April i i, 1^95] 



NA TURE 



5&7 



which is not very common, but the study of which is all im- 

 portant for our present purpose. It is called a spiral nebula, 

 it is one of the nebulre: in the constellation of the Great 

 Bear. I wish to point out that in the centre we have a 

 condensation, and from the centre of the condensation the 

 luminosity gradually gels less and less until at last we have 

 no luminosity greater than that of the surrounding sky. In 

 the nebula itself we find exquisite spirals, starting apparently 

 from different points, and gradually coming towards the centre, 

 and if you look along these spirals you will see that the star- 

 like masses, which may not be stars, are in many cases located 

 on the spirals, representing apparently minor conden- 

 sations, each spiral itself being probably brighter than 

 the other parts because it is more disturbed. 

 Next we have an absolutely unlouched photo- 

 graph of the famous Dumb-bell Nebula. I am 

 certain that many here have studied the drawings 

 of this nebula given in encyclopedias and in 

 books of astronomy during the last forty years, 

 and that it is a great comfort to you to see, as ii 

 is to me to be able to show you, the autobio- 

 graphical account that it gives of itself, because 

 if you refer to those drawings it will be very 

 difficult to find any two alike, even if it is 

 distinctly stated that one has been copied from 

 the other. In this again we find a central con- 

 densation, and associated with it arcs in which the luminosity 

 is greater than in the adjacent regions. 



The other nebula that I have to exhibit is one remarkable for 

 its difference from the other two, inasmuch as no condensation 

 is suggested. This nebula, which you see stretching across the 

 screen like a sort of celestial river (Fig. 13), seemsto be careering 

 through space, and I call your attention specially to this because 

 it is well to remember that, if we have meteoritic swarms in space, 

 i.e. swarms which are condensing, it is quite possible that «e 

 may have meteoritic streams. I think you will consider that it is 

 not any misuse of words to say that we have there a possibility 

 of a meteoritic stream. 



So much then for some typical representations of some of the 

 different forms of nebuloe. 



While, however. Dr. Huggins in his presidential address, 

 apparently from quite independent inquiry, announced my main 

 contention, viz. that nebulse and stars do belong to the same 

 order of celestial bodies, and withdrew his unfortunate state- 

 ment as having been made on theological grounds, I am compelled 

 to say, but wish to say it with the utmo>t courtesy, that a com 

 plete study of the literature shows that he was quite familiar 

 with my work all the time, and that while he thought fit to re- 

 publish my main contention as his own on the one hand, on the 

 other he was engaged in attempting to throw discredit on my 

 work, and to conceal his retreat after the manner of the sepia by a 



I propose to go into this matter in some detail, because it will 

 enable me to indicate the closeness with which the skill of 

 trained observers and the magnificent instruments of modern 

 research that I have already referred to, enable us now to 

 deal with facts, and to replace the imperfect observations 

 of the past with others of which the accuracy may be relied 

 upon. 



Among the many lines of evidence which had been brought 

 forward, it was stated by myself that in following up the 

 suggestion of Prof. Tait and experimenting upon meteoritic dust, 

 a line had been seen very near the position of the chief line which 

 Dr. lluggins had discovered in the year 1864 in the spectrum 

 of the nebulae. In fact, after accumulating all the spectroscopic 



l^ic. 



-Line-spectr.i 01 bariutn and iron. 



Iron. 



great cloud of ink— printer's ink, referring to a minor 

 point. He endeavoured to suggest to anybody who was not 

 really completely acquainted with my work, that the methods 

 employed by my assistants and myself for something like 

 three years were inaccurate, and that the conclusion 

 reached, which must have bnen right because he had come to 

 agree with it, had been got at in the wrong way. Alihuugh 

 the charges of inaccuracy which Dr. Huggins thought lit 10 

 make were general, in his printed papers the chief stress hss 

 been laid upon a statement I had made with regard to a 

 nialter of secontlary importance in the general discussion, I 

 refer lo the possible origin of the chief line in the nebular 

 spectrum. 



NO. I 328, VOL. 51] 



Fi-;. 16 — Fliitingsof c.aibon. 



observations which I could lay my hands on, I went on to 

 experiment myself, and I have here some apparatus which 

 will give you an idea of the kind of experiment which was 

 undertaken (Kig. 14.) Meteoritic dust is placed in a horizontal 

 spectrum tube connected with a .Snrengel air-pump, so that an 

 electric spark can be passed through the dust ; an image is 

 formed on the slit of the spectroscTpe, and an arrangement for 

 an ordinary electric spark in air serves for a comparison 

 spectrum. The point was to see whether there was any 

 probability that Prof. Tail's suggestion was right, by examining 

 the spectrum of meteoritic dust. For this purpose some dust 

 was placed in a tube resembling the one now on the table, and 

 an electric current v/as sent through it. Now it had long been 

 known that when one heats meteoritic dust, it gives out com- 

 pounds of carbon, and also hydrogen gas ; what I did was to 

 observe the change in the spectrum of that tube under different 

 conditions. For instance, if it were wished to expose the 

 dust to a higher temperature, a liunsen burner was placed 

 underneath it. 



Vou will be able to see that, in a little time, the heat will make 

 a considerable difference in the phenomenon observed in the 

 region which comes under its influence, and I think you will 

 also see that in some parts we get a distinct indication of green 

 colour. Now what I found was that in the spectrum of dust 

 from several meteorites so examined, there was a line very near 

 the position which had been stated by Dr. Huggins to represent 

 the aclual position of the chief line seen in the spectrum of the 

 nebula;. That line I was able to trace home by comparative 

 work to olivine, a substance which occurs in almost all meteor- 

 ites, even in iron meteorites, and not only to olivine, but to 

 one of the constituents of it, which is magnesium. I have here 

 a diagram of some of the results obtained in the green part of the 

 spectrum, and it will be setn that we get in the nebula of Orion, 

 and in the comets of 1S66 and 1886, a bright line apparently in 

 the same position. When I say line I should correct myself, 

 this luminosity given out by magnesium does not take the form 

 of a line as ordinarily so called. I will throw on the screen 

 photographs of two spectra of the vapours of two metallic 

 substances, barium and iron (Fig. 15), and you will then see 

 what is meant by men of science when they talk about a line 

 spectrum. 



But besides what we call line spectra, there is another 

 thoroughly well- recognised class, which we call fluted spectra, 

 because it reminds one of the flutings of a column. Here, for 

 instance, is a fluting of carbon (Fig. 16). In these flutings, 

 instead of the lines being distributed irregularly, as in the case 

 of iron and barium, we get a beautiful rhythm from one part 

 where the light rapidly degrades to another where there is an 

 enhancement of the light, followed by another degradation, and 

 so on. Indeed, we not only get main flutings, but we get 

 subsidiary flutings. 



J. Norman Lockyer. 



( To be conlinved, ) 



