590 
ASTRONOMY: W. H. WRIGHT 
This research has been supported by a grant of three hundred dollars 
from the Warren Fund of the American Academy of Arts and Sciences, 
and for this aid we wish to express our indebtedness. 
^ Cambridge University Press. 
^Ann. Physik, Leipzig, Ser. 4, 20, 237-68, 606-18 (1906); Zs. physik. Chem., Leipzig, 
64, 686 (1908); 84, 410 (1913). 
^ 18 papers in /. Amer. Chem. Soc, 30, 33, 35. 
^J. Amer. Chem. Soc, 33, 1060 (1911). 
^Richards and Coombs, Ibid., 37, 1656-76 (1915); these Proceedings, 1, 404 (1915). 
'Ann. Physik., Ser. 4, 9, 434 (1902). 
OUTLINES OF A PROPOSED SYSTEM OF CLASSIFICATION OF 
THE NEBULAE BY MEANS OF THEIR SPECTRA* 
By W. H. Wright 
UCK OBSERVATORY, UNIVERSITY OF CALIFORNIA 
Presented to the Academy, October 22, 1915 
This paper may properly be considered a continuation of one pre- 
viously published in these Proceedings, 1, 266 (1915). In that article 
the opinion is expressed that the behavior of the line 4686A might serve 
as the basis of a classification of the nebulae. The notion will be dis- 
cussed here in greater detail. About eleven of the planetary nebulae 
have been studied with a fair degree of completeness, and while this 
number is too low to afford the most secure basis for broad generaliza- 
tions, the observations seem to point the way to a rational system of 
classification of these objects on the basis of their spectra. 
In figure 1 are reproduced the spectra of nine planetary nebulae 
and the great nebula in Orion. As stated in the earlier paper the method 
adopted for observing the spectra of such nebulae consists in placing the 
slit of the spectrograph directly across the image. In this way the 
length of a spectral line is made to furnish a measure of the extent of 
the occurrence of the emitting material in the nebula. 
The first spectrum shown is that of N. G. C. 7027. This nebula con- 
sists of two nuclei, of unequal brightness, surrounded by fainter nebulos- 
ity. In photographing the spectrum the slit was placed in the line 
of the two nuclei. The spectrum shows the nebula to be unusually homo- 
geneous. Some of the fainter lines appear to be short but that is prob- 
ably merely the result of their faintness, as they are no shorter than the 
* This and the following paper contains, in abbreviated form, the substance of one 
read before the eighteenth (Pacific Coast) meeting of the American Astronomical Society, 
under the title: The spectra of the gaseous nebulae and some points of correspondence be- 
tween them and other celestial spectra. 
