Talking later to George Agassiz, Percival attributed the change to the fact that Schiaparelli, who had first observed the fine lines on the planet Mars which he called “canali,” found that his failing eyesight prevented his pursuing his observations farther, and that he had determined to carry them on. That may well have directed his attention to the particular planet; but the interest in astronomy lay far deeper, extending back to the little telescope of boyhood on the roof of his father’s house at Brookline. We have seen that his Commencement Part at graduation was on the nebular hypothesis, and he never lost his early love of such things. In July, 1891, he writes to his brother-in-law, William L. Putnam, about a project for writing on what he calls the philosophy of the cosmos, with illustrations from celestial mechanics. That was just before he went to Ontake and there became involved in the study of trances, “which,” as he says in his next letter to the same, “adds another to my budget of literary eventualities.” In fact, the trances occupied most of his time for the next two years, without banishing the thought of later taking up other things, or effacing the lure of astronomy, for in 1892 he took with him to Japan a six-inch telescope, no small encumbrance unless really desired, and he writes of observing Saturn therewith. Whatever may have been the reason, it seems probable from the rapidity with which he threw himself into astronomy and into its planetary branch, that at least he had something of the kind in his mind before he returned from Japan in the autumn of 1893.
When, returning from Japan late in 1893, Percival Lowell found himself quickly absorbed by astronomical research, he was by no means without immediate equipment for the task. His mathematical capacity, that in college had so impressed Professor Benjamin Peirce, had not been allowed to rust away; for, when at home, he had kept it bright in the Mathematical and Physical (commonly called the M. P.) Club, a group of men interested in the subject, mainly from Harvard University and the Massachusetts Institute of Technology. So fresh was it that we find him using, at the outset, with apparent ease his calculus—both differential and integral—tools that have a habit of losing edge with disuse. Physically, also, he had a qualification of great importance for the special work he was to undertake,—that of perceiving on the disks of the planets, very fine markings close to the limit of visibility; for the late Dr. Hasket Derby, then the leading practitioner in Ophthalmology in Boston, told Professor Julian Coolidge that Percival’s eyesight was the keenest he had ever examined.
One essential remained, to find the best atmosphere for his purpose. In entering our air the rays of light from the stars are deflected, that is bent, and bent again when they strike a denser or less dense stratum. But these strata are continually changing with currents of warmer or colder air rising and falling above the surface of the earth, andhence the rays of light are being shifted a little from side to side as they reach us. Everyone is familiar with the twinkling of the stars, caused in this way; for before entering our atmosphere their light is perfectly steady. Moreover, everyone must have observed that the amount of twinkling varies greatly. At times it is unusually intense, and at others the stars seem wonderfully still. Now, although the planets, being near enough to show a disk visible through a telescope, do not seem to twinkle, the same thing in fact occurs. The light is deflected, and the shaking makes it very difficult to see the smaller markings. Imagine trying to make out the detail on an elaborately decorated plate held up by a man with a palsied hand. The plate would be seen easily, but for the detail one would wish it held in a steadier grasp, and for observing the planets this corresponds to a steadier atmosphere.
Percival’s own account of the reason for his expedition of 1894 to observe the planet Mars, why he selected Flagstaff as the site, what he did there and how the plan developed into the permanent observatory that bears his name were told in what was intended to be an introduction to the first volume of the Annals of the Observatory. Perhaps owing to the author’s illness in the last years of the century this statement was mislaid and was not found until February 22, 1901. It is here printed in full.
In the summer of 1877 occurred an event which was to mark a new departure in astronomy,—the detection by Schiaparelliof the so-called canals of the planet Mars. The detection of these markings has led to the turning over of an entirely new page in cosmogony.
Schiaparelli’s discovery shared the fate of all important astronomical advances,—even Newton’s theory of gravitation was duly combatted in its day,—it, and still more the possibilities with which it was fraught, distanced the comprehension of its time. In consequence, partly from general disbelief, partly from special difficulty, no notable addition was made to Schiaparelli’s own work until 1892, when Professor W. H. Pickering attacked the planet at the Boyden Station of the Harvard Observatory at Arequipa, Peru, and made the next addition to our knowledge of our neighbor world.
Intrinsically important as was Pickering’s work, it was even more important extrinsically. Schiaparelli’s discoveries were due solely to the genius of the man,—his insight, not his eyesight, for at the telescope eyes differ surprisingly little, brains surprisingly much; Pickering’s brought into coöperation a practically new instrument, the air itself. For at the same time with his specific advance came a general one,—the realization of the supreme importance of atmosphere in astronomical research. To the Harvard Observatory is due the first really far-reaching move in this direction, and to Professor W. H. Pickering of that observatory the first fruits in carrying it out.
It was at this stage in our knowledge of the possibilities in planetary work and of the means to that end, in the winter of 1893-94, that the writer determined to make an expedition which included the putting up of an observatory for the primary purpose of studying, under the best procurableconditions, the planet Mars at his then coming opposition,—an opposition at which the planet, though not quite so close to us as in 1892, would be better placed for northern observers. In this expedition he associated with himself Prof. W. H. Pickering and Mr. A. E. Douglass.
The writer had two objects in view:
1st, the determination of the physical condition of the planets of our solar system, primarily Mars;
2d, the determination of the conditions conducive to the best astronomical observations.
How vital was the inter-connection of the two was demonstrated by the results.
Important as atmosphere is to any astronomical investigation, it is all-important to the study of the planets. To get, therefore, within the limits of the United States—limits at the time for several reasons advisable—as steady air as possible, Prof. W. H. Pickering, who had already had experience of Southern California as well as of Arequipa, Peru, proposed Arizona as the most promising spot. Accordingly, Mr. A. E. Douglass left Boston in March, 1894, with a six-inch Clark refractor belonging to the writer, to make a test of the seeing throughout the Territory. From his report, Flagstaff was selected for the observatory site.
Flagstaff, then a town of eight hundred inhabitants, lies on the line of the Atlantic and Pacific Railroad, in the centre of the great plateau of northern Arizona, half way across the Territory from east to west, and two fifths way down from north to south. This plateau, whose mean elevation is between 6000 and 7000 feet, is a great pine oasis a hundred miles or more in diameter, rising some 3000 feet from out the Arizona desert. It culminates in the mass known as theSan Francisco Peaks, ten miles north of Flagstaff, whose highest summit rises 12,872 feet above the level of the sea.[9]
The spot chosen was the eastern edge of the mesa (table-land) to the west of Flagstaff. The site lay open to the east and south, and was shielded on the north by the San Francisco Peaks. The distance from the observatory to Mt. Agassiz, the most conspicuous of the Peaks from the Flagstaff side, was about eight miles and three fifths in an air-line, and the distance to the town about a mile and a quarter. As soon as the site was selected, the town very kindly deeded to the observatory a piece of land and built a road up to it.
The observatory stood 350 feet above the town, and 7250 feet above the level of the sea, in latitude 35° 11′ north and longitude 111° 40′ west.
Prof. W. H. Pickering, to whose skill and ability was chiefly due the successful setting up of the observatory, suggested arrangements with Brashear for the use of an eighteen-inch refractor which Brashear had recently constructed,—the largest glass to be had at the time,—arrangements which were accordingly made. He then devised and superintended the construction of a dome intended to be of a temporary character, which worked admirably. The upper part of it was made in sections in Cambridgeport, Mass., and then shipped West, the lower part being constructed according to his specifications on the spot, under the superintendence of Mr. Douglass.
The telescope was supported on one of the Clark mountings. The bed-plate, clock-work, and a twelve-inch telescope were leased of the Harvard College Observatory, and themounting then altered by Alvan Clark & Sons to carry both the twelve and the eighteen-inch telescopes.
Six weeks from the time ground was broken, on April 23, 1894, regular observations with the eighteen-inch were begun.
The results of the year’s work surpassed anticipation. Details invisible at the average observatory were presented at times with copper-plate distinctness, and, what is as vital, the markings were seen hour after hour, day after day, month after month. First sight; then system; and the one of these factors was as fundamental to the results as the other. Systematic work, first made possible and then properly performed, was the open sesame to that most difficult branch of astronomical observations, the study of our nearest neighbors in the universe.
The chief results obtained were:—
1st, the detection of the physical characteristics of the planet Mars to a degree of completeness sufficient to permit of the forming of a general theory of its condition, revealing beyond reasonable doubt first its general habitability, and second its particular habitation at the present moment by some form of local intelligence;
2d, corroboration and extension by Professor Pickering of his discoveries at Arequipa with regard to the forms of Jupiter’s Satellites;[10]
3d, the discovery and study by Mr. Douglass of the atmospheric causes upon which good seeing depends.
It is of the observations connected with the first of these that the present volume of the Annals alone treats.
As the publication of this volume has been so long delayed,it seems fitting to add here a brief continuation of the history of the observatory to the present time.
The results of the expedition in 1894, in the detection of planetary detail, turned out to be so important an advance upon what had previously been accomplished that the writer decided to form of the temporary expedition a permanent observatory. Accordingly, he had Alvan Clark & Sons make him a twenty-four-inch refractor, which fate decided should be their last large glass; the Yerkes glass, although not yet in operation at the time this goes to press, having been finished at nearly the time his was begun. The glass received from Mantois happened to be singularly flawless and its working the same. It was made twenty-four inches in clear aperture, and of a focal length of thirty-one feet. Alvan G. Clark accompanied the writer to Flagstaff and put the glass in place himself.
The mounting for the telescope was likewise made by the Clarks. Rigidity was the prime essential, in order to secure as stable an image as possible, and this has been admirably carried out, the mounting being the heaviest and most stable for a glass of its size yet made.
In July, 1896, Dr. T. J. J. See joined the observatory, to continue there the line of research for which he was already well known—the study of the double stars. This added to the two initial objects of the observatory a third,—
3d, the study of double-star systems, including a complete catalogue of those in the southern heavens.
During the summer and autumn of 1896 the importance of good atmosphere was further demonstrated in an interesting and somewhat surprising quarter. The air by day was found to be as practicable as that by night. While Marswas being studied by night, the study of Venus and Mercury was taken up during the daytime systematically, and the results proved as significant as had been those on Mars. Instead of the vague diffused patches hitherto commonly recorded, both planets’ surfaces turned out to be diversified by markings of so distinct a character as not only to disclose their rotation periods but to furnish the fundamental facts of the physical conditions of their surfaces. We know now more about Mercury and Venus than we previously knew of Mars.
As the winter in Flagstaff is not so good as the summer, it was thought well to try Mexico during that season of the year. Accordingly, a new dome was made; the telescope was taken down; and dome, mounting, and glasses were carried to Mexico and set up for the winter at Tacubaya, a suburb of the City of Mexico, at an elevation of 7500 feet. There the observatory received every kindness at the hands of the President, the Government, and the National Observatory.
Observations at Mexico fully corroborated those at Flagstaff with regard to both Mars, Mercury and Venus, and enabled Mr. Douglass to make the first full determination of the markings on Jupiter’s third and fourth satellites, thus fixing their rotation periods.
Dr. See in the mean time, who while at Flagstaff had discovered a very large number of new doubles, in Mexico added to his list;...
With the spring the observatory was shipped back again to Flagstaff.
Of the particular results in planetary work obtained, several papers have been published in various astronomicaljournals, while of them subsequent volumes of the Annals will speak in detail. In the meantime two general conclusions to which they have led the writer may, as possessing future interest, fittingly be mentioned here:
1st, that the physical condition of the various members of our solar system appears to be such as evolution from a primal nebula would demand;
2d, that what we call life is an inevitable detail of cosmic evolution, as inherent a property of matter from an eventual standpoint as gravitation itself is from an instant one: as a primal nebula or meteoric swarm, actuated by purely natural laws, evolves a system of bodies, so each body under the same laws, conditioned only by size and position, inevitably evolves upon itself organic forms.
The reasons for the first of these conclusions have sprung directly from the writer’s study of the several members of our own solar system; his reason for the second, upon the further facts,—
1st, that where the physical conditions upon these bodies point to the apparent possibility of life, we find apparent signs of life;
2d, where they do not, we find none.
This implies that, however much its detail may vary, life is essentially the same everywhere, since we can reason apparently correctly as to its presence or absence, a result which is in striking accord with the spectroscopic evidence of a practical identity of material.
Evidently the expedition to observe Mars was undertaken quite suddenly, but if it was to be made at all it must be done quickly. Anyone, however unfamiliar with astronomy, willperceive that two planets revolving about the sun in independent orbits will be nearest together when they are on the same side of the sun and farthest apart when on opposite sides of it, and that the difference is especially great if, as in the case of the earth and Mars, their orbits are not far apart, for when on the same side the separation is only the difference of their distances from the sun, and when on opposite sides it is the sum of those distances. Moreover, Mars being outside of the Earth its whole face is seen in the full light of the sun when both bodies are on the same side of it. Now such a condition, called opposition, was to occur in the summer after Percival’s return from Japan, and therefore there was no time to spare in getting an observatory ready for use.
From the experience of others elsewhere, Percival was convinced that the most favorable atmospheric situations would lie in one of the two desert bands that encircle a great part of the Earth, north and south of the equator, caused by the sucking up of moisture by the trade winds; and that a mountain, with the currents of air running up and down it, did not offer so steady an atmosphere as a high table-land. The height is important because the amount of atmosphere through which the light travels is much less than at sea level. He was aware that the best position of this kind might well be found in some foreign country; but again there was no time to search for it, or indeed to build an observatory far away, if it must be equipped by the early summer. The fairly dry and high plateau of northern Arizona seemed, therefore, to offer the best chance of a favorable site for this immediate and temporary expedition.
With the aid of suggestions by Professor William H.Pickering, who knew what was needed in observing Mars, he sent Mr. Douglass, with the six-inch telescope brought back from Japan, to Arizona to inspect the astronomic steadiness of the atmosphere. The instructions, apparently drawn up by Professor Pickering, were dated February 28th, directing him to observe on two nights each at Tombstone, Tucson and Phoenix; and Percival, keeping in constant touch with Mr. Douglass by letter and telegraph, added among other places Flagstaff. This was shortly followed by instructions about constructing the circular vertical part of the dome for the observatory by local contract as soon as the site was selected, while the spherical part above, which was to be of parallel arches covered with wire netting and canvas, was being made in the East and to be shipped shortly. Meanwhile the pier was being built by Alvan Clark & Sons (who had made most of the large telescopes in this country) and the mounting for both the eighteen-inch and the twelve-inch telescope thereon, balancing each other. Mr. Douglass was to report constantly; and in April Percival wrote him to take a photograph of the site of the observatory “now,” then every day as the work progressed, and have the negatives developed, a blue print made of each as speedily as possible and sent East. All this is stated here to show the speed, and at the same time the careful thought, with which the work was done. Percival and his colleagues came as near as possible to carrying out the principle, “when you have made up your mind that a thing must be done, and done quickly, do it yesterday.”
In fact Percival did not select any of the three places first examined, but on consideration of Mr. Douglass’ reports preferred Flagstaff; and his choice has been abundantly confirmedby the pioneering problems undertaken there, and by the fact that this site was retained for the later permanent Observatory. Everyone, indeed, deserves much credit for the rapid work done at such a distance from principals busy with the preparation of the instruments. It was characteristic of Percival that he got the very best out of those who worked with and under him.
Although the closest point of the opposition did not occur until the autumn, the two planets, travelling in the same direction, were near enough together for fair observation some months earlier; and on May 28th, arriving at Flagstaff, Percival writes to his mother: “Here on the day. Telescope ready for use tonight for its Arizonian virgin view.... After lunch all to the observatory where carpenters were giving their finishing touches.... Today has been cloudy but now shows signs of a beautiful night and so, not to bed, but to post and then to gaze.” The sky was not clear that night, for an unprecedented rain came and lasted several days, falling through the still uncanvased dome on Professor Pickering and Percival, who had been lured by a “fairing” sky into camping out there in the evening to be on time for the early rising Mars. But it was not long before the weather cleared and the strenuous work began. As the observatory was a mile and a half from the hotel in the town, and uphill, it was uncomfortable to arrive there at three o’clock in the morning, the hour when at that season Mars came in sight. So in the summer a cottage was built hard by the dome, where they could sleep and get their meals.
The observations were, of course, continuous throughout the rest of the year; and except for two trips East on business, one for a few weeks at the end of June, another in September,and a few days in Los Angeles, Percival was there all the time. As usual he worked furiously; for beside observing most of the night he spent much of the day writing reports and papers, making drawings for publication in scientific and other periodicals, and investigating collateral questions that bore upon their significance; and while he had computers for mechanical detail, he and his colleagues had to prepare and supervise their work. To his mother he wrote, as a rule, every day; and in some of these letters he gave an account of his time. On September 2nd, he writes of being up the greater part of the night, and naturally perpetually sleepy. “But the number of canals increases encouragingly—in the Lake of the Sun region we have seen nearly all Schiaparelli’s and about as many more.” On October 10th: “Observed the better part of last night, after being welcomed by everybody—and have been as a busy as a beaver today, writing an article, drawing for ditto etc, etc.”; and, two days later, “Chock full of work; scrabbling each day for the post—proof etc. Mr. Douglass is now on the hill observing Mercury. We all dine there at seven. Then I take Mars and at 3A.M.Professor Pickering, Jupiter. So you see none of the planets are neglected.”
In one of these letters he encloses a clipping from a San Francisco newspaper satirizing Professor Holden for saying that the canals of Mars reported at Flagstaff were not confirmed by observations at Mount Hamilton. Denial or doubt that he had really seen what—after many observations confirmed by those of his colleagues—he reported as seen always vexed Percival, and naturally so. Yet they were not uncommon and sometimes attributed to defective vision. He was well aware that while a belief that a thing exists may makeone think he has seen it when he has not, yet it is also true that one person perfectly familiar with an object sought will find it when another, unacquainted with its precise appearance, will miss it altogether. Everyone knows that people in the habit of looking for four-leaved clovers are constantly picking them while others never see them; or that a skilled archaeologist finds arrowheads with much greater facility than a tyro, who will, however, improve rapidly with a little experience; and all this is especially true of things near the very limit of visibility. Gradually more and more observers began to see the finer markings and the canals on Mars, until finally the question of their existence was set at rest when it became possible to photograph them.
But in spite of work and vexation the life was far from dull, for the observatory was as hospitable as its limited quarters would allow. Visitors were attracted by its growing reputation, and on August 25th he writes: “Just as we were plodding up there last evening in the dark we heard a carriage-full of folk coming down. We suspected what they had been after and were not surprised when they challenged us with ‘Are you observatory people?’ It seems they were, as they informed us pathetically, people from the East and had gone up to look through the glass, if they might, before taking the train at 12.30 that night. Of course we could not resist their appeals and so, though we had thought to turn in betimes because of early observations in the morning, entertained these angels—half of them were women—on ‘just like diamonds’ as they said of the stars. The out-of-focus views pleased them the most—as turns out to be the case generally. This morning when I went to take Pickering’s place I found another angel in the shape of a Coloradoman, out here for his health, in the dome with Pickering—a nice fellow he turned out. It was then 4 h. 8 m. o’clock in the morning,—a matutinal hour for a man to trudge a mile and a half on no breakfast up to an observatory on a hill—That shows real astronomical interest. He was rewarded gastronomically with some coffee of my brewing, all three of us breakfasting standing by the platform.”
There were occasional picnics and trips to the cave dwellings, the Grand Cañon, the petrified forest and other sights. Moreover, Percival greatly enjoyed the scenery about Flagstaff, and took an interest in the people of the town, although well aware of inexperience in some matters. On October 13th he says: “There was a grand republican rally last night and the young Flagstaff band that is learning to play in tune serenaded the speaker of the occasion under the hotel windows in fine style. When you knew the air beforehand you could follow it with enthusiasm.”
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 darkareas 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 interpretationof 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 southernhemisphere—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 polarcap, 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 backgroundof 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 itselfboth 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.
“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.” In order that the reader may not be confused, and wonder why the changes at the north pole do not begin shortly after those in the southern hemisphere are over, he must remember that the Martian year has 687 days, and is thus nearly twice as long as ours, or in other words that the period of these observations covered only about four months in Mars.
“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,” although the dark areas were then at their darkest. “For some time the dark areas continued largely unchanged in appearance; that is, during the earlier and most extensive melting of thesnow-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.... 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.” He points out that such a change is inexplicable if the dark areas were water, for there was no place for it to go to. “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.” By the continental areas he meant the barren regions, formerly thought to stand out from seas in contrast with the darker ones supposed to be water.
“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.” And as a planet grows old its water retreats through cracks and caverns into its interior. The so-called seas were,he thinks, once such, and “are still the lowest portions of the planet, and therefore stand to receive what scant water may yet travel over the surface.” With this agrees the fact that the divisions between the dark and light areas run south-east north-west; as they would if made by currents in water flowing from the pole toward the equator.
“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.[11]...
“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....
“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.”
He then takes up these so-called canals or lines which start from the edge of the blue-green regions, proceed directly to what seem centres in the middle of the ochre areas, where they meet other lines that come, he says, “with apparently a like determinate intent. And this state of things is not confined to any one part of the planet, but takes place allover the reddish-ochre regions,” that is the arid belt of the planet. “Plotting upon a globe betrays them to be arcs of great circles almost invariably, even the few outstanding exceptions seeming to be but polygonal combinations of the same.” These two facts, that the lines are great circles, or the shortest distance between points on the surface of the planet, and that several of them often meet at the same place, must be borne in mind, because they are essential elements in his argument that they are the result of an intelligent plan.
The lines are of enormous length, the shortest being 250 miles, and the longest 3,540, and at times three, four, five, and even seven come together at one spot. By them the whole region is cut up, and how many there may be cannot now, he says, be determined, for the better the air at the observatory the more of them become visible. At Flagstaff they detected 183, seen from once to 127 times, and there were in the aggregate 3,240 records made of them.[12]
In seeking for the origin of the lines he begins by discarding natural causation on the ground first of their straightness, and second of their uniform width, regularities not to be found to any such a degree in the processes of nature. His third ground is “that the lines form a system; that, instead of running anywhither, they join certain points to certain others, making thus, not a simple network, but one whose meshes connect centres directly with one another.... If lines be drawn haphazard over the surface of a globe, the chances are ever so many to one against more than two lines crossing each other at any point. Simple crossings of two lines will of course be common in something like factorialproportion to the number of lines; but that any other line should contrive to cross at the same point would be a coincidence whose improbability only a mathematician can properly appreciate, so very great is it.... In other words, we might search in vain for a single instance of such encounter. On the surface of Mars, however, instead of searching in vain, we find the thing occurringpassim; thisa priorimost improbable rendezvousing proving the rule, not the exception. Of the crossings that are best seen, all are meeting places for more than two canals.”
He then takes up the question of cracks radiating from centres of explosion or fissure, and points out that such cracks would not be of uniform breadth. There are cracks on the moon which look like cracks, while the lines on Mars do not. Moreover, the lines fit into one another which would not be true of cracks radiating from different centres. The lines cannot be rivers for those would not be the same width throughout, or run on arcs of great circles. Nor can the lines be furrows ploughed by meteorites, since these would not run straight from one centre to another; in short the objection from the infinitesimal chance of several lines crossing at the same point applies. “In truth,” he concludes, “no natural theory has yet been advanced which will explain these lines.”
The development, or order in the visibility, of the canals throws light on their nature. Early in the Martian spring they were invisible, then those nearest to the melting snows of its south pole appeared, and in a general succession those farther and farther away; but when they did appear they were always in the same place where they had been seen before. Each canal, however, did not darken all at once, butgradually; and this he accounts for by saying that what we see is not water but vegetation which takes time to develop. “If, therefore, we suppose what we call a canal to be, not the canal proper, but the vegetation along its banks, the observed phenomena stand accounted for. This suggestion was first made some years ago by Professor W. H. Pickering.
“That what we see is not the canal proper, but the line of land it irrigates, disposes incidentally of the difficulty of conceiving a canal several miles wide. On the other hand, a narrow, fertilized strip of country is what we should expect to find; for, as we have seen, the general physical condition of the planet leads us to the conception, not of canals constructed for waterways,—like our Suez Canal,—but of canals dug for irrigation purposes. We cannot, of course, be sure that such is their character, appearances being often highly deceitful; we can only say that, so far, the supposition best explains what we see. Further details of their development point to this same conclusion.” Such as that with time they darken rather than broaden.
To the objection that canals could not be built in straight lines because of mountain ranges he replies that the surface of Mars is surprisingly flat, and this he proves by careful observations of the terminator, that is the edge of that part of the planet lighted by the Sun, where any considerable sudden changes of elevation on the surface of the planet would appear, and do not.
He then tells of the discovery by Mr. Douglass of the canals in the dark regions toward the south pole. They could not be seen while those regions remained dark, but when they faded out the canals became visible, and suppliedthe missing link explaining how the water from the melting polar cap was conveyed to the canals in the arid space north and south of the equator. Mr. Douglass found no less than forty-four of them, almost all of which he saw more than once, one on as many as thirty-seven occasions.
Then came the phenomenon that convinced Percival of an artificial system of irrigation: “Dotted all over the reddish-ochre ground of the desert stretches of the planet ... are an innumerable number of dark circular or oval spots. They appear, furthermore, always in intimate association with the canals. They constitute so many hubs to which the canals make spokes”; and there is not a single instance of such a spot, unconnected by a canal, and by more than one, with the rest of the system. These spots are in general circular, from 120 to 150 miles in diameter, and make their appearance after, but not long after, the canals that lead to them, those that appear first becoming after a time less conspicuous, those seen later more so. In short they behave as oases of vegetation would when a supply of water had reached them, and thus give “an end and object for the existence of canals, and the most natural one in the world, namely, that the canals are constructed for the express purpose of fertilizing the oases.... This, at least, is the only explanation that fully accounts for the facts. Of course all such evidence of design may be purely fortuitous, with about as much probability, as it has happily been put, as that a chance collection of numbers should take the form of the multiplication table.” He does not fail to point out that great circles for the canals, and circular shapes for the oases, are the forms most economical if artificially constructed; nor does his reasoning rest upon a small number of instances, for up to the close ofobservations at that time fifty-three oases had been discovered.
Finally he deals with the corroborating phenomena of double canals and the curious dark spots where the canals in the dark regions debouch into those that run through the deserts.
In his conclusion he sums up his ideas as follows:
“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.”
Such was the harvest of facts and ideas garnered from Mars at the Observatory during this summer of tireless watching. Both the facts and the conclusions drawn from them were received with incredulity by astronomers whose atmospheres and unfamiliarity with the things to be observed hindered their seeing the phenomena, and to whom the explanations seemed fantastic. With more careful observation skepticism about the phenomena decreased, one observer after another seeing the change of color on theplanet, the growth of vegetation, and in some form the lines and the dots, although many skilled observers still see them as irregular markings rather than as fine uniform lines. The hypothesis of artificial construction of the canals by intelligent beings has met with much more resistance. It runs against the blade of Occam’s razor, that nothing should be attributed to conscious intelligent action unless it cannot be explained by natural forces. Percival seems to have made a very strong argument against any natural cause yet suggested, and a rational case for an intelligent agency if no natural one can be found. There, for the present, his hypothesis may be said to rest.
The favorable period for observation during the opposition of Mars having come to an end, the two larger telescopes, which had been hired or borrowed for the expedition, were returned in the spring to their owners, the observatory at Flagstaff being dismantled, and the rest of the apparatus brought East and stored; but plans for further work on Mars were by no means given up; and Percival—bent on still better equipment for the next opposition of Mars, in the summer of 1896—arranged with Alvan Clark & Sons for the manufacture of a 24-inch refractor lens. The Clarks were then the most successful makers of large lenses in the world; for up to that time it had not been possible to cast and cool these large pieces of glass so that they were perfectly uniform in density, and the art of the Clarks consisted in grinding and rubbing the surface so as to make its slight departure from the calculated curves compensate for any unevenness in density; and to a less extent it is still necessary. It required a skill of eye and hand unequalled elsewhere, and Percivals’ lens was one of the most perfect they ever made.