S54 The Secondary Spectrum of Hydrogen. 



Also 



ai + « 2 + a 3 = {mC + LC^- + l/} -rLCp. 



Using these last expressions, (11) becomes 



c{Lt+M+pr\-. JMC + LC^ +l/}=0. 



i.e. ; -(L-O 2 ) = 0, or L = 2 . 



Therefore, in the case of the oscillatory discharge of the 

 condenser, with a constant E.M.F., the relation L=0 2 

 holds. Hence the expression for the inductance of the coil 

 is independent of the inductance of the galvanometer. 



Cass Institute, E.O., 

 Feb. 23, 1909. 



LXXX. The Secondary Spectrum of Hydrogen. 

 By A. Dufour * 



IN a recent note f Mr. C. F. Hogley has studied the 

 secondary spectrum of hydrogen with the object of 

 ascertaining whether it is really due to this gas. With this 

 view, he works with vacuum-tubes having a bulb containing 

 charcoal that can be cooled by liquid air ; it is known that in 

 these conditions the charcoal absorbs all gases except hydrogen, 

 neon, and helium. Mr. Hogley finds that the stellar spectrum 

 and the secondary spectrum of hydrogen have, in his tubes, 

 relative intensities that remain unchanged, when the charcoal 

 is cooled by liquid air ; this would not take place if the 

 secondary spectrum of hydrogen was due to an absorbable 

 gas different from hydrogen. He is led to the following 

 conclusion : — " So far, then, as this method can decide, the 

 evidence points to the conclusion that hydrogen is really the 

 source of the secondary spectrum." 



This conclusion is, then, the same as the conclusion I had 

 pointed out formerly in an investigation dealing with the 

 same subject J. In this work I relate at first the numerous 

 researches previously made on this subject, and next 

 various experiments that I have made either with vacuum- 

 tubes constituted of different materials, or with tubes filled 



* Communicated by the Author. 



t C. F. Hogley, Phil. Mag. s. 6, vol. xvii. p. 581 (1909). 

 % A. Dufour, Ann. de Chimie et de Physique, 8 e ser. t. ix. pp. 361-432 

 (1907). 



