SOLAR OBSERVATORY. 1 77 



perature rises, while other Hnes appear at higher temperatures and strengthen 

 at different rates with increase of temperature. The Hnes of each spectrum 

 are thus classified according to their sensitiveness to temperature change. A 

 comparison with sun-spot spectra based on this classification is being pre- 

 pared for publication. A large majority of the lines relatively strong in sun- 

 spots appear either at low temperature in the furnace or -'t slightly higher 

 temperatures and, in the latter case, show a rapid rate of increase in intensity 

 as the temperature rises. Thus the mass of spectroscopic evidence points to 

 a relatively low temperature in sun-spots as being at any rate in large measure 

 responsible for the differences in the spectrum of the spot and of the body of 

 the sun. 



The arc-furnace of the Moissan type has been used by Dr. Olmsted to 

 obtain the band spectrum of calcium when vaporized in an atmosphere of 

 hydrogen. These bands, which had been shown to be present in the spectra 

 of sun-spots, have now been photographed on a large scale, and a full com- 

 parison made with the spot spectrum, resulting in the identification of about 

 600 spot-lines. 



An investigation of the spectrum of the electric spark under high pressures 

 was taken up by Dr. Gale, with reference to the shifts of solar lines at the 

 limb and center of the sun. As already explained, however, an accident made 

 necessary a postponement of the work. 



Other investigations carried out in the laboratory include a study of the 

 iron spectrum, which resulted in a considerable addition to the list of "en- 

 hanced" lines for iron ; experiments by Mr. Babcock on the discharge con- 

 ditions in a vacuum-tube as affecting the relative intensity of the hydrogen 

 lines; and a study of the photographic Purkinje phenomenon by Dr. Fath. 



A large amount of measurement and reduction in connection with the 

 laboratory work has been done by Miss Wickham, of the Computing Division. 



COMPUTING DIVISION. 



The work of the computing division was continued under the direction of 

 Mr. Adams until August i, when Professor Scares was placed in charge. 



As already stated, the continuation of Miss Ware's measurements of the 

 hydrogen flocculi, for the determination of the solar rotation, has been post- 

 poned until better photographs can be obtained. Her work during the year 

 has consisted mainly in the study of changes in the solar vortices and the 

 measurement of doublets and triplets in sun-spot spectra, stellar spectra made 

 with the 60-inch reflector and 1 8- foot spectrograph, and stellar photographs 

 taken for the determination of parallaxes. 



By an improvement in the method of measurement suggested by Mr. 

 Adams, the approximate areas of the calcium flocculi have been determined 

 by Miss Smith much more rapidly than before. Prints are made from each 



