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, will perceive 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 confirmed by 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 3 A.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 make one 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 Colorado man, 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.”