On the Chief Line in the Spectrum of the Nebulae. 197 



identification of it with the low-temperature magnesium fluting near 

 500, an origin that seemed most probable from my experiments on 

 the spectra of meteorites. The fact that one or two published obser- 

 vations have now been practically withdrawn does not affect the 

 main issue in the faintest degree. 



Whatever the chemical origin of the line, the historical statement 

 I have just given affords good grounds for believing that it is certainly 

 a remnant of a fluting. 



V. CONCLUSION. 



The facts recorded in this paper seem to me to demonstrate con- 

 clusively that the line under discussion is due as the induction 

 suggested to magnesium. 



High dispersion has been employed, and we now know that the line 

 seen in the meteoritic glows is truly the remnant of the magnesium 

 fluting. We further know that the nebula line is coincident with the 

 edge of the magnesium fluting when the two are compared with a 

 four-prism spectroscope and a high magnifying power, both nebula 

 and magnesium being observed under absolutely the same conditions. 

 Even if we accept Dr. Hogging's observation of 1868, the nebula line 

 only differs in position from the magnesium fluting by a quarter of 

 the distance between the D lines, and we know that many sources of 

 error may explain that difference. 



Finally, many observations, both new and old, show that the nebula 

 line resembles the first maximum of the magnesium fluting in having 

 a fringe on its more refrangible side, and I have shown that the 

 spectrum of magnesium may be observed under such conditions that 

 only the first maximum and its fringe are visible. 



The discussion of the other lines is reserved for a further communi- 

 cation, as the work connected with them is not yet completed. 



With regard to the concluding part of Dr. and Mrs. Huggins's 

 paper, I have recently sent in communications to the Royal Society 

 from which it will be gathered how independent the meteoritic hypo- 

 thesis is of the visible radiation of magnesium in meteorites at the 

 temperature of nebulae . But whether the line referred to in this 

 paper be due to magnesium or not, I am glad to find that Dr. Huggins 

 has so far accepted the views which I have recently put forward 

 as to admit in the paper under reply that the nebulae may 

 "represent an early stage in the evolutionary changes of the 

 heavenly bodies," and that they may stand at or near tbe beginning 

 of the evolutionary cycle so far as we can know it;* whereas he 

 formerly held that " the nebulae which give a gaseous spectrum 

 are systems possessing a structure, and a purpose in relation to 

 * ' Roy. Soc. Proc.,' vol. 46, p. 59. 



