344 



NATURE 



[August 7, 1890 



temperature (magnesium) and the hot carbon stages of 

 comets are both represented in nebulas, and the inter- 

 mediate cool carbon stage is therefore not likely to be 

 entirely absent. 



The absence of the hot carbon fluting at 564 from the 

 spectra of nebulas may possiby be due to two causes. It 

 is much fainter than either 517 or 468-474, and may have 

 escaped notice on that account ; or, as in the nebula in 

 Andromeda,it maybe masked in the same way as in comets. 



It is suggested that the ordinary nebulae are not hot 

 enough to give the line or fluting at 568, but it appears 

 when the swarms become more condensed — that is, in 

 bright-line stars. The absence of 568 is therefore prob- 

 ably due to the low temperature of nebulas. 



II. Cojuparison of Comets and Aurorce. 



If we exclude the exceptional cases of Comet Wells 

 and the Great Comet of 1882, the number of lines and 

 flutings recorded in comets is small, and therefore only 

 the most general list of auroral lines must be taken for 

 comparison. It would be unfair, for example, to take the 

 long list of lines given by Gyllenskiold. The lines stated 

 are taken from the table which I gave in a note in 

 January 1888 (Roy. Soc. Proc, vol. xliii. p. 321) which has 

 since been slightly rearranged before taking the means. 



Here, again, it will be seen, that there are many striking 

 coincidences. The hydrocarbon fluting at 431 and the 

 hot and cool carbon flutings at 468-474, 483, 517, and 

 519 are common to both. The flutings of magnesium 

 500 and 521 and the flutings of lead and manganese at 

 546 and 558 are also common. The iron fluting at 615 

 is not seen in comets at ordinary temperatures, but since 

 it was recorded in the Great Comet of 1882, it has been 

 added, in brackets, to the list of cometary flutings. The 

 line at 426, which was seen in Comet Wells, has also 

 been added. It will be noted also that there are apparent 

 discrepancies ; some lines appearing only in comets and 

 others only in auroras. The explanation of the absence 

 of hydrogen lines from comets which has already been 

 given applies equally in this case. As there is no repul- 

 sion in the aurora similar to that exercised upon comets 

 by the sun, there is no reason for the absence of hydro- 

 gen. In the aurora the hydrogen lines may also be pro- 

 duced partly from aqueous vapour. The citron carbon 

 flutings 561 and 564 have not been recorded in the aurora, 

 although they are often seen in comets ; their apparent 

 absence from the aurora is probably because they 



NO. 1084, VOL. 42] 



fall in the brightest part of the continuous spectrum, 

 and are consequently masked. 



Thelines special toaurorae are 531,535, 539, 6o6,and 630. 



III. Comparison between Comets and Bright-line Stars. 



In the Bakerian Lecture for 1888 I gave a complete dis- 

 cussion of the spectra of bright-line stars, as far as the 

 observations then went, and the conclusion arrived at 

 was that they are nothing more than swarms of meteorites 

 a little more condensed than those which we know as 

 nebulae. The main argument in favour of this conclusion 

 was the presence of the bright fluting of carbon which 

 extends from 468 to 474. This, standing out bright 

 beyond their short continuous spectrum, gives rise to an 

 apparent absorption-band in the blue. The varying 

 measurements made by diff'erent observers may possibly 

 have thrown a little doubt upon the conclusion that the 

 bright band was due to carbon, but recent observations at 

 Kensington have placed this beyond doubt. Direct com- 

 parisons of the spectrum of all the three stars in Cygnus 

 with the flame of a spirit lamp have been made by Mr. 

 Fowler, and these showed an absolute coincidence of the 

 bright band in the stars with the blue band of carbon seen 

 in the flame. It was found quite easy to get the narrow- 

 spectrum of the star superposed upon the broader spectrum 

 of the flame, so that both could be observed simultaneously. 



Other evidence of carbon flutings was shown by slight 

 rises in Vogel's light-curves near 517 and 564. These, 

 however, could not be as well seen as the band in the 

 blue, because they fall on the bright continuous spectrun* 

 from the meteorites. In the stars in Cygnus, Mr. Fowler 

 detected brightenings near 517, and perfect coincidences 

 were found with the fluting at 517 in the spirit-lamp 

 flame. In this case both 517 and 468-474 were simul- 

 taneously seen to be coincident with flame-bands. 



Measurements were made of the brightenings in the 

 spectrum of 7 Cassiopeiae by Mr. Fowler on September 

 18, and these were also found to be coincident with the 

 carbon flutings 517 and 468-474 ; the citron fluting at 564 

 was not seen. It may be remarked that C, F, and Dj 

 were seen very bright. 



The conclusions drawn from my suggestions as to the 

 presence of carbon, as well as hydrogen, in bright-line 

 stars, are therefore strengthened. 



In the following table, all the lines and flutings recorded 

 in bright-line stars, with the exception of y Cassiopeiae,. 

 are given. The lines recorded by Sherman in 7 Cassiopeise 

 have not yet been confirmed. 



