This whole arrangement presents an indescribable simplicity and symmetry which cannot be the work of chance.

Schiaparelli, in writing of the canals.

In a discussion of the surface markings of Mars a broad sketch of what has already been accomplished in the study of that planet should be given for the general reader. I know of no better way of doing this than by giving a brief abstract of Percival Lowell's epoch-making work entitled "Mars." In this book he presents in a clear and striking manner the results of his own work covering continuous observations of the planet for many years. The preface is dated from Flagstaff, Arizona, 1895. Since that time he has issued three volumes of Memoirs, in quarto, of the Lowell Observatory, and a number of Bulletins in which he presents many additional facts confirming previous observations, besides new observations; and finally, in a late Bulletin, he has presented photographs of Mars made by his assistant, Mr. Lampland, in which a number of canals plainly show, thus setting forever at rest the question of the subjective character of the markings. The student must, however, follow the advice of an English reviewer and by all means read the book.

"To determine," says Mr. Lowell, "whether a planet be the abode of life in the least resembling that with which we are acquainted, two questions about it must be answered in turn: first, are its physical conditions such as render it, in our general sense, habitable; and secondly, are there any signs of its actual habitation? These problems must be attacked in their order, for unless we can answer the first satisfactorily, it were largely futile to seek for evidence of the second." The reason why Mars in certain years becomes so conspicuous is that its orbit is highly eccentric. Every two years?—?the period of its revolution about the Sun?—?brings it nearest to the Sun, and once in fifteen years we find ourselves between it and the Sun at its nearest approach.

Huyghens, in 1659, made a drawing of the dark region on Mars now known as the Syrtis Major, and, through its disappearance and reappearance, he discovered that the planet rotated on its axis, and roughly determined a daily period of twenty-four hours. For the first time it was known that Mars had a day and a night. As some doubts existed as to the correctness of Huyghens's figures, Cassini in 1666 determined anew the rotation period of Mars and found it to be twenty-four hours and forty minutes. From the white polar caps, the study of which we first owe to Maraldi, it was found that the tilt of its axis to the plane of its orbit was very nearly the same as that of the Earth. As this inclination determines the seasons, it was seen that Mars, like the Earth, had its spring, summer, autumn, and winter. A polar flattening was also observed which was slightly in excess of ours.

"To all forms of life of which we have any conception, two things in Nature are vital, air and water." Has it an atmosphere? Without air no change could take place. The Moon without air remains unchanged, except what gravitation accomplishes in pulling down crater walls. "With Mars it is otherwise. Over the surface of that planet changes do occur, changes upon a scale vast enough to be visible from the Earth." The first sign of change occurs in the polar snow cap. It dwindles in size every two years (the time of a single revolution of Mars around the sun). For nearly two hundred years these white polar caps have been observed to wax and wane. As the Martian winter comes on in the northern hemisphere, for example, the polar cap extends its borders to the temperate zone. As summer comes on the snow cap is seen to dwindle gradually away, till by early autumn it presents but a tiny patch a few hundred miles across. Schiaparelli observed changes in tint which he noticed were correlated with the seasons. In 1894 observations were made continuously from early June till late in November. These dates, in Mars, represent the last of April till the last of August. During this time marked changes took place in the bluish-green areas of the planet. A wave of seasonal change swept down from the pole to the equator. The fact of this occurrence constitutes positive proof of the presence of an atmosphere. In another way the evidence was shown. A series of measurements of the polar and equatorial diameters of Mars were made, and these indicated that a visible layer of twilight atmosphere had been measured. This, Lowell explains by a diagram and other data. It is found, according to Lowell's observations, that the atmosphere is much freer from clouds than had been supposed. He shows conclusively that it is much rarer than that of the Earth. Appearances have been seen, however, which are best explained by assuming them to be clouds. During the opposition of 1892, Mr. Douglass, at that time an assistant astronomer at the Lowell Observatory, made a special study of the terminator of Mars.2 A careful study of the terminator for almost every degree of latitude was made, and 733 irregularities were detected. Of this large number, 694 were not only recorded, but measured; and of these, 403 were depressions, and 291 were elevations of the surface. Many of these irregularities were supposed to be clouds, but the arguments to support this attribution are too technical to be presented here. Unmistakable clouds have also been seen moving at a definite rate of speed, as if carried along by the wind.

"To sum up, now, what we know about the atmosphere of Mars: we have proof positive that Mars has an atmosphere; we have reason to believe this atmosphere to be very thin,?—?thinner at least by half than the air upon the summit of the Himalayas,?—?and in constitution, not to differ greatly from our own."

As to the existence of water on the planet, one has only to consider the polar snow caps. In the height of the southern winter, the polar cap of snow measures over two thousand miles across, covering fifty-five degrees of latitude, with one unbroken waste of white. As spring advances the snow begins to melt, disappearing rapidly as summer comes on, and, as it melts, a dark band is seen bordering this edge. As the snow recedes the dark band recedes. This band is, therefore, not a permanent marking on the planet, but obviously water, the result of the melting snow?—?an arctic sea, in fact. This band is irregular, varying in width in different longitudes, as if the water filled up large areas of depression. When finally the snow cap disappears, as it did for the first time on record on the notable occasion of October 13, 1894, the dark band, which had become thinner, disappeared also, leaving only a yellow stretch of surface. An additional proof that this dark band is water, was established by Professor W.H. Pickering, for he discovered that the light reflected from its surface was polarized. The absurdity of the suggestion that these white polar caps are not snow, but congealed carbonic acid gas, is fully shown by Lowell.

The asymmetry of the outline of these snow caps is paralleled by the irregularity of the Earth's polar caps. Glints of brilliant light are seen to flash out from this region, as if produced by sunlight reflected from a sloping surface. On comparing these flashes of light with observations made by Green, in 1877, they were found to be in the same place. Detached fields of snow were also observed below the receding line, an evidence that these regions were at a higher elevation. As before stated, on October 13, 1894, for the first time in the record of polar observations, the southern polar cap disappeared entirely. In this connection it may be of interest to observe that in the United States, in the summer of 1894, the temperature ranged a few degrees above the normal. (For this fact I am indebted to Professor Cleveland Abbe, E.S. M.)

The large, irregular, dark regions on the planet have been supposed to be bodies of water, or seas, and have been described and named as such by astronomers. Lowell shows, however, that there is every reason to doubt this conclusion. "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 large 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."

Lowell also shows that if these regions were seas, or water surfaces of the shallowest kind, sunlight would certainly be reflected from some portion of the surface so as to be visible from the Earth. A calculation of the region from which such a beam of light might be reflected has been carefully made, but no light of this nature has ever been seen. These regions change in color, and Schiaparelli suggested that in some way these changes were dependent on the Martian seasons. Lowell, by continuous observations covering many presentations of the planet, has demonstrated that the changes in color are synchronous with the seasons, and they further show that these regions change in expanse as well. The reader must refer to Lowell's book to understand the very minute way in which the author traces out the behavior of these so-called seas as the Martian summer advances and autumn comes on. His evidence is overwhelming that the regions heretofore regarded as seas are vast tracts of vegetation, doubtless on lower levels, or depressions of the surface, old sea bottoms, in fact, where springs and the natural settlings of stray waters might keep the ground sufficiently moist to support a scanty growth. The regions not marked by the dark shading, from their reddish and yellowish tinge, have always been regarded as land, probably desert land, as they remain fixed from year to year, dead and unchangeable as deserts are.

The question naturally arises, if the water of Mars is piled up at the poles as snow, how does it find its way back on its melting? A discovery made by Schiaparelli in 1877 revealed the existence of various lines marking the surface which he called canali, or channels.3 These lines cover the face of the planet like a net, they are laid out with geodetic precision. "The lines start from points on the coast of the blue-green regions, commonly well-marked bays, and proceed directly to what seem centres in the middle of the continent, since, most surprisingly, they meet there other lines that have come to the same spot with apparently a like determinate intent." In other words these lines?—?fine, straight, dark, as if cut by an engraver, some of them running for hundreds of miles?—?converge at certain centres. They all start, as Schiaparelli first observed, from definite regions and terminate at definite points. Many of them follow the arcs of great circles. These lines may be thirty or more miles in width, apparently preserving the same width throughout, though slightly wider where they leave the dark bands. They run in every direction, a number often converging at a common centre, and, when they do so, a round, dark area appears which Lowell has called an oasis.

In the clear and steady atmosphere of Flagstaff, Mr. Lowell, by the aid of his superb telescope, has added about four times as many canals as are shown on Schiaparelli's chart. These canals form an intricate network of lines, and no one can contemplate these curious features without being impressed by their artificial character. Schiaparelli, who first discovered them in 1877, continued his observations from year to year despite the fact that no one else could see them. In the course of a few years he discovered a still more remarkable condition, and this was that a number of the canals appeared double. This, indeed, seemed an optical illusion, and by no means strengthened his position, as the single canals proclaimed by him were supposed to be figments of the imagination. Undeterred by the general scepticism, Schiaparelli established, at each fresh opposition, his previous announcements. For nine years no one was able to confirm his marvellous discoveries. In the year 1886, however, Perrotin, at Nice, with his assistant, Thollon, managed to make out a number of the canals, single and double, which were carefully drawn. Reference to Perrotin's work will be made further on. The reason why so few have seen them is the lack of observers with acute eyesight and patient devotion to the work, coupled with unsteady air. Size of aperture seems to be of little importance. That Schiaparelli, with an 8-1/3 inch glass, discovered the canals, while with the twenty-six inch glass of the Naval Observatory at Washington they have never been seen, is emphatic evidence of what a clear and steady atmosphere means in the study of delicate planetary markings. The artificiality of the canals is shown by the "supernaturally regular appearance of the system, upon three distinct counts: first, the straightness of the lines; second, their individually uniform width; and, third, their systematic radiation from special points." It was the mathematical shape of the Ohio mounds that first suggested their artificial character. That these lines are artificial and not natural is seen in the fact that at times they are not visible. The lines while temporary in appearance are permanently in place. "Not only do they not change in position during one opposition; they seem not to do so from one opposition to another." "Unchangeable, apparently, in position, the canals are otherwise among the most changeable features of the Martian disk." The order of their appearance synchronizes with the changes of the season, as the snow caps begin to melt the canals begin to appear; in appearance strengthened first at the borders of the polar seas and gradually stretching down towards the equator. In minute detail Lowell presents the successive visibility of the different canals. To account for all these phenomena we have to look at our own Earth for a parallel, and we see it in the great irrigation tracks of the West, and in the vast irrigated regions in India depending upon the melting of the Himalaya snow cap.

The accumulative evidence is overwhelming that here is a dry planet, and an intelligence of some kind that can only survive by utilizing the few remaining sources of water supply. It is to the merit of Professor W.H. Pickering, to whom Professor Lowell gives the credit of having first suggested the idea of irrigation to account for the great width of the canals. What we see, then, is not the canal, which may be a slender stream of water, but a broad band of vegetation irrigated from these narrow channels. These lines penetrate and cross the dark regions in various directions, which again offer additional proof that the so-called seas are not seas but areas of vegetation sparsely scattered, against which the irrigated portions are of sufficient strength and color to show.4

Among the most interesting features of the planet's surface are the round, or oval spots which Lowell calls oases; these invariably occur at the junction of the canals. "In spite of the great number of the spots, not one of them stands isolate. There is not a single instance of a spot that is not connected by a canal to the rest of the dark areas." There appears to be no spot that has not two or more canals running to it, and apparently no canal junction is without its spot. The majority of the spots are 120 to 150 miles in diameter. There are many smaller ones. These spots, like the canals, appear and disappear coincidently with seasonal changes. The canals and the oases follow the same method and order in their growth. "Both are affected by one progressive change that sweeps over the face of the planet from the pole to the equator." The reader cannot dwell too strongly on the fact that the visibility of these various markings appears first in northern latitudes, and gradually darkens toward the equator, precisely the reverse of the unfolding of plant life on the Earth. From Mars our Earth would show its tropical vegetation the year round, while in Mars no tropical vegetable coloration would appear until water from the melting polar snow caps animates its growth.

Lowell shows conclusively that the seas are not seas, nor the canals waterways, nor the spots lakes. Apparently, the spots appear not so much by an increase in size as by a deepening in tint. They start, it would seem, as big as they are to be, but faint in tone; they then proceed to darken throughout. If these spots are areas of vegetation, the explanation of their appearance is at once evident. Even more markedly unnatural is another phenomenon of this phenomenal system, of which almost every one has heard and almost nobody has seen,?—?the double canals. Upon a part of the disk where, up to that time, a single canal has been visible, of a sudden, some night, in place of the single canal, twin canals are perceived, similar in character and inclination, absolutely parallel, reminding one of the twin rails of a railroad track. The regularity of the thing is startling. In details the doubles vary, chiefly, it would seem, in the distance the twin lines lie apart. Lowell says the widest he has seen is the Ganges, in which six degrees separate the two lines,?—?in the narrowest, the Phison, four degrees and a quarter. From 120 to 175 miles of clear country is found between the paralleling lines. "One element of mystery may be eliminated at the outset.... It is perceived of a sudden, by the observer, because of some specially favorable night. But it has been for some time developing. So much is apparent from my observations. Suggestions of duality occurred weeks before the thing stood definitely revealed. Furthermore, the gemination may lie concealed from the observer some time after it is quite complete, owing to lack of favorable atmospheric conditions. For it takes emphatically steady air to see it unmistakably." Each canal has its individual behavior of doubling, and the varying widths, and their evident seasonal relations utterly forbid the conception that their appearance is due to optical illusion. Mr. Lowell feels tolerably sure that the doubling, or gemination of the canals, show that the phenomenon is not only seasonal but vegetal. Why it should take this form is one of the most pregnant problems about the planet. For it is the most artificial-looking phenomenon of an artificial-looking disk. We quote a paragraph from the concluding chapter in his book: "To review, now, the chain of reasoning by which we have been led to regard it probable that upon the surface of Mars we see the effects of local intelligence. We find, in the first place, that the broad physical conditions of the planet are not antagonistic to some form of life; secondly, that there is an apparent dearth of water upon the planet's surface, and, therefore, if beings of sufficient intelligence inhabited it, they would have to resort to irrigation to support life; thirdly, that there turns out to be a network of markings covering the disk, precisely counterparting what a system of irrigation would look like; and, lastly, that there is a set of spots placed where we should expect to find the lands thus artificially fertilized, and behaving as such constructed oases should. All this, of course, may be a set of coincidences, signifying nothing; but the probability points the other way. As to details of explanation, any we may adopt will undoubtedly be found, on closer acquaintance, to vary from the actual Martian state of things; for any Martian life must differ markedly from our own."

In this brief rÉsumÉ of Lowell's work on Mars but scant justice has been done to the many novel and convincing suggestions in explanation of the varied features marking the surface of Mars. There are many enigmas, however, awaiting solution, if we endeavor to explain them by comparison with the methods pursued by man on this Earth, and Mr. Lowell frankly admits the many difficulties in the way of a clear solution. I have already mentioned how puzzling the checker-board appearance of our Western townships would seem to a Martian, but this comparison does not help us to understand the so-called gemination of the canals, though we might have parallel sets of canals, as we have parallel lines of railways. The enormous distance which the water travels in the Martian canals must presuppose an artificial method of urging it on. Precisely how this operation might be accomplished is a question to be solved by the mechanical and hydraulic engineer.

Beside the doubling, or so-called gemination, of the canals, there are other enigmas in the markings. At certain times there has been observed in the equatorial region of Mars a number of white spots, which have greatly puzzled the student of Mars and for which no explanation has yet been offered. That they are not clouds is seen in the fact that they do not move or drift. Furthermore these white spots are fixed features of the region, as they appear in the same places. It might be suggested that they represent snow-capped elevations or mountain peaks, but this is difficult to believe, as an examination of the terminator of Mars reveals no evidences of high elevations. These white spots appear only in mid-summer, which would argue against the idea of their being snow caps, as in mid-summer they would certainly melt and disappear. The time of their appearance coincides with the time of greatest equatorial heat. For a reasonable suggestion it might be offered that these white spots are due to vegetation of some kind. The cotton belt of the South, if one could imagine the cotton bolls a little larger and more crowded together, would make white areas. Masses of white flowers, such as the whiteweed or daisy, may be seen covering hundreds of acres of meadow land in New England. I have noticed from the tops of mountains in New Hampshire, in July, extensive meadow lands resembling fields of snow from the profusion of white daisies. The blossoming of fruit trees in the Santa Clara valley, California, whitens the surface for miles. Since the appearance of these white spots in Mars corresponds with the period of greatest evaporation, it is conceivable that an intelligence in Mars might utilize the same method which has been recently adopted in Connecticut and Porto Rico in the raising of tobacco; namely, to protect the fields with white cotton cloth; or, as in Florida, where extensive orange groves are covered with white cloth to guard against sudden frost. That this supposition has something to commend it may be seen in the accompanying reproduction of a photograph (Plate I), made in Porto Rico, of tobacco plantations when the fields are covered with white cloth supported on suitable frames. This picture appeared in an article by Eugene P. Lyle, Jr., on Porto Rico, in the January number of "World's Work," to the publishers of which we are indebted for the privilege of using it.

These various guesses may all be wrong, as, after all, we are judging Mars from conditions belonging to our own planet. This, however, we are compelled to do, as we have no other standards of comparison.