39 o THE POPULAR SCIENCE MONTHLY. 



a telescope, be examined with a spectroscope, one might hope to see at 

 the edge of the disk the bright lines belonging to the spectrum of the 

 prominences, in case they are really gaseous. 



Mr. Lockyer and Mr. Huggins both tried the experiment as early 

 as 1867, but without success; partly because their instruments had 

 not sufficient power to bring out the lines conspicuously, but more be- 

 cause they did not know whereabouts in the spectrum to look for 

 them, and were not even sure of their existence. At any rate, as soon 

 as the discovery was announced, Mr. Huggins immediately saw the 

 lines without difficulty, with the same instrument which had failed to 

 show them to him before. It is a fact, too often forgotten, that to per- 

 ceive a thing known to exist does not require one-half the instrumental 

 power or acuteness of sense as to discover it. 



Mr. Lockyer, immediately after his suggestion was published, had 

 set about procuring a suitable instrument, and was assisted by a grant 

 from the treasury of the Royal Society. After a long delay, conse- 

 quent in part upon the death of the optician who had first undertaken 

 its construction, and partly due to other causes, he received the new 

 spectroscope just as the report of Herschel's and Tennant's observa- 

 tions reached England. Hastily adjusting the instrument, not yet 

 entirely completed, he at once applied it to his telescope, and without 

 difficulty found the lines, and verified their position. He immediately 

 also discovered them to be visible around the whole circumference of 

 the sun, and consequently that the protuberances are mere extensions 

 of a continuous solar envelope, to which, as mentioned above, was given 

 the name of Chromosphere. (He does not seem to have been aware 

 of the earlier and similar conclusions of Arago, Grant, Secchi, and 

 others.) He at once communicated his results to the Royal Society, 

 and also to the French Academy of Sciences, and, by one of the curious 

 coincidences which so frequently occur, his letter and Janssen's were 

 read at the same meeting, and within a few minutes of each other. 



The discovery excited the greatest enthusiasm, and in 1872 the 

 French Government struck a gold medal in honor of the two astrono- 

 mers, bearing their united effigies. 



It immediately occurred to several observers, Janssen, Lockyer, 

 Zollner, and others, that by giving a rapid motion of vibration or rota- 

 tion to the slit of the spectroscope it would be possible to perceive 

 the whole contour and detail of a protuberance at once, but it seems 

 to have been reserved for Mr. Huggins to be the first to show practi- 

 cally that a still simpler device would answer the same purpose. With 

 a spectroscope of sufficient dispersive power it is only necessary to 

 widen the slit of the instrument by the proper adjusting screw. As 

 the slit is widened, more and more of the protuberance becomes visible, 

 and if not too large the whole can be seen at once : with the widening 

 of the slit, however, the brightness of the background increases, so 

 that the finer details of the object are less clearly seen, and a limit 



