ASTRONOMY. 1 1 1 



some further more or less probable assumptions) deduces an exi)ros 

 siou for tbe magnitude of the cooling star at luiy time, lu order to 

 compare this formula with Herr Midler's photometric measures of the 

 Xova, extending from 1885, iSeptember 2, to October 13, Professor Seel- 

 iger assumes that n=l, and that the epoch for which the time i=0, 

 is 1885, August 27, 8^ Berlin mean time. Using quite api)roximate 

 values of the constants involved in his formula, it appears that there is 

 a good general agreement (the mean discordanc^e being O.Il of a stellar 

 magnitude) between the computed and observed values. The computed 

 magnitude corresponding to the epoch for which f=0, is 7.73. The fair 

 agreement shown by this comjjarison induces Professor Seeliger to 

 think that the form of the expression which he has deduced is such as 

 would accurately represent the observations, provided that it were pos- 

 sible to determine the necessary constants with sufficient precision. 

 And as there is evidence to show that the nebula in Andromeda is, 

 l)artly at least, (!om posed of a vast number of faint stars, it appears, in 

 Professor Seeliger's opinion, not unreasonable to suppose that a collis- 

 ion was the cause of the sudden development of heat and light which 

 revealed itself to us as the appearance of a " new " star. 



With reference to the point thus raised by Professor Seeliger, TIerr 

 Auwers points out (Astron. Nachr.,]Sro. 2715) that the great similarity of 

 the outburst in Andromeda in 1885 to the phenomenon observed by him 

 in 1860 in the cluster 80 Messier in Scorpio is a strong confirmation of 

 Professor Seeliger's views. The probability that two variable stars of 

 such exceptional character should be i)rojected, in" one case on a close 

 star-cluster, in the other case on an object which appears to be, in 

 part at least, a close star-cluster, is so small that it is almost necessary 

 to refer these outbursts to physical changes in the Jiebulai in which they 

 resi)ectively appeared. (Observatory, April, 1886.) 



Dr. Mills (Nature 33 : 440) in criticising Professor Seeliger's collision 

 hypothesis suggests that the blazing out of the Noi^a may be merely a 

 physico-chemical consequence of cooling; and it has been pointed out 

 by Mr. Castell-Evans (Nature, 33: 486) that practically the same expla- 

 nation was suggested in 1878 by Prof. E. Meldola in a paper i)ublished 

 in the Philosophical Magazine for July of that year. Professor Mel- 

 dola says: " It is conceivable that in certain cases the composition of 

 a star's atmosphere maybe such as to permit a considerable amount of 

 cooling before any combination takes place among its constituents ; un- 

 der such circumstances a sudden catastrophe might mark the i)eriod of 

 combination, and a star of leeble light would blaze forth suddenly, as 

 occurred in 1806 to r Coronte Borealis. In other cases, again, it is 

 possible that the composition of a star's atmosphere ma^' be ot such a 

 nature as to lead to a state of periodically unstable chemical equilib- 

 rium ; that is to say, during a certain period condiination may be going 

 on with the accompanying evolution of heat, till at length dissociation 



