MILLER— SPROUL OBSERVATORY ECLIPSE EXPEDITION. 277 



The Skeleton Prominence and its arches cover 37.5° along the 

 margin of the sun, the highest arch is 108,000 miles ; this means that 

 if these arches are a mechanical effect that a volume of gas of more 

 than 2,540.470,000 millions of cubic miles has been affected. 



There are other things suggesting changes of form, but hardly 

 such things as one could measure. It is not unusual for streamers 

 to issue from small projections on the prominences. From each of 

 three tips of the Southeastern Prominence there issues streams each 

 of which assume the approximate form of the arches above them. 



In interpreting these measures, one must not be unmindful of 

 the difficulties of these measures and the consequent uncertainty. 

 The streamers themselves are somewhat indefinite objects to meas- 

 ure. An error in plotting the center of the sun on the plates might 

 cause the differences of p and p'. On the other hand, the measures 

 have been very conscientiously made. No one could have been more 

 painstaking than Miss Powell has been. The center of the sun was 

 plotted separately on the plate for the first and for the second meas- 

 ures. Any two series are reasonably consistent, and in one thing 

 they are very consistent — p-p', though small, is almost always posi- 

 tive. Moreover, the three prominences are so distributed about the 

 sun's limb that an error in plotting the center should have affected 

 p-p' in different ways for different arches. In my judgment these 

 measures make it probable that these arches of the corona changed 

 in the twenty-five minutes between the eclipse at Goldendale and 

 that at Brandon, and that they are going outward from the sun. 



The other study is of quite a different nature. There are in 

 every corona a number of streamers, those around the poles of the 

 sun being most conspicuous, but streamers are by no means confined 

 to these regions. In 191 1 I published a paper^ in which I assumed 

 that what we see or photograph as the^streamers of the corona are 

 projections on a plane perpendicular to the line of sight, of streams 

 of particles the motion of which is produced by ejection, by the rota- 

 tion of the sun, by the attraction of the sun and by radiant pressure 

 from the sun. At that time Director Campbell generously placed 

 at my disposal the most excellent series of long focus photographs 

 that had been made by eclipse expeditions from Lick Observatory. 



1 Astrophysical Journal, XXXIII., 4, page 303. 



