L89L] which produce the Phenomena of New Stars. 



445 



iow that the spectrum of the Nova can be reproduced by integrating 

 the spectrum of a comet at a certain temperature, and a nebula of a 

 ertain degree of condensation. The resulting spectrum differs only 

 irery slightly from that of the Nova, and the differences can be 

 3counted for by difficulties of observation. 



Nova Cygni is by far the most important new star which has 

 ippeared in spectroscopic times. Numerous observations were made, 

 ind they are, on the whole, in reasonable agreement. The most 

 >mplete observations were made by Vogel. When first observed, the 

 spectrum consisted of several bright lines and flutings, the lines of 

 hydrogen being very conspicuous. As the star gradually faded away, 

 there was a general diminution in the number and brightness of the 

 lines, but the most striking feature was the brightening of the line in 

 ic green, near X 500, which is generally accepted to be the nebula 

 le, as the other lines faded. Finally, the spectrum consisted solely 

 jf the line 500. The discussion indicates that, in addition to hydrogen, 

 icre was the radiation of carbon vapour, the flutings seen being those 

 are most frequently observed in comets. They are, however, 

 lodified by the superposition of the spectra of other substances, 

 tactically all the lines and flutings seen in the spectrum of Nova 

 }ygni can be explained by reference to laboratory work at low tem- 

 sratures. As in the case of Nova Coronse, the spectrum of Nova 

 /ygni can be reproduced by integrating the spectra of bodies which 

 re have reason to believe are swarms of meteorites. Several examples 

 of this are given in the paper. In the earlier stages, it is necessary 

 integrate the spectra of at least three swarms of different degrees 

 condensation, but as the spectrum became simpler, two are suffi- 

 cient. The compound origin and character of the spectrum of a 

 Tova is thus clearly indicated. It is not to be supposed from these 

 itegrations that in the first instance there are really three or more 

 swarms engaged. A Nova is probably produced by the collision of 

 ily two swarms, but the resulting mixed swarm is so complicated 

 lat we can only represent it by assuming at least three temperature 

 jnditions. There will be the temperatures corresponding to each of 

 the central condensations, and that corresponding to the outliers. As 

 le swarm cools, the temperature becomes more equal throughout, and 

 lally the swarm resembles a planetary nebula. 



The spectrum of Nova Andrornedee was at no time a very striking 

 le, and was always difficult to observe. It was also further compli- 

 ited by being superposed upon the then imperfectly recognised 

 actrum of the Great Nebula, in which it was involved. The 

 jectrum was almost continuous, with brighter portions here and 

 lere, which could only be measured with difficulty. Consequently, 

 results obtained by different observers are somewhat discordant, 

 ["he discussion shows that what was really observed after the star had 



