686 Professor Deioar [June 10, 



The series of ex23eriments, unless proved to be wrong, are almost 

 conclusive proof that Mr. Lockjer's views regarding the origin and 

 variation of the carbon spectrum have no real experimental basis. 



Spectrum of Magnesium. 



The absorption spectrum of magnesium and of magnesium with 

 potassium and sodium, as seen in iron tubes in a hydrogen atmo- 

 sphere, described in the former lecture, correspond to no known 

 emission lines of magnesium. We could only ascribe their origin to the 

 mixtures employed as distinct from the separate elements, and there- 

 fore were led to investigate the conditions under which corresj^onding 

 emission lines could be produced. 



In ' Proc. Eoy. Soc' vol. xxvii. p. 494, the emission spectrum of 

 sparks from an induction coil taken between mRguesium points in an 

 atmosphere of hydrogen is described as follows : — 



" A bright line regularly appeared with a wave-length about 



5210 This line does not usually extend across the whole 



interval between the electrodes, and is sometimes seen only at the 

 negative electrode. Its presence seems to depend on the tempera- 

 ture, as it is not seen continuously when a large Leyden jar is 

 employed, until the pressure of the hydrogen, and its resistance, is 

 very much reduced. When well-dried nitrogen or carbonic oxide is 

 substituted for hydrogen, this line disappears entirely; but if any 

 hydrogen or traces of moisture be present, it comes out when the 

 pressure is much reduced. In such cases the hydrogen lines C and F 

 are always visible as well. Sometimes several fine lines appear on 

 the more refrangible side of this line between it and the h group, 

 which give it the appearance of being a narrow baud shaded on that 

 side." " In addition to the above-mentioned line, we observed that 

 there is also produced a series of fine lines, commencing close to the 

 most refrangible line of the h group, and extending, with gradually 

 diminishing intensity, towards the blue .... from forty-five to 

 fifty being visible, and placed at nearly equal distances from each 

 other." 



In a paper entitled " A New Method of Spectrum Observation," * 

 Mr. Lockyer regards this spectrum as illustrative and confirmatory 

 of his views regarding the jiossibility of elemental dissociation at 

 difierent heat-levels. The view taken by Mr. Lockyer may be 

 expressed in his own words : — 



" The flame spectrum of magnesium perhaps presents us best 

 with the beautiful effects produced by the passage from the lower to 

 tlic higher heat-level, and shows the important bearing upon solar 

 physics of the results obtained by this new method of work. ... In 

 the flame the two least refrangible of the components of h are seen 

 associated with a line less refrangible so as to form a triplet. A 



Proc. Roy. Soc' vol. xxx. p. 22. 



