312 Royal Society. 



edges. In the more refrangible part of the spectrum, probably not 

 far from G of the solar spectrum, glimpses were obtained of a fourth 

 and faint bright line. At the extreme end of the visible part of 

 the less refrangible end of the spectrum, about C, appeared a line 

 brighter than the normal relative brilliancy of this part of the spec- 

 trum. The brightness of this line, however, was not nearly so marked 

 in proportion to that of the part of the spectrum where it occurs, 

 as was that of the lines in the green and blue *. 



General Conclusions. — It is difficult to imagine the present phy- 

 sical constitution of this remarkable object. There must be a pho- 

 tosphere of matter in the solid or liquid state emitting light of all 

 refrangibilities. Surrounding this must exist also an atmosphere of 

 cooler vapours, which give rise by absorption to the groups of dark 

 lines. 



Besides this constitution, which it possesses in common with the 

 sun and the stars, there must exist the source of the gaseous spectrum. 

 That this is not produced by the faint nebulosity seen about the star 

 is evident by the brightness of the lines, and the circumstance that 

 they do not extend in the instrument beyond the boundaries of the 

 continuous spectrum. The gaseous mass from which this light ema- 

 nates must be at a much higher temperature than the photosphere 

 of the star ; otherwise it would appear impossible to explain the great 

 brilliancy of the lines compared with the corresponding parts of the 

 continuous spectrum of the photosphere. The position of two of 

 the bright lines suggests that this gas may consist chiefly of hy- 

 drogen. 



If, however, hydrogen be really the source of some of the bright 

 lines,the conditions under which the gas emits the light must be dif- 

 ferent from those to which it has been submitted in terrestrial ob- 

 servations ; for it is well known that the line of hydrogen in the 

 green is always fainter and more expanded than the brilliant red line 

 which characterizes the spectrum of this gas. On the other hand, 

 the strong absorption indicated by the line F of the solar spectrum, 

 and the still stronger corresponding lines in some stars, would indi- 

 cate that under suitable conditions hydrogen may emit a strong lu- 

 minous radiation of this refrangibilityt. 



The character of the spectrum of this star, taken together with its 

 sudden outburst in brilliancy and its rapid decline in brightness, sug- 

 gest to us the rather bold speculation that, in consequence of some 



* The spectra of the star were observed again on the 17th, the 19th, the 21st, 

 and the 23rd. On these evenings no important alteration had taken place. On 

 the 17th and succeeding evenings, though the spectrum of the waning star was 

 fainter than on the 16th, the red bright line appeared a little brighter relatively 

 to the green and blue bright lines. On the 19th and 21st the absorption lines about 

 b were stronger than on the 16th. From the 16th the continuous spectrum di- 

 minished in brightness more rapidly than the gaseous spectrum, so that on 

 the 23rd, though the spectrum as a whole was faint, the bright lines were bril- 

 liant when compared with the continuous spectrum. 



t On the dependence of the relative characters of the bright lines of hydrogen 

 upon conditions of pressure and temperature see Plucker and Hittorf, Phil. Trans. 

 18'J5. p. 21 



