Returning from the transit of Venus in 1882, Copeland of Edinburgh visited several sites in the Andes of Peru, ascending on the railway from Mollendo. Vincocaya was one of the highest, something over 14,000 feet elevation. His report was most enthusiastic, not only as to clearness and transparency of the atmosphere, but also as to its steadiness, which for planetary and double star observations is almost as important. Copeland's investigation of this region of the Andes has led many other astronomers to make critical tests in the same general region. Climatic conditions are particularly favorable, and the sites for high-level research are among the best known, the atmosphere being not only clear a large part of the year, but in certain favored spots exceedingly steady.
In 1887 the writer ascended the summit of Fujiyama, Japan, 12,400 feet elevation. The early September conditions as to steadiness of atmosphere were extraordinarily fine, but the mountain is covered by cloud many months in each year. There is a saddle on the inside of the crater that would form an ideal location for a high-level observatory. This expedition was undertaken at the request of the late Professor Pickering, director of Harvard College Observatory, which had recently received a bequest from Uriah A. Boyden, amounting to nearly a quarter of a million dollars, to "establish and maintain, in conjunction with others, an astronomical observatory on some mountain peak."
Great elevations were systematically investigated in Colorado and California, the Chilean desert of Atacama was visited, and a temporary station established at Chosica, Peru, elevation about 5,000 feet. Atmospheric conditions becoming unfavorable, a permanent station was established in 1891 at Arequipa, Peru, elevation 8,000 feet, which has been maintained as an annex to the Harvard Observatory ever since. The cloud conditions have been on the whole less favorable than was expected, but the steadiness of the air has been very satisfactory. In addition to planetary researches conducted there in the earlier years by W. H. Pickering, many large programs of stellar research have been executed, especially relating to the magnitudes and spectra of the stars. In conjunction with the home observatory in the northern hemisphere, this afforded a vast advantage in embracing all the stars of the entire heavens, on a scale not attempted elsewhere. The Bruce photographic telescope of 24-inch aperture has been employed for many years at Arequipa, and with it the plates were taken which enabled Pickering to discover the ninth satellite of Saturn (Phœbe), and the splendid photographs of southern globular clusters in which Bailey has found numerous variable stars of very short periods—very faint objects, but none the less interesting, and of much significance in modern study of the evolution and structure of the stellar universe. The crowning research of the observatory is the Henry Draper catalogue of stellar spectra, now in process of publication, which is of the first order of importance in statistical studies of stellar distribution with reference to spectral type, and in studying the relation of parallax and distance, proper motion, radial velocity and its variation to the spectral characteristics of the stars.
Perrine of Cordova is now establishing on Sierra Chica about twenty-five miles southwest of Cordova, a great reflecting telescope comparable in size with the instruments of the northern hemisphere, for investigation of the southern nebulæ and clusters, and motions of the stars. The elevation of this new Argentine observatory will be 4,000 feet above sea level.
Another observatory at mountain elevation and in a highly favorable climate is the Lowell Observatory, located at about 7,000 feet elevation at Flagstaff, Arizona. Many localities were visited and the atmosphere tested especially for steadiness, an optical quality very essential for research on the planetary surfaces. Mexico was one of these stations, but local air currents and changes of temperature there were such that good seeing was far from prevalent, as had been expected. At Flagstaff, on the other hand, conditions have been pretty uniformly good, and an enormous amount of work on the planet Mars has been accumulated and published. The first successful photographs of this planet were taken there in 1905, and Jupiter, Saturn, the zodiacal light and many other test objects have been photographed, which demonstrates the excellence of the site for astronomical research. Within recent years spectrum research by Slipher, especially on the nebulæ, has been added to the program, and the rotation and radial velocities of many nebulæ have been determined.
On Mount Wilson, near Pasadena, California, at an elevation of nearly 6,000 feet, is the Carnegie Solar Observatory, founded and equipped under the direction of Professor George E. Hale, as a department of the Carnegie Institution of Washington, of which Dr. John Campbell Merriam is President. The climatology of the region was carefully investigated and tests of the seeing made by Hussey and others. Although equipped primarily for study of the sun, the program of the observatory has been widely amplified to include the stars and nebulæ. The instrumental equipment is unique in many respects. To avoid the harmful effect of unsteadiness of air strata close to the ground a tower 150 feet high was erected, with a dome surmounting it and covering a cœlostat with mirror for reflecting the sun's rays vertically downward. Underneath the tower a dry well was excavated to a depth equal to ½ the height of the tower above it. In the subterranean chamber is the spectroheliograph of exceptional size and power. The sun's original image is nearly 17 inches in diameter on the plate, and the solar chromosphere and prominences, together with the photosphere and faculæ, are all recorded by monochromatic light.
Connected with the observatory on Mount Wilson are the laboratories, offices and instrument shops in Pasadena, 16 miles distant, where the remarkable apparatus for use on the mountain is constructed. A reflecting telescope with silver-on-glass mirror 60 inches in diameter was first built by Ritchey and thoroughly tested by stellar photographs. Also the northern spiral nebulæ were photographed, exhibiting an extraordinary wealth of detail in apparent star formation. The success of this instrument paved the way for one similar in design, but with a mirror 100 inches in diameter, provided by gift of the late John D. Hooker of Los Angeles. The telescope was completed in 1919. Notwithstanding its huge size and enormous weight, the mounting is very successful, as well as the mirror. Mercurial bearings counterbalance the weight of the polar axis in large part. This great telescope, by far the largest and most powerful ever constructed, is now employed on a program of research in which its vast light-gathering power will be utilized to the full. Under the skillful management of Hale and his enthusiastic and capable colleagues, the confines of the stellar heavens will be enormously extended, and secrets of evolution of the universe and of its structure no doubt revealed.
In all the mountain stations hitherto established, as the Lick Observatory at 4,000 feet, the Mount Wilson Observatory at 6,000 feet, the Lowell Observatory at 7,000 feet, the Harvard Observatory at 8,000 feet; and Teneriffe and Etna at 10,000, Fujiyama at 12,000, Pike's Peak at 14,000, Mont Blanc and Mount Whitney at 15,000, the researches that have been carried on have fully demonstrated the vast advantage of increased elevation in localities where climatological conditions as well as elevation are favorable. Nevertheless, only one-half of the extreme altitude contemplated by Sir Isaac Newton has yet been attained.
Can the greater heights be reached and permanently occupied? Geographically and astronomically the most favorably located mountain for a great observatory is Mount Chimborazo in Ecuador. Its elevation is 22,000 feet, and it was ascended by Edward Whymper in 1880. Situated very nearly on the earth's equator, almost the entire sidereal heavens are visible from this single station, and all the planets are favored by circumzenith conditions when passing the meridian. No other mountain in the world approaches Chimborazo in this respect. But the summit is perpetually snow-capped, exceedingly inaccessible, and the defect of barometric pressure would make life impossible up there in the open.
Only one method of occupation appears to be feasible. The permanent snow line is at about 16,000 feet, where excellent water power is available. By tunneling into the mountain at this point, and diagonally upward to the summit, permanent occupation could be accomplished, at a cost not to exceed one million dollars.