288 CARNEGIE INSTITUTION OF WASHINGTON. 



accordingly. Spectrograms for this purpose with iron-arc comparison 

 were made and measured. 



Ultra-Violet Spectrtjm of Ikon. 



Approximately 1,000 liaes of wave-lengths shorter than X3885, the 

 limit of the list previously published, and extending to X2448, have been 

 identified in the furnace spectrum of iron and classified according to 

 intensity at different temperatures and in the arc. In spite of the 

 complexity of the iron spectrum, certain types of lines are very defi- 

 nitely selected in this way, and the similarity can be used as a basis 

 in studying the structure of the spectrum. The arc spectrum in the 

 ultra-violet was also studied with regard to the variation from pole to 

 pole of different types of lines. Their behavior is definitely connected 

 with their appearance in the furnace. 



Miscellaneous. 



Furnace spectrograms for yttrium, neodymium, and zirconium have 

 been made to supplement former material on the rare-earth spectra. 

 The cadmium spectrum also has been photographed at different tem- 

 peratures. The silicon line X3906, important in stellar spectra, was 

 examined and found to show about the same response to temperature 

 change as the iron lines of Class III. 



Observations of the Zeeman Effect. 



Both the solenoid magnets with their respective furnaces were given 

 preliminary trials by Mr. King to test the action of the apparatus. 

 The solenoid of w^ater-cooled tubing was used with the contained fur- 

 nace at various angles to the lines of force. Most of the tests were on 

 absorption spectra, the spectrograph being provided with Nicol and 

 compound quarter-wave plate. The effect of variable inclination of 

 magnetic field in sun-spots could thus be imitated. 



The solenoid for high fields was used with vacuum furnace. Only a 

 few trials were made before the magnet was adapted to the Stark- 

 effect experiments, but some promising spectrograms were obtained, 

 the vacuum furnace giving a temperature of 2400° C. without exces- 

 sive heating of the parts. The magnet and furnace thus seem well 

 adapted to the study, under high fields, of the lines given with special 

 strength by the furnace. 



COMBINED EFFECT OF ELECTRIC AND MAGNETIC FIELDS ON RADIATION. 



Reference has been made in previous reports to our inability to de- 

 tect any evidence of the Stark effect in the sun-spot spectrum. During 

 the past year Mr. Hale, assisted by Mr. Sinclair Smith, has under- 

 taken an investigation of the combined effect of electric and magnetic 

 fields on radiation. If, in spite of present indications, an electric 

 field exists in sun-spots, its influence on the light emitted will be exer- 



