ARTICLES 



THE SIGNIFICANCE OF SPECTROSCOPY 



By HERBERT DINGLE, D.I.C., A.R.C.Sc, B.Sc. 

 Imperial College of Science and Technology, London. 



The advance of spectroscopy during the last few decades is 

 one of the most striking movements in the vast campaign of 

 physical science. It is not so very long since the spectrum 

 was, if not a disregarded, at any rate an insignificant unit in 

 the battalions of material phenomena. To-day it is hardly 

 an exaggeration to say that it dominates the situation. We 

 no longer look for light to be shed on the structure of matter. 

 We examine the light that matter itself emits, and find there, 

 as well the secrets of the stars as the path to the knowledge 

 of the ultimate constituents of the atom. 



Spectroscopy originates in the general subject of radiation, 

 and this in turn arises out of the interaction of matter and 

 ether. For, despite many apparent inconsistencies, we have 

 as yet no better working conception of the physical universe 

 than that of a number of material objects swimming in and 

 interpenetrated by a boundless sea of ether. It is in terms of 

 this conception that we can best approach the question of 

 radiation. It is supposed that every fragment of matter that 

 exists — presumed to be above the absolute zero of temperature 

 — is ceaselessly sending out energy into space. This energy 

 is transmitted by the ether in the form of waves, and is either 

 absorbed by other pieces of matter or goes on travelling to 

 eternity. The higher the temperature of the radiating body, 

 the greater is the rate of radiation. We shall see shortly that 

 not only the rate, but also the kind of radiation emitted, is 

 dependent on the temperature. Now there are three extremely 

 important characteristics of any one kind of etherial radiation. 

 There is the velocity, F, with which it travels ; the " wave- 

 length," X, i.e. the distance between two adjacent crests in 

 the wave-train ; and the frequency, n, i.e. the number of waves 

 emitted per second — or, which is the same thing, the number 

 of waves passing any fixed point in the medium per second. 



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