146 T. C. CHAM BERLIN 



Observatory by Pettit and associates.^ These disclose motions of 

 quite an astonishing nature. Fortunately for our purposes, the 

 photographs were taken with one of the calcium Unes, and as cal- 

 cium has the atomic weight 40 and enters widely into the constitu- 

 tion of the earth body, its projection in this effective way has more 

 significance than if it were one of the Hghtest elements. The gen- 

 eral facts of the two cases are shown by Plates I and II, reproduced 

 here from Plates IV and VI of Pettit's article. Both eruptions gave 

 rise to archlike forms. The apex of each arch vanished while it was 

 still ascending, the first disappearing at a height of 760,000 km. 

 above the surface of the sun, the second at 720,000 km., that is, at 

 heights somewhat more than the radius of the sun in each case. At 

 the time of disappearance the first had an ascensive velocity of 60 

 km. per sec, the second, 163.9 km. per sec. Perhaps the most 

 remarkable features disclosed were suddenly increased rates of 

 ascent taken on at intervals, while the rates of ascent between 

 these stages of increase were essentially uniform. . Thus in the 

 eruption of May 29, there was a rise, for 50,000 km., from a point 

 1 50,000 km. above the surface of the sun at a rate of 5 . 5 km. per 

 sec, when the rate changed to 9.2 km. per sec, which was main- 

 tained for 119,000 km., when the velocity again changed to 27.9 

 km. per sec, which was held for 91,000 km., when the rate again 

 increased to 60 km. per sec, which was maintained for 230,000 

 km. and was still being held when the prominence vanished, 

 doubtless either by coohng or dispersion or both. In the eruption 

 of July 15, it was found that from 200,000 km. to 294,000 km. 

 above the sun's surface the rate of ascent of the center of the arch 

 was 37 km. per sec; at the latter height the velocity abruptly 

 increased to 163.9 km. per sec, which was held for no less than 

 426,000 km., and was still retained at the disappearance of the 

 projected mass. 



However these extraordinary phenomena are to be explained, 

 two significant things are implied: (i) that in some way the gravi- 

 tation of the sun is offset or neutrahzed sufficiently to permit 

 uniform motion, so far at least as the projected matter was con- 



I Edison Pettit, "The Great Eruptive Prominences of May 29 and July 15, 1919." 

 Astrophys. Jour., L (October, 1919), pp. 206-19. 



