Page:Popular Science Monthly Volume 64.djvu/521

Rh Draper, The funds for this research were furnished by Mrs. Draper. From a study of the spectral peculiarities of the stars thus photographed, Mrs. Fleming has discovered a large number of variable stars and several new stars. Charts of the southern sky are made with this instrument each year. This work is in extension of that done in Cambridge for the northern sky. This collection is now of great value in tracing the history of any newly discovered celestial object.

A similar but more frequent photographic survey of the sky is also made by means of a Cooke lens with an aperture of about one inch. Photographs are made each month with this instrument of the available sky. An exposure of one hour shows stars to about the eleventh magnitude, and a plate eight inches by ten covers a region more than thirty degrees square, or about one fortieth part of the whole sky.

The thirteen-inch Boyden telescope has been used photographically for the detailed study of the spectra of the brighter stars, and for charts of special regions. The power of this instrument is such that, by the use of a battery of two or three prisms, spectra of the bright stars are obtained several inches in length, which show hundreds of lines. By an examination of these spectra several spectroscopic