Ami 2, 1874 j 



NAIURE 



429 



CELESTIAL CHEMISTRY* 

 II. 



■y^E have now gone through as briefly as I can manage to do it, 

 the principal jioints in chemistry and the principal points in 

 • spectrum analysis with which we have to deal when we are 

 dealing with the chemical substances of our own planet. You see 

 the point of inquiry is the chemical and spectroscopic study 

 of the differences between atoms and molecules. We have 

 now to apply these two lines of thought to a consideration of 

 what I have called Celestial Chemistry. 



In the first place, how is the study of Celestial Chemistry 

 carried on ? To answer this question I will give you an idea of 

 the way in which the spectroscope is added to the telescope. 

 We, of course, require a spectroscope in order to bring into play 

 refraction or diffraction, and we equally, of course, require a tele- 

 scope in order to collect the light which comes to us from the 

 various light sources which are to be found in the sky. Vou 

 now see a photograph of wh.at is technically called the eye-piece 

 end of the most perfect and most powerful telescope in the 

 world, which I am proud to say is in England. It is the tele- 

 scope belonging to Mr. Newall of Gateshead. We see the prin- 

 cipal telescope .and tlie various finders, which enable the observer 

 to find the most delicate object which shines in the sky. 



You will get an idea of the enormous quantity of light col- 

 lected by this instrument, when I tell you that the diameter of 

 the pupil of the eye is less than a quarter of an inch, and that the 

 diameter of the object-glass of this telescope is 25 inches, and 

 that the quantity of light utilised depends upon the squares of 

 the diameters. Of course, when we have to deal with feeble 

 celestial objects lying at an immense distance from us, and which 

 give but little light, it would be absolutely impossible to use 

 the prism with any effect unless in the fir.st instance we thus 

 collected a large amount of light to work willi. 



Now then, having our spectroscope attached to our telescope 

 in the way indicated, to what must we turn our attention ? 

 You will see in a moment that it is useless to consider such a 

 body as the moon. I say useless, of course bearing in mind that 

 we are here dealing with chemical considerations, because the 

 light which we get from the moon is simply sunshine second 

 hand, and the moon has no atmosphere. The same remark 

 applies to a certain extent when we deal with the planets, because 

 they also, as you know, are lit up like the moon by the sun, but 

 they have atmospheres, and much is to be learned from them in 

 this way. What we have to do in the main to get a just general 

 outline, in order to study this Celestial Chemistry is, to confine our 

 attention to those bodies which shine by their own light. And 

 if you think the matter over for a minute you will see that there 

 are two distinct classes of such bodies. In the first place there 

 are the jYflniLr, and Comets, and Mdrors, which shine by their 

 own light. And again, there are the sun and the fixed stats, 

 which shine also by their own light ; but with this important difler- 

 ence, that while we get the initial light radiated by a nebula, a 

 comet, or meieor, the light which we get from a star is not the 

 initial light, but a difference light ; a great de.al of the light 

 radiated haying been stopped by the atmosphere of the star, bo 

 that in the case of a sun, by which of course I mean a star — our 

 sun being merely the star which is nearest to us — although it 

 shines by its own light, we get a difference light while we get 

 what we may call the total light from the first class. 



And here let me add that i is the chemical composition of the 

 atmosphere of the star which thus stops the light which we can 

 study. If the stars had no atmospheres there could be no star 

 chemisti'y, because their spectra would be continuous, and in that 

 case neither qualitative nor quantitative spectrum analysts would 

 be possible. 



We deal then with radiation in objects of the first class and 

 with absorption in objects of the second class. 



Let us commence our study of those objects which shine by 

 their own light by the study of the comets and the meteors. It 

 is unfortunate that since the more general use o f the 

 spectroscope, no large comet has made its appearance, but still 

 some small ones have been observed. 



There is a spectrum which in the main is common to a great 

 many of the compounds of carbon ; and here I may paren- 

 thetically remark that carbon is, of the sixty-three elements 

 to which I have referred, the only element which with the electric 

 power that we can employ in the arc presents us with the distinct 



• Revised from short-band notes of a Lecture delivered at the Quebec 

 Institute, on Tuesday, December j6, 1873. Continued from p. 414. 



appearance of a compound spectrum. .Side by side with this 

 generic spectrum of the compounds of carbon I will show you 

 the spectrum of the head of a comet which was observed some 

 years ago ; and I may add that several other comets have been 

 observed since, with the indication that their spectra are to a 

 very large extent, if not absolutely, the same ; so that we mav 



say there is a probability that, in the case of some of the comets 

 at all events, we are dealing with a class of bodies in which a 

 compound of carbon is concerned, or if not that, that the mole- 

 cules of the comet resemble somewhat those of the chemical 

 substances which give us such spectra. 



Closely connected with comets by the recent hypothesis of 



Schiaparelli, are meteor-?, and lalling-stars. So far as I kno»' 

 at present, in the case of filling stars the cometary spec- 

 trum has not been seen, but it has been noticed in several 

 shooting-stars that the vapour of sodium is present, indicated by 

 the double bright line in the yellow part of the spectrum. 

 Now the meteorites are large meteors which have fallen to the 



