544 



SCIENCE 



[N. S. Vol. XXXII. No. 825 



a decide de cooperer avee I'TJnioii solaire pour 

 I'eclipse de 1912. 



2. L'Observatoire de I'Ebro a Tortosa, peut 

 fournir une copie photographique des ele- 

 ments magnetiques, si I'on veut etudier le 

 rapport des eclipses avee le magnetisme ter- 

 restre. 



3. L'Observatoire de I'Ebro a tire quelques 

 photographies de I'eclipse partiel du soleil de 

 Juin 1908. n peut fournir des copies : le lieu 

 et I'heure sont exactment connues pour faire 

 des etudes astronomiques. 



Professor Campbell explained a method that 

 he has developed for obtaining a continuous 

 photographic record of the change from the 

 ordinary Fraunhofer spectrum into a bright 

 line spectrum at the time of a solar eclipse. 



At the third session reports were heard from 

 the committees on solar rotation and on work 

 with the spectroheliograph. 



The solar rotation committee discussed the 

 following topics: 



1. The accurate determination of the angu- 

 lar velocity of rotation at various latitudes 

 and the derivation of a formula representing 

 with a high degree of precision the variation 

 of velocity with latitude. 



2. A definite conclusion as to the existence 

 of secular or periodic variations in the sun's 

 rate of rotation. 



3. The investigation of the rate of rotation 

 as shown by the lines of diilerent elements and 

 of the arc and enhanced lines of the same ele- 

 ment, with a view to determining whether 

 either the absolute rate of rotation or the law 

 of variation with latitude differs for different 

 substances. 



4. The study of lines selected from different 

 regions of the spectrum. 



5. The detection of possible systematic 

 proper motions or drifts in the sun's reversing 

 layer. 



The committee made the following recom- 

 mendations to observers : 



1. That the observers select at least to a 

 partial extent different regions of the spec- 

 trum so that the total range of wave-length 

 under observation may be as great as possible. 



By general consent of those present at the 



meeting of the committee, the following re- 

 gions of the spectrum were selected by the 

 various observers : 



X3S00-X4000 Bglopolsky. 



X4000-X4140 Schlesinger. 



X4300-X4500 Newall. 



X4500-\4700 Adams. 



X5100-X5300 Adams. 



X5500-X5700 Plaskett. 



X6250-X6350 Dyson. 



2. That within these regions the selection 

 of lines be made with a view to the inclusion 

 of a considerable number of elements, particu- 

 larly such as are of very high or very low 

 atomic weight, and also the enhanced and the 

 arc lines of the same element. 



3. That an agreement be made upon the 

 latitudes to be observed. 



After considerable discussion the committee 

 decided to recommend the following points of 

 heliographic latitude : 0°, 15°, 30°, 45°, 60°, 75°. 



4. That an especial attempt be made to se- 

 cure observations in the highest latitudes, par- 

 ticularly between 75° and 90°. 



One or two of the observers present ex- 

 pressed their willingness to attempt deter- 

 minations at latitudes 80° and 85°. 



5. That a short list of selected lines be em- 

 ployed by all of the observers in common, the 

 results to serve as a check upon instrumental 

 or personal errors, and that a list of the points 

 of latitude to be observed accompany this list. 



The committee selected for this purpose the 

 portion of the spectrum between A4220 and 

 A4280, and the three points of latitude 0°, 30° 

 and 60°. The secretary was authorized to 

 choose a list of lines and forward it to the 

 various observers for approval. 



That an attempt be made to secure at least 

 one independent series of observations in each 

 of the solar hemispheres with a view to de- 

 termining a possible difference in the rate of 

 rotation. 



Several observers expressed their willingness 

 to undertake such observations of this char- 

 acter as the construction of their instruments 

 would permit. 



