192. 



Mr. J. Norman Lockyer. 



Fluting s represent Vibrations of Complex Molecules. 



I take the change of the continuous spectrum successively into 

 flutings and lines first, and in justification of the statement that in 

 this matter my view is now generally accepted, I give the following 

 quotations from Schuster and Eder and Valenta : — 



" That the discontinuous spectra of different orders (line and band 

 spectra) are due to different molecular combination I consider to be 

 pretty well established, and analogy has led me (and Mr. Lockyer 

 before me) to explain the continuous spectra by the same cause ; for 

 the change of the continuous spectrum to the line or baud spectrum 

 takes place in exactly the same way as the change of spectra of 

 different orders into each other.* 



" Spater fiihrte Lockyer weiter aus, dass die Gase, solange ihre 

 Molekiile aus mehreren Atomen zerf alien, Linienspectren geben 

 miissen. Diese Anschauung wurde seither ziemlich allgemein accep- 

 tirt."f 



The Complexity of the Line Spectrum. 



With regard to the view that the line spectrum integrates for us 

 the vibrations of several sets of molecules, as I have already stated 

 this is not accepted. The number of objections is legion, and it is 

 impossible to refer to all of them here. But, at the same time, the 

 opinion of some of those workers who have approached the subject 

 .from both points of view is, I think, coming round to my side, and I 

 shall briefly refer to one or two instances, the first bringing confirma- 

 tion from a new line of inquiry. 



The effect of Pressure on Wave-length. 



Messrs. Humphreys and Mohler have recently made, at the Johns 

 Hopkins University, a series of experiments upon the effects of 

 pressure on the wave-lengths of metallic lines.]; Using an electric 

 arc inclosed in a cast-iron cylinder, they have observed the spectra 

 at pressures varying up to fourteen atmospheres. 



The general effect of pressure was to broaden the lines and to 

 bring out the reversals, but cadmium was found to be an exception. 

 With one exception, all the measurements actually made of the 

 spectra of twenty-three elements showed that " the shifts were 

 invariably towards the less refrangible, i.e., the red end of the 

 spectrum, and that they were directly proportional, not only to the 



* Schuster, ' Phil. Trans.,' 1879, Part 1, vol. 169, p. 39. 



f Eder and Valenta, ' Denkschriften der kaiserlichen Akademie der Wissen- 

 schaften,' Wien, Bd. 61, p. 426, 1894. 

 X ' Astrophysical Journal,' vol. 3, p. 114. 



