Spectrum Analysis 159 



illustrated his views by striking experiments on the relation 

 between radiation and absorption. Incidentally, he corrected 

 a wrong idea based on erroneous experiments by a Dr. Bache 

 in the United States, who claimed to have shown that, while 

 the surface colour greatly affected the absorption, it had no 

 effect on the radiation of a body. 



Bearing in mind what has been said, it is not surprising 

 that, notwithstanding all that had been done before their time, 

 Kirchhoff's and Bunsen's work created a deep impression. 

 The combination of a physicist and chemist was almost 

 necessary to bring out the full significance of the observations ; 

 and the accumulated experimental evidence furnished by 

 them was complete in itself, and left no doubt as to the 

 value of the new method of investigation, which formed not 

 only a most delicate test of the chemical nature of substances 

 which we handle in the laboratory, but would also be applied 

 to the analysis of any light-emitting body however great 

 its distance might be. It is well known how the spectroscope 

 at once- revealed a number of new metals, among them being 

 thallium, which was first identified by Sir William Crookes. 



The further development of the subject disclosed a far 

 greater potentiality of the spectroscopic attack than was 

 dreamed of by its originators. At first it was considered 

 that the spectrum was an atomic property ; in other words, 

 that each atom preserved its spectrum when combined 

 with other elements, so long at any rate as the substance 

 remained in the gaseous state. There was not much oppo- 

 sition to the next step, by which compounds were shown 

 to have independent spectra, but when it appeared that 

 even one and the same element could give a number of 

 different spectra under different conditions, fresh fields of 

 investigation were opened out. In the further elucidation 

 of the subject, this country has helped as much as, and 

 perhaps more than, any other. It will be sufficient to mention 

 the work of Lockyer, Liveing and Dewar, and the investi- 

 gations of Lord Rayleigh on the Optics of the Spectroscope, 

 which, by pointing out the limits of their power for given 

 optical appliances, have shown the direction in which an 

 extension of these limits is possible. In the investigation of 

 the absorption spectra of organic compounds a prominent 



