MOUNT WII.SON SOI<AR OBSERVATORY. 1/7 



it seemed best to employ moderate and low pressures for this particular 

 study, the more so in view of the fact that the pressures encountered in the 

 solar atmosphere and in stars are of a moderate order of magnitude. The 

 main results of the investigation have already been summarized. In addition 

 to the direct study of the pressure effect, Mr. Gale examined the qualitative 

 influence of gases of various sorts upon the intensities of the lines of 

 different elements. 



The study of the pressure effects for electric-furnace spectra was taken 

 up by Mr. King primarily with the object of testing whether a source of 

 radiation different in many respects from the arc and the spark would give 

 results differing from those given by the latter sources. A considerable 

 number of photographs for iron, titanium, and vanadium are now available, 

 and the results appear to show consistently larger values for the furnace 

 lines than for the arc lines at the same pressures. The displacements do not 

 appear to vary throughout the range of temperature which it is possible to 

 secure in the furnace. An interesting feature of the use of the furnace is 

 the possibility of obtaining the pressure displacements of absorption lines by 

 passing white light through the furnace when under pressure. The shifts 

 found in this way are the same as those for emission lines. This line of 

 work is still in progress. 



The equipment of the laboratory has been increased during the year by 

 the purchase of several electrical measuring instruments and a number of 

 pieces of optical apparatus. A small concave grating of i meter radius has 

 been secured for work requiring moderate dispersion. 



THE COMPUTING DIVISION. 



The Computing Division has remained throughout the year under the 

 direction of Mr. Scares. 



Miss Burwell continued during the autumn and winter of 1910 her study 

 of the photographs of sun-spot spectra, giving especial attention to the effect 

 upon the spectrum lines of the presence of the magnetic field. This has 

 involved the classification of the lines in accordance with the system devised 

 by Mr. Hale and outlined in the report of last year. A careful comparison 

 of the spectra of a Bootis, a Taiiri, and a Ononis with the sun-spot spectrum 

 was also completed. During the summer months Miss Burwell was given 

 leave of absence to carry on studies at the University of Chicago. She 

 returned to Pasadena in September. 



Miss Griffin continued, up to the time of her resignation July i, the meas- 

 urement and reduction of laboratory photographs and various investigations 

 in photographic photometry. Her work included the determination of the 

 separations of lines in the magnetic field for several elements and the dis- 

 placements of lines under pressure in the electric furnace. In addition to 58 

 laboratory plates Miss Griffin carried out the measurement and reduction of 

 94 photometric negatives. 



12 — YB 



