SOLAR OBSERVATORY. I4I 



During the spring Mr. EUerman made from our negatives a preliminary 

 photographic map of the spot spectrum, extending from X 4600 to X 7200. 

 The map consists of 26 strips, each including 100 Angstroms, and is provided 

 with a solar spectrum for comparison purposes and an approximate scale to 

 aid in the identification of spot lines. At the recent Paris meeting of the 

 International Union for Cooperation in Solar Research this map, which is 

 the first photographic representation of a large extent of the spot spectrum, 

 was adopted for the use of the cooperating observers. Each visual observer 

 will select a certain limited region of the spot spectrum and compare the lines, 

 as seen at the telescope, with those recorded on the map. In this way any 

 changes in the relative intensities of the lines, if such occur, can be readily 

 detected. Copies of the map have been placed in the hands of all observers 

 who are cooperating in this work. Mr. Adams is engaged in extensive 

 studies of the photographs, for the purpose of drawing up a definitive list 

 of the weakened and strengthened lines. It is hoped that the 30-foot Littrow 

 spectroheliograph of the tower telescope will permit still better photographs 

 to be obtained for use in this investigation. 



Since the Snow telescope is not well adapted for stellar work, further 

 investigations of stellar spectra have been deferred until the completion of 

 the 60-inch reflector. It is evident that our discovery in sun-spots of the 

 titanium oxide flutings, which form the most conspicuous feature of the 

 spectra of the red stars of Secchi's third type, will suggest further inquiries 

 into the relationship between stellar and sun-spot spectra. In this connection 

 it is interesting to note that Mr. Newall has already found the red fluting of 

 titanium oxide (shown in our spot photographs) in the spectrum of a Orionis. 



Photographic Comparisons of the Spectra of Various Parts of the Sun's 

 Disk. — In endeavoring to interpret the spectra of sun-spots, it seemed advis- 

 able to determine photographically whether the solar spectrum undergoes any 

 changes in passing from the center of the sun to the limb. The literature of 

 the subject showed that little had been done in this field, with the exception 

 of the early visual observations of Hastings and the recent visual work of 

 Halm, who found that certain lines, when measured near the sun's limb, were 

 slightly shifted toward the red, as compared with their position at the sun's 

 center. We were therefore wholly unprepared to find such remarkable 

 changes in the appearances of the solar spectrum as our photographs 

 recorded. The principal changes in the solar spectrum, when observed at 

 points very near the limb, may be summarized as follows : 



(i) Most of the lines that are strengthened in sun-spots are strength- 

 ened near the sun's limb. 



(2) Most of the lines that are weakened in sun-spots are weakened near 

 the limb. 



