soivAR obse;rvatory. 167 



continued in the laboratory the study of the behavior of these Hnes in an 

 electric furnace, with results in harmony with the hypothesis that the relative 

 intensities of the spot-lines are determined by the reduced temperature of the 

 spot-vapors. Mr. Ellerman is preparing a new photographic map of the spot- 

 spectrum, to replace the provisional map issued to members of the Inter- 

 national Solar Union in 1907. 



Photographic Comparison of the Spectra of the Center and Limb of the Sun. 



Mr. Adams has continued his comparative study of the spectra of the 

 center and limb of the sun, and a special study of certain phases of this prob- 

 lem was undertaken by Dr. Gale last spring. As the enhanced lines had been 

 found by Mr. Adams to be relatively displaced more than other lines at the 

 sun's limb, it became necessary to study their displacements in the laboratory, 

 using a spark in a gaseous atmosphere under pressure. This laboratory work 

 had been well started by Dr. Gale when he most unfortunately came in con- 

 tact with the high-potential wires of the transformer used to produce the 

 spark. The shock, though not fatal, was a very serious one, and Dr. Gale 

 has only recently recovered from the severe burns he received. The work 

 will be taken up again as soon as possible. 



Photographic Investigation of the "Flash" Spectrum. 



In view of experiments made at the Kenwood and Yerkes observatories, it 

 seemed probable that the spectrum of the lower chromosphere, hitherto pho- 

 tographed only at eclipses as the "flash" spectrum, could be studied at any 

 time in full sunlight, provided the instrumental and atmospheric conditions 

 were favorable. With the 60-foot tower telescope it has already been possible 

 to photograph a great number of bright lines in various regions of the spot- 

 spectrum, including the numerous lines of the green carbon fluting, only a 

 part of which has been obtained at eclipses. A catalogue of the lines 

 hitherto photographed is now being prepared by Mr. Adams. The wave- 

 lengths can be measured much more accurately than on eclipse plates, because 

 of the high dispersion of the 30-foot spectrograph. The work will be con- 

 tinued to much better advantage when the 150- foot tower telescope has been 

 completed. 



Spectrographic Investigation of the Solar Rotation. 



The continuation of Mr. Adams's work on the rotation of the sun during 

 1908 has led to the following conclusions : 



(i) Observations of the rotation of the sun during 1908 give values 

 agreeing closely with those of 1906-07 between latitudes 0° and 50°. Above 

 50° they give larger values, the difiference in linear velocity reaching at a 

 maximum G.036 km. 



(2) The general agreement of the results and the excellent accord with 

 Duner's values are opposed to the existence of a variation in the rotation rate 



