132 kiloux City Academy of Science and Letters. 



occasionally they reach to much higher altitudes; while 

 the quiescent form vary in height from about 7,000 or 

 9,000 to 30,000, not infrequently to 80,000 and 100,000 

 miles, and some have attained the enormous altitude of 

 350,000 miles above the surface of the photosphere. 



The spectrum of the quiescent variety is usually 

 simple — hydrogen and helium being the principal constit- 

 uents, although magnesium and sodium are sometimes 

 present, but the eruptive prominences emit a very com- 

 plicated and interesting spectrum which consists mainly 

 of bright lines due to iron, barium, magnesium, sodium, 

 calcium, manganese and chromium. These prominences 

 are usually seen in the vicinity of sunspots, and seem 

 to be connected with them by some means. An instance 

 of a particularly brilliant prominence came under the 

 writer's attention on October 23, 1896, when a small but 

 violently agitated prominence was observed very near 

 or perhaps directly over a sunspot which was at the 

 extreme edge of the sun's eastern limb just coming into 

 view; the hydrogen lines were blazing, the Ha line 

 especially presenting a winged appearance, with jets of 

 hydrogen directed towards both ends of the spectrum, 

 indicating motion of the gases away from us and 

 towards us in the line of sight. Such disturbances usu- 

 ally change their form very rapidly; a period of fifteen to 

 twenty minutes suffices to produce changes in the 

 appearance which would hardly be recognizable by the 

 same observer. This disturbance completely subsided in 

 an hour's time. 



The enormous velocities observed in these objects 

 which often exceeds a hundred miles per second, and 

 occasionally goes beyond the critical rate of 383 miles 

 per second, which is in excess of the power of the sun's 

 gravitation to retain a substance, presents a problem' 

 which is baffling to solar physicists. Quite recently, how- 

 ever, Prof. W. Michelson has given a new explanation 

 of the displacement of spectral lines on the sun which 

 may throw new light on these objects; he shows that a 

 displacement of lines must occur when a denser mass is 

 introduced in the path of a ray of light. While this 

 theory does not supplant Doppler's principle which can- 

 not be done away with, it seems to permit of a more 



