SPECTRUM OF THE GREAT NEBULA IN ORION. 81 
Coming now to the region of the nebula about the stars of the trapezium, it will be 
seen from fig. 8 that the bright lines are considerably widened where they intersect 
the spectra of the trapezium stars. In this case the hydrogen line at \ 4340 is 
widened very little on the less refrangible side, while, on the more refrangible side, 
the widening is nearly as great as its own breadth. Further, on each side of the line 
there is a decided break in the continuous spectrum of the stars, giving the appearance 
of a broad absorption band, with the bright hydrogen line running through it. This 
appearance is almost exactly reproduced at H;. 
Dr. Draper* appears to have noticed a peculiarity in the hydrogen lines where 
they crossed the spectra of the trapezium stars in his photographs of 1882. He says :— 
“The hydrogen line near G, wave-length 4340, is strong and sharply defined ; that 
at h, wave-length, 4101, is more delicate ; and there are faint traces of other lines in 
the violet. Among these lines there is one point of difference, especially well shown 
in a photograph where the slit was placed in a north and south direction across the 
trapezium; the H, line, \ 4340, is of the same length as the slit, and, where it 
intersects the spectrum of the trapezium stars, a duplication of effect is noticed. If 
this is not due to flickering motion in the atmosphere, it would indicate that 
hydrogen gas was present even between the eye and the trapezium. 
“ T think the same is true of the H; line, \ 4101.” 
The line at 500 is only feebly impressed in the neighbourhood of the trapezium 
stars, and no reversal is visible. 
It is clear, therefore, that the spectrum of the nebula varies very considerably in 
different regions. 
Y. Discussion oF RESULTS IN RELATION TO THE MeEtTEorRITIC HYPorHEsts. 
In my paper, “On the Photographic Spectra of some of the Brighter Stars,” com- 
municated to the Royal Society in November, 1892,t I made reference to the spectra 
of nebulee in relation to the meteoritic hypothesis. The statements were based upon 
an incomplete reduction of the photographs of the spectrum of the Orion nebula, and 
I now proceed to show how the hypothesis bears the test when the final reductions 
are considered. 
On the hypothesis :— 
(a) The normal spectrum of the nebule, including planetary nebule, should have 
a complex origin. 
(b) The bright-line stars are simply nebulee further condensed. 
(c) With further condensation a group of stars of increasing temperature, with 
spectra consisting of mixed bright and dark flutings, is produced. 
(d) Still further condensation results in a group of stars of increasing temperature, 
with spectra of dark lines, differing from the solar spectrum. 
% ¢ Amer. Journ. of Sci.’ (3), vol. 23, p. 339, 1882. 
+ ‘Phil. Trans.,’ A, 1898, vol. 184, p. 713. 
MDCCCXCV.—A, M 
