SCIENCE. 



27 



held together by the forceps, and slightly warmed, 

 just sufficient to soften thegutta percha ; the forceps 

 may now be laid aside, or used simply to press the 

 cover home, warming the slide gently, also the 

 cover ; the perfect contact of the softened " tissue" 

 with the cover and slide is easily recognized, and 

 with a little care this can be effected very quickly, 

 and nothing further is necessary. A finishing ring 

 of colored cement makes a very neat mount, but it 

 is not necessary. 



ON MULTIPLE SPECTRA. 



" Nunc age, quo motu genitalia materiai 

 Corpora res varias gignant, genitasque resolvant 

 Et qua vi facere id cogantur." 



Lucretius ii . , 61-2. 



" Prima moventur enim per se primordia rerum : 

 Inde ea, quae parvo sunt corpora conciliatu, 

 Et quasi proxima sunt ad vireis principiorum, 

 Ictibus iilorum C3ecis impulsa cientur 

 Ipsaque, quae porro paulo maiora, lacessunt." 



Lucretius, ii., 132-6. 



'• It is conceivable that the various kinds of matters, now rec- 

 ognized in different elementary substances, may possess one and 

 he same ultimate or atomic molecule existing in different con- 

 ditions of movement. 



"The essential unity of ma^er is an hypothesis in harmony 

 with the equal action of gravity upon all bodies." — Graham's Re- 

 searches, p. 299. 



In a recent paper* I showed that a study of the minute 

 anatomy of spectra, both terrestrial and celestial, forces 

 upon us the conclusion that both in the electric arc and in 

 the hottest region of the sun the so-called chemical ele- 

 ments behave after the manner of compound bodies. 



I then dealt more especially with the question of the 

 basic lines in the various spectra, and it is clear that if at 

 any one temperature, there be some lines only truly basic 

 in the spectrum of any element, we at once divide the lines 

 visible at that temperature into two groups, those which 

 are basic and those which are not. This would give a 

 compound origin to the lines, and this is the real point. 



It is now years ago since the view was first held that the 

 elementary bodies had double spectra, that is, that each, of 

 at all events several, under changed conditions of temper- 

 ature or electric tension, gave us now a fluted spectrum 

 and now one composed of lines. 



I glimpsed the idea some time afterward that the line 

 spectrum was in its turn in all probability a complex 

 whole, in other words that it was the summation of the 

 spectra of various molecular groupings. 



Recent work has to my mind not only shown that this is 

 true, but that in the case of many bodies the complexity, 

 and therefore the number, of the molecular groupings 

 which give rise to that compound whole called a line spec- 

 trum, is considerable. 



It is therefore important from my point of view to recon- 

 sider the evidence on which the assertion that the fluted 

 bands and the line spectrum (taken as a whole) of a sub- 

 stance really belong to that substance, because if we find 

 that this must be accepted and that it can easily be ex- 

 plained on the view that the two kinds of spectra are pro- 

 duced by different molecular groupings, the fact of other 

 molecular groupings, giving rise to a complex line spec- 

 trum can be more readily accepted, contrary though it be 

 to modern "chemical philosophy," as taught at all events 

 in the text-books. 



Pliicker and Hittorf were, I believe, the first to point out 

 that the same chemical substance, when in a state of gas 



*"° n the Necessity for a New Departure in Spectrum Analysis" 

 (Nature, vol. xxi. p. 8.) 



or vapor, gave out different spectra under different con- 

 ditions. On this point they wrote fifteen years ago: 



" The first fact which we discovered in operating with our 

 tubes . . was the following one : 



" There is a certain number of elementary stibstances which, 

 when differently heated, furnish two kinds of spectra of quite 

 a different character, not having any line or any band in com- 

 mon. 



" The fact is important, as well with regard to theoretical 

 conceptions as to practical applications — the more so as 

 the passage from one kind of spectrum to the other is by 

 no means a continuous one, but takes place abruply. By 

 regulating the temperature you may repeat the two spectra 

 in any succession ad libitum." (Pliicker and Hittorf on 

 the Spectra of Ignited Gases and Vapors: Phil. Trans. 

 Royal Society, 1865, part i. p. 6.) 



Angstrom, whose name must ever be mentioned with 

 the highest respect by any worker in spectrum analysis, 

 was distinctly opposed to this view, and in the text which 

 accompanies- his Spectre Normal we find the following 

 statement : 



" Dans un Memoire sur les spectres ' doubles' des corps 

 e'ementairesque nous publierons prochainement, M.Thalen 

 et moi, dans les Actes de la Societe" des Sciences d'Upsal, 

 nous traiterons d'une maniere suffisamment complete les 

 questions importantes qu'on peut se proposer sur cet 

 interessant sujet. Pour le present, je me borne a dire 

 que res rdsultats auxquels nous sommes arrives, ne con- 

 firment aucunement l'opinion emise par Pliicker, qu'un 

 corps ele'mentaire pourrait donner, suivant sa temperature 

 plus ou moins elevee, des spectres tout-a-fait differents. 

 C'est le contraire qui est exact. En effet en augmentant 

 successivement la temperature, on trouve que les raies 

 varient en intensite d'une maniere trescompliquee, et que, 

 par suite, de nouvelles raies peuvent meme se presenter, 

 si la temperature s'eleve suffisamment. Mais, independ- 

 amment de toutes ces mutations, le spectre d'un certain 

 corps conservera toujours son caractere individual." * 



Angstrom did noi; object merely on theoretical grounds. 

 He saw, or thought he saw, room to ascribe ail these fluted 

 spectra to impurities. 



He was strengthened in this view by observing how, in 

 the case of the spectra of known compounds, there were 

 always flutings in one part of the spectrum or another; a 

 rapid induction naturally, therefore, ascribed all flutings 

 to compounds. The continuity of the gaseous and liquid 

 states of matter, let alone the continuity of Nature's pro- 

 cesses generally, never entered into the question. For 

 Angstrom, as for the modern chemist, there was no such 

 thing as evolution, no possibility of a close physical rela- 

 tionship between elements, so called, driven to incand- 

 escence from the solid state, and binary compounds of 

 those elements. 



In a memoir, however, which appeared after Angstrom's 

 death, and which, though under a different title, was in all 

 probability the one referred to, this opinion was to a large 

 extent recalled, and in favor of Pliicker's view, in the fol- 

 lowing words : — 



'• . . . Nous ne nions certainement pas qu'un corps 

 simple ne puisse dans certains cas donner differents spectres. 

 Citons, par exemple, le spectre d'absorption d'iode que ne 

 ressemble en aucune fa<;on au systeme des raies brillantes 

 du meme corps, obtenues au moyen de l'electricite ; et 

 remarquons de plus qu'en general tout corps simple, pre- 

 sentant la propriete d'allotropie, doit donner a l'etat d'in- 

 candescence des spectres differents, pourvu que la dite prop- 

 riete de la substance subsiste non seulement a l'etat gazeux 

 du corps, mais encore a la temperature meme de l'incand- 

 escence. . . 



" Le soufre solid possede, somme on sait, plusieurs etats 

 allotropiques, et, d'apres certaines observations, ce corps, 

 meme a son etat gazeux, prendrait des formes differentes. 

 Par consequent, en supposant que cela soit vrai, le soufre 

 gazeux doit donner plusieurs spectres d'absorptio, tandis 

 que la possibilite d'un seul on de plusieurs spectres brillants 

 dependra de la circonstance suivante, savoir si les etats 

 allotropiques plus complexes de cette substance supporter- 

 ont la temperature de l'incandescence, avant de se decom- 

 poser. 



♦Angstrom sur " Le Spectre normal du Soleil," page 39, 





