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by the excavation of great cisterns. Buildings are rapidly being pushed forward from designs prepared by Professors Holden and Newcomb. Most of the subsidiary instruments have for some time been in their places, constituting in themselves an equipment of no mean order. With their aid Professor Holden and Mr. Burnham observed the transit of Mercury of November 7th, 1881, and Professor Todd obtained, December 6th, 1882, a series of 147 photographs (of which seventy-one were of the highest excellence) recording the progress of Venus across the face of the sun.
We are informed that a great hotel will eventually add the inducement of material well-being to those of astronomical interest and enchanting scenery. No more delightful summer resort can well be imagined. The road to the summit, of which the construction formed the subject of a species of treaty between Mr. Lick and the county of Santa Clara in 1875, traverses from San José a distance, as a bird flies, of less than thirteen miles, but doubled by the windings necessary in order to secure moderate gradients. So successfully has this been accomplished, that a horse drawing a light waggon can reach the observatory buildings without breaking his trot.5 As the ascending track draws its coils closer and closer round the mountain, the view becomes at every turn more varied and more extensive. On one side the tumultuous coast ranges, stooping gradually to the shore, magnificently clad with forests of pine and red cedar; the island-studded bay of San Francisco, and, farther south, a shining glimpse of the Pacific; on the other, the thronging pinnacles of the Sierras – granite needles, lava-topped bastions – fire-rent, water-worn; right underneath, the rich valleys of Santa Clara and San Joaquim, and, 175 miles away to the north (when the sapphire of the sky is purest), the snowy cone of Mount Shasta.
Thus, there seems some reason to apprehend that Mount Hamilton, with its monster telescope, may become one of the show places of the New World. Absit omen! Such a desecration would effectually mar one of the fairest prospects opened in our time before astronomy. The true votaries of Urania will then be driven to seek sanctuary in some less accessible and less inviting spot. Indeed, the present needs of science are by no means met by an elevation above the sea of four thousand and odd feet, even under the most translucent sky in the world. Already observing stations are recommended at four times that altitude, and the ambition of the new species of climbing astronomers seems unlikely to be satisfied until he can no longer find wherewith to fill his lungs (for even an astronomer must breathe), or whereon to plant his instruments.
This ambition is no casual caprice. It has grown out of the growing exigencies of celestial observation.
From the time that Lord Rosse’s great reflector was pointed to the sky in February, 1845, it began to be distinctly felt that instrumental power had outrun its opportunities. To the sounding of further depths of space it came to be understood that Atlantic mists and tremulous light formed an obstacle far more serious than any mere optical or mechanical difficulties. The late Mr. Lassell was the first to act on this new idea. Towards the close of 1852 he transported his beautiful 24-inch Newtonian to Malta, and, in 1859-60, constructed, for service there, one of four times its light capacity. Yet the chief results of several years’ continuous observation under rarely favorable conditions were, in his own words, “rather negative than positive.”6 He dispelled the “ghosts” of four Uranian moons which had, by glimpses, haunted the usually unerring vision of the elder Herschel, and showed that our acquaintance with the satellite families of Saturn, Uranus, and Neptune must, for the present at any rate, be regarded as complete; but the discoveries by which his name is chiefly remembered were made in the murky air of Lancashire.
The celebrated expedition to the Peak of Teneriffe, carried out in the summer of 1856 by the present Astronomer Royal for Scotland, was an experiment made with the express object of ascertaining “how much astronomical observation can be benefited by eliminating the lower third or fourth part of the atmosphere.”7 So striking were the advantages of which it seemed to hold out the promise, that we count with surprise the many years suffered to elapse before any adequate attempt was made to realize them.8 Professor Piazzi Smyth made his principal station at Guajara, 8,903 feet above the sea, close to the rim of the ancient crater from which the actual peak rises to a further height of more than 3,000 feet. There he found that his equatorial (five feet in focal length) showed stars fainter by four magnitudes than at Edinburgh. On the Calton Hill the companion of Alpha Lyræ (eleventh magnitude) could never, under any circumstances, be made out. At Guajara it was an easy object twenty-five degrees from the zenith; and stars of the fourteenth magnitude were discernible. Now, according to the usual estimate, a step downwards from one magnitude to another means a decrease of lustre in the proportion of two to five. A star of the fourteenth order of brightness sends us accordingly only 1/39th as much light as an average one of the tenth order. So that, in Professor Smyth’s judgment, the grasp of his instrument was virtually multiplied thirty-nine times by getting rid of the lowest quarter of the atmosphere.9 In other words (since light falls off in intensity as the square of the distance of its source increases), the range of vision was more than sextupled, further depths of space being penetrated to an extent probably to be measured by thousands of billions of miles!
This vast augmentation of telescopic compass was due as much to the increased tranquillity as to the increased transparency of the air. The stars hardly seemed to twinkle at all. Their rays, instead of being broken and scattered by continual changes of refractive power in the atmospheric layers through which their path lay, travelled with relatively little disturbance, and thus produced a far more vivid and concentrated impression upon the eye. Their images in the telescope, with a magnifying power of 150, showed no longer the “amorphous figures” seen at Edinburgh, but such minute, sharply-defined discs as gladden the eyes of an astronomer, and seem, in Professor Smyth’s phrase, to “provoke” (as the “cocked-hat” appearance surely baffles) “the application of a wire-micrometer” for the purposes of measurement.10
The lustre of the milky way and zodiacal light at this elevated station was indescribable, and Jupiter shone with extraordinary splendor. Nevertheless, not even the most fugitive glimpse of any of his satellites was to be had without optical aid.11 This was possibly attributable to the prevalent “dust-haze”, which must have caused a diffusion of light in the neighborhood of the planet more than sufficient to blot from sight such faint objects. The same cause completely neutralized the darkening of the sky usually attendant upon ascents into the more ethereal regions, and surrounded the sun with an intense glare of reflected light. For reasons presently to be explained, this circumstance alone would render the Peak of Teneriffe wholly unfit to be the site of a modern observatory.
Within the last thirty years a remarkable change, long in preparation,12 has conspicuously affected the methods and aims of astronomy; or, rather, beside the old astronomy – the astronomy of Laplace, of Bessel, of Airy, Adams, and Leverrier – has grown up a younger science, vigorous, inspiring, seductive, revolutionary, walking with hurried or halting footsteps along paths far removed from the staid courses of its predecessor. This new science concerns itself with the nature of the heavenly bodies; the elder regarded exclusively their movements. The aim of the one is description, of the other prediction. This younger science inquires what sun, moon, stars, and nebulæ are made of, what stores of heat they possess, what changes are in progress within their substance, what vicissitudes they have undergone or are likely to undergo. The elder has attained its object when the theory of celestial motions shows no discrepancy with fact – when the calculus can be brought to agree perfectly with the telescope – when the coursers of the heavens come strictly up to time, and their observed places square to a hair’s-breadth with their predicted places.
It is evident that very different modes of investigation must be employed to further such different objects; in fact, the invention of novel modes of investigation has had a prime share in bringing about the change in question. Geometrical astronomy, or the astronomy of position, seeks above all to measure with exactness, and is thus more fundamentally interested in the accurate division and accurate centering of circles than in the development
E. Holden, “The Lick Observatory,” Nature, vol. xxv. p. 298.
Monthly Notices, R. Astr. Soc. vol. xiv. p. 133 (1854).
Phil. Trans. vol. cxlviii. p. 455.
Captain Jacob unfortunately died August 16, 1862, when about to assume the direction of a hill observatory at Poonah.
The height of the mercury at Guajara is 21·7 to 22 inches.
Phil. Trans. vol. cxlviii. p. 477.
We are told that three American observers in the Rocky Mountains, belonging to the Eclipse Expedition of 1878, easily saw Jupiter’s satellites night after night with the naked eye. That their discernment is possible, even under comparatively disadvantageous circumstances is rendered certain by the well-authenticated instance (related by Humboldt, “Cosmos,” vol. iii. p. 66, Otte’s trans.) of a tailor named Schön, who died at Breslau in 1837. This man habitually perceived the first and third, but never could see the second or fourth Jovian moons.
Sir W. Herschel’s great undertakings, Bessel remarks (“Populäre Vorlesungen,” p. 15), “were directed rather towards a physical description of the heavens, than to astronomy proper.”