ASTRONOMY: CAMPBELL AND MOORE 
129 
Ancient man beginning with one important and two minor free metals 
acquired by heat tin and iron giving him an acquaintance with five 
metals. Modern man has freed 52 more, knows 85 elemental substances 
and predicts the eventual discovery of several others. 
iRollain, A., Scories de fer antehistoriques., Bull. Soc. Anth., Paris, 4 s, 1899, p. 318. 
Discussion by M. Lionel Bonnem^re. 
ON THE OBSERVED ROTATIONS OF A PLANETARY NEBULA 
By W. W. Campbell and J. H. Moore 
UCK OBSERVATORY. UNIVERSITY OF CAUFORNIA 
Received by the Academy, February 9, 1916 
The geometric forms of certain classes of nebulae are such as to sug- 
gest that they are in rotation about axes passing through their effective 
centers. We refer especially to the spiral nebulae and to those so-called 
planetary nebulae which are of ring, circular, or elliptical form with 
relatively condensed or stellar nuclei. 
In the latter part of 1915 we tested several planetary nebulae by means 
of observations made with the Mills 3-prism spectrograph and obtained 
positive evidences of rotation, as Doppler-Fizeau effects. 
The planetary nebula No. 7009 in Dreyer's New General Catalogue, 
right ascension 20h. 58m., illustrated herewith, was submitted to the 
test of four spectrograms. In each case the sHt of the spectrograph 
was placed centrally across the image of the nebula and made slightly 
longer than the diameter of the elliptical outline of the nebula, and the 
condensed nucleus of the nebula was kept central in the slit during the 
exposures. In two exposures the slit was placed upon the longer axis 
of the nebular image, parallel to the slender rectangle drawn above the 
nebula in the illustration to represent the slit in length and direction. 
In a third exposure the slit was placed east and west across the image. 
On these spectrograms the bright lines of nebulium (4959 and 5O07A) 
and of hydrogen (H Beta), comprising the recorded nebular spectrum, 
were inclined to the ^zero' direction, as indicated by the comparison 
spectra of hydrogen, helium and titanium on the same plates. This in- 
clination of the lines is illustrated (exaggerated) by the direction of the 
bright line on the diagram of the slit in the upper part of the figure. 
The section of the lines corresponding to the western parts of the nebula 
are displaced to the violet, and the sections corresponding to the eastern 
parts, to the red. Interpreted as Doppler-Fizeau effects, the western 
parts of the nebula are approaching us and the eastern parts are reced- 
ing from us by virtue of the rotation of the nebula. The fainter ends 
