1 J 8 Royal Institution : — 



(4) That there are bright lines in the solar spectrum itself. 



All these are facts which indicate that the absorption to which the 

 reversal of the spectrum and the Fraunhofer lines are due takes place 

 in the photosphere itself or extremely near to it, instead of in an 

 extensive outer absorbing atmosphere. And this conclusion is 

 strengthened by the consideration that otherwise the newly disco- 

 vered bright lines of hydrogen should themselves show traces of ab- 

 sorption on KirchhofFs theory ; but I shall show you presently that, 

 so far from this being the case, they appear bright actually in the very 

 centre of the disk; and, moreover, the vapours of sodium, iron, mag- 

 nesium, and barium are often bright in the chromosphere, showing 

 that they would always be bright there if the vapours were always 

 present, as they should be on Kirchhoff's hypothesis ; so that we 

 may say that the photosphere plus the chromosphere is the real at- 

 mosphere of the sun, and that the sun itself is in such a state of 

 fervid heat that the actual outer boundary of its atmosphere (z. e. the 

 chromosphere) is in a state of incandescence. 



With regard to the line in the orange I have nothing yet to tell. 

 Dr. Frankland and myself are at the present moment working upon it. 



I have next to take you a stage lower into the bowels, not of the 

 earth, but of the sun. 



As a rule, the chromosphere rests conformably, as geologists would 

 say, on the photosphere ; but the atmosphere (as I have just defined 

 it) is tremendously riddled by convection-currents ; and where these 

 are most powerfully at work, the upper layers of the photosphere are 

 injected into the chromosphere. Thus I have observed the lines due 

 to the vapour of sodium, magnesium, barium, and iron in the spec- 

 trum of the chromosphere, appearing there as very short and very 

 thin lines, generally much thinner than the black lines due to their 

 absorption in the solar spectrum. 



These injections are nearly always accompanied by the strangest 

 contortions of the hydrogen-lines, of which more presently. Some- 

 times during their occurrence the chromosphere seems full of lines, 

 those due to the hydrogen towering above the rest. 



At the same time we have tremendous changes in the prominences 

 themselves, which I have recently been able to see in all their beauty. 

 I have attempted to accomplish this in the first instance by means 

 of an oscillating slit ; but hearing that Mr. Huggins had succeeded 

 in doing the same thing by means of absorptive media, using an open 

 slit, it struck me at once that an open slit was quite sufficient ; and 

 this I find to be the case. By this method the smallest details of the 

 prominences and of the chromosphere itself are rendered perfectly 

 visible and easy of observation, and for the following reason. As you 

 already know, the hydrogen Fraunhofer lines (like all the others) ap- 

 pear dark, because the light which would otherwise paint an image of 

 the slit in the place they occupy is absorbed ; but when we have a pro- 

 minence on the slit, there is light to paint the slit ; and as, in the case 

 of any one of the hydrogen-lines, we are working with light of one 

 refrangibility only, on which the prisms have no dispersive power, 

 we may consider the prisms abolished. Further, as we have the 



