Jan. 2, 1879] 



NATURE 



201 



say, therefore, that there is no impurity of iron in man- 

 ganese, but although the longest iron lines are not there, 

 some of the fainter basic ones are. This I hold to be 

 the explanation of the apparent confusion in which we 

 are landed on the supposition that the elements are 

 elementary. 



Application of these Considerations to Known 



Compounds 

 Now to apply this reasoning to the dissociation of a 

 known compound body into its elements — 



A compound body, such as a salt of calcium, has as 

 definite a spectrum as a simple one ; but while the spec- 

 trum of the metal itself consists of lines, the number and 

 thickness of some of which increase with increased quan- 

 tity, the spectrum of the compound consists in the main 

 of channelled spaces and bands, which increase in hke 

 manner. 



In short, the molecules of a simple body and a com- 

 pound one are affected in the same manner by quantity 

 in so far as their spectra are concerned ; in other words, 

 both spectra have their long and short lines, the lines in 

 the spectrum of the element being represented by bands 

 or fluted lines in the spectrum of the compound ; and in 

 each case the greatest simplicity of the spectrum depends 

 upon the smallest quantity, and the greatest complexity (a 

 continuous spectrum) upon the greatest. 



The heat required to act upon such a compound as a 

 salt of calcium so as to render its spectrum visible, dis- 

 sociates the compound according to its volatility ; the 

 number of true metallic lines which thus appear is a 

 measure of the quantity of the metal resulting from the 

 dissociation, and as the metal lines increase in number, 

 the compound bands thin out. 



I have shown in previous papers how we have been 

 led to the conclusion that binary compounds have spectra 

 of their own, and how this idea has been established by 

 considerations having for a basis the observations of the 

 long and short lines. 



It is absolutely similar observations and similar reason- 

 ing which I have to bring forward in discussing the com- 

 pound nature of the chemical elements themselves. 



In a paper communicated to the Royal Society in 1874, 

 referring, among other matters, to the rerersal of some 

 lines in the solar spectrum, I remarked * : — 



" It is obvious that greater attention will have to be 

 given to the precise character as well as to the position 

 of each of the Fraunhofer lines, in the thickness of 

 which I have already observed several anomalies. I 

 may refer more particularly at present to the two H lines 

 3933 and 3968 belonging to calcium, which are much 

 thicker in all photographs of the solar spectrum [I might 

 have added that they were by far the thickest lines in the 

 solar spectmm] than the largest calcium line of this 

 region (4226"3), this latter being invariably thicker than 

 the H lines in all photographs of the calcium spec- 

 trum, and remaining, moreover, visible in the spectrum 

 of substances containing calcium in such small quantities 

 as not to show any traces of the H lines. 



"How far this and similar variations between photo- 

 graphic records and the solar spectrum are due to causes 

 incident to the photographic record itself, or to variations 

 in the intensities of the various molecular vibrations 

 imder solar and terrestrial conditions, are questions 

 which up to the^ present time I have been unable to 

 discuss." 



An Objection Discussed 

 I was careful at the very commencement of this paper to 

 point out that the conclusions I have advanced are based 

 upon the analogies furnished by those bodies which, by 

 common consent and beyond cavil and discussion are 

 compound bodies. Indeed, had I not been careful to 

 urge this point the remark might have been made that 

 the various changes in the spectra to which I shall draw 



' Phil. Tram., vol. clxiv., part 2, p. 807. 



attention are not the results of successive dissociations, 

 but are effects due to putting the same mass into different 

 kinds of vibration or of producing the vibration in different 

 ways. Thus the many high notes, both true and false, 

 which can be produced out of a bell with or without its 

 fundamental one, might have been put forward as 

 analogous with those spectral lines which are produced 

 at different degrees of temperature with or without 

 the line, due to each substance when yibrating visibly 

 with the lowest temperature. To this argument, how- 

 ever, if it were brought forward, the reply would 

 be that it proves too much. If it demonstrates that 

 the // hydrogen line in the sun is produced by the same 

 molecular grouping of hydrogen as that which gives us two 

 green lines only when the weakest possible spark is taken 

 in hydrogen inclosed in a large glass globe, it also proves 

 that calcium is identical with its salts. For we can get 

 the spectrum of any of the salts alone without its common 

 base, calcium, as we can get the green lines of hydrogen 

 without the red one. 



I submit, therefore, that the argument founded on the 

 ovemotes of a sounding body, such as a bell, cannot be 

 urged by any one who believes in the existence of any 

 compound bodies at all, because there is no spectroscopic 

 break between acknowledged compounds and the sup- 

 posed elementary bodies. The spectroscopic differences 

 between calcium itself at different temperatures is, as I 

 shall show, as great as when we pass from known com- 

 pounds of calcium to calcium itself. There is a perfect 

 continuity of phenomena from one end of the scale of 

 temperature to the other. 



Inquiry into the Probable Arrangement of the Basic 

 Molecules 



As the results obtained from the above considerations 

 seemed to be so far satisfactorj', inasmuch as they at once 

 furnished an explanation of the basic lines actually ob- 

 served, the inquiry seemed worthy of being carried to a 

 further stage. 



The next point I considered was to obtain a clear 

 mental view of the manner in"which, on the principle of 

 evolution, various bases might now be formed, and then 

 become basic themselves. 



It did not seem unnatural that the bases should increase 

 their complexity by a process of continual multiplication, 

 the factor being i, 2, or even 3, if conditions were avail- 

 able under which the temperature of their environment 

 should decrease, as we imagined it to do from the furnace 

 A down to furnace D. This would bring about a condi- 

 tion of molecular complexity in which the proportion of 

 the molecular weight of a substance so produced in a 

 combination with another substance would go on con- 

 tinually increasing. 



Another method of increasing molecular complexity 

 would be represented by the addition of molecules of 

 different origins. Representing the first method by 

 A -|- A, we could represent the second by A -f B. A varia- 

 tion of the last process would consist in a still further 

 complexity being brought about by the addition of 

 another molecule of B, so that instead of (A -}- B)2 merely, 

 we should have A -j- Bg. 



Of these three processes the first one seemed that 

 which it was possible to attack under the best conditions, 

 because the consideration of impurities was eliminated ; 

 the prior work has left no doubt upon the mind about 

 such and such lines being due to calcium, others to iron, 

 and so forth. That is to say, they are visible in the 

 spectra of these substances as a rule. The inquiry took 

 this form : Granting that these lines are special to such 

 and such a substance, does each become basic in turn 

 as the temperature is changed ? 



I therefore began the search by reviewing the evidence 

 concerning calcium and seeing if hydrogen, iron, and 

 lithium behaved in the same way. 



{To be continited.') _ 



