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By permission of McClure's Magazine

M. JANSSEN'S OBSERVATORY AT THE SUMMIT OF MONT-BLANC

MOUNTAIN OBSERVATORIES

BY EDWARD S. HOLDEN

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might be better in the pure air of high mountains. He says:

"If the theory of making telescopes could at length be brought fully into practice, yet there would be certain bounds beyond which telescopes could not perform. For the air through which we look upon the stars is in a perpetual tremor, as may be seen by the twinkling of the fixed stars. The only remedy is a most serene and quiet air, such as may perhaps be found on the tops of the highest mountains above the grosser clouds."

Sir Isaac Newton's statement is admirable in its concise completeness. To understand the question of the advantage of mountain observatories we have simply to interpret and expand his suggestions. The air must be serene and pure; that is, free from the dust and smoke and vapors of the lower levels. It must be quiet; that is, the higher levels must be arranged in parallel strata of something like equal temperature, so that the rays from the fixed stars may pass in smooth curves through the atmosphere to the eye, and not in broken, jagged lines such as are indicated by intermittent twinkling. If one looks at a twinkling star with a magnifying power of one thousand diameters, not only is the star magnified one thousand times, but the twinkling, also, is so magnified. High magnifying powers can not be employed except in a most quiet

air. Two conditions of good vision are imperatively required; a pure atmosphere, free from dust; and a quiet air permitting the use of high magnifying powers. The latter condition is far more important. Perhaps, says Newton, perhaps these conditions may be found on the tops of the highest mountains. He is not certain. He has not tried the experiment. He offers the suggestion. Perhaps it may be true.

Newton's proposal remained unfertile for more than a century. In the mean time telescopes were being improved beyond his most sanguine hopes. In the year 1852 Mr. William Lassell of Liverpool took his powerful two-foot reflector to Malta in the hope (and with the result) of obtaining better views of the planets. In 1856 Professor Piazzi Smyth, Royal Astronomer for Scotland, made his famous expedition to the

From a painting by T. Moran

MOUNTAIN CAMP, MT WHITNEY, CALIFORNIA-(12,000)

peak of Teneriffe, where he established telescopes at two stations of 8903 and 10,702 feet, respectively. The whole question of good vision was thoroughly studied during a two months stay. The effects of fogs, local clouds, wind, dust, moisture, etc., were noted. The general conclusion was extremely favorable to that particular mountain station. The results of the expedition were printed in scientific journals and also in a popular book which had a wide circulation "Teneriffe, an Astronomer's Experiment."

Lassell's expedition of 1852 was, however, the first practical recognition of the fact that a large telescope can only do its work well under conditions especially favorable. These conditions may be found on a high mountain, or (for some work) they may be found at sea-level, as at Malta. If the necessity for a specially favorable site be once recognized, the search for the proper conditions is a matter of detail.

The American Association for the Advancement of Science was the first scientific body to take up the matter. In its meetings of 1868 and 1870 the question was discussed and a special committee was appointed to memorialize Congress on the importance of an astronomical

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By permission of McClure's Magazine ON THE WAY TO THE MONT-BLANC OBSERVATORY- (Passage of a Crevasse)

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a long stay in the Rocky mountains of Colorado and reported adversely on the suggestion to move the twenty-six-inch telescope to the region examined. The skies were clear, but the stars were most unsteady. No high magnifying powers could be employed, and no delicate observations made. The eclipse expeditions of July, 1878, to the Rocky mountains of Wyoming and Colorado familiarized many astronomers with the question, and the general verdict on these regions was that the skies were extraordinarily clear, while at the same time the stars were so unsteady as to preclude refined observations. Professor Langley's famous expedition to Mount Whitney in Southern California (1881) showed, on the other hand, that this particular station combined both the requisites of a pure and quiet air.

The plans for Mr. Lick's observatory on Mount Hamilton (4209 feet in height) were made in 1874, and the observations made there in 1879, 1881, and 1882, called attention to the excellence of the selected site.

The observatory on Etna, built in 1881, but proposed by Professor Tacchini as early as 1871, performed the same service for Europe. It may fairly be said that the many mountain observatories now built or building in all parts of the world are the children of the observatories on Etna and Mount Hamilton.

In the choice of the Mount Hamilton station the principle was clearly laid down that no site should be selected until it had been previously tested, and until the test had shown a marked improvement over conditions at the level of the sea. This is the essence of the whole matter, It is necessary to test the conditions before establishing the station, because experience has shown that only a few out of many available mountains are suitable for astronomical observations.

There are many objections to mountain stations. The cost of building is very large. M. Vallot's Observatory on the flanks of Mont-Blanc (14,321 feet), cost seventy-four dollars per cubic metre. The cost of M. Janssen's small observatory building on the summit (15,781 feet) is said to have been

sixty thousand dollars. Again, such establishments are very expensive to maintain. Transportation to the summit of Mont-Blanc costs about fifty-two cents per pound, for example. There are difficulties in arranging for an adequate food and water supply (though melted snow is always available on the higher peaks). In the United States (owing to our deplorable policy in the matter of forest-conservation) bush fires which fill the air with haze, are very troublesome. On the highest peaks snow-blindness is a constant danger. Mountain-sickness (giddiness, nausea, great discomfort and disorder) is almost always felt. The experiments of Mr. Whymper and others, in the high Andes and elsewhere, show that long residence at high levels may enable one to resist acute attacks of mountain-sickness. But no amount of habitude, apparently, counteract the "diminished living which results from an insufficient supply of air for breathing. Observers at extreme altitudes must always be subjected to great discomfort, and their abilities must be correspondingly decreased. De Saussure, in his expedition to Mont-Blanc, remarks that

can

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From a negative by Joseph Le Conte, Jr., reprinted from the Bulletin of the Sierra Club

MT. WHITNEY (14,900 feet) FROM THE WEST

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