274 MILLER— SPROUL OBSERVATORY ECLIPSE EXPEDITION. 



different scales. The plates were reduced to the same scale by 

 measuring the diameter of the moon's shadow on each plate and 

 finding the ratio of these two measured diameters. The center of 

 the sun for each of the three plates was found and plotted on each 

 plate, the necessary corrections being made for different times of 

 exposure, parallax, etc. The conspicuous prominences were as fol- 

 lows : Two small quiescent northern prominences, a large north- 

 western quiescent prominence, a large eruptive prominence in the 

 southwest called from its shape the Skeleton prominence, and a 

 large northeastern prominence called the Pyramid prominence. 



Around the eruptive prominences there are series of arches de- 

 scribed so well in the preceding paper by Professor Lampland that 

 further comments are unnecessary. 



Following my suggestion Aliss Margaret E. Powell, a graduate 

 student at Swarthmore College, made a study of these plates. All 

 the measures which I shall give presently were made by Aliss 

 Powell. We selected three arches which seemed definite enough to 

 measure. 



The measures were made in this way. A point is selected which 

 can be certainly identified on each of the three plates. Choosing a 

 line through this point and the center of the sun as an initial line 

 and the center of the sun as origin, we may locate any point in the 

 streamer by its polar coordinates 6 and p. The arches were about 

 equally well defined in the Lick plates and each of the two Sproul 

 plates. The polar coordinates of a series of points on an arch were 

 measured on the Lick plate, then setting off the same series of vec- 

 torial angles on a Sproul plate and measuring the radii vectors, we 

 obtained the polar coordinates of the corresponding points on the 

 Sproul plate. If these radii vectors are the same the arch is un- 

 changed, but if they are different (assuming the measures are ex- 

 act) the shape or the position of the arch has changed. 



Miss Powell measured three arches in this way. The accom- 

 panying tables give the details of the measures. The vectorial an- 

 gle is given by 6. The cjuantities p and p are the radii vectors in 

 inches measured on the Sproul and Lick plates respectively and 

 reduced to the scale of the Sproul plate. 



The eclipse at Brandon occurred twenty-five minutes after it 



