By far the most considerable of these experiments is that of the “Lick Observatory.” Its founder was from the first determined that the powers of his great telescope should, as little as possible, be fettered by the hostility of the elements. The choice of its local habitation was, accordingly, a matter of grave deliberation to him for some time previous to his death. Although close upon his eightieth year, he himself spent a night upon the summit of Mount St. Helena with a view to testing its astronomical capabilities, and a site already secured in the Sierra Nevada was abandoned on the ground of climatic disqualifications. Finally, one of the culminating peaks of the Coast Range, elevated 4,440 feet above the sea, was fixed upon. Situated about fifty miles south-east of San Francisco, Mount Hamilton lies far enough inland to escape the sea-fog, which only on the rarest occasions drifts upward to its triple crest. All through the summer the sky above it is limpid and cloudless; and though winter storms are frequent, their raging is not without highly available lucid intervals. As to the essential point—the quality of telescopic vision—the testimony of Mr. S. W. Burnham is in the highest degree encouraging. This well-known observer spent two months on the mountain in the autumn of 1879, and concluded, as the result of his experience during that time—with the full concurrence of Professor Newcomb—that, “it is the finest observing location in the United States.” Out of sixty nights he found forty-two as nearly perfect as nights can well be, seven of medium quality, and only eleven cloudy or foggy;[2] his stay, nevertheless, embraced the first half of October, by no means considered to belong to the choice part of the season. Nor was his trip barren of discovery. A list of forty-two new double stars gave an earnest of what may be expected from systematic work in such an unrivalled situation. Most of these are objects which never rise high enough in the sky to be examined with any profit through the grosser atmosphere of the plains east of the Rocky Mountains; some are well-known stars, not before seen clearly enough for the discernment of their composite character; yet Mr. Burnham used the lesser of two telescopes—a 6-inch and an 18-inch achromatic—with which he had been accustomed to observe at Chicago.