DIASTROPHISM AND THE FORMATIVE PROCESSES 147 



cerned; and (2) that this matter received successive strong outward 

 impulses, amounting in the last case to an increase of projection 

 no less than 126 . 9 km. per sec. It is to be noted that this impulse 

 was received after the arch had reached a height of 290,000 km. 

 above the sun's surface. It is further to be observed that at 

 the time the projections became invisible, in each case, more than 

 half the restraining power of the sun, measured in terms of velocity, 

 had been overcome. In the second case, the speed, at the time the 

 projected matter became invisible, was competent to overcome more 

 than half the remainder of the sun's restraining power. 



Pettit finds data confirming these strange modes of movement, 

 but of a less conclusive kind, in the photographs of certain other 

 prominences already taken. He regards this singular mode of 

 ascent by sudden accessions of speed with uniform motion between 

 as the common one. However, none of these cases are sufiiciently 

 complete in themselves to show the full nature of these remarkable 

 phenomena, for the ejected material passed out of sight while still 

 under the highest observed uniform motion, and the extent to 

 which this uniform motion may have continued and what followed 

 it are left undetermined. 



While further disclosures are required, and can only be awaited 

 with eagerness, enough has already been revealed to give radical 

 suggestiveness to these phenomena. They show that even at 

 present and without obvious external stimulus there come into 

 action, in addition to the internal eruptive forces, projectile forces 

 of a high order which became effective at horizons high above the 

 sun's surface, and that the combined projectile effect of these had 

 overcome a large fraction of the restraining power of the sun 

 before they passed out of sight. 



Still another feature of the solar eruptions of May 29 and July 

 15, 1919, is scarcely less remarkable than their singular increments 

 of motion. The projections on each of the two dates took the 

 form of arches whose centers, at first low, rose impulsively into the 

 forms shown on Plates I and II. The arch of May 29 was transverse 

 to the sun's equator and had a chord of 584,000 km.; that of July 

 15 stood obliquely across the equator and had a chord of 363,000 

 km. as seen in perspective. The two ends of the arches appear 



