4o; 



NATURE 



'\_Sept. 6, 1877 



and Herr Vogel owns that, however small the similarity 

 between these spectra and that of the new star may have 

 been at first, a certain resemblance appeared when the 

 latter grew fainter ; not only the line in question coin- 

 cided with one in these spectra, a coincidence was 

 also evident in a maximum of brightness in the blue 

 (467 wave-length) and in a dark broad band close to this 

 maximum. 



Mr. Backhouse, of Sunderland, observed the spectrum 

 on January 26, and found the brightest line to be of 503 

 wave-length. He remarked in a note to Nature (vol. 

 XV. p. 295), that at the end of December, not this line but 

 line F was brightest ; Herr Vogel's observations quite 

 agree with those of Mr. Backhouse. 



In summing up and in his final remarks on this subject, 

 Herr Vogel first of all declares that he cannot agree with 

 M. Coinu's view as expressed by this observer in the 

 following phrase : — " Malgre tout ce qu'il y aurait de 

 seduisant et de grandiose \ tirer de ce fait des inductions 

 relatives i I'dtat physique de cette dtoile nouvelle, a sa 

 temperature, aux refactions chimiques dont elle peut etre 

 le siege, je m'abstiendra de tout commentaire et de toute 

 hypothese .\ ce sujtt. Je crois que nous manquons des 

 donnees necessaires pour arriver a une conclusion utile, 

 ou tout au moins susceptible de controle ; quelque 

 aitrayantes que soient ces hypotheses, il ne faut pas 

 oublier qu'elles sont en dehors de la science, et que loin 

 de la sei vir, elles risquent fort de I'entraver." 



Herr Vogel thinks that the fear that a hypothesis might 

 do harm to science is only justifiable in very rare cases ; 

 in most cases it will further science, in the first place 

 because it draws the attention of the observer upon things, 

 which, without the hypothesis, he might have neglected. 

 Of course, if the observer is so strongly influenced, that in 

 favour of a hypothesis he sees things which do not exist — 

 and this may happen sometimes — science may for a while 

 ' be arrested in its progress, but in that case the observer 

 is far more to blame than the author of the hypothesis. 

 On the other hand it is very possible that an observer 

 may — involuntarily — arrest the progress of science, even 

 without originating a hypothesis, by pronouncing and 

 publishing sentences which have a tendency to diminish 

 the general interest in a question, and which do not place 

 ' its high significance in the proper Ught. Herr Vogel is 

 alir.ost inclined to think that such an effect might result 

 from the reading of the above phrase by M. Cornu, and is 

 of opinion that nowhere better than in the present case, 

 where in short periods colossal changes showed themselves 

 occurring upon a heavenly body, the necessary data might 

 be obtained for drawing useful conclusions, and the test 

 of those hypotheses which have been ventured with regard 

 to the physical condition of heavenly bodies, might be 

 made. 



A stellar spectrum with bright lines is always a highly 

 interesting phenomenon for any one acquainted with 

 stellar spectrum-analysis, and is well worthy of deep 

 consideration. Although in the chromosphere of our sun, 

 near the limb, we see numerous bright lines, yet 

 only dark lines appear in the spectrum whenever we 

 produce a small star-like image of the sun and examine it 

 through the spectroscope. It is generally believed that 

 the bright lines in some few star-spectra result from gases 

 which break forth from the interior of the luminous body, 

 and the temperature of which is higher than that of the 

 surface of the body, /.(■., the same phenomenon we 

 observe sometimes in the spectra of solar spots, where 

 incandescent hydrogen, rushing out of the hot interior, 

 becomes visible above the colder spots through the 

 hydrogen lines turning bright. But this is not the only 

 explanation. We may also suppose that the atinosphere 

 of a star, consisting of incandescent gases, as is the case 

 in our sun, is on the whole colder than the nucleus, 

 but with regard to the latter is extremely large. Herr 

 Vogel cannot well imagine how the phenomenon can last 



for any long period if the first hypothesis be correct. The 

 gas breaking forth from the hot interior of the body will 

 impart a portion of its heat to the surface of the body 

 and thus raise the temperature of the latter ; conse- 

 quently the difference of temperature between the incan- 

 descent gas and the surface of the body will soon be in- 

 sufficient to produce bright lines, and these will disappear 

 from the spectrum. This view applies perfectly to stars 

 which suddenly appear and soon disappear again, or at laast 

 decrease considerably in intensity, i.e., for so-called new 

 stars, in the spectra of which biiglit lines are apparent, if 

 the hypothesis mentioned below is admitted for their 

 explanation. For a more stable state of things the second 

 hypothesis seems to Herr Vogel to be far more adapted ; 

 he thinks, therefore, that stars like |3 Lyra;, y Cassiopeiie, 

 and others, which show the hydrogen lines and line D, 

 bright on a continuous spectrum, with only small oscil- 

 lations of intensity, possess very large atmospheres in 

 proportion, consisting of hydrogen and the unknown 

 element which produces the line U3. With regard to the 

 new star Herr Vogel points to a hypothesis which Herr 

 Zoellner deduced from Tycho's observations of the star 

 named after him, long before the considerable progress 

 had been made in stellar physics by means of spectrum 

 analysis. Zoellner supposes that upon the surface of a 

 star, through the constant exhalation of heat, the products 

 of cooling, which in the case of our sun we call sun-spots, 

 accumulate in such a way that finally the whole surface of 

 the body is covered with a colder stratum which gives 

 much less light or none at all. Through a sudden and 

 violent tearing up of this stratunt the interior incan- 

 descent materials, which it incloses, must naturally break 

 forth, and must, in consequence, according to the ex- 

 tent of their eruption, cause larger or smaller patches 

 of the dark envelope of the body to become luminous 

 again. To a distant observer such an eruption from the 

 hot and still incandescent interior of a heavenly body 

 must appear as the sudden flashing up of a nczu star. 

 That this evolution of light may under certain conditions 

 be an extretrtely powerful one, could be explained by the 

 circumstance that all the chemical compounds which under 

 the influence of a lower temperature had already formed 

 upon the surface, are again decomposed through the 

 sudden eruption of these hot materials, and that this decom- 

 position, as in the case of terrestrial substances, takes 

 place under evolution of light and heat. Thus the bright 

 flashing up is not only ascribed to the parts of the surface 

 which through the eruption of the incandescent matter 

 have again become luminous, but also to a simultaneous 

 process of combustion, which is initiated through the 

 colder compounds coming into contact with the incan- 

 descent matter. 



Zoellner's hypothesis on the gradual development of 

 heavenly bodies, as he states it in his " Photometric 

 Researches " (p. 231, &c.), has been confirmed in its 

 essoitiat points by the application of spectrum-analysis to 

 the stars. We recognise the difterent states of cooling in 

 the spectrum, and in the cases of some fainter stars we 

 have distinct data that in the atmospheres surrounding 

 incandescent bodies, chemical compounds may already 

 form and continue to exist. The hypothesis on //tzc stars is 

 in no wise contradicted by the spectral observations made 

 of the two new stars of 1866 and 1S76. The very bright 

 continuous spectrum and the bright lines, which at the 

 beginning only slightly exceeded its brilliancy, could not 

 be well explained if we only suppose a violent eruption 

 from the interior, which again rendered the surface (or 

 part of it) luminous, but are easily explained by the hypo- 

 thesis that the quantity of light is considerably augmented 

 through a simultaneous process of combustion. If this 

 process is of short duration, then the continuous spectrum, 

 as was the case with the new star of 1S76, will very quickly 

 decrease in intensity down to a certain limit, while the 

 bright lines in the spectrum, which result from the incan- 



