SECTIONAL TRANSACTIONS.—A. 351 
some of the components displaced to the violet agreeing with those found 
earlier from the absorption spectrum. Forbidden lines appear, notably of 
[O1], including the green auroral line, of [Feir] and later of [O1t), the 
well-known nebular lines. The final spectrum is that of a Wolf-Rayet star, 
broad bright bands, suggesting the continued emission of gases. A spectro- 
scopic examination of the growing disc round the nova shows that different 
parts of the bright bands come from different portions of the envelope. 
In the case of N Pictoris 1925, the nucleus of the star became multiple 
and the spectra suggest.in general jets or streams of gas rather than spherical 
shells. 
Prof. W. H. McCrea.—Problems of the atmospheres of nove (11.0). 
Theoretical work on the motion of the outer layers of a nova and of gases 
ejected by it; propagation of radiation, and radiation pressure, in the 
moving gases ; ‘ diffusion drag ’ of the gases on each other. 
Mr. E. G. WiLL1ams.—The photometry of new stars (11.20). 
Photometric measurements give important additional information about 
nove. ‘The measurements are of three types, as follows : 
(1) Magnitude observations—These indicate that in a typical nova the 
light flux increases by about.a hundred-thousand fold at the outburst. 
When in addition the colour and distance are known it is possible to estimate 
the amount of energy liberated. 
(2) Energy distribution data for the continued spectrum—When we know 
this we can find the ‘ colour temperature’ of the star. For R S Ophiuchi 
1933 this was found to be 4,000°, a low value which may be explained by 
selective scattering of the star’s light in space. Nova Herculis, however, 
appears to have hada colour temperature of about 10,000°, which is what 
might be expected from the type of its spectrum. 
(3) Intensity-distribution measures for absorption lines and emission bands in 
the spectrum.—A great deal may be learnt from study of such contours. We 
may note here that the shape of the several bright bands, due to hydrogen, 
conforms with the ejection hypothesis ; in fact, it is possible, on certain 
assumptions, to derive from them the velocity distribution of the hydrogen 
-atoms. Also, measures of the intensity of undisplaced absorption lines, due 
to ionised calcium atoms scattered in interstellar space, provide a very 
useful indication of the distance of the star. This method, when applied 
to R S Ophiuchi, gave a distance of over 3,000 light-years, whilst for Nova 
Herculis we find 1,200 light-years for the distance, so that the star at 
“maximum was 30,000 times as bright as the sun. 
Dr. A. B. Wyse and Mr. R. H. Stoy.—Recent nova observations 
made at the Lick Observatory, California (11.40). 
(1) The scope of the Lick observations and their relation to a proposed 
general co-operative scheme for the observation of nove. 
__ (2) A summary of the more conspicuous changes in the spectrum of 
Nova Herculis since the beginning of April 1935, the time of its rapid 
diminution in brightness, with special attention to the behaviour of the 
forbidden emissions, the permitted oxygen and nitrogen emissions, and to 
the continuous spectra. 
(3) On some recent observations in the spectra of the gaseous nebule of 
‘some emissions, previously observed in the later stages of certain nove. 
N 
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