SPECTRUM OF THE GREAT NEBULA IN ORION. 83 
intimate connection between these objects, if established by further observations, 
would place the bright-line stars first in the order of development. The D; line 
appears in the central condensation of a number of bright nebule, and with sufficient 
light would probably be seen in many of them, and this line is also predominant in 
most of the bright-line stars.” 
One of the main points of this paper is to show that the relationship indicated 
between the planetary nebule and bright-line stars also holds good for such a nebula 
as that of Orion. 
The bright lines seen in the visual spectra of the two classes of nebulee have long 
been known to be identical, and a comparison of the Westgate photographs with the 
results obtained by Professor PickERING, and the more recent work of GorHarD,* and 
of Professor CAMPBELL, at the Lick Observatory, on the spectra of the planetary 
nebulee,t has shown that the similarity also extends to the photographic region. 
The fact that some of the nebular lines were apparently coincident with lines in the 
bright-line stars, was recognized at an early stage in the reduction of the Westgate 
photographs, and in the preliminary note I wrote as follows: ‘ It is a very striking 
fact that some of the chief lines are apparently coincident, although the statement 
is made with reserve, with the chief bright lines in P Cygni, a magniticent photo- 
graph of which I owe to the kindness of Professor PICKERING; it is one of the 
Henry Draper Memorial photographs.” 
The bright lines here referred to were those of hydrogen, and lines at 4025 and 
4471. All these have since been photographed at Kensington, in the spectrum of 
P Cygni, and there is no longer any doubt as to their identity with bright lines in 
the nebula. Additional bright lines in the spectrum of P Cygni, photographed at 
Kensington, are also seen in the nebula, as shown in the following table :— 
Tasie II.—Comparison of Orion Nebula with P Cygni. 


Orion nebula. P Cygni (Kensington). 
3968 3968 H. 
4015 
4025 4025 
4035 
4101 4101 Hs 
| 4147 
| 4340 4340 H, 
| 4471 AAT 1 
4715 A715 
4840 
486 | 4361 He 
4.923 4923 



* © Astr, and Ast.-Phys.,’ 1893, p. 51. 
+ Ibid., p. 276. 
M 2 
