OP ARTS AND SCIENCES. 



189 



which may cause the spots of absorption often observed in the vicinity 

 of spots. 



The phenomenon of the gradual illumination of a protuberance was 

 observed in 1869, at Des Moines, Iowa, during the total eclipse of the 

 sun, by Professor William A. Rogers, who accompanied Dr. C. H. 

 F. Peters, on the Litchfield Eclipse Expedition. Professor Rogers 

 was observing a large protuberance on the sun with a 9-inch-aperture 

 refractor, when he saw several protuberances form gradually in the 

 vicinity of the large flame, and at a considerable height above the 

 chromosphere. 



The projection of the hydrogen flames on the spectrum is not a very 

 rare phenomenon during the period of maximum of sun spots, and it 

 has been observed several times. However, it may be worth while to 

 record a characteristic case of projection, accompanied with remarkable 

 changes of form, and a visible motion of the protuberance. 



On Sept. 10, 1872, at 12'' 33", I was observing a small narrow 

 flame forming an arch on the chromosphere, the height of which was 

 equal to 36". Fig. 3. Nothing remarkable was to be seen in this 

 protuberance, although it was in the vicinity of a group of spots which 

 was then very near the eastern limb of the sun ; but, two minutes later, 

 one of the extremities of the arch reposing on the chromosphere was 



FIG. 3 



FIG. 4- 



FfC. 5 



suddenly detached from the limb, springing up like a distended bow, 

 ascending in an instant to a height of 70", tlien appearing straight and 

 rigid, but twisted like a rope. Fig. 4. For a few seconds, it con- 

 tinued to ascend, at the same time growing wider; and at 12'' 37", 

 it had attained its maximum altitude of 118". It was then slightly 

 curved. Fig. o. At 12'' 43", the force which had carried it up began 

 to give way, and it then descended rapidly towards the sun, folding 



