SOLAR PKOMINENCES IN MOTION — McMATH 129 



vertically through the center of the picture, as shown in A. This 

 bright area expanded, and another, beginnhig apparently somewhat 

 nearer the chromosphere, developed to give the light distribution 

 illustrated in B. 



The start of observations on August 25 found the prominence in 

 the eruptive stage, with the light pattern much more pronounced. 

 In plate 6, C and Z?, the localized illumination has the appearance 

 of a searchlight beam, and this impression is enhanced by the promi- 

 nence materia] brightening as it moves into the "spotlight" and then 

 leaving its brilliancy behind as it moves on out again. Tliis effect 

 continued until, near the end of the scene, the prominence material 

 had all moved along the streamer trajectories to disappear into the 

 chromosphere. In order to include all the extended activity within 

 the area of the film, the scale of the image was diminished to 50 

 percent, and later to 15 percent, of the size of the original image. 

 The maximum extension of the prominence was nearly 400,000 km., 

 and it reached a level about 240,000 km. above the sun. This scene 

 illustrates many characteristic motions of quasi-eruptive promi- 

 nences, and discloses a new phenomenon of light distribution which 

 may prove to be additional evidence in our search for the now 

 hidden reasons for prominence behavior; or, on the other hand, it 

 may prove to be another problem added to the number already in- 

 volved in the study of solar physics. 



These records of solar prominences in motion have been treated 

 here in a purely descriptive manner, but we should emphasize their 

 value as records of solar phenomena which can, at will, be reenacted 

 for study. Their greatest value, however, lies in the fact that each 

 scene forms an uninterrupted, accurately timed series of observations. 

 This mass of scientific data is contributing to our knowledge of the 

 true characteristics of motions in the outer surface of the sun. 



In conclusion, I wish to acknowledge my indebtedness to H. E. 

 Sawyer and Dr. O. C. Mohler, of our staff. They have taken many 

 of the pictures shown in connection with this lecture, and in addition 

 have collaborated in the preparation of this paper. The plates 

 accompanying this paper were prepared by Sawyer and J. T. Brodie, 

 of our staff. I most especially wish to thank Dr. Abbot, Secretary 

 of the Smithsonian Institution, for the honor and privilege of giving 

 the James Arthur lecture here in Washington this month of January 

 1940. 



