152 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1937 



MOTIONS IN THE CORONA 



Although the shapes of the corona at spot-minimum all resemble 

 each other in having long equatorial streamers and pronounced polar 

 brushes, yet each corona has its own distinctive features with the 

 result that one corona could never be mistaken for another. In the 

 circular coronas corresponding to maximum of spots the streamers 

 shoot out at various angles differing in each eclipse. We are, therefore, 

 forced to the conclusion that changes are continually going on within 

 the corona. Beginning in 1889, attempts have been made repeatedly 

 to measure these changes. It is evident that the greater the interval 

 of time between the photographs to be compared at two stations the 

 higher will be the accuracy. A splendid opportunity was presented 

 in 1905 when the Lick Observatory established three stations, each 

 with a camera of 40-foot focus, one in Labrador, one in Spain, 

 one in Egypt. Unfortunately for the success of the scheme, it 

 was totally cloudy in Labrador, there were thin clouds in Spain, 

 and, although clear in Egypt, the definition of the photographs was 

 poor. At the American eclipse of 1918, from a comparison of 

 Lick and Swarthmore photographs, it seemed likely that motions of 

 the order of 10 miles per second were found in the coronal arches over- 

 topping prominences. However, at the eclipse of 192G, a comparison 

 of photographs made in East Africa and Sumatra revealed that, if the 

 coronal domes moved at all, the velocities were probably not greater 

 than 1 mile per second. 



Much valuable information regarding coronal disturbance was ob- 

 tained on Niuafoou Islan<l in 1930. This was the first time in the 

 liistory of eclij)ses that so much detailed structure was visible in the 

 spectral lines of the corona, this structure being made possible by the 

 fine definition of the grating spectra taken without slit. A comparison 

 of all the 1930 spectrograms, but more particularly the H and K lines, 

 reveals the interesting fact that 2 years after sunspot maximum the 

 sun was in a condition of great activity on the day of the eclipse. 

 The coronal rings of the spectra and the direct photographs taken with 

 the 63-foot tower telescope show prominences completely circling the 

 sun. Comparisons were also made with spectroheliograms on 4 

 successive days, taken at Mount Wilson or Kodaikanal. The 

 superb definition of the eclipse photographs showed both the promi- 

 nences and mner corona in great beauty. 



A comparison of all the photographs, the spectroheliograms \nth. 

 the eclipse plates both direct and spectrograpliic, showed that the great 

 activity of the sun was found not only at eclipse time but persisted 

 throughout the whole period of 4 days covered by the plates. The 

 direct photographs and the eclipse spectra show that the whole south- 

 east quadrant was a tremendously stormy region on the sun. The 

 center of the longest coronal streamer was situated 30° to the east of 



