224 CARNEGIE INSTITUTION OF WASHINGTON. 



Miscellaneous work on instruments by Mr. Babeock has included 

 a determination of the variation of field-strength with pole-gap and 

 with magnetizing current for the large Weiss electro-magnet, and 

 the preparation of curves showing the effect; a study of the Leeds 

 & Northrop synchronizing fork for constant angular velocities, in the 

 hope that it might be used to control the driving mechanism of the 

 100-inch reflector; the testing of a 1 : 1000 alcoholic solution of pina- 

 cyanol five years old for sensitizing action, which proved to be unim- 

 paired ; and the remounting of the Werlein compound quarter-wave 

 plate, which had been injured by long exposure to the solar image in 

 the study of the sun's general magnetic field. 



Electric-Furnace Spectra. 



The work of Mr. King in the Pasadena laboratory has been a 

 continuation of the study of spectra produced at various tempera- 

 tures of the electric furnace, together with other experimental work 

 closely related to this investigation. 



In the last annual report, the leading features of electric-furnace 

 spectra were summarized, sufficient material being then on hand to 

 indicate the general phenomena presented by the spectrum of this 

 source. During the past year the results for the visible portion of 

 the iron spectrum have been published, and a similar paper for the 

 spectrum of titanium is in press. The region of spectrum studied 

 for each element extends from X 3880 to X 7400, the number of lines 

 examined being 512 for iron and 625 for titanium. The range of 

 furnace temperature employed was from 1800° C. to above 2600° C. 

 Within this range, three stages of temperature have been chosen, 

 designated as low, medium, and high, the spectra for w^hich show de- 

 cided differences. The lines are then divided into five main classes, 

 according to the temperature at which they appear and the rate of 

 growth in intensity as the temperature increases. A comparison 

 has also been made between the arc spectrum and the spectra given 

 b}^ the furnace at different temperatures. This promises to furnish 

 much evidence, as the material becomes more extensive, on the rela- 

 tion between these two sources, the spectra of which show many 

 striking differences. In the case of iron, a comparison between the 

 furnace spectra and data published on flame spectra has shown how 

 the various flames are probably related as to effective temperatures 

 in producing radiation. The titanium spectrum shows a noteworthy 

 richness in lines in spite of the high melting-point of this substance. 

 A temperature of 2600° C. gives practically all lines shown by the 

 arc except enhanced lines, and the stronger among even these may 

 be photographed by prolonged exposure. 



The variations in furnace radiation with wave-length have been 

 studied by means of a small concave-grating spectrograph. The 

 red end of the spectrum for both iron and titanium is found to 

 require a higher temperature for its production than the blue region, 



