Page:Popular Science Monthly Volume 36.djvu/290

278 filled the valleys and covered up all the mountains. The thickness must be regulated by the quantity of snow falling, and this is largest toward the coast, gradually diminishing toward the interior. Hence the thickness of the ice would be greatest on both sides toward the coast, just as has been observed. The surface of the snow-field in the interior is even and as if polished, resembling the undisturbed surface of a frozen sea, the long but not high billows of which, rolling from east to west, are not easily distinguishable to the eye. The principal factor in giving the surface this shape is the wind. A careful observation of a snow and ice covering like that of Greenland is of great importance for the theory of the formation of valleys and fiords. It seems that the more we study Greenland, its coasts, and its inland ice, the more convinced we must feel of the power of the ice to perform this work.

The Bruce Photographic Telescope.—The Astronomical Observatory of Harvard College has received from Miss C. W. Bruce a gift of fifty thousand dollars for the construction of a photographic telescope such as the director had described in his circular of November 28, 1888, as desirable. The instrument will have an objective of about twenty-four inches aperture, and a focal length of about eleven feet. It will differ from other large telescopes in the construction of its object-glass, which will be a compound lens of the form used by photographers and known as the portrait lens. The focal length of such a lens is very small compared with its diameter, and much fainter stars can be photographed in consequence. The advantage is even greater in photographing nebulæ or other faint surfaces. Moreover, this form of lens will enable each photographic plate to cover an area several times as great as that which is covered by an instrument of the usual form. The time required to photograph the entire sky is reduced in the same proportion. A telescope of the proposed form, having an aperture of eight inches, has been in constant use in Cambridge for the last four years, and is now in Peru photographing the southern stars. It has proved useful for a great variety of researches. Stars have been photographed with it too faint to be visible in the fifteen-inch refractor of the observatory. Its short focal length enables it to photograph as faint stars as any which can be taken with an excellent photographic telescope having an aperture of thirteen inches. The eight-inch telescope will photograph stars about two magnitudes fainter than can be taken with a similar instrument having an aperture of four inches. A corresponding advantage is expected from the increase of the aperture to twenty-four inches. Other advantages to be anticipated from the use of such an instrument will arise from the opportunities which the photographs will give for continuous and detailed study. With them work can be done at any place and any time, and, by multiplying copies, by any number of observers. And with them more could be added by a single lens to our knowledge of the stars than could be obtained by any number of telescopes of the usual kind. Prof. Pickering is seeking the best possible location at which to mount the instrument. Owing to the difficulty in maintaining regular observations in the Eastern States that arise from the prevalence of cloudiness, he suggests one of the mountains of southern California as likely to offer the most favorable climatic conditions attainable.

What it takes to play a Piece of Music.—Science, says Sir James Paget, will supply the natural man with wonders uncounted. The author had once heard Mile. Janotha play a presto by Mendelssohn. She played 5,595 notes in four minutes and three seconds. Every one of these notes involved certain movements of a finger, at least two, and many of them involved an additional movement laterally as well as those up and down. They also involved repeated movements of the wrists, elbows, and arms, altogether probably not less than one movement for each note. Therefore there were three distinct movements for each note. As there were twenty-four notes per second, and each of these notes involved three distinct musical movements, that amounted to seventy-two movements in each second. Moreover, each of those notes was determined by the will to a chosen place, with a certain force, at a certain time, and with a certain duration. Therefore there were four distinct qualities in each of the seventy-two