MOUNT WILSON SOLAR OBSERVATORY. 281 



hoods or arches of smoke on one side of the axis (the side toward 

 which the inner edges of the paddles are moving) contrasting markedly 

 with the stream-lines on the opposite side, which are at right angles 

 to the axis at the center and become more and more convex toward 

 the two ends. Reference has already been made to the apparent 

 presence of similar structure in the hydrogen flocculi (p. 256). 



The difference in the form of the stream-lines at different levels can 

 be seen by illuminating the smoke at any desired height above the 

 water with a horizontal slit of sunlight. By placing this slit in a ver- 

 tical plane, the smoke is shown flowing into the "spots," as in Slocum's 

 photographs of prominences near sun-spots at the limb. Although 

 purely qualitative, the experiments are very interesting and suggestive, 

 and will be developed in a form more closely corresponding with solar 

 conditions. 



COMPUTING DIVISION. 



The Computing Division has remained throughout the year under 

 the direction of Mr. Seares. 



Miss Bray ton was appointed to the division on June 1, and for the 

 present will divide her time between the work in stellar spectroscopy 

 and photometry. 



Miss Burns joined the division on July 5, and is at present engaged 

 in the work of stellar photometry. 



Miss Burwell has continued her work in connection with the investi- 

 gations in stellar spectroscopy. She has measured 700 spectrograms 

 and has given a large amount of time to the compilation of the data 

 for the radial velocities of 500 stars appearing in Mount Wilson Con- 

 iribution No. 105, besides having measured several plates of nebular 

 spectra for Mr. Pease. She has also given much time to the prepara- 

 tion of the ''flash" spectrum results appearing in Mount Wilson Con- 

 tribution No. 95. 



Miss Davis joined the division on September 14, and has been asso- 

 ciated mainly with the work in stellar spectroscopy. She has measured 

 and reduced 150 spectrograms and has made the least-squares reduc- 

 tions connected with the determination of stellar parallaxes. 



Mrs. Fretter has continued with the work of the physical laboratory. 

 Twenty Zeeman photographs have been measured and reduced, and 

 the results from all of the earlier plates have been brought into final 

 form. A number of pressure plates have also been measured, and Hke- 

 wise various interferometer plates. Much measurement and recording 

 was done with the Hartmann microphotometer in the investigation of 

 the Stark effect, and a large number of intensity curves registered with 

 the Koch microphotometer have also been measured. 



Until the date of her resignation on March 1, Miss High continued 

 her work in stellar photometry. 18 Selected Area plates, 2 long 



