154 REPORTS OP INVESTIGATIONS AND PROJECTS. 



During April an electric furnace of the Aloissan type, inclosed in an air- 

 tight chamber, was set up and has been used by Dr. Olmsted for the investi- 

 gation of the spectra of hydrides, to be used for comparison with solar spectra 

 in the identification of unknown lines, especially of the flutings obtained in 

 the spectra of sun-spots. Good results for the spectra of magnesium and 

 calcium hydrides are being obtained. 



The recent discovery of the separation of lines in sun-spots, indicating the 

 presence of magnetic fields on the sun, has led to a supplementary laboratory 

 investigation of the Zeeman effect, the large Du Bois electro-magnet being 

 arranged so that an electric spark between the poles may be photographed 

 either parallel to the lines of magnetic force or at an angle to them. The 

 magnet gives a field strength up to 36,000 c. g. s. units. Photographs are 

 being obtained of the spectra of iron and other substances, giving an excellent 

 separation of the spectrum lines for magnetic fields of known strength, allow- 

 ing a detailed comparison with the separations obtained in the solar photo- 

 graphs. 



Most of the laboratory investigations cover the whole range of the visible 

 spectrum, requiring the use of photographic plates sensitive to red light in 

 addition to those commercially obtainable. The laboratory dark-room is 

 fitted up for the sensitizing of plates for the red region, which are thus used 

 while perfectly fresh and are handled with the same facility as the ordinary 

 plates. 



The comparison of intensities of lines on photographic plates has been car- 

 ried on by Miss Wickham of the computing division through the use of the 

 Zeiss spectrocomparator, adapted so as to show a portion of the spectrum 

 under examination and a specially prepared photographic scale in the field of 

 view at the same time, giving a definite value to the intensity of each spec- 

 trum line and allowing an accurate comparison of the intensities of lines in 

 different spectra. 



COMPUTING DIVISION. 



Some of the results obtained in the computing division, under the direction 

 of Mr. Adams, have already been given. The heliomicrometer has been used 

 by Miss Ware for all measurements of the positions of flocculi. The rapidity 

 of measurement has been greatly increased by ruling one hemisphere of the 

 globe with meridians and parallels i ° apart. The position of the cross-hairs, 

 after they have been set on a flocculus, is estimated to tenths of a degree. 

 The precision of measurement proves to be amply sufficient ; in fact, the 

 latitudes and longitudes are almost as precise as those obtained with the aid 

 of the circles. 



The measurement of the areas covered by the calcium flocculi, to serve as 

 an index of the solar activity, has been continued throughout the vear. This 



