CHROMOSPHERE AND SOLAR PROMINENCES. 391 



is soon reached beyond which further widening is disadvantageous. 

 The higher the dispersive power of the spectroscope the wider the slit 

 that can be used, and the larger the protuberance that can be exam- 

 ined as a whole. 



Fig. 1. 



Huggins's First Observation of a Prominence in fuxl Sunshine. 



Mr. Huggins's first successful observation of the form of a solar 

 protuberance was made on February 13, 1869. Fig. 1, copied from 

 the Proceedings of the Royal Society, presents his delineation of 

 what he saw. As his instrument had only the dispersive power of 

 two prisms, and included in its field of view a large portion of the 

 spectrum at once, he found it necessary to supplement its powers by 

 using a red glass to cut off stray light of other colors, and by insert- 

 ing a diaphragm at the focus of the small telescope of the spectroscope 

 to limit the field of view to the portion of the spectrum immediately ad- 

 joining the C line. With the instruments now in use, these precautions 

 are seldom necessary. 



Fig. 2. 



Spectroscope, with Train op Prisms. 



It may be noticed, in passing, that Mr. Huggins had previously 

 (and has subsequently) made many experiments with different absorb- 

 ing media, in hopes of finding some substance which, by cutting off all 

 light of other color than that emitted by the prominences, should ren- 

 der them visible in the telescope ; thus far, however, without success. 



The spectroscopes used by different astronomers for observations 

 of this sort differ greatly in form and power. Fig. 2 represents the 



