at the Royal Institution, 1908-1916 741 



spectra of metals. It is well known that the foundation of solar and 

 stellar spectroscopy, to which we owe our knowledge of the constitu- 

 tion of the sun and other hot stars, w^as laid by Kirchoff's discovery 

 that bright lines in the spectra of certain metals could be reversed 

 by passing their light through relatively cool vapours of the metals ; 

 the discovery gave the clue to the interpretation of the dark lines in 

 the Solar Spectrum. 



Bunsen and Kirchoff succeeded in reversing certain lines in the 

 spectra of the alkali and alkaline-earth metals ; the French observer 

 Cornu extended the list to thalium, lead, silver, aluminium, mag- 

 nesium, calcium, zinc and copper ; Liveing and De war's investiga- 

 tions were of a far-reaching character and added much to our 

 knowledge of the conditions under which reversal takes place. The 

 inquiry was extended in a variety of directions and the spectroscope 

 grew naturally to be a favoured instrument in the Institution labora- 

 tory and lecture room. 



The introduction of powerful dynamo-electric machines into the 

 laboratory, gifts of the President— the Duke of Northumberland— and 

 of Mr. Siemens, gave the opportunity to study the chemical inter- 

 actions taking place at the temperature of the electric arc. These 

 were first referred to in a Friday evening lecture, on January 16, 1880, 

 under the title " Investigations at High Tem]^eratures." 



The conclusion arrived at (by Pliicker, Angstrom and Thalen) 

 that the so-called carbon spectrum is invariably associated with the 

 formation of acetylene led to trials whether this gas could be 

 extracted from the electric arc. 



A long series of experiments were made in dry atmospheres, with 

 purified carbon poles, which all led to the conclusion that hydrogen 

 cyanide, HCN (and perhaps cyanogen, C2N2), was invariably formed 

 and that it was impossible to deprive the carbons completely of com- 

 bined hydrogen. 



Hence the conclusion that " the inference drawn by Mr. Lockyer 

 as to the elementary character of the so-called carbon spectrum from 

 an examination of the arc in dry chlorine could not be regarded as 

 satisfactory, seeing that undoubtedly hydrogen was present in the 

 carbon and in all probability nitrogen in the chlorine." 



The subject was again dealt with in 1881 (Friday, June 10) in a 

 lecture on the " Origin and Identity of Spectra." Stress was laid 

 upon the imperfection of the evidence that carbon can take the 

 state of vapour at the temperature of the electric arc. It appeared 

 probable that the spectra attributed to carbon were more likely to be 

 those given by compounds such as cyanogen and hydrogen cyanide, 

 acetylene and carbonic oxide, all of which are formed under the 

 conditions of practice. 



