# Mars (Lowell)/Chapter 3

III
WATER
I. THE POLAR CAP
After air, water. If Mars be capable of supporting life, there must be water upon his surface; for, to all forms of life, water is as vital a matter as air. On the question of habitability, therefore, it becomes all-important to know whether there be water on Mars.
To the solution of this inquiry, also, the planet's polar cap turns out to hold the key. For just as the fact of change in the cap proves the presence of air, so the manner of that change implies the presence of water. It not only does this; it turns out to do a deal more. For to the whole water question it appears to play the part not only of occasion but of cause. In more senses than one, it is in that great glistening white patch that our water problem takes its rise.
On the 3d of June, 1894, the south polar cap stretched, almost one unbroken waste of white, over about 55 degrees of latitude. A degree on Mars measures 37 miles; consequently the ​cap was 2,035 miles across. Inasmuch as the inclination of the Martian equator to the plane of the Martian orbit is, according to Schiaparelli, 24° 52', it must have then covered more than the whole south frigid zone of the planet.
Now, to take in the full meaning of the condition of the cap at this time and of the changes that ensued, we must begin by determining the Martian time of year. This is done by fixing the dates at which the Martian pole reached its maximum tilt toward or from the Sun, and the dates at which it was not tilted either to or from, but sideways to, the Sun; the former gives us the Martian solstices, and the latter the Martian equinoxes. It thus appears that on April 7, 1894, occurred the vernal equinox of the Martian southern hemisphere, on August 31, its summer solstice, and on February 7, 1895, its autumnal equinox. From these dates it is easy to transform the one calendar into the other. On the 3d of June, 1894, therefore, it was about May 1 on the southern hemisphere of Mars.
On May 1, then, Martian time, the cap was already in rapid process of melting; and the speed with which it proceeded to dwindle showed that hundreds of square miles of it were disappearing daily. As it melted, a dark band appeared surrounding it on all sides. Except, as I have since learned, at Arequipa, this band has ​never, I believe, been distinctively noted or commented on before, which is singular, considering how conspicuous it was at Flagstaff. It is specially remarkable that it should never have been remarked upon elsewhere, in that a similar one girdling the north polar cap was seen by Beer and Mädler as far back as 1830. For it is, as we shall shortly see, a most significant phenomenon. In the first place, it was the darkest marking upon the disk, and was of a blue color. It was of different widths at different longitudes, and was especially pronounced in tint where it was widest, notably in two spots where it expanded into great bays, one in longitude 270° and one in longitude 330°. The former of these was very striking for its color, a deep blue, like some other-world grotto of Capri. The band was bounded on the north, that is, on the side toward the equator, by the bluish-green areas of the disk. It was contrasted with those both in tone and tint. It was both darker and more blue.
The band not only varied in width at different longitudes, but its width corresponded to the amount of the blue-green areas of the disk visible at these longitudes below it. It was widest where these were greatest in extent, and narrowest where they were least. If we consult the map of Mars we shall see that below the bay in longitude 330° lies the great dark ​area, the Syrtis Major, and, below the one in longitude 270°, the Syrtis Minor. This correlation was highly suggestive in itself. As if, however, to remove all question as to possible coincidence having a hand in the matter, the agreement in position was emphasized by visible connection. Two long dark streaks appeared joining respectively each bay to its corresponding Syrtis.
But the most significant fact about the band was that it kept pace with the polar cap's retreat toward the pole. As the white cap shrank it followed pari passu so as always to border the edge of the snow. It thus showed itself not to be a permanent marking of the planet's surface, since it changed its place, but a temporary one, dependent directly upon the waning of the cap itself. In short, it was an associated detail, and itself instantly suggested its character, namely, that it was water at the edge of the cap due to the melting of the polar snow.
Not only did the band conform with the cap in position; it did so in size. As the snows dwindled, the blue band about them shrank in width to correspond. By August it was a barely discernible thread drawn round the tiny white patch which was all that remained of the enormous snow-fields of some months before. Finally, on October 13, when the snow entirely disappeared, as we shall presently see, the spot ​where it and its girdle, long since grown too small for detection, had been became one yellow stretch.
That the blue was water at the edge of the melting snow seems unquestionable. That it was the color of water; that it so persistently bordered the melting snow; and that it subsequently vanished, are three facts mutually confirmatory to this deduction. But a fourth bit of proof, due to the ingenuity of Professor W. H. Pickering, adds its weight to the other three. For he made the polariscope tell the same tale. On scrutinizing the great bay through an Arago polariscope, he found the light coming from the bay to be polarized. Now, to polarize the light it reflects is a property, as we know, of a smooth surface such as that of water is.
Before going further we will take up here at the outset the question of the constitution of these polar caps, which in their general behavior so strikingly suggest our own ice-caps as they would appear could they be seen from a distance of forty millions of miles. That they so instantly suggest snow has suggested, to that class of mind which likes to make of molehills of question mountains of doubt, the possibility that instead of ice we have here snow-caps of solid carbonic acid gas (carbon dioxide). The occasion of the suggestion is the fact that carbonic dioxide under certain conditions becomes ​a colorless liquid, and then a solid of a floccular, snow-like character. It assumes, in short, under proper conditions of pressure and cold, the various appearances presented by water under higher temperatures, although it does so with very different degrees of ease. Superficially, therefore, the idea seems plausible. Let us see if it still seems so when critically examined.
Faraday made experiments on the relation of the congealing point of carbonic acid gas to the pressure, and found that at 0° C. it took a pressure of 36 atmospheres, that is, 540 pounds to the square inch, to solidify the gas, and that at −99° C., the lowest temperature with which he experimented, it took 1.14 atmospheres. At this point the curve representing the relation was becoming apparently asymptotic, that is, a slight decrease in pressure involved a great falling off of temperature. Under a pressure of one atmosphere, therefore, the temperature would be about −170° F., that is, on the surface of the Earth this would be the congealing point of the gas.
He found further that the curve for the liquefaction point lay very close to that for the congealing point, and approached yet closer as the pressure decreased. In other words, the gas passed almost immediately from the gaseous to the solid state.
In the light of these facts let us consider the ​condition of Mars. Three points arise which we will take in the inverse order of their importance. First: the appearance of the planet shows conclusively that, if the polar caps be composed of solid carbonic acid gas, then either there is no water at all on Mars in any form whatsoever, or what there is is ice so overlaid with detritus as to be invisible. For if the two substances were there together, and the cold at the surface of the planet of so extreme a character as to congeal the carbon dioxide, the water must a fortiori be frozen, and would continue so long after the temperature rose above the melting point of the former substance. We should therefore still have snow-fields of snow after the melting of those formed of carbonic acid gas, either visible as white patches or so covered up with dirt as to pass for land. Now there are no such additional white patches to be seen, nor, so far as we can judge, does any part of the planet behave as if it were glacier-bound.
Second: carbonic dioxide passes, as we saw, almost simultaneously into the liquid and solid states, especially under slight pressure. Now, the pressure is certainly very slight on the surface of Mars; not probably more than, and probably less than, one seventh of an atmosphere. In consequence, on a rise of temperature the frozen carbonic acid gas would there pass practically straight from the solid into the gaseous ​state. Now, from the existence of the surrounding polar sea, we remark that in the substance composing the polar caps of Mars this does not occur. A considerable portion of it is always in the transition state of a liquid. Carbonic dioxide would not thus tarry: water would.
Third: from the curve of metamorphosis, it is evident that the temperature necessary to freeze the gas under the pressure of one seventh of an atmosphere must lie between −100° C. and −200° C., if not lower. −200° C. is, so far as we can judge, about the temperature of inter-planetary space, or what would be the temperature of the night side of Mars were the planet destitute of atmosphere. But there is an atmosphere on Mars, and, even if there were not, on melting the carbonic dioxide would itself make an atmosphere. This would instantly raise the temperature, and under any rise in temperature the congealing of the gas at once becomes an impossibility. The gas itself thus suggests its own refutation.
There is no such apparent objection to water. With an atmosphere properly constituted (and there is nothing to show that the Martian atmosphere is not so constituted), the temperature might easily rise high enough to melt ice. We may therefore conclude water to be the most probable solution of the question.
With such more or less solid ground to ​stand on, we may now go on to describe the behavior of the cap as constituted of snow. Whether we call it snow-cap or ice-cap is immaterial, as, although it would probably be deposited as hoar-frost rather than as snow in the first instance, owing to the thinness of the Martian air, the latter end of either form of the substance would be much the same,—glacier-ice.
It will, be interesting to examine more in detail the annual history of the ice-cap, especially as this history was unrolled before us last year more minutely than has been the case for the last fifteen years, and than will be the case for fifteen years to come. This was due not only to the relative proximity of the planet during the last opposition, but to the further fact that its south pole was tilted toward us at maximum angle. The vicissitudes which the polar cap underwent stood, in consequence, remarkably well displayed. To such advantage were they seen that it has been possible to construct a map of the Martian south circumpolar regions to a degree of detail such as has never been possible before, and which I have accordingly done. It will be seen from it (on the opposite page) how much farther advanced is our knowledge of the Martian south pole, and the regions about it, than is our knowledge of either of our own.
Plate II
MAP OF THE SOUTH POLE OF MARS Showing the polar cap and its changes in 1894
On examining the chart in which the successive appearances of the southern ice-cap are depicted at different times, from June 3 to October 13, or, in terms of the Martian time of year, from May 1 to July 15, the first point to strike one is that the cap was during its whole existence eccentrically placed with regard to the geographical pole of the planet. In other words, the pole of rotation and the pole of cold did not coincide. The latter lay on the average some six degrees distant from the former. This shows that the isotherms in the southern hemisphere of Mars do not coincide with the parallels of latitude.
The manner of the cap's melting further shows that differences of level exist in it. For, in addition to melting round its edge, the cap proceeded to melt asymmetrically. On the first night that Professor W. H. Pickering observed it, on May 22, with the six-inch telescope, he suspected a rift crossing the cap from longitude 330° to longitude 170°. This rift grew more and more evident, until, in the early part of June, it was unmistakable. It grew in visibility chiefly from actual growth in size. On June 6 ​it was estimated, on a scale of ruled lines made for the purpose, to be about 100 miles wide. On June 15 it was similarly found to measure 220 miles.
Meanwhile an interesting phenomenon occurred in the cap on June 7. On that morning, at about a quarter of six (or, more precisely, on June 8, 1h. 17m., G. M. T.), as I was watching the planet, I saw suddenly two points like stars flash out in the midst of the polar cap. Dazzlingly bright upon the duller white background of the snow, these stars shone for a few moments and then slowly disappeared. The seeing at the time was very good. It is at once evident what the other-world apparitions were,—not the fabled signal-lights of Martian folk, but the glint of ice-slopes flashing for a moment earthward as the rotation of the planet turned the slope to the proper angle; just as, in sailing by some glass-windowed house near set of sun, you shall for a moment or two catch a dazzling glint of glory from its panes, which then vanishes as it came. But though no intelligence lay behind the action of these lights, they were none the less startling for being Nature's own flash-lights across one hundred millions of miles of space. It had taken them nine minutes to make the journey; nine minutes before they reached Earth they had ceased to be on Mars, and, after their travel of ​one hundred millions of miles, found to note them but one watcher, alone on a hill-top with the dawn.
Calculation showed the position of the star-points to be in longitude 280° and 290° and in latitude 76° south. At this place on the planet, then, there was a range of slopes sufficiently tilted to reflect the Sun from their ice-clad sides. On comparing its position with Green's map of his observations upon the cap at Madeira in 1877, it appeared that this was the identical position of the spot where he had seen star-points then, and where Mitchell had seen them in 1846, to whom they had suggested the same conclusion. Green christened them the "Mitchell Mountains." At the times both these observers saw them, they were detached from the rest of the cap. At the time of this observation in June, they were still in the midst of the cap. We shall see that they eventually became islands, just as Green saw them, and that the observation in June marked an earlier stage in their history.
On June 10 Mr. Douglass detected a second rift in the cap backing the range of slopes. And on June 13 I noticed that behind the bright points the snow fell off shaded to this rift. Meanwhile a third rift had been made out by him, running from longitude 170 degrees to longitude 90 degrees,—very nearly, therefore, at right ​angles to the first rift and debouching into it. Bright points continued to be seen at various points to the westward round the cap. They are marked by crosses on the chart. Throughout these days, the cap was wont to appear shaded upon the terminator side, as one might expect of a snow or ice slope. During June, also, the contour of the cap was apparently elliptical. But on June 25 Professor W. H. Pickering noted, for the first time, that it no longer looked so. The melting had resulted in making its asymmetry perceptible.
On July 1 our Martian polar expedition disclosed what used to be the supreme quest of earthly expeditions,—that dream of arctic explorers, an open polar sea. On that day Professor Pickering perceived, in the midst of the cap, in longitude 260° and latitude 80°, a sheet of water about 250 miles long by 150 broad. It was in fact the spreading of the first rift about midway across the cap, and lay not far from the geographical pole of the planet, though not, it is to be noticed, near the pole of cold for it lay on the further side of the geographical pole from it. There is a touch of the irony of fate in this detection of an open polar sea on Mars before explorers have succeeded in doing so on the Earth.
In addition to these rifts and other irregularities of melting, small detached bits of the ​cap showed from time to time, one being seen by Professor Pickering on July 9 in longitude 284°, and another by him on July 23 in about longitude 160°.
Meanwhile the cap had been steadily decreasing in size, its progressive diminutions being shown on the map in the successive contour lines. The polar sea faithfully followed it in its shrinkage, even the bays keeping their longitudes unchanged. But, whereas early in June the bay at longitude 270° had been blue, it now appeared brown; of that mud-color land does from which the water has recently been drained off.
After various vicissitudes, too numerous to mention in detail, on August 6 a separate patch of snow showed very conspicuous, to the left of the main body. The smaller detachment lay in longitude 290°, and in latitude 75-78°. Now, on turning to the record of the star-points that had appeared two months before, it will be seen that this was their position. Here, then, was proof of the identity of the star-points seen in June with the islands recorded by Mitchell and Green. The detached patch was in fact the range of slopes left in isolated insularity after all about it had melted away. From this we have an interesting bit of corroborative testimony that it stood on higher ground.
On August 11 the detached patch was yet ​farther separated from the main body of the cap, the smaller patch being many degrees distant to the north of either the geographical pole or the pole of cold, with water and even dry land to the south of it. It will be remembered, for the points of the compass, that this is the southern hemisphere of which we are speaking, and that, for climatic purposes, north and south here stand interchanged. On August 13 the detached patch is recorded for the last time, or, in other words, about this time it melted away. The larger one remained, contracting in size, however, as time went on. So it continued through August, September, and well into October.
On October 12, at 10h. 40m., I made the following entry about it: "Polar cap has been very faint for some time; barely visible." At 13h. 26m., or, in other words, at about half past one that night, Mr. Douglass measured its position and estimated its size, as was his wont every few days. He found it to be six degrees distant from the planet's pole, in longitude 54° The patch was very small, covering about one hundred and fifty miles square. On looking at the planet on October 13, at 8h. 15m., to his surprise he found the cap gone. Not a trace of it could be seen; nor could either he or I detect it during the rest of that night although such was the longitude of the central ​meridian throughout it as to bring the cap on the nearer side of the pole, and therefore show it to best advantage. What had certainly been there on the 12th was not there on the 13th. The ice-cap had disappeared.
No such occurrence has ever been chronicled before. It is the first time since man began to observe the planet that the ice-cap has completely disappeared. Hitherto it has been seen to diminish to a minimum of from 7° to 4°, and then begin to increase again. This last autumn, for the first time, it vanished entirely. The date of this occurrence was, in Martian chronology, about July 20. Evidently, for some reason unknown to us, it was a phenomenally hot season in the southern hemisphere of the planet.
Practically it never reappeared again during the season. That it did return occasionally, as a very small speck, was from time to time suspected, and doubtless did take place. Certainly it left for some time behind it a glimmer where it had been, due presumably to the moisture from its melting, still tarrying on the ground or lingering in the air. Otherwise, to all intents and purposes, where the polar ice-cap and polar sea had been was now one ochre stretch of desert.
Having thus followed to its vanishing point the polar cap, we will now return to it in the ​heyday of its youth, in June, 1894, when it was girdled by its broad blue belt. We have seen that we have reason to believe this to be in all probability a polar sea, a real body of water. There is, therefore, water on the surface of Mars. We also mark that this body of water is ephemeral. It exists while the ice-cap is melting, and then it somehow vanishes. What becomes of it, and whether there be other bodies of water on the planet, either permanent or temporary, we will now go on to inquire.
II. AREOGRAPHY
As in the course of our inquiry we shall have occasion to refer familiarly to different Martian features, we had best begin it with some slight exposition of Martian geography, or of areography, as it may by analogy be called. To get this we will, by the help of Plates III. to XIV., suppose ourselves to be viewing the planet from some standpoint in space, and watching the surface features pass in procession under our gaze as the rotation of the planet brings them successively round into view. In the matter of names the map of the planet toward the end of the book, with its accompanying index, will give identification. We may thus make a far journey without leaving home, and from the depths of our arm-chairs travel in spirit to lands we have no hope of ever reaching in body. ​We may add to this the natural delight of the explorer, for we shall be gazing upon details of Martian geography never till last summer seen by man.
Areography is a true geography, as real as our own. Quite unlike the markings upon Jupiter or Saturn, where all we see is cloud, in the markings on Mars we gaze upon the actual surface features of the Martian globe. That we do so we know from the permanency of the spots and patches thus revealed to us. They change in appearance, indeed, according to times and seasons, but they alter as true surface features would, not like cloud-belts that gather to-day and vanish forever to-morrow. That the markings are essentially permanent has been known ever since Cassini in 1666 definitely discovered, what Huyghens had thought to detect in 1659, the rotation of the planet, by means of their periodic presentations.
The twelve views we shall here scan are of the nature of a map, made in November, 1894. They represent the ensemble of the drawings from this observatory, for about that date. The details from these drawings were plotted upon a globe, which was then tilted toward the observer at the angle at which the Martian south pole itself was tilted toward the Earth during November, and photographed at intervals of 30°. The negatives were then made to ​conform as near as might be to the actual look of the planet. To photograph minute planetary markings directly is, for reasons too long to state here, impossible. The views give between them the whole surface of the planet shown us at what corresponds to our first of August. Thus, neither the polar cap nor the polar sea appear in the pictures, for both had then disappeared. Nor do the southern parts of the so called straits show, for a similar reason. But from a knowledge of the features here presented the reader will find interpolation of any others referred to easy.
Previous to the present chart, the most detailed map of the planet was Schiaparelli's, made in 1888. On comparison with his, it will be seen that the present one substantially confirms all his detail, and adds to it about as much more. I have adopted his nomenclature, and in the naming of the newly found features have selected names conformable to his scheme, which commends itself both on practical and on poetic grounds.
We will begin our journey at the origin of Martian longitudes and travel west, taking the points of the compass as they would appear were we standing upon the planet. As all astronomical pictures are, for optical reasons, upside down, south lies at the top of the pictures, west to the right, north at the bottom, ​and east to the left. Mars rotates as the Earth does, from west to east, so that day as it advances across the face of the planet follows the order here shown in Plates III. to XIV., the order in which we shall observe them. Places on the right of the picture are in the morning of their Martian day; places on the left, in its afternoon. To facilitate reference by longitude and latitude, the globe has been belted by meridians and parallels each 10° apart, and the meridians have been numbered along the equator. This premised, we will suppose ourselves to be standing on the equator at its intersection with the 0° meridian. (Plate III.)
It will be noticed that the 0° meridian passes through the tip of a triangular peninsula that juts out into a dark area curiously forked, half way across the picture and about two thirds way down it. The tip of this triangle is the received Greenwich of Martian longitudes, and has been named by Schiaparelli the Fastigium Aryn, such having been the name of a mythologic spot supposed by the ancients to lie midway between the east and west, the north and south, the zenith and nadir. It thus makes a fitting name for the starting-point of Martian longitudes and the beginning of Lime. The dark forked area, called by Proctor “Dawes’ Forked Bay,” is now commonly called the Sabaeus Sinus. At the times these marine ​names were bestowed, it was supposed that the dark markings really represented water. We have now reason to believe that such is not the case. But it is better to keep the old names, although I shall employ them in a Pickwickian sense, much as we still speak of the Seas of the Moon, the Mare Tranquillitatis, or the Mare Serenitatis, of which only the adjectives have in them anything of truth.
To the west of the Sabaeus Sinus lies another dark, wedge-shaped area, longer than it but single instead of double. This is the Margaritifer Sinus, or the Pearl-bearing Gulf, so named before it was known that that name possessed any significance. But a prescience must have presided over its christening. For we now know that there is indeed a pearl at the bottom of it,—the round spot shown in the picture.
Plate III
MARS Longitude 0° on the Meridian
Plate IV
MARS Longitude 30° on the Meridian
Nearly in the center of the disk are seen two of those strange comet-tail peninsulas that constitute so peculiar a feature of Martian geography. The lower is Deucalionis Regio; the upper, Pyrrhae Regio. Across then show two streaks, which, followed up, will be found to join other streaks traversing the dark regions. These introduce us to Mr. Douglass' discovery of the whole system of canals in the dark regions, paralleling the system in the bright areas,—being similarly straight and similarly intersecting one another, with spots at the intersections, making what Mr. Douglass aptly terms a checkerboard effect, as we shall see more strikingly when we get round to the other side of the planet.
In Plate IV. the markings have, under the rotation of the planet, all swung 30° to the east, thus bringing others into view from the west. The great swath obliquely belting the disk is the canal called the Jamuna. It was, at the time this picture represents it, apparently in process of doubling. Crossing it obliquely is the Hydraotes. More conspicuous are two dark ​swaths that make with the Jamuna a nearly right-angled triangle. The lower one parallel to the edge of the disk is the Dardanus; the other, ending at the south with the Jamuna in the Aurorae Sinus, is the Ganges, one of the largest and most important Martian canals. At the date of the drawing, it was distinctly double. The doubling is very curiously prolonged by a narrow rectangle lying in the midst of the dark regions of the south. Some idea of the size of these strangely geometrical markings may be got by remembering that a degree on Mars represents thirty-seven miles. Skirting the edge of the dark regions westward, we come to a short canal, the Hebe, leading to Fons Juventae, one of the tiniest markings perceptible on the disk, from which, however, some six canals have been found to radiate. Schiaparelli detected it in 1877, searched for it in vain in 1879, but at subsequent oppositions found it again, happier than Ponce de Leon in his futile quest after an earthly Fountain of Youth. Proceeding still farther west, we reach the entrance of the Agathodaemon, at the point where the edge of the dark regions abruptly trends southward. This canal brings us to the Solis Lacus region, one of the most interesting parts of the planet.
Plate V
MARS Longitude 60° on the Meridian
But a second feature of this region is no less note worthy. Surrounding the Solis Lacus is a perfect cordon of canals and spots, the chief of which are the Tithonius Lacus, nearly due north, and the Lacus Phoenicis, or Phoenix Lake, north- west. The spots are strung like beads upon the loop of the Agathodaemon and the Daemon. From the northeast end of this string of spots runs the Chrysorrhoas to the Lacus Lunae on the fifty-eighth meridian. Below it is the Labeatis Lacus, from which the Gigas starts west, to be lost in the limb-light.
In the next plate (Plate VI.), the Solis Lacus is central, the Lacus Phoenicis somewhat to the right of the centre; and southwest of the Lacus Phoenicis is the Beak of the Sirens, the eastern ​end of the sea of the same name, which has just come round the corner of the disk. The canal connecting it with the Phoenix Lake is the Araxes; and at various angles to this, like spokes of a wheel about the Phoenix Lake for hub, are many more canals, the one lying most nearly due south being the Phasis. Connecting with this network of canals is a similar network of streaks in the dark regions, making a set of triangles, from which still other canals run up almost straight toward the south pole.
Between the dark regions and the Beak of the Sirens is the peninsula Phaetontis, crossing which some way up is a short canal known as Herculis Columnae. Due north of the Lacus Phoenicis is the spot Ceraunius, joined to the Lacus Phoenicis by the Iris, and to the Tithonius Lacus by the Fortunae. it is also crossed by the Gigas, the very long canal in the right-hand lower part of the disk, of which we saw the beginning in the last plate, and shall not see the end till we reach the next one.
Plate VI
MARS Longitude 90° on the Meridian
Plate VII
MARS Longitude 120° on the Meridian
In Plate VIII. the Sinus Titanum has come round into view. Owing to its conspicuousness at certain seasons, it is one of time most important features on the planet to us, and seems to be to the planet itself, as some seven canals radiate from it. These are the Gigas, previously described, and to the right, in the order here enumerated, the Steropes, the Brontes, the Titan,—the one straight down the disk,—the Arges, the Gyes, and the Tartarus; the last traveling to the Trivium Charontis invisible in this plate. Of the separate existence of the Arges and the Gyes I am not quite certain. These great canals show like the sticks of a fan, with the Sinus itself for pivot.
​The Sea of the Sirens is now nearly central. To the west, dividing it from the Mare Cimmerium, which is just coming into view, is the peninsula Atlantis, curiously uniting the continents to the islands to the south. Belting the disk from east to west is the Eumenides-Orcus, strung with spots.
Parallel to the Eumenides-Orcus, and skirting the north shore of the Sea of the Sirens, is the Erynnis. Half way between this and the Eumenides is another parallel canal, the Parcae. Curving round the bottom of the disk is a chain of canals, the Pyriphlegethon, Acheron, and Erebus, the last of which runs to the Trivium Charontis. At the junctions of these various canals may be seen any number of spots.
Plate VIII
MARS Longitude 150° on the Meridian
Plate IX
MARS Longitude 180° on the Meridian
In Plate X. the Mare Cimmerium is central. So, also, well down the disk, is the Trivium Charontis. This is a very important junction, no less than nine canals already being known to connect with it, which, taken in the order, east, north, west, and south, are the Orcus, the Erebus, the twin Tiades, the Styx, the Cambyses, the Cerberus, the Laestrygon, the Tartarus, and so back to the Orcus again. In this picture the Laestrygon traverses nearly the centre of the disk. To the right of the Trivium Charontis is the region called Elysium, one of the brightest parts of the planet. It was here that Mr. Douglass made his ​interesting observation, last September, of a remarkable change of tint from bright to sombre, and back to bright again, in the course of forty-eight hours; suggesting perhaps the formation and dissipation of cloud, perhaps the deposition and subsequent melting of hoar-frost over an area of some hundreds of square miles.
Returning to the Mare Cimmerium, we observe in the middle of it a long, lighter streak, Cimmeria, scarcely perceptible at this last opposition, and, barring its western end, the second in the procession of similarly inclined peninsulas that follow one another westward upon this side of the planet., the peninsula Hesperia, a place with a history, as will appear later on.
In the next picture (Plate. XI) Hesperia is central, dividing the Mare Cimmerium on the left from the Mare Tyrrhenum on the right. The lower end of the latter is called the Syrtis Minor, in contradistinction to the Syrtis Major, which is just appearing round the western limb. From the bay, so to speak, upon the left of Hesperia, two canals proceed down the disk in divergent directions,—the most easterly one the Aethiops, the other the Achelous. From the Syrtis Minor proceed two others, more or less similarly inclined,—the Lethes and the Amenthes.
Plate X
MARS Longitude 210° on the Meridian
Plate XI
MARS Longitude 240° on the Meridian
Plate XII
MARS Longitude 270° on the Meridian
Parallel in a general way to the Nepenthes, and about as much below it as it is below the coast-line, lies the Astapus, which joins the bottom of the Syrtis Major to the ends of the Amenthes, Lethes, and Achelous.
In Plate XIII. two features are striking, both not far from central on time disk,—the lower, the Syrtis Major; the tipper, Hellas. The Syrtis Major was the first marking to be certainly recognized on Mars. It appears in a drawing by Huyghens made on October 13, 1659, the first drawing of Mars worthy the name ever made by man, and reproduced on ​page 20 from Flammarion's "La Planète Mars." It is thus our oldest Martian acquaintance. Hellas is the surprisingly round, bright area nearly on the meridian, and nearly half way from the equator to the south pole. It is very strangely quartered by two canals, the Alpheus, dividing it almost due north and south; and the Peneus, cutting it almost due east and west. Between it and the Syrtis Major is the Mare Hadriaticum, a blue-green area intersected by bright causeways and seamed by dark canals.
Plate XIII
MARS Longitude 330° on the Meridian
Plate XIV
MARS Longitude 330° on the Meridian
Between the Euphrates and the Sabacus Sinus are several canals and spots that show the minute manner in which the Martian surface is cut up. But so much only hints at the state of things existent there. From the markings, not well enough seen to admit of mapping, it is apparent that the system of lines and spots is very complete all over the planet.
This brings us back again to the Sabaeus Sinus and the Fastigium Aryn, from which we set out, after a journey which it takes the rotation of the planet twenty-four hours thirty-seven minutes and about twenty-three seconds to accomplish.
III. SEAS.
While it existed in any size, the polar sea was bordered on the north, all the way round ​and during all the time it was visible, by blue-green areas. These blue-green areas were strewn with several more or less bright regions, while below them came the great reddish-ochre stretches of the disk. Now, the blue-green areas have generally been considered to be seas, just as the reddish-ochre regions have been held to be land. That the latter are land there is very little doubt; not only land, but nothing but land,—land very pure and simple; that is, deserts. For they behave just as deserts should behave, that is, by not behaving at all; remaining, except for certain phenomena to be specified later, unchangeable.
With the so-called seas, however, the case is different. Several important facts conspire to throw grave doubt, and worse, upon their aquatic character. To begin with, they are of every grade of tint,—a very curious feature for seas to exhibit, unless they were everywhere but a few feet deep; which again is a most singular characteristic for seas that cover hundreds of thousands of square miles in extent,—seas, that is, as big as the Bay of Bengal. The Martian surface would have to be amazingly flat for this to be possible. We know it to be relatively flat, but to be as flat as all this would seem to pass the bounds of credible simplicity. Here also Professor W. H. Pickering’s polariscope investigations come in with ​effect, for he found the light from the supposed seas to show no trace of polarization. Hence these were probably not water.
In parenthesis we may here take notice of the absence of a certain phenomenon whose presence, apparently, should follow upon water surfaces such as the so-called seas would offer us. Although its absence is not perhaps definitive as to their marine character, it is certainly curious, and worth noting. If a planet were covered by a sheet of water, that water surface would, mirror-like, reflect the sun in one more or less definite spot. Looked at from a distance, this spot would, were it bright enough, be seen as a high light on the dark background of the ocean about it. It would seem to be a fixed star at a certain point on the disk, the surface features rotating under it. The necessary position is easily calculated, and this shows that parts of the so-called seas, especially at oppositions like the last one, pass under the point. There remains merely the question of sufficient brilliancy in the spot for visibility; but as in the case of Mars its brilliancy should be equal to that of a star of the first magnitude, it would seem brilliant enough to be seen. No such starlike effect in such position has ever been noticed coming from the blue-green regions. From this bit of negative evidence, to be taken for what it is worth, we return again to what there is of a positive sort.
​ Not only do different parts of the so-called seas contrast in tint with one another, but the same part of the same sea varies in tint at different times. Schiaparelli noticed that, at successive oppositions, the same sea showed different degrees of darkness, and he suggested that the change in tone was dependent in some way upon the Martian seasons.
Observations at Flagstaff have demonstrated this to be the case, for it has been possible to see the tints occur consecutively. In consequence, we know not only that changes take place on the surface of Mars other than in the polar cap, and very conspicuous ones too, but that these are due to the changing seasons of the planet’s year. We will now see what they look like.
Plate XV
Fig. I. Syrtis Major at June presentation Long. 290°. Lat. centre of disk 24° South
Fig. II. Syrtis Major at October presentation Long. 305°. Lat. centre of disk 20° South
SYRTIS MAJOR Showing seasonal change during 1894
To have drawings simply swear at one another across a page is, in the interests of deduction, objectionable. For their testimony to be worth having, they must agree to differ. If, therefore, Mars is to be many, his draughtsman must be one. So much, at least, is fulfilled by the drawings in which the changes now to be described are recorded; for they were all made by me, at the same instrument, under the same general atmospheric conditions. As the same personality enters all of them, it stands, as between them, eliminated from all, to increased certainty of deduction. Since, furthermore, the drawings were all made in the months preceding and following one opposition, change due to secular variation is reduced to a minimum. As a matter of fact, the changes are such as to betray their own seasonal character. They constitute a kinematical as opposed to a statical study of the planet’s surface.
The changes are much more evident than might be supposed. Indeed, they are quite unmistakable. As for their importance, it need ​only be said that deduction from them furnishes, in the first place, inference that Mars is a living world, subject to an annual cycle of surface growth, activity, and decay; and shows, in the second place, that this Martian yearly round of life must differ in certain interesting particulars from that which forms our terrestrial experience. The phenomena evidently make part of a definite chain of changes of annual development. So consecutive, and, in their broad characteristics, apparently so regular, are these changes, that I have been able to find corroboration of what appears to be their general scheme in drawings made at a previous opposition. In consequence, I believe it will be possible in future to foretell, with something approaching the certainty of our esteemed weather bureau’s prognostications, not indeed what the weather will be on Mars,—for, as we have seen, it is more than doubtful whether Mars has what we call weather to prognosticate,—but the aspect of any part of the planet at any given time.
The changes in appearance now to be chronicled refer, not to the melting of the polar snows, except as such melting forms the necessary preliminary to what follows, but to the subsequent changes in look of the surface itself. To their exposition, however, the polar phenomena become inseparable adjuncts, since they are inevitable ancillaries to the result.
​ With the familiar melting of the snow-cap begins the yearly round of the planet’s life. With the melting of our own arctic or antarctic cap might similarly be said to begin the earth’s annual activity. But here at the very outset there appears to be one important difference between the two planets. On the earth the relation of the melting of the polar snows to the awakening of surface activity is a case of post hoc simply; on Mars it seems to be a case of propter hoc as well. For, unlike the earth, which has water to spare, and to which, therefore, the unlocking of its polar snows is a matter of no direct economic value, Mars is apparently in straits for the article, and has to draw on its polar reservoir for its annual supply. Upon the melting of its polar cap, and the transference of the water thus annually set free to go its rounds, seem to depend all the seasonal phenomena on the surface of the planet.
The observations upon which this deduction is based extend over a period of nearly six months, from the last day of May to the 22d of November. They cover the regions from the south pole to about latitude forty north. That changes analogous to those recorded, differing, however, in details, occur six Martian months later in the planet’s northern hemisphere, is proved by what Schiaparelli has seen; for though the general system is, curiously, one for ​the whole planet, the particular character of different parts of the surface alters the action there to some extent.
For an appreciation of the meaning of the changes, it is to be borne in mind throughout that the vernal equinox of Mars’ southern hemisphere occurred on April 7, 1894; the summer solstice of the same hemisphere on August 31; and its autumnal equinox on February 7, 1895.
On the 31st of May, therefore, it was toward the end of April on Mars. The south polar cap was, as we have seen, very large, and the polar sea in proportion. That the polar sea was the darkest and the bluest marking on the disk implies that it was, at least, the deepest body of water on the planet, whether the so-called seas were seas or not. But from the fact that it was quite wide,—350 miles,—and that it all eventually vanished, it can hardly have been very deep. Its relative appearance, therefore, casts a first doubt upon the fact that the others were seas at all. This polar sea plays deus ex machina to all that follows.
So soon as the melting of the snow was well under way, long straits, of deeper tint than their surroundings, made their appearance in the midst of the dark areas. I did not see them come, but as I afterward saw them go it is evident that they must have come. They were ​already there on the last day of May. The most conspicuous of them lay between Noachis and Hellas, in the Mare Australe. It began in the great polar bay, and thence traversed the Mare Erythræum to the hourglass Sea (Syrtis Major). The next most conspicuous one started in the other bay, and came down between Hellas and Ausonia. Although these straits were distinguishably darker than the seas through which they passed, the seas themselves were then at their darkest. The fact that these straits traversed the seas suffices to raise a second doubt as to the genuineness of seas; the first suspicion as to their character—coming from their being a little off color; not so blue, that is, as what we practically know to be water, the polar sea—finding thus corroboration. It will appear later that in all probability the straits themselves were impostors, and that neither seas nor straits were water.
The appearance of things at this initial stage of the Martian Nile-like inundation last June was most destructive to modern maps of Mars, for all the markings between the south polar cap and the continental coast-line seemed with one consent to have, as nearly as might be, obliterated themselves.
It was impossible to fix any definite boundaries to the south temperate chain of islands, so indistinguishably did the light areas and the ​dark ones merge into each other. What was still more striking, the curious peninsulas which connect the continent with the chain of islands to the south of it, and form so singular a feature of the planet’s geography, were invisible. One continuous belt of blue-green stretched from the Syrtis Major to the Columns of Hercules.
For some time the dark areas continued largely unchanged in appearance; that is, during the earlier and most extensive melting of the snow-cap. After this their history became one long chronicle of fading out. Their lighter parts grew lighter, and their darker ones less dark. For, to start with, they were made up of many tints; various shades of blue-green interspersed with glints of orange-yellow. The gulfs and bays bordering the continental coast were the darkest of these markings; the long straits between the polar sea and the Syrtis Major were the next deepest in tone.
Plate XVI
Fig. I. Hesperia at June presentation Long. 242°, Lat. centre of disk 24° South
Fig. II. Hesperia at August presentation Long. 247°, Lat. centre of disk 17° South
Fig. III. Hesperia at October presentation Long. 237°, Lat. centre of disk 21° South
HESPERIA Showing seasonal change during 1894
As yet nothing could be seen of Atlantis. It was not until the 30th of October that I caught sight of it. About the same time, the straits between the islands, Xanthus, Scamander, Psychrus, and Simois, came out saliently dark, a darkness due to contrast. The line of south temperate islands, with their separate identity, was then for the first time apparent.
Meanwhile the history of Hesperia continued to be instructive. From having been absent in June and conspicuous in August, it returned in October to a mid-position of visibility. Vacillating as these fluctuations in appearance may seem at first sight, they were really quite consistent; for they were probably due to progressive change in the one direction, a change that was manifested first in Hesperia itself, and then in the regions round about it. From June to August, Hesperia changed from a previous blue-green, indistinguishable from its surroundings, to yellow, the parts adjacent remaining much as before. As a consequence, the ​peninsula stood out in marked contrast to the still deep blue-green regions by its side. Later the surroundings themselves faded, and their bleaching had the effect of once more partially obliterating Hesperia.
While Hesperia was thus getting itself noticed, the rest of the south temperate zone, as we may call it for identification’s sake, was unobtrusively pursuing the same course. Whereas in June all that part of the disk comprising the two Thyle, Argyre II., and like latitudes was chiefly blue-green, by October it had become chiefly yellow. Still further south, what had been first white, then blue, then brown, turned ochre.
Plate XVII
Fig. I. Sea of the Sirens at June presentation Long. 141°. Lat. centre of disk 24° South
Fig. II. Sea of the Sirens at November presentation Long. 156°. Lat. centre of disk 22° South
SEA OF THE SIRENS AND ATLANTIS AT THE OPPOSITION OF 1894 Showing seasonal change
Another curious causeway of the same sort made its appearance in November, connecting the promontory known as Hammonis Cornu with Hellas. Both of these necks of orange-ochre were of more or less uniform breadth throughout.
The long, dark streaks that in June had joined the Syrtis Major to the polar sea had by October nearly disappeared; in their southern parts they had vanished completely, and they had very much faded in their northern ones. The same process of fading uncovered certain curious rhomboidal bright areas in the midst of the Syrtis Major.
It will be seen that the extent of these changes was enormous. Their size, indeed, was only second in importance to their character; for it will also have been noticed that the changes were all in one direction. A wholesale transformation of the blue-green regions into orange-ochre ones was in progress upon that other world.
What can explain so general and so consecutive a change in hue? Water suggests itself; for a vast transference of water from the pole to the equator might account for it. But there are facts connected with the change which seem ​irreconcilable with the idea of water. In the first place, Professor W. H. Pickering found that the light from the great blue-green areas showed no trace of polarization. This tended to strengthen a theory put forth by him some years ago, that the greater part of the blue-green areas are not water, but something which at such a distance would also look blue-green, namely, vegetation. Observations at Flagstaff not only confirm this, but limit the water areas still further; in fact, practically do away with them entirely. Not only do the above polariscopic tests tend to this conclusion, but so does the following observation of mine in October.
Toward the end of October, a strange, and, for observational purposes, a distressing phenomenon took place. What remained of the more southern dark regions showed a desire to vanish, so completely did those regions proceed to fade in tint throughout. This was first noticeable in the Cimmerian Sea, then in the Sea of the Sirens, and in November in the Mare Erythraeum about the Lake of the Sun. The fading steadily progressed until it had advanced so far that in poor seeing the markings were almost imperceptible, and the planet presented a nearly uniform ochre disk.
This was not a case of obscuration; for in the first place it was general, and in the second place the coast-lines were not obliterated. The ​change, therefore, was not due to clouds or mist.
What was suggestive about the occurrence was that it was unaccompanied by a corresponding increase of blue-green elsewhere. It was not simply that portions of the planet's surface changed tint, but that, taking the disk in its entirety, the whole amount of the blue-green upon it had diminished, and that of the orange-yellow had proportionally increased. Mars looked more Martian than he had in June. The canals, indeed, began at the same time to darken; but, highly important as this was for other reasons, the whole area of their fine lines and associated patches did not begin to make up for what the dark regions lost.
If the blue-green color was due to water, where had all the water gone? Nowhere on the visible parts of the planet; that is certain. Nor could it very well have gone to those north circumpolar regions hid from view by the tilt of the disk; for there was no sign of a growing north polar cap, and, furthermore, Schiaparelli's observations upon that cap show that there should not have been. At the opposition of 1881, he found that it developed late, apparently one month or so after the vernal equinox of its hemisphere, whereas at the time the above change occurred it was not long after that hemisphere's winter solstice.
​But if, instead of being due to water, the blue-green tint had been due to leaves and grasses, just such a fading out as was observed should have taken place as autumn came on, and that without proportionate increase of green elsewhere; for the great continental areas, being desert, are incapable of supporting vegetation, and therefore of turning green.
Thus we see that several independent phenomena all agree to show that the blue-green regions of Mars are not water, but, generally at least, areas of vegetation; from which it follows that Mars is very badly off for water, and that the planet is dependent on the melting of its polar snows for practically its whole supply.
Such scarcity of water on Mars is just what theory would lead us to expect. Mars is a smaller planet than the Earth, and therefore is relatively more advanced in his evolutionary career. He is older in age, if not in years; for whether his birth as a separate world antedated ours or not, his smaller size, by causing him to cool more quickly, would necessarily age him faster. But as a planet grows old, its oceans, in all probability, dry up, the water retreating through cracks and caverns into its interior. Water thus disappears from its surface, to say nothing of what is being continually imprisoned by chemical combination. Signs of having thus parted with its oceans we see in the case of the ​Moon, whose so-called seas were probably seas in their day, but have now become old sea-bottoms. On Mars the same process is going on, but would seem not yet to have progressed so far, the seas there being midway in their career from real seas to arid depressed deserts; no longer water surfaces, they are still the lowest portions of the planet, and therefore stand to receive what scant water may yet travel over the surface. They thus become fertilized, while higher regions escape the freshet, and remain permanently barren. That they were once seas we have something more than general inference to warrant us in believing.
There is a certain peculiarity about the surface markings of Mars, which is pretty sure to strike any thoughtful observer who examines the planet's disk, with a two- or a three-inch object-glass,—their singular sameness night after night. With quite disheartening regularity, each evening presents him with the same appearance he noted the evening before,—a dark band obliquely belting the disk, strangely keeping its place in spite of the nightly procession of the meridians ten degrees to the east, in consequence of our faster rotation gaining on the slower rotation of Mars. By attention, he will notice, however, that the belt creeps slowly upwards towards the pole. Then suddenly some night he finds that it has slipped ​bodily down, to begin again its Sisyphus-like, inconclusive spiral climb.
Often as this rhumb line must have been noticed, no explanation of it has ever, to my knowledge, been given. Yet so singular an arrangement points to something other than chance. Suspicion of its non-fortuitous character is strengthened when it is scanned through a bigger glass. Increase of aperture discloses details that help explain its significance. With sufficient telescopic power, the continuity of the dark belt is seen to be broken by a series of parallel peninsulas or semi-peninsulas that jut out from the lower edge of the belt, all running with one accord in a southeasterly direction, and dividing the belt into a similar series of parallel dark areas. Such oblong areas are the Mare Tyrrhenum, the Mare Cimmerium, the Mare Sirenum, and those unnamed straits that stretch southeasterly from the Aurorae Sinus, the Margaritifer Sinus, and the Sabaeus Sinus. The islands and peninsulas trending in the same direction are Ausonia, Hesperia, Cimmeria, Atlantis, Pyrrhae Regio, Deucalionis Regio, and the two causeways from the Fastigium Aryn and Hammonis Cornu. It will further be noticed that these areas lie more nearly north and south as they lie nearer the pole, and curve in general to the west as they approach the equator.
​With this fact noted, let us return to the water formed by the melting of the ice-cap, at the time it is produced around the south pole. We may be sure it would not stay there long. No sooner liberated from its winter fetters than it would begin, under the pull of gravity, to run toward the equator. The reason why it would flow away from the pole is that it would find itself in unstable equilibrium where it was. Successive depositions of frost would have piled up a mound of ice which, so long as it remained solid, cohesion would keep in that unnatural position; but the moment it changed to a liquid this would flow out on all sides, seeking its level. Once started, its own withdrawal would cause the centre of gravity to shift away from the pole, and this would pull the particles of the water yet more toward the equator. Each particle would start due north; but its course would not continue in that direction, for at each mile it traveled it would find itself in a lower latitude, where, owing to the rotation of the planet, the surface would be whirling faster toward the east, inasmuch as a point on the equator has to get over much more space in twenty-four hours than one nearer the pole. In short, supposing there were no friction, the surface would be constantly slipping away from under the particle toward the east. As a result, the northerly motion of the particle would be ​continually changing with regard to the surface into a more and more westerly one. If the surface were not frictionless, friction would somewhat reduce the westerly component, but could never wholly destroy it without stopping the particle.
We see, therefore, that any body, whether solid, liquid, or gaseous, must, in traveling away from the pole of a sphere or spheroid, necessarily deviate to the west as it goes on, if the spheroid itself revolve, as Mars does, in the opposite direction.
Now this inevitable trend induced in anything flowing from the pole to the equator is precisely the one that we notice stereotyped so conspicuously in the Martian south temperate markings. Here, then, we have at once a suspiciously suggestive hint that they once held water, and that that water flowed.
Corroborating this deduction is the fact that the northern sides of all the dark areas are very perceptibly darker than the southern ones; for the northern side is the one which a descending current would plough out, since it is the northern coasts that would be constantly opposing the current's northerly inertia. Consequently, although at present the descending stream be quite inadequate to such task, it still finds its way, from preference, to these lowest levels, and makes them greener than the rest.
Though seas no longer, we perceive, then, ​that there is some reason to believe the so-called seas of Mars to have been seas in their day, and to be at the present moment midway in evolution from the seas of Earth to the seas of the Moon.
Now, if a planet were at any stage of its career able to support life, it is probable that a diminishing water supply would be the beginning of the end of that life, for the air would outlast the available water. Those of its inhabitants who had succeeded in surviving would find themselves at last face to face with the relentlessness of a scarcity of water constantly growing greater, till at last they would all die of thirst, either directly or indirectly; for either they themselves would not have water enough to drink, or the plants or animals which constituted their diet would perish for lack of it,—an alternative of small choice to them, unless they were conventionally particular as to their mode of death. Before this lamentable conclusion was reached, however, there would come a time in the course of the planet's history when water was not yet wanting, but simply scarce and requiring to be husbanded; when, for the inhabitants, the one supreme problem of existence would be the water problem,—how to get water enough to sustain life, and how best to utilize every drop of water they could get.
​Mars is, apparently, in this distressing plight at the present moment, the signs being that its water supply is now exceedingly low. If, therefore, the planet possess inhabitants, there is but one course open to them in order to support life. Irrigation, and upon as vast a scale as possible, must be the all-engrossing Martian pursuit. So much is directly deducible from what we have learned at Flagstaff of the physical condition of the planet, quite apart from any question as to possible inhabitants. What the physical phenomena assert is this: if there be inhabitants, then irrigation must be the chief material concern of their lives.
At this point in our inquiry, when direct deduction from the general physical phenomena observable on the planet's surface shows that, were there inhabitants there, a system of irrigation would be an all-essential of their existence, the telescope presents us with perhaps the most startling discovery of modern times,—the so-called canals of Mars. These strange phenomena, together with the inferences to be drawn from them, we will now proceed to envisage.