August 7, 1890] 



NATURE 



343 



brackets, as sometimes the phenomena compared may 

 attain a temperature slightly higher than that of comets 

 at mean temperature. 



For the nebulas, all the lines recorded in the visible 

 spectrum by Messrs. Huggins, Vogel, Copeland, Fowler, 

 and Taylor, are given. The list of lines has been con- 

 siderably extended since my preliminary discussion of the 

 spectra of nebulse in November 1887. D3 and a line at 

 447 have been observed in the spectrum of the nebula in 

 Orion by Copeland, and Mr. Taylor has also recorded D3 

 and lines, or remnants of flutings, at 559 and 520, In the 

 nebula in Andromeda, carbon flutings and the lead 

 flutings at 546 have been observed by Mr. Fowler and 

 confirmed by Mr. Taylor ; since these observations were 

 made, I find that Vogel {Bothkamp, Bcob., Heft i, 1872, 

 p. 57) observed a line at 518, probably carbon 517, in 

 nebulae numbered in Sir J. Herschel's General Catalogue 

 4234, 4373. and 4390. 



Other nebula lines with which I was not previously 

 acquainted are 479, 509, and 554. All these lines were 

 observed by Vogel in the nebula G.C. 4378 {Bothkamp^ 

 Beob., Heft i, 1872, p. 57). 



With reference to the appearance of D3 in nebulee and 

 bright-line stars, I wrote, in November 1887 (Roy. Soc. 

 Proc, vol. xliii. p. 139) :— " It is right that I should here 

 point out that some observers of bright lines in these so- 

 called stars have recorded a line in the yellow which they 

 affirm to be in the position of D3 ; while, on the other 

 hand, in my experiments on meteorites, whether in the 

 glow or in the air, I have seen no line occupying this 

 position. 



" I trust that some observer with greater optical means 

 will think it worth his time to make a special inquiry on 

 this point. The arguments against this line indicating 

 the spectrum of the so-called helium are absolutely over- 

 whelming. The helium line so far has only been seen in 

 the very hottest part of the sun which we can get at. It 

 is there associated with b, and with lines of iron which 

 require the largest coil and the largest jar to bring them 

 out, whereas it is stated to have been observed in stars 

 where the absence of iron lines and of b shows that the 

 temperature is very low. Further, no trace of it was seen 

 in Nova Cygni, and it has even been recorded in a 

 spectrum in which C was absent, and once as the edge of 

 a fluting.^ 



" It is even possible that the line in question merely 

 occupies the position of D3 by reason of the displacement 

 of D by motion of the ' stars ' in the line of sight. On this 

 point no information is at hand regarding any reference 

 spectrum employed. 



" If^ however, it should eventually be established that 

 the line is really D^, which probably represents afine/ortn 

 of hydrogen, it can only be suggested that the degree of 

 fineness which is brought about by temperature in the 

 case of the sun, is brought about in the spaces between 

 meteorites by extreme tenuity." 



The observations of Dr. Copeland {Monthly Notices 

 R.A.S., vol. xlviii. p. 360), have now, I think, established 

 the identity of the yellow line, in the nebula of Orion 

 at all events, with D3. In a letter to Dr. Copeland, I 

 suggested that the line at 447 was in all probability 

 Lorenzoni's / of the chromosphere spectrum, seeing that 

 it was associated both in the nebulae and chromosphere 

 with hydrogen and D3. This he believes to be very prob- 

 able. The line makes its appearance in the chromosphere 

 spectrum about 75 times to 100 appearances of D3 or the 

 lines of hydrogen. 



The association of the line at 447 with D3 therefore 

 strengthens the view that there is an action in space, 

 away from condensations, whereby matter is reduced to 

 its finest forms. 



'".... The spectrum is very bright ; two strong bands are seen in the 

 red, then the D line, followed by a bright line (D3) as the edge of a band. 

 . . . ." (Konkoly, •• Neuer Stern bei x Orionis," Astr. Nachr., No. 2712). 



NO. 1084, VOL. 42] 



The table shows that there are many striking similarities 

 between the two spectra, and there is no doubt that many 

 of the lines are identical. The flutings of hot carbon, 

 for example, are common to both, as are also the flutings 

 of magnesium, manganese, and lead. The hydrogen line 

 486 has onlv been seen in one comet, namely. Comet III. 

 i88q, by Konkoly (" O'Gyalla Observations," 1881, p. 5.) 

 Other flutings and lines again are special to comets and 

 others to nebula;. Thus, there are practically no indica- 

 tions of hydrogen in comets, although the hydrogen lines 

 are amongst the brightest in nebulas. Again, the lines 

 447, 479, 495, 509, and 554 are seen in nebulas, but 

 not in comets. On the other hand, the cool carbon 

 flutings and the fluting at 568 are seen in comets, but not 

 in nebula. Most of these apparent discrepancies are 

 explained by a consideration of the differences in the 

 conditions of comets and nebulae. It must be remembered 

 that in the case of comets there is an action which repels 

 the vapours produced by collisions, and the vapours first 

 affected will, of course, be those which are least dense. 

 Hydrogen will thus be repelled from the comets, whilst 

 the denser vapours of magnesium and carbon remain. 

 There is then a good reason why hydrogen lines should 

 not be seen in cometary spectra. As there can be no such 

 repulsion in the sparse swarms which constitute nebulae, 

 hydrogen lines are seen in them. 



Two other lines special to nebulae are 5872 and 447, 

 to which reference has already been made. The evidence 

 tends to show that D3 and / are finer vapours than 

 hydrogen, and hence there is even greater reason for the 

 absence of these lines from cometary spectra, even were 

 the temperature higher, than for the absence of the lines 

 of hydrogen. 



The line at 527 is probably the iron line E ; this was 

 seen in the hotter comets, namely, Comet Wells and the 

 Great Comet of 1882, so that there is no discordance with 

 regard to the appearance of this line. The other lines 

 special to nebulae are 479, 495, 509, and 554 ; but as no 

 origins for these have yet been determined, it is not 

 possible to explain their absence from cometary spectra. 

 It is not improbable that 554 is an error in measurement 

 for the manganese fluting at 558, the latter having been 

 recorded by Mr. Taylor in the nebula of Orion. 



The apparent absence of the cool carbon flutings from 

 nebulee is in all probability due to insufficient observations, 

 as indicated by the discussion of comets. The lowest 



