DEFENDANT'S EXHIBIT D-31 



On the Absorption of Gas in a Crookes Tale. 503 



development o£ the Swan spectrum depends upon the che- 

 mical nature o£ the atmosphere in which the discharge takes 

 place. 



l'u concluding this paper I wish to say that for the sake ot" 

 brevity I have refrained from alluding at all fully to the 

 literature of the carbon spectra, and have confined my re- 

 ferences to previous researches which bear most directly on 

 the matter under investigation. I say this lest it might be 

 thought that I had not given due attention to the work of 

 previous observers. As a matter of fact I have made a 

 careful critical study of all the papers to which 1 could find 

 references. 



I have not discussed the astrophysical bearing of the origin 

 of the Swan spectrum as I do not feel qualified to deal with 

 the subject, but so far as I can judge, the view which I have 

 advanced does not conflict with any established astrophysical 

 theory. 



During the progress of this investigation I have received 

 considerable assistance from students ot the Yorkshire College, 

 notably Dr. Guthrie, Dr. Dent, and Dr. H. A. Wilson, and 

 to them my thanks are due. I am especially indebted to 

 Dr. Wilson and to my assistant Mr. A. Dickson for their skilful 

 assistance in the construction and manipulation of apparatus 

 employed in the electrical experiments. 



The Yorkshire College, Leeds. 



XLTV. On the Absorption of Gas in a Crookes Tube. By 

 R. S. Willows, B.A., JD.Sc, Trinity College, Cambridge, 

 1851 Exhibition Scholar *. 



Introduction. 



IT has been observed by different experimenters that the 

 continued passage of a discharge through rarefied gas 

 contained in a sealed tube introduces a difference in the 

 appearance of the discharge. Thus Pliicker f found that on 

 many occasions striae only appeared in a Geissler tube after 

 the discharge from a RuhmkorfFs coil had been pas>ing for 

 some time, and that a continuance of the discharge served to 

 make the striae better defined. Miiller and De la Rue found 

 that the continuous discharge from their large battery, 

 as distinguished from the intermittent discharge from an 



* Communicated by Prof. J. J. Thomson, F.R.S. 

 t Plucker, Pogg. Annal. 1858, vol. ciii. p. 91. 



