The rooms of the summit observatory would need to be built as steel caissons, and supplied with compressed air at sea-level tension. The practicability of this plan was demonstrated by the writer in September, 1907, at Cerro de Pasco, Peru. A steel caisson was carried up to an elevation exceeding 14,000 feet. Patients suffering acutely with mountain sickness were placed inside this caisson, and on restoring the atmospheric pressure within it artificially all unfavorable symptoms—headache, high respiration and accelerated pulse—disappeared. There was every indication that if persons liable to this uncomfortable complaint were brought up to this elevation, or indeed any attainable elevation, under unreduced pressure, the symptoms of mountain sickness would be unknown. Comfortable occupation of the highest mountain summits was thereby assured.
The working of astronomical instruments from within air-tight compartments does not present any insurmountable difficulties, either mechanical or physical. Since the time these experiments were made, the Guayaquil-Quito railway has been constructed over a saddle of Chimborazo, at an elevation of 12,000 feet; and only six miles of railway would need to be built from this station to the point where the tunnel would enter the mountain.
Only by the execution of some such plan as this can astronomers hope to overcome the baleful effects of an ever mobile atmosphere, and secure the advantages contemplated by Sir Isaac Newton in that tranquillity of atmosphere, which he conceived as perpetually surrounding the summits of the highest mountains.
In Russell's theory of the progressive development of the stars, from the giant class to the dwarf, an element of verification from observation is lacking, because hitherto no certain method of measuring the very minute angular diameters of the stars has been successfully applied. The apparent surface brightness corresponding to each spectral type is pretty well known, and by dividing it into the total apparent brightness, we have the angular area subtended by the star, quite independent of the star's distance. This makes it easy to estimate the angular diameter of a star, and Betelgeuse is the one which has the greatest angular diameter of all whose distances we know. Antares is next in order of angular diameter, 0".043, Aldebaran 0".022, Arcturus 0".020, Pollux 0".013, and Sirius only 0".007.
Can these theoretical estimates be verified by observation? Clearly it is of the utmost importance and the exceedingly difficult inquiry has been undertaken with the 100-inch reflector on Mount Wilson, employing the method of the interferometer developed by Michelson and described later on, an instrument undoubtedly capable of measuring much smaller angles than can be measured by any other known method. Unquestionably the interference of atmospheric waves, or in other words what astronomers call "poor seeing," will ultimately set the limit to what can be accomplished. "But even if," says Eddington, "we have to send special expeditions to the top of one of the highest mountains in the world, the attack on this far-reaching problem must not be allowed to languish."
CHAPTER XXIII
THE PROGRAM OF A GREAT OBSERVATORY
The Mount Wilson Observatory has now been in operation about fifteen years. The novelty in construction of its instruments, the investigations undertaken with them and the discoveries made, the interpretation of celestial phenomena by laboratory experiment, and the recent addition to its equipment of a telescope 100 inches in diameter, surpassing all others in power, directs especial attention to the extensive activities of this institution, whose budget now exceeds a million dollars annually. Results are only achieved by a carefully elaborated program, such as the following, for which the reader is mainly indebted to Dr. Hale, the director of the observatory, who gives a very clear idea of the trend of present-day research on the magnetic nature of the sun, and the structure and evolution of the sidereal universe.
The purpose of the observatory, as defined at its inception, was to undertake a general study of stellar evolution, laying especial emphasis upon the study of the sun, considered as a typical star; physical researches on stars and nebulæ; and the interpretation of solar and stellar phenomena by laboratory experiments. Recognizing that the development of new instruments and methods afforded the most promising means of progress, well-equipped machine shops and optical shops were provided with this end in view.