262 ANNUAL OF SCIENTIFIC DISCOVERY. 



selves attracted towards the idea of unity of substance. Gas, liquid, 

 solids, vacuum and plenum, bodies and celestial spaces, satellites, 

 planets, suns, &c., would be but transitory forms of something eternal, 

 the ephemeral images of something which cannot change ; in the vor- 

 tex of phenomena, in the eternal movement of all substance, the 

 cosmic history everywhere shows us the future in the present, and the 

 present in the future. Revue des deux mondes. 



ON THE THEORY AND APPLICATION OF SPECTRUM ANALYSIS. 



We copy from the Intellectual Observer (London), the following 

 remarks on the theory and application of " spectrum analysis,' 1 which 

 may assist our readers in obtaining a clear idea of the nature of 

 this discovery. 



In the first place we would remind them, that a solar spectrum, or 

 prismatic image of the sun, consists of a ray of sunlight, opened like 

 a fan, and spread out so as to exhibit exquisite gradations of color, 

 from red at one end to violet at the other. If we attempt to form a 

 spectrum by allowing a broad mass of light to fall upon a prism, we 

 shall only partially succeed. We shall indeed see rainbow colors, 

 but they will be overlapped and confused. If, however, we permit 

 the light to reach the prism through a narrow slit, and exclude ex- 

 traneous rays, the confusion will be avoided, and a neat, well-defined, 

 ribbon of parti-colored light will be obtained, in which, at certain 

 intervals, dark lines will be observed. These lines, which would 

 appear to a casual observer as insignificant as so many threads of a 

 cobweb, are the hieroglyphic letters which the spectroscopist has to 

 decipher, in accordance with the principles explained in the articles 

 to which we have already made reference. To Sir J. Herschel be- 

 longs the credit of first pointing out that as the spectra of incandes- 

 cent volatilized substances differed from each other, they might be 

 made use of for purposes of analysis. There are only two modes in 

 which such spectra can differ from each other, or from the solar spec- 

 trum which may be taken as a standard. Either they will afford 

 bright lines in the place of dark lines, or dark lines in place of light 

 ones. We have used the term lines, but when the breadth is consid- 

 erable, spaces or bands is a better appellation. 



When a glass prism acts upon a ray of light so as to give a spec- 

 trum, two distinct actions take place. First, the light ray is refracted, 

 or bent out of its course ; secondly, it is opened or spread out like a 

 fon. This last action is called dispersion, and, like refraction, its 

 amount varies with the substance employed in the formation of the 

 prism. 



For the detection of the metals and many other substances, a very 

 minute examination of the spectrum is seldom required, as the spaces 

 or bands by which their presence is indicated are conspicuously shown 

 by any instrument that will display the chief lines of the solar spec- 

 trum. There are, however, many thousand finer lines that can be 

 discerned if a sufficiently powerful and delicate apparatus is employed, 

 and many lines that appear single under ordinary circumstances are 

 found to be multiple when examined with superior means. 



The size and character of the spectroscope should be regulated by 

 the work n quired of it. A very small one, that can be carried in the 



