144 Royal Institution : — 



The tremendous atmosphere, which apparently the spectroscope 

 had now proved to be a cool absorbing one, was supposed to be 

 indicated during eclipses by a halo of light called the "Corona," in 

 which corona the red flames are visible. Now as the red flames are 

 always observed to give out more light than the corona, they were 

 probably hotter than it ; and reasoning thus on the matter with my 

 friend Dr. Balfour Stewart one day, we came to the conclusion that 

 they were most probably masses of glowing gas. 



Now this being so, the spectroscope could help us, and in this wrj. 



The light from solid or liquid bodies, as you all I am sure know, 

 is scattered broadcast, so to speak, by the prism into a long band of 

 light, called a continuous spectrum, because from one end of it to 

 the other the light is persistent. 



The light from gaseous and vaporous bodies, on the contrary, is 

 most brilliant in a few channels ; it is husbanded, and, instead of 

 being scattered broadcast over a long band, is limited to a few lines 

 in the band — in some cases to a very few lines. 



Hence, if we have two bodies, one solid or liquid and the other 

 gaseous or vaporous, which give out exactly equal amounts of light, 

 then the bright lines of the latter will be brighter than those parts 

 of the spectrum of the other to which they correspond in colour or 

 refrangibility. 



Again, if the gaseous or vaporous substance gives out but few lines, 

 then, although the light which emanates from it may be much less 

 brilliant than that radiated by a solid or liquid, the light may be so 

 localized, and therefore intensified, in one case, and so spread out, 

 and therefore diluted, in the other, that the bright lines from the 

 feeble-light source may in the spectroscope appear much brighter 

 than the corresponding parts of the spectrum of the more lustrous 

 solid body. Now here comes a very important point : supposing 

 the continuous spectrum of a solid or liquid to be mixed with the 

 discontinuous spectrum of a gas, we can, by increasing the number 

 of prisms in a spectroscope, dilute the continuous spectrum of the 

 solid or liquid body very much indeed, and the dispersion will not 

 seemingly reduce the brilliancy of the lines given out by the gas ; 

 as a consequence, the more dispersion we employ the brighter re- 

 latively will the lines of the gaseous spectrum appear. 



The reason why we do not see the prominences every day in our 

 telescopes is that they are put out by the tremendous brightness of 

 our atmosphere near the sun, a brightness due to the fact that the 

 particles in the atmosphere reflect to us the continuous solar spec- 

 trum. There is, as it were, a battle between the light proceeding 

 from the prominences and the light reflected by the atmosphere, and, 

 except in eclipses, the victory always remains with the atmosphere. 



You will see, however, in a moment, after what I have said, that 

 there was a possibility that if we could bring a spectroscope on the 

 field we might turn the tide of battle altogether, assuming the 

 prominences to be gaseous, as the reflected continuous spectrum 

 might be dispersed almost into invisibility, the brilliancy of the pro- 

 minence-lines scarcely suffering any diminution by the process. 



