58 



NA TURE 



{May 17, 1888 



carbon, or upon a dark band in the spectrum of some 

 other element. In the former case the dark band will be 

 cancelled or masked ; in the latter case the two 

 absorptions will be added together, and form a darker 

 band of a different shape. 



The Question of Masking. 



If we consider the masking effects of the bright carbon 

 flutings upon the absorption spectrum of each of the 

 elements which, according to the results obtained, enter 

 into the formation of DuneYs bands, we have the follow- 

 ing as the main results : — 



Magnesium. — There are two flutings of magnesium to 

 be considered, the brightest at 500 and the other at 5201. 

 In the earlier stages of Duner's stars only the fainter one 

 at 5201 is visible, but the absence of the brightest at 500 

 is accounted for by the masking effect of the bright carbon 

 fluting starting at 517. As the carbon fades, the 517 

 fluting narrows and the absorption of magnesium 500 

 becomes evident. 



Manganese. — The two chief flutings of manganese are 

 at 558 and 586, the former being the brightest fluting in 

 the spectrum. The second fluting is seen in all of DuneYs 

 stars. The first fluting, 558, however, does not appear 

 as an absorption fluting until the radiation fluting of 

 carbon starting at 564 has narrowed sufficiently to unmask 

 it. It is thus easy to understand why, in some stars, there 

 should be the second fluting of manganese without the 

 first. 



Barium. — The spectrum of barium consists of a set of 

 flutings extending the whole length of the spectrum, and 

 standing out on this as a background are three bright 

 bands ; the brightest band is at 515, the second is at 525, 

 and the third, a broader band, is about 485. The second 

 band is recorded as an absorption band in Duner's stars, 

 the apparent absence of the first band being due to the 

 masking effect of the bright carbon at 517. The third 

 band at 485 probably forms a portion of band 9. A 

 fourth band, at 533, and the three brightest flutings at 

 602, 635, and 648 are also seen in a Ononis. 



Lead. — The brightest fluting of lead is at 546. This 

 first appears in species 5, as a result of increased tem- 

 perature, and not on account of the removal of any 

 previous mask. The second fluting of lead, at 568, also 

 appears in two cases. 



Chro?nium. — The flutings of chromium do not form 

 portions of the ten principal bands of Dune>, but the 

 brightest are seen in a Orionis. The brightest fluting is 

 at 580, and this forms band I. ; the second, at 557, is 

 masked by the manganese fluting at 558, and the third at 

 536 is seen as line 2. The chromium triplet about 520, 

 which is visible in the bunsen, is seen as line 3. 



Bismuth. — The brightest fluting of bismuth is at 620, 

 the second is at 571, the third at 602, and the fourth is 

 at 646. The first is masked by the iron fluting at 615, the 

 second is probably seen in a Orionis as band II. (570-577). 



The points I consider as most firmly established are 

 the masking effects of the bright carbon flutings and the 

 possibility of the demonstration of the existence of some 

 of the flutings in the spectrum by this means, if there 

 were no other.- There are two chief cases, the masking 

 of the "nebula" fluting 500 by the bright carbon fluting 

 with its brightest, less refrangible edge at 517, and that of 

 the strongest fluting of Mn = M'n(i) 558, by the other with 

 its brightest edge at 564. I have little doubt that in some 

 quarters my anxiety not to be content to refer to the second 

 fluting of Mn without being able to explain the absence 

 of the first one, will be considered thrown away, as it is so 

 easy to ascribe any non-understood and therefore " ab- 

 normal " spectrum to unknown physical laws ; but when 

 a special research had shown me that at all temperatures 

 at which the flutings of manganese are seen at all, the one 

 at 558 retained its supremacy, I felt myself quite justi- 

 fied in ascribing its absence in species 1-4 to the cause I 



have assigned, the more especially as the Mg fluting 

 which is visible even in the nebula followed suit. 



• The Characteristics of the Various Species. 



I append the following remarks and references to the 

 number of the bodies in Duner's catalogue, in which the 

 specific differences come out most strongly, to the tabular 

 statement. I also refer to some difficulties. 



Sp. 1. The characteristic here is the almost cometary 

 condition. All three bright carbon flutings generally seen 

 in comets are visible ; 474 standing out beyond the end 

 of the dull blue continuous spectrum of the meteorites, 516 

 masking Mg 500, and 564 masking Mn(i) 558. The bands 

 visible in the spectra of bodies belonging to this species 

 will therefore be Mn(2) 586, and Mg(2) 521 ; band 9 will 

 be so wide and pale that it would most likely escape de- 

 tection. It is very doubtful whether any of the bodies 

 the spectra of which have hitherto been recorded can be 

 classed in this species, but laboratory work assuredly 

 points to their existence ; it will therefore be extremely in- 

 teresting if future observations result in their discovery. 

 It is possible, however, that No. 150 of Duner's list belongs 

 to this species, but the details are insufficient to say with 

 certainty. His description is as follows :—" 150. lime 

 parait y avoir une bande e'troite dans le rouge, et une plus 

 large dans le vert " (p. 55). 



Sp. 2. Characteristics : appearance of Fe. The number 

 of bands now visible is three — namely, 2, 3, and 7. The 

 iron comes out as a result of the increased tempera- 

 ture. Mg(i) and Mn(i) are still masked by the bright 

 carbon flutings, and there is still insufficient luminosity 

 to make the apparent absorption band 9 dark enough to 

 be noticed. 



Sp. 3. Characteristics : appearance of Mg 500, which 

 has previously been masked by the carbon bright flut- 

 ing 517. 8 and 7 are now the darkest bands in the 

 spectrum, 37. 



Sp. 4. Characteristics : appearance of Pb(i) 546, i.e. 

 band 5. This, if present in the earlier species at all, 

 would be masked by the bright carbon at 564. 



Sp. 5. Characteristics: Mnfi) is now unmasked. The 

 bands now visible are 2, 3, 4, 5, 7, and 8, the two latter 

 still being the widest and darkest, because they are 

 essentially low-temperature phenomena. 



Sp. 6. Characteristic : band 6, i.e. Ba(2), 525, is now 

 added. The first band of Ba at 515 is masked by the 

 bright carbon at 517. The bands now visible are 2-8, 7 

 and 8 still being widest and darkest. They will all be 

 pretty wide, and they will be dark because the continuous 

 spectrum will be feebly developed. 



Sp- 7. Characteristics : appearance of band 9. This, 

 which has been already specially referred to, has been too 

 wide and pale to be observed in the earlier species. Its 

 present appearance is due to the narrowing and brighten- 

 ing of the carbon at 474 and the brightening of the con- 

 tinuous spectrum, the result being a greater contrast. 

 Bands 7 and 8 still retain their supremacy, but all the 

 bands will be moderately wide and dark. 



Sp. 8. Characteristics : all the bands 2-9 are more 

 prominent, so that 7 and 8 have almost lost their 

 supremacy. 



Sp. 9. Characteristic: appearance of band 1, the 

 origin of which has not yet been determined. All the 

 bands are well seen, and are moderately wide and dark. 



Sp. 10. Characteristics: appearance of band 10, and 

 in some cases n. These become visible on account of 

 the brightening of the carbon B fluting and the hydro- 

 carbon fluting at 431. The spectrum is now at its greatest 

 beauty, and is discontinuous. 



Sp. n. Characteristics: the bands are now becoming 

 wider, and 2 and 3 are gaining in supremacy ; 7 and 8 

 become narrower on account of the increased tempera- 

 ture. 1 and 10 are only occasionally seen in this 

 species. 



