Biography of Percival Lowell

by A. Lawrence Lowell

CHAPTER X
MARS

Meanwhile the work of the Observatory went on, partly in the direction of the special lines of the several observers, but mainly in that of the founder whose interest was then predominantly planetary, especially in Mars; and from this the site of the dome came to be called Mars Hill. The clear atmosphere yielded the results that had been hoped for, and much was discovered about the planets, their period of rotation, satellites etc., but above all were the Martian observations fruitful. There the object was to watch the seasonal changes beginning with the vernal equinox, or spring of the southern hemisphere, the one inclined toward the earth when the two bodies approach most closely, and follow them through the summer and autumn of our neighbor. For those not familiar with the topography of Mars it may be said that the greater part of its surface is a reddish or orange color interspersed with patches or broken bands of a blue, or greenish blue, in the southern temperate zone. These had been supposed to be seas, and are still known by names recalling that opinion, while the lighter regions derived their nomenclature from the theory that they are continents or islands standing out of the water. This is confusing, but must be borne in mind by anyone who looks at a map of the planet and tries to understand the meaning of the terms. There are several reasons for thinking that the dark areas are not seas: one that they change in depth of color with the seasons; another that light reflected from water is polarized and in this case it is not; also they never show a brilliant specular reflection of the Sun as seas would do.

Now in the winter of the Martian southern hemisphere the region around that pole turned white, that is it became covered by a mantle appearing like snow or ice, and as the summer advanced this became less and less until it disappeared altogether. Meanwhile there formed around it a dark mass that spread downwards, toward the temperate zone and into the bluish areas there, which assumed a darker hue. After the deepening color had reached the edge of the wrongly called sea, very thin straight lines appeared proceeding from it into the lighter reddish regions (mistaken for continents) toward the equator, and increased rapidly in number until there was a great network of them. It very often happened that more than two of these intersected at the same point, and when that occurred there usually came a distinct dot much larger than the thickness of the lines themselves. After this process was fairly under way the dark areas faded down again, and then similar fine lines appeared in them, connecting with those in the light areas, and apparently continuing toward the pole. Moreover, some of the lines in the light region doubled, that is two parallel lines appeared usually running in this case not to the centres, but to the two sides of the dark dots. It is essential to add that the limit of thickness for any line on Mars to be seen by their telescopes was estimated at about fifteen miles, so that these fine lines must have been at least of that width.

Such is in brief the outline of that which the observers saw. What did these things mean? What was the interpretation of the phenomena, their opinion on the causes and operation? This, with the details of the observations, is given by Percival in his book “Mars,” written immediately after this first year of observation, the preface bearing the date November, 1895. But it must not be supposed that he started to observe with any preconceived idea that the planet was inhabited, or with the object of proving that the so-called canals were the work of intelligent beings, for in the preface to the fourth edition he says: “The theory contained in this book was conceived by me toward the end of the first year’s work at Flagstaff. Up to that time, although the habitability of Mars had been often suggested and strenuously opposed, no theory based upon sufficient facts had ever been put forth that bound the facts into a logical consistent whole—the final rivet perhaps was when the idea of the oases occurred to me.” The oases were the dots at the intersection of the fine lines which were called by Schiaparelli “canali” and have retained the name canals.

“Mars” begins with a description of the planet, of its orbit, size and shape, as compared with that of the Earth. By means of its trifling satellites its mass was determined, and from this and its dimensions the force of gravity at its surface, which was found to be a little over one third of that on the Earth; so that living creatures, if any, could be much larger than those of the same type here. From the markings that could be seen on its face the period of rotation, that is the length of the Martian day, was measured with great accuracy, being about forty minutes longer than our own; while the Martian year, known from its revolution round the sun, was about twice the length of ours. All this led to a calculation of the nature of the planet’s seasons, which for its southern hemisphere—the one turned toward the Earth when the two bodies are near together as in 1894—gave a long cold winter and a summer short and hot.

He then takes up the question of atmosphere, which, with water, is absolutely necessary for life, and even for physical changes of any kind “when once what was friable had crumbled to pieces under the alternate roasting and refrigerating, relatively speaking, to which the body’s surface would be exposed as it turned round on its axis into and out of the sun’s rays. Such disintegration once accomplished, the planet would roll thenceforth a mummy world through space,” like our own moon, as he says, where, except for the possible tumbling in of a crater wall, all is now deathly still. But on Mars changes occur on a scale vast enough to be visible from the Earth, and he tells in greater detail the first of those noted in the preceding summary, the formation and melting of the polar snows. Moreover, a change was observed in the diameter of the planet, which could be explained only by the presence of a twilight zone, and this meant an atmosphere refracting the rays of the sun, a phenomenon that he dwells upon at some length. He then turns to the nature of the atmosphere, and from the relative cloudlessness and the lesser force of gravity concludes that its density is probably about one seventh of that on the surface of the Earth. So much for its quantity. For its quality he considers the kinetic theory of gases, and calculates that in spite of its lesser gravity it could retain oxygen, nitrogen, water vapor, and in fact all the elements of our atmosphere.

He next considers the question of water, the other essential to the existence of life, animal or vegetable; the phenomenon of the diminution, and final disappearance, of the polar cap, the behavior of the dark blue band which formed along it; and says: “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.” The great bay of which he speaks is the widest part of the blue band. He discusses the suggestion that the white cap is due, as had been suggested, to congealed carbonic acid gas instead of ice or snow from water, and points out that with the slight density of the Martian atmosphere this would require a degree of cold impossible under the conditions of the planet; an important conclusion later fully confirmed by radiometric measures at Flagstaff and Mt. Wilson.

Assuming therefore that the polar cap is composed of snow or ice, he traced its history, as observed more closely than ever before at Flagstaff, and gives a map of its gradual shrinking and final disappearance, with the corresponding condition of the blue water at its edge. All this from June 3 to October 13 of our year, or from May 1 to July 13 of the Martian seasons, and this was the first time the cap had been seen to vanish wholly. It is interesting to note that in the early morning of June 8 “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 ... nine minutes before they reach 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.”

Seven years before Green, at Madeira, had seen the same thing at the same spot on the planet, drawn the same conclusion, and named the heights the Mitchell Mountains, after the man who had done the like in 1846. Later the blue belt below the cap turned brown; “of that mud-color land does from which the water has recently been drained off,” and at last, “where the polar ice-cap and polar sea had been was now one ochre stretch of desert.”

The geography of Mars he describes, but what he tells cannot be made intelligible without the twelve successive views he gives of the planet as it turns around; while the names of places, given in the main by Schiaparelli, are based in large part on the mistaken impression that the dark regions were seas and bays, the light ones continents and islands. “Previous to the present chart,” Percival writes, “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.” By this, of course, he does not mean to commend naming the dark areas as seas, for his description of the features on the planet’s surface is followed by a statement of the reasons, apparently conclusive, for assuming that the blue-green regions cannot be seas, but must be vegetation; while the reddish ochre ones are simply desert.