Page:Popular Science Monthly Volume 68.djvu/384

380 by Janssen, but the first practical results were obtained by Hale. The principle of the instrument is simple, but the construction and manipulation of a spectroheliograph which will give the best results calls for the highest skill, while the interpretation of the results obtained taxes the keenest minds. With an ordinary slit spectroscope one may obtain the familiar solar spectrum. Crossing this luminous band are the relatively dark absorption lines characteristic of the various elements found in the solar atmosphere. Each line corresponds to light of a certain wave-length. If now this spectrum is all covered, with the exception of a single line, e. g., the Hβ line of hydrogen, and a photographic plate is placed behind this screen and the spectroscope is moved at right angles to the optical axis, an image of the sun and prominences in monochromatic light is obtained on the plate from successive images of the slit.

With such an apparatus Professor Hale is planning to photograph the sun and prominences each day in various kinds of monochromatic light, one photograph showing a Hydrogen sun, another a calcium sun, etc. Recently he has found it possible by setting the slit with special care to obtain photographs of calcium vapor of different densities, and hence at different levels.

Such studies must add greatly to our knowledge of the sun, especially since Mr. Abbot. Dr. Langley's able associate in bolometric determinations of the solar constant, has made a series of observations at Mount Wilson. The original plan for a solar observatory included an elaborate study of the solar constant and any changes in its value, extending over at least one sunspot period. It was also proposed to have one station at as great an elevation as possible in connection with a lower station, in order to measure the absorption by the earth's atmosphere, and so eliminate it from the determination of the solar constant. To this end an auxiliary station will probably be temporarily occupied on a mountain not far from Mount Wilson at an elevation of some 12,000 feet. Mount Wilson itself has an altitude of 5,886 feet, and overlooks the city of Pasadena, southern California. With the completion of the solar observatory not only will the summit of the mountain make a picturesque sight, with its various instruments and buildings, but from this lofty spot may come much of interest, and perhaps of utility, for the human race.

contents of the Warren Museum of Natural History have been acquired by the American Museum of Natural History, New York City. The collection was made by Dr. John C. Warren, who is little more than a name to the present generation, the son of John Warren, first professor of anatomy and surgery at the Harvard Medical School. He became adjunct professor to his father in 1809 and succeeded him in 1815, occupying the chair till 1847, when he retired at the age of sixty-nine. Besides being an eminent surgeon he was an enthusiastic anatomist, comparative as well as human. It is through him that Massachusetts has the honor of having passed the first anatomy law in America in 1831, one year before Great Britain. As a token of consistency he left orders that his body should be dissected and the skeleton kept in the Warren Museum of the Harvard Medical School (not to be confounded with the above-mentioned one). It hangs there to-day. In his later years he found more time to devote to science. In 1848 he was chosen president of the Boston Society of Natural History. In 1852 he published a very handsome monograph on the Mastodon giganteus, the finest specimen of which is the centerpiece of this collection.