NA TURE 



[May 4, 189^ 



longed to a radiant in Cassiopeia, and possibly to the same system 

 which furnished the fireballs of April 10, 1874, and April 9, 

 1876, with radiants at i9°+57°and I7° + S7° respectively, ac- 

 cording to Von Niessl. A fireball seen on May 30, 1877, had 

 a radiant at 20° + 58°, which is virtually the same position as 

 the others. I would be glad to hear of any additional observa- 

 tions of the large meteor of April 15, 1893, or of any of the 

 meteors seen at Bristol on the nights of April 18, 20, and 21 last, 

 and referred to in the first of the foregoing tables. 



W. F. Denning. 



Smithsonian Institution Documents. 



I DO not know whether your numerous readers realise that 

 many of the public documents published by the United States 

 Government and the Smithsonian Institution can be obtained by 

 direct personal application to the author, at least as long as 

 copies remain undistributed. 



The volume entitled "Mechanics of the Atmosphere," recently 

 published by the Smithsonian Institution, was compiled in the 

 confident hope of stimulating the study of this difficult subject 

 by English-speaking scholars throughout the world ; further 

 volumes will follow if it becomes evident that this hope is being 

 realised. This collection of translations appeals especially to 

 the mathematical physicist, and I should be pleased to hear from 

 any one who desires to study or teach this subject. 



Cleveland Abbe. 



Weather Bureau, Washington, April 15. 



THE GENESIS OF NOVA AURIGA. 



T T is a common belief that everything is created for a 

 ■'• beneficial purpose, and a commoner one that the 

 chief purpose is the delectation of mankind. Without 

 occupying the stilted position involved in the acceptation 

 of such an idea, it can be said that all things that are 

 made are useful for the extension of knowledge. Viewed 

 from this standpoint, the universe is a field containing an 

 infinite number of facts which have to be reaped and 

 garnered before they can be threshed. In the case of 

 the new star that appeared in Auriga last year, a rich 

 harvest of facts has been gathered in. Astronomers 

 from their watch-towers have scanned the celestial 

 visitor through optic-glasses ; estimated its glory ; 

 measured its place ; photographed it, and caused it to 

 weave its pattern in the spectroscope. But it is not 

 enough to make observations and store them up in musty 

 libraries without the proper understanding of their import. 

 At all events, the greatest possible good should be wrung 

 from the facts, and an attempt should be made to dis- 

 criminate the theory that best explains them. For this 

 reason the subject of Nova Aurigae is here resuscitated. 

 Theories galore have been propounded to account for 

 that star's genesis, and the most important are de- 

 scribed in this note, so that every one can judge for 

 himself the explanation which sufficiently satisfies the 

 phenomena. 



Before the advent of the new star of 1866 the 

 general opinion was that such objects represented 

 new creations. Spectroscopic observations then caused 

 a revulsion of that idea, and we find Dr. Huggins 

 suggesting in an italicised expression, that " the star 

 became suddenly enrapt in burning hydrogen " {" Spec- 

 trum Analysis," p. 28, Huggins, 1866). To quote 

 more fully, "In consequence it may be of some great 

 convulsion, of the precise nature of which it would 

 be idle to speculate, enormous quantities of gas were set 

 free. A large part of this gas consisted of hydrogen, 

 which was burning about the star in combination with 

 some other element. This flaming gas emitted the light 

 represented by the spectrum of bright lines. The greatly 

 increased brightness of the spectrum of the other part of 

 the star's light may show that this fierce gaseous con- 



NO. 1227, VOL. 48] 



flagration had heated to a more vivid incandescence the 

 matter of the photosphere. As the free hydrogen be- 

 came exhausted the flames gradually abated, the 

 photosphere became less vivid, and the star waned down 

 to its former brightness." More or less modified forms of 

 this theory of a fiery cataclysm were afterwards put for- 

 ward, to account for the formation of Nova Cygni in 

 1876. Mr. Lockyer, however, advanced the idea that the 

 outburst wasdue to cosmica! collisions (Nature, vol. xvi. 

 p. 413). In his words, "We are driven from the idea 

 that these phenomena are produced by the incandescence 

 of large masses of matter because, if they were so pro- 

 duced, the running down of brilliancy would be 

 exceedingly slow. Let us consider the case, then, on the 

 supposition of small masses of matter. Where are we 

 to find them ? The answer is easy : in those small meteoric 

 masses which an ever-increasing mass of evidence tends 

 to show occupy all the realms of space." Practically all 

 the theories with regard to the origin of new stars are 

 modifications of one or the other of these ; either an 

 internal convulsion, or an external collision, is hypo- 

 theticated. Let us see how each will stand the test put 

 upon it by Nova Aurigae. 



The discovery by Mr. Lockyer that the bright lines in 

 the spectrum of the new star were accompanied by ds rk 

 lines on their more refrangible sides seemed at once to 

 be a striking confirmation of his views. The interpreta- 

 tion naturally put upon such a composite appearance was 

 that two discrete masses were engaged in producing the 

 body's light ; one, having a spectrum of dark lines, was 

 rushing towards the earth, while the bright-line star or 

 nebula was running away. As Mr. Lockyer remarked in a 

 paper communicated to the Royal Society on February y, 

 1892, "the spectrum of Nova Aurigae would suggest that a 

 moderately dense swarm [of meteorites] is now moving 

 towards the earth with a great velocity, and is disturbed 

 by a sparser one which is receding. The great agitations 

 set up in the dense swarm would produce the dark-line 

 spectrum, while the sparser swarm would give the bright 

 lines." In spite of its simplicity, however, and its ability 

 to account for the observed facts, the meteoritic theory 

 did not commend itself to the minds of some astronomers. 

 Dr. Huggins clung to ithe idea that the outburst was 

 the result of eruptions similar in kind to those upon the 

 sun, but the acquisition of knowledge of the light changes 

 of stars forced him to withdraw the original suggestion 

 that the luminosity of a Nova is produced by chemical 

 combustion {Fortnightly Reuieiu, June 1892, p. 827), in 

 fact, to relinquish entirely the crude conception of a burn- 

 ing world propounded in 1866. In its place Dr. Hug- 

 gins put the view that Nova Aurigae owed its birth to 

 the near approach of two gaseous bodies. " But," he 

 admits {Ibid. p. 825), "a casual near approach of two 

 , bodies of great size would be a greatly less improbable 

 event than an actual collision. The phenomena of the 

 . new star scarcely permit us to suppose even a partial 

 '. collision, though if the bodies were diffused enough, or 

 the approach close enough, there may have been possibly 

 some mutual interpenetration and mingling of the rare 

 I gases near their boundaries." 



" An explanation which would better accord with 



what we know of the behaviour of the Nova may, 



I perhaps, be found in a view put forward many years 



ago by Klinkerfues, and recently developed by Wilsing, 



that under such circumstances of near approach enormous 



tidal disturbances would beset up, amounting, it may be, 



to partial deformation in the case of a gaseous body, and 



I producing sufficiently great changes of pressure in the in- 



i terior of the bodies to give rise to enormous eruptions of 



the hotter matter from within, immensely greater but 



similar in kind to solar eruptions." Serious objections to 



the Klinkerfues- Wilsing hypothesis are pointed out by 



Herr Seelinger {Astr. Nach.,^o. 3118, and Nature, 



