164 Mr. J. N. Lockyer. Researches in Spectrum [Dec. 12, 



Application of these Considerations to Known Compounds. 



Now to apply this reasoning to the dissociation of a known com- 

 pound 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 spectrum of the metal itself 

 consists of lines, the number and thickness of some of which increase 

 with increased quantity, the spectrum of the compound consists in the 

 main of channelled spaces and bands, which increase in like manner. 



In short, the molecules of a simple body and a compound 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, dissociates 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 dissocia- 

 tion, 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 con- 

 clusion 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 reasoning which I 

 have to bring forward in discussing the compound nature of the 

 chemical elements themselves. 



In a paper communicated to the Royal Society in 1874, referring, 

 among other matters, to the reversal of some lines in the solar spec- 

 trum, 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 spectrum] 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 spectrum, 

 and remaining, moreover, visible in the spectrum of substances con- 



* " Phil. Trans.," vol. clxiv, part 2, p. 807. 



