194 



NA TURE 



[December 29, 1892 



photographed by Dr. Huggins in 1890," in the great 

 nebula in Orion is also a mistake. 



Mr. Gore has evidently failed .to appreciate the 

 importance of several portions of Prof. Lockyer's 

 book, and has consequently omitted to mention them 

 in his summary. Thus the observations of meteoritic 

 glows recorded on pp. 49-51 of the "Meteoritic 

 Hypothesis " are entirely passed over. In these 

 experiments it was found that on slowly warming 

 meteorites in a vacuum tube through which electric dis- 

 charges were passing, the spectrum of hydrogen was 

 first developed, then carbon was added, and the first 

 line due to any metal was the 500 line which is the 

 characteristic nebular line. Further heating gave the 495 

 line and then the B magnesium lines. These experi- 

 ments, omitted in Mr. Gore's summary, are an effective 

 answer to the objections of Messrs. Liveing and Dewar 

 given on p. 116 of this book, for we have here the 

 500 line developed in presence of hydrogen, and at a 

 lower temperature than the B lines. 



Mr. Gore believes that " one of the crucial tests of the 

 meteoritic hypothesis" is the question of the identity of 

 the 500 nebular line with the m <gnesium fluting at this 

 wave-length. He says (p. 86) that " it is on the identity of 

 this fluting (or rather its brightest edge) with the chief 

 line in the spectrum of the nebulae that the meteoritic 

 hypothesis mainly depends," and from pp. 118-121 it is 

 obvious that he thinks the evidence conclusively against 

 the hypothesis on this point. 



In the first case the identity of the 500 nebular line 

 with magnesium is not essential to the meteoritic hypo- 

 thesis, although the latest observations have strongly 

 supported the case for the identity. The main point is 

 whether the 500 nebular line is due to high or to low 

 temperature, and whether nebulae are high or low tempera- 

 ture phenomena. Previous to the publication of Prof. 

 Lockyer's book all cosmical bodies were believed to be 

 cooling. The nebulae were considered to be the hottest 

 of all bodies, and on losing heat were supposed to pass 

 into stars of the Sirian type. Further loss of heat con- 

 verted them into stars of the solar type, and by still further 

 loss they became red stars with banded spectra before 

 reaching final extinction. This hypothesis was sup- 

 plemented by Dr. Croll, who suggested that nebulas were 

 formed b) the complete and almost instantaneous vola- 

 tilisation of these dark bodies on collision, the heat 

 generated by impact being sufficient for the purpose. 

 Lockyer's hypothesis supposes nebulas to be loose swarms 

 of colliding meteorites. Condensation of these swarms by 

 gravitation increases the number of collisions, and as the 

 temperature rises we get stars with bright lines in their 

 spectra. Further increase of temperature gives red stars 

 of Secchi's III. class, which pass with still rising tem- 

 perature into stars with fine absorption lines in their 

 spectra, and so on until the Sirian type is reached, in 

 which we have the highest temperature. Collisions have 

 now ceased and the process of coohng begins, the stars 

 passing into the solar type, then into red stars of Secchi's 

 IV. class, and to final extinction. 



The lines in the spectra of nebulae and bright line stars 



according to this theory may be due to three causes. 



(a) Radiating vapours fillmg the interspaces between 



the meteorites ; the lines of hydrogen and the bands of 



NO. 1209, VOL. 47] 



carbon being due to these, {b) Low (e?nperature lines of 

 metals, due to grazing collisions of meteorites, {c) High 

 temperature lines of metals, due to direct collisions. It 

 is essential to the theory that low temperature lines o 

 metals should be found in nebulae spectra, and the low 

 temperature origin of the 500 line seems clearly esta- 

 blished. Its chemical origin is of quite secondary im- 

 portance. That it is due to low temperature is shown by 

 the experiments on meteoritic glows which Mr. Gore 

 omits ; by its presence in comets away from the sun, as 

 observed by Huggins in 1866 and 1867 (this being the 

 only line present), by Vogel in Coggia's comet, and 

 Konkoly in the great September comet of 1882 ; and also 

 by the fact that it persists in all temporary stars as the 

 temperature falls and is the last line to disappear. Until 

 these facts are explained away the foundation of the 

 meteoritic hypothesis remains unshaken. Mr. Gore seems 

 unaware that this main point is now generally admitted, 

 for although the low temperature origin of nebulae was 

 denied by Dr. Huggins as late as 1889, it was adopted 

 in his Address to the British Association at Cardiff in 

 1892. 



There is early evidence in the book that Mr. Gore has 

 entirely failed to grasp this essential point of the hypo- 

 thesis. On p. 41, discussing Croll's impact theory of the 

 formation of nebulae, he says, " accord mg to Prof. Lockyer 

 the temperature of the original solar nebula was as high 

 as that of the sun at present." Mr. Gore would have 

 done well to have noted that on p. 528 of his book Prof. 

 Lockyer explicitly states that ''the temperature of the 

 most prominent radiating vapours in nebulae is about 

 that of the Bunsen burner." 



Mr. Gore's misconception of the theory and the spirit 

 in which he approached its discussion are also shown on 

 p. loi, where he says, " All these conclusions rest, of 

 course, on the supposed coincidence of certain lines in the 

 spectra of comets, nebulae, and stars, with bright lines and 

 flutings, a coincidence which has been disputed by other 

 observers. Relying, however, on the accuracy of his 

 experiments, Lockyer proposes a newgrouping of cosmical 

 bodies. He supposes some of these bodies to be increas- 

 ing in temperature, while others — like our own sun — are 

 cooling." To this he adds a footnote, " Lockyer's curve 

 rests on this assumption, but it should be stated that 

 some astronomers doubt that the sun is really cooling.'" 

 We should be glad to know who these " astronomers " are. 

 Mr. Gore himself is evidently not of their number, for he 

 distinctly recognizes the sun as a cooling body in his 

 chapter on the fuel of the sun, and specially mentions it 

 as such on pp. 42 and 53. It is possible that Mr. Gore has 

 misunderstood the apparently paradoxical fact that a body, 

 in changing from a gas to a liquid, may rise in tempera- 

 ture while losing heat, but that will not justify the loose 

 style which leaves it to be understood by the general 

 reader that Lockyer's curve rests solely on his experi- 

 ments, and the " assumption " that the sun is cooling, and 

 that this fact is doubted by some astronomers. We are 

 quite aware that Mr. Gore s expression will bear other in- 

 terpretations; but this is the idea conveyed to several 

 readers to whom we have shown the book. 



Returning to the question of the coincidence of the 500 

 nebular line with magnesium, the evidence recorded by 

 Mr. Gore is in favour of, rather than against, the identity. 



