11 Publications of the Lick Observatory, 13, 12, 1918.
12 Hβ is brighter than N2. Patches with similar spectra are often found in the arms of late-type spirals—N.G.C. 253, M 33, M 101. The typical planetary spectrum, where Hβ is fainter than N2, is found in the rare cases of apparently stellar nuclei of spirals; for instance, in N.G.C. 1068, 4051, and 4151. Here also the emission spectra are localized and do not extend over the nebulae.
13 Monthly Notices. 74, 699, 1914.
14 Annalen der Wiener Sternwarte, 20, 1907.
15 Astronomische Nachrichten, 214, 425, 1921.
16 Publications of the Lick Observatory, 13, 1918.
17 Since C is constant for all nebulae in a given class, the linear relation between Δ log d and C for the different classes is something more than a mere geometrical relation arising from the observed equality of the mean mT in the various classes.
18 This is apparent even among the observed classes. Referring to formula (3), mT + 5 log b will be constant in so far as Ce + 5 log (1 – e) is constant. The following table indicates that the latter term is approximately constant throughout the sequence of elliptical nebulae. The values of Ce were read from the smooth curve in Fig. 6.
e Ce 5 log (1 – e) C0 Res.
0 10.30 0.0 10.30 –0.14
1 10.65 – .23 10.42 – .02
2 11.00 .48 10.52 + .10
3 11.35 0.78 10.57 + .13
4 11.70 1.11 10.59 + .15
5 12.05 1.50 10.55 + .11
6 12.40 1.99 10.41 – .03
7 12.75 –2.62 10.13 –0.31
Mean 10.44 0.12
19 Mt. Wilson Contr., No. 191; Astrophysical Journal, 52, 162, 1920.
20 Pease, Mt. Wilson Comm., No. 51; Proceedings of the National Academy of Sciences, 4, 21, 1918.
21 Pease, Mt. Wilson Comm., No. 32: ibid., 2, 517, 1916.
22 Astrophysical Journal, 55, 406, 1922.
23 Monthly Notices, 82, 133, 1922.
24 Astronomical Journal, 28, 75, 1914.
25 Mt. Wilson Contr., No. 297; Astrophysical Journal, 62, 168, 1925.
26 The latest and most reliable results bearing on the distribution of faint (hence apparently distant) nebulae are found in Seares’s revision and discussion of the counts made by Fath on plates of the Selected Areas with the 60-inch reflector. When the influence of the cluster in Virgo is eliminated the density appears to be roughly uniform for all latitudes greater than about 25°.
27 Monthly Notices, 78, 3, 1917.
28 Haas, Introduction to Theoretical Physics, 2, 373, 1925.

Transcriber’s Notes

Text notes:

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  6. The original printed text is available from HathiTrust at:
    https://hdl.handle.net/2027/uc1.b3805680 (see pg 353).
  7. The outline “CLASSIFICATION OF NEBULAE” starting on page 3 lists N.G.C. 2117 as a type E7 nebula. The version of this paper printed in Contributions from the Mount Wilson Observatory No. 324 lists N.G.C 3115. Otherwise the papers are essentially identical.