeter (.15 sq. in.) of the Earth’s surface when at right angle to the radiation and on mean distance from the Sun. On Mars, the radiating energy received under similar conditions is only about 1.1 calories. The surface of the planet is heated until it radiates as much energy into space as it receives from the Sun. In this way we obtain an average temperature of -37°C. (-34.6°F.) for the entire surface of Mars. The regions, exposed to the Sun in zenith at noon, might, if heat were not conveyed therefrom, possibly reach a daily mean temperature of +8°C. (46.4°F.) and perhaps slightly more at noon. Probably not even the freezing point is reached, as the heat is rapidly carried away by the freely circulating air. The above-mentioned mean temperature of -37°C. (-34.6°F.) seems on the whole to agree well with the observations by Campbell on Mount Whitney.

Recent accurate determinations of the intensity of the solar radiation by Abbot, K. ÅngstrÖm and others, indicate that it has been estimated about 20 per cent. too high. If we take the solar constant to an even 2.0 calories, which is a trifle high, we reach the conclusion that the mean temperature on Mars would fall about 50 degrees below freezing. Equatorial regions might then reach an average of -8°C. (+17.6°F.) and at noon the temperature might possibly rise slightly above zero (32°F.). A higher temperature yet might be attained at the pole where the Sun during the summer remains for months above the horizon or a high mark of +8°C. (46.4°F.) provided no heat were carried away by air currents. Such losses naturally must occur, and the temperature probably hovers around freezing. At the martian poles we might possibly imagine the existence of some low forms of vegetation (snow-algÆ, etc.) during the height of the short summer.

When we hitherto on the authority of Lowell, Very, and others, have assumed an average temperature of +10°C. (50°F.) on Mars, we have done so on the supposition that the atmosphere of the planet contained great quantities of heat-conserving gases. This assumption appears to be no more tenable than the belief in the high temperature on Mars. After all, the temperature is probably about 10°C. (18°F.) higher than our last calculation would indicate—or about -40°C. (-40°F.)—because the air on Mars is very clear and admits, therefore, all sun-rays, retaining also a fraction by virtue of what little water vapour, carbon dioxide, and other heat-conserving gases there may be present in the atmosphere. The mean summer temperature at the martian equator (-27°C. or -16.6°F. acc. to Campbell’s data) would then lie about 13°C. (23.4°F.) above the mean for the planet. This agrees closely with conditions on the Earth where the highest mean in July at the equator is 27°C. (80.6°F.) and the mean for the earth 16°C. (60.8°F.).

We are consequently obliged to revise in their entirety our ideas about Mars. The belief that organic life (green vegetation) causes the colour of the so-called seas on Mars, as assumed by Lowell, or that the red tints belong to the gorgeous dress in which autumn arrays the plants before their leaves are shed under the attacks of frost, as intimated by Flammarion, must nowadays take its place in the shadowy realm of dreams.

Those who do not believe that the so-called canals are real waterways, devoted to freight carrying and irrigation, or illusions, which conception the photographs contradict (for example Fig. 18), generally consider that they signify cracks or fissures. As in the crust of the Earth, they generally run in nearly straight lines or in regularly bent curves (Fig. 17 and 17a). Flammarion mentions that the renowned physicist Fizeau looked upon the “canals” as cracks in the ice-coverings of the oceans on Mars. Penard, in 1888, expressed the more likely opinion that they correspond to the fissures in the crust of the Earth. Flammarion contends that such fissures do not have the rectilinear configuration of the “canals.” This is completely in error, as shown on the map here reproduced (Fig. 16). It is also stated that they are so inexplicably long, for instance the canal Phison is 2250 English miles (Lowell) or 3620 km. in length. The longest known earthquake crack along the entire length of which a dislocation has taken place at one time is 600 km. (373 miles) in extension; the violent earthquake in California, 1906, originated from this crack. There is no doubt, moreover, that a great fissure in the Earth follows the coast of Chile from Arica to the Strait of Magellan in a nearly north and south direction for a distance of about 32 parallels or 3560 km. (2210 miles). This fissure is almost as long as Phison on Mars. Such cracks exist along the entire coast of the Pacific Ocean. As yet, we do not know their position in much detail, because long stretches run below the sea or through territories not yet occupied by civilized people. As an example of a small fissure, a picture taken by Sederholm from SegelskÄr, east of HangÖ in the Baltic, may serve (see Fig. 15). As the studies of earthquakes are prosecuted with increasing interest in later years, fissures of all dimensions will undoubtedly soon be discovered. The solid crust on Mars is, furthermore, somewhat thicker than that of the Earth as the cooling of that planet has progressed further. The sections broken off at the bursting of the Martian crust ought therefore to be much larger both in breadth and in length. No doubt, the facts that the intensity of gravity on Mars is only three-eights of its intensity on the Earth and that the curvature of the Martian surface is twice as sharp as the Earth’s contribute to this result. Imagine two vaults, one built with higher and broader wedge-shaped stones than the other and with half the radius and furthermore loaded only one-third as heavily as the other, and it will become evident that we can permit a much larger span in the former than in the latter case without fear of collapse. In other words, it requires a much more extensive caving or shrinkage of the molten mass beneath the crust of Mars to cause a rupture than under the terrestrial crust.

As a consequence, the fissures on Mars ought to be longer than the corresponding formations on the Earth. A thorough study of the large fissure in Calabria shows that it consists of a veritable network of smaller straight cracks (as is apparent on Figure 16, which is taken from a work by the well-known Finnish geologist Sederholm). On this map the radial cracks (see Worlds in the Making, Fig. 16), charted by Suess, are also shown, and their direction under the sea designated by dotted lines. The sketch in the upper left corner of Fig. 16 is in striking similarity to a picture drawn by Schiaparelli in Mercator’s projection of the planet Mars (see map at the end of book). We notice on both, the numerous equidistant lines corresponding to parallel cracks and duplex canals. Not every fissure has its parallel and not every canal its mate—generally only one of the latter is visible and sometimes both disappear.

As the radial cracks in the drawing by Suess if extended meet in the Lipari Islands, so also several canals on Mars run together in a so-called lake (Lowell called them “groves” or “oases”) which evidently is a centre of collapse (many appear on Fig. 17). It is plain that all crossings of the “canals” are not necessarily such centres of collapse. (See maps Figs. 17 and 17a at end of book).

We shall consequently assume that the canals on Mars correspond to the geological dislocation fissures on the Earth. Along these fissures emerge the gases liberated in the cooling process on both planets; which are similar gases to those which escape through the volcanoes. These vapours are primarily water, next carbon dioxide and, in considerably smaller quantities, sulphuretted gases and hydrochloric acid. They discharge through cracks in regions which, geologically speaking, not so long ago were the scene of volcanic activity. In the dislocation-grooves, lakes, and water courses are often formed, as we may observe in several places in Sweden, for instance near Stockholm.

Assume now a gradual cooling of our earth. Most territories are covered by stratified, comparatively light rocks. To the dislocation fissures water gathers from the surrounding strata and occasionally from the interior, partly washes away the loose material and transforms the fissures into furrows, generally with flat bottoms. Dissolved salts are carried to the sea. As cooling proceeds, the ocean commences to freeze. Each summer the surface melts to a certain extent, as is the case now in our polar regions. Finally, the entire ocean freezes to the bottom, the ice is now to be considered as a kind of rock, flexures and dislocations cease and the ice assumes a smooth surface. In the strong sunlight during the summer this surface thaws, as do the water-courses on the mainland, and these continue to carry their salts to the open surface water. At the approach of winter the latter solidifies again but not as the water in our inland lakes from the top but from the bottom, as ordinary sea-water possesses its greatest density below the freezing point while the opposite is true of fresh water. The consequence is that the ice foundation grows upward and as the surface water becomes increasingly shallow it is turned into a concentrated salt solution. With a further drop in temperature the ice formation is accompanied by crystallization of the salts.

Something similar takes place on the Martian mainland in its flat river basins, which correspond to the salt lakes in our deserts. On account of the bitter cold and the consumption of the water in the process of disintegration (the carbon dioxide has been largely used up in the same manner), precipitation has almost ceased on Mars and most of the water in circulation emerges from the interior of the planet along the fissures. As it contains hydrochloric acid and carbon dioxide it extracts from the soil salts, such as the chlorides of sodium (common salt), of calcium and of magnesium, all present in common sea-water to which it was brought by the rivers. The compounds of calcium and magnesium are not precipitated as carbonated salts through the medium of crustacea as is the case on earth. The strong solar radiation during the summer partly evaporates the water into the thin air, leaving the salts behind. On account of the low temperature, this vaporization on Mars is probably slower than on the Earth. Along the cracks in the crust, a kind of dry salt-lakes are formed similar to the generally shallow and occasionally dry lakes common in the deserts of Central Asia as described by Hedin. We know that Mars possesses a pronounced desert climate. There finally remains in the lowest sections of the water courses a concentrated salt solution, which parts with its water more and more reluctantly, so that the salts which most strongly hold the water crystallize at the deepest points. If the winter’s cold is sufficiently severe (below -55°C. or -67°F.) ice is extracted even from the most concentrated solutions, which mainly contain chloride of calcium. In spite of such extreme temperatures, evaporation into the rare atmosphere is not negligible and the ice crystals partly vanish, to reappear in the coldest regions of the planet, that is, around the pole which at the time is turned away from the sun. On the ocean, now frozen solid throughout, a polar-cap of snow and hoar-frost is formed which finally reaches as far as the 38th parallel on the southern hemisphere (see Figs. 18 and 19), where winter occurs when Mars is most removed from the sun, and to the 58th parallel (see Fig. 19) on the northern hemisphere where winter reigns while Mars is nearest to the Sun and consequently not quite so cold. Similar conditions obtain on the Earth although not to such a marked degree.

In the vicinity of the snow-white polar cap, whether there be continent or sea, bodies of water occur with solidly frozen surface covered by crystals of very hygroscopic salts, such as the chlorides of calcium, magnesium, and sodium. When the summer warmth returns and the polar cap is heated, the hoar-frost evaporates, and the now comparatively humid air spreads over the surrounding territory. We observe also frequent mist-formations in these places. The ground near the edge of the polar snow assumes then often a dark hue on account of the moisture (Fig. 19). Occasionally canals and lakes appear in the polar cap (see Fig. 20). This is evidently due to hot emanations along the cracks. The moist air sweeps over the salts, which then absorb water and dissolve into concentrated solutions. New quantities of water vapour are supplied from the pole as they distill over toward the other pole, where winter now exists, and push on toward the equator which they finally pass. In their course they dissolve the salts in the depressions along the fissures and particularly at the deep crossings where the centres of collapse or the so-called “oases” are located. Lowell has observed that the “canals” in this manner gradually “liquify” from 78° N. Lat. to the equator in fifty-two days.

The canal theory presents great difficulties to the explanation of this curious phenomenon. In order to make the water flow it must be assumed that the surface of Mars is entirely smooth or at least very nearly so and that the inhabitants convey the water melted at the poles through pumping stations. The canals vary in width; according to Lowell, their mean is 16 km. (10 miles), according to Flammarion between 300 and 60 km. (185 and 37 miles) which latter estimate probably is too high. The same canal differs widely in breadth in successive years and sometime disappears altogether. When the supply of water vapour is scant, only the most hygroscopic salts are dissolved, i.e., those deposited in the deepest furrow of the canal, but when the moisture sweeping over the canal is more abundant the broader portions absorb water, darken and thus become visible. The same holds true in regard to the inland lakes (“oases”). As the water vapour diffuses in the air, the canal becomes liquid along its entire length independent of the altitude of its various parts.

All agree upon the desert climate of the mainland on Mars. Like most deserts on the Earth, it is, therefore, probably a table-land, where one plateau mounts above the other, each one nearly level. By the action of the wind, the upper layers have been transformed into fine sand. On the dead planet no further sediments are deposited by the sea. The only accretions to the planet are meteorites and cosmic dust which slowly rains down. It contains among other substances iron, partly metallic and partly in the form of protoxides (which have a light green colour).5 The oxygen in the atmosphere of Mars transforms these compounds to ferro-oxide which has different colours according to its coarseness, but generally is ochre. The surface of Mars is also described as possessing this colour. Dross has, therefore, assumed that the Martian soil is mingled with ferro-oxide. The finest dust, however, is yellow while larger crystals tend toward violet. We often observe on Mars that the details are covered by a yellow veil. This is of course finely powdered ferro-oxide probably mixed with less coloured sand which the desert wind whirls up over large portions of Mars. Vast sections of the planet bore such wrappings in the autumn of 1909, as observed and described by Antoniadi in Paris (see Fig. 21). Similar observations have previously been made by W.H. Pickering and others.

As a rule, only the central and the polar regions of the surface of Mars can be seen. Territories near the equator more than 40 to 50 degrees removed from the point in line with the Sun and the centre of the planet are generally hidden behind a thin, white veil of mist. As soon as the Sun leaves the zenith and reaches half-way to the horizon the moisture of the air is precipitated near the ground. This shows that the planet does not possess any quantities of heat-conserving vapours in its gas shell. The mist does not extend to the poles, whose white caps always appear distinctly, because the Sun cannot greatly affect the evaporation in regions where the Sun’s altitude is neither very high nor very variable. The same holds true for other snow-covered tracts, even if they are not located in the immediate vicinity of the pole.

When the supply of water vapour is scant, only the most salient canals come into view. As a rule they do not then appear double, as one of the mates is always less prominent. Lowell showed, he believed, that it always is the same canal out of a pair which first comes to sight and that its position always remains unchanged in contrast to Schiaparelli who has reached the opposite conclusion. This, of course, is quite natural.

On account of the small amount of water vapour in the atmosphere of Mars true clouds are rare. Figure 22 shows such a cloud at the edge of the planet. The aforementioned mists are often called clouds, for instance by Pickering.

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 Phoenix 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.

This fact, that the most prominent canals in such manner now suddenly appear and now as rapidly vanish, ought to convince us beyond doubt that they are not magnificent products of engineering skill, for the construction of which we should require centuries on the Earth.

The theory that intelligent men exist on Mars is very popular. With its help everything may be explained, particularly if we attribute an intelligence vastly superior to our own to these beings, so that we not always are able to fathom the wisdom with which their canals are constructed. The crossings of the latter are said to be cities (Lowell) fifty times greater than London. The trouble with these “explanations” is that they explain anything, and therefore in fact nothing. If we would endeavour to understand the phenomena on Mars, we must in the first place avoid the formerly so popular principle of “purposiveness” which led even the most prominent scientists into so many amusing errors. Neither may we base our conceptions, as does Flammarion, on the assumption of natural forces unknown to us, no matter how much such a course may appeal to mystics. Only forces with which we are familiar can be resorted to, if we really are to understand nature. It seems to me that such method of research might with good results be applied also to the planet Mars.