128 ANNUAL REPORT SMITHSONIAN mSTITUTION, 1940 



with the sunspot-type prominence of September 21, 1939, is illus- 

 trated in plate 5. In both prominences shown, all detectable mo- 

 tions were downward along the streamers, and downward from the 

 crests of the loops along both branches and into the chromosphere. 

 The relative intensities, or relative densities, of material in different 

 parts of the loops were continually changing while the paths of 

 motion persisted. These prominences exhibited a characteristic 

 gradual increase in height during the time of observation. Because 

 of the great predominance of downward motions, this general growth 

 of the entire phenomenon would seem to be an extension of activity, 

 rather than any sort of material expansion. Plate 5, A^ B, and 6', 

 are reproductions from the record of September 21, 1939, showing 

 the behavior of a loop formation which measured about 142,000 km. 

 in height and 170,000 km. in width at the beginning of the record, 

 and increased in over-all dimensions about 25 percent during the 

 scene. The changes in relative intensity of different parts of the 

 loop in the 24 minutes wliich intervened between A and B are quite 

 evident, and paths of motion 2 hours later are indicated in C by the 

 broken streamers. 



The prominence of September 7, 1939 (pi. 5, Z>, E^ and F), pro- 

 vided a remarkable motion-picture scene of continuous and varied 

 activity. At the beginning of the record bright knots and delicate 

 streamers cascaded downward 200,000 km. into the sun. As the 

 scene progressed, the general pattern became more intricate, includ- 

 ing a background of faint gigantic loops and many small isolated 

 condensations moving at high velocities toward the seething chromo- 

 sphere. The loop formation previously described occurred during 

 this scene and is illustrated in its later stages in plate 5, E and F. 

 The scene closed with the longest streamers extending outside the 

 field of the film, reaching somewhere beyond 240,000 km. above the 

 limb. 



Another very interesting, and perhaps the most impressive, 

 motion-picture scene of prominence activity that we have obtained 

 so far is illustrated in plate 6. This is a record of the quasi-eruptive 

 prominence of August 24 and 25, 1939, photographed in the light 

 of ionized calcium. Throughout the scene the delicate details of 

 the internal prominence structure revealed a surprising activity in 

 the behavior of the motions and the distribution of light intensities. 

 A and B are reproductions of frames photographed on August 24, 

 1939, and illustrate the form and dimensions of the prominence in 

 its "active" stage. At this stage the prominence was about 170,000 

 km. in height and extended even a greater distance along the limb. 

 Not noticeable in the reproduction, but clearly defined from the very 

 beginning of the record, is a narrow "pillar of light" that extends 



