3 So 



POPULAR SCIENCE MONTHLY 



by Janssen, but tne first practical re- 

 sults'were obtained by Hale. Tbe prin- 

 ciple of tbe 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 spec- 

 trum. 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 H/3 line of hydro- 

 gen, 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 prom- 

 inences in monochromatic light is ob- 

 tained 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 vari- 

 ous 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 photo- 

 graphs 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 sun- 

 spot period. It was also proposed to 

 have one station at as great an eleva- 

 tion as possible in connection with a 

 lower station, in order to measure the 

 absorption \>\ the earth's atmosphere, 

 and so eliminate it from the determina- 

 tion 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 eleva- 

 tion of some 12,000 feet. Mount Wil- 

 son itself has an altitude of 5,886 feet, 

 and overlooks the city of Pasadena, 

 southern California. 1 With the comple- 

 tion 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 in- 

 terest, and perhaps of utility, for the 

 human race. 



THE WARREN MUSEUM OF 

 NATURAu HISTORY 



The contents of the Warren Museum 

 of Natural History have been acquired 

 by the American Museum of Natural 

 History, New York City. The collec- 

 tion 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 sur- 

 geon be 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 skele- 

 ton kept in the Warren Museum of tbe 

 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 de- 

 vote to science. In 184S he was chosen 

 president of the Boston Society of Nat- 

 ural History. In 18.32 he published a 

 very handsome monograph on the 

 Mastodon giganteus, the finest speci- 

 men of which is the centerpiece of this 

 collection. 



1 During the years 1889 and 1890 a temporary 

 astronomical station was maintained at the 

 summit bv the Harvard College Observatory. 



