1887.] Researches on the Spectra of Meteorites. 



137 



that strong lines of the H structure at 607 — 610 and 574 have not 

 been recorded in star spectra with those at 540 and 580. 



In the nebulas we deal chiefly with lines seen in the spectrum of 

 magnesium at the lowest temperature ; and these, as far as observa- 

 tions go, have not yet been associated with the lines at 540 and 580 

 to which reference has just been made, although they may or may not 

 be associated with the bright lines C and F of hydrogen. In the 

 nebula?, however, no lines coincident with the lines of cool hydrogen 

 have been observed. It will be seen, therefore, that we have here 

 again strong grounds for rejecting the view that the lines seen in 

 " stars " at 540 and 580 are due to cool H, for since hydrogen is 

 common to both nebulas and stars, there is no reason why structure- 

 lines should occur in " stars " any more than in nebulas. 



Another ground for rejecting cool hydrogen as the origin of any of 

 the lines in " stars" is that the structure -spectrum of hydrogen is 

 only seen in confined glows, which is just the condition which cannot 

 occur in space. 



At the same time, the apparent coincidences of so many meteorite 

 lines with structure-lines of hydrogen greatly increases the difficulties 

 of laboratory work ; in fact, the structure spectrum of hydrogen is to 

 observations of meteorite glows in the laboratory what continuous 

 spectrum is to observations of bright lines in stars. 



If it be agreed that we are not dealing with cool hydrogen, then it 

 will follow that the only difference between celestial bodies with 

 bright lines in their spectra comes from no difference of origin or 

 chemical constitution, but from a difference of temperature. 



At one point in these researches I was under the impression that 

 the differences in the sj^stems of bright lines seen in the nebulas and 

 the bright-line stars might arise from a preponderance of irons or 

 stones in the swarms. But I was led to abandon this idea, not only 

 by the observation of the meteoritic glows, but by the consideration 

 that even telescopically the "stars" in question are more condensed 

 than the nebulas. 



The spectrum of the nebulas, except in some cases, is associated with 

 a certain amount of continuous spectrum, and meteorites glowing at a 

 low temperature would be competent to give the continuous spectrum 

 with its highest intensity in the yellow part of the spectrum ; so that 

 in this way we should understand that lines due to any gas or vapour 

 in that part would be very much more likely to escape record than 

 those in the part of the spectrum which the continuous spectrum 

 hardly reaches. The general absence, however, of bright lines of 

 metallic vapours, except 495 and 500, and of the bright lines of 

 hydrogen, evidently justifies the conclusion that we are here in 

 presence of those bodies in celestial space, connected with which the 

 temperature and the- electrical excitation are at the minimum, and it 



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