r,i) PR W. GEOFFREY DUFFIELD ON THE 



indefinite patch of light. There is some indication of this in the gold spectrum, but 

 tlir phenomenon is not nearly as fully developed. A small amount of continuous 

 spectrum appears at the highest pressures, and is partly caused by the incandescent 

 poles being focussed upon the slit during a portion of the exposure, and partly also by 

 the spreading out of the wings of the strong lines as in the silver spectrum. 



Individual references to the lines on these plates will be found throughout the text. 



5. Broadening of the Lines. From the photographs we learn the following 

 facts : 



1. All lines broaden under pressure. 



2. The broadening increases with the pressure, but different amounts of exposure 

 necessarily make it difficult to determine if the relation between the two quantities is 

 a linear one. 



The broadening of the lines of the spectrum of the gold arc is of two types : 

 (a) Symmetrical. (6) Unsymmetrical. 



Unsymmetrical 



b 

 Fig. 1. 



F,g. 1 is intended to illustrate these types and to draw attention to a feature 

 characteristic of many of the lines of the gold spectrum under moderate 

 their appearance as strong lines superposed upon hazy wings against 

 ch they are more or less sharply defined 



. respect they afford a contrast to the lines of the copper spectrum,* in 

 he wings seem more intimately related to the original line. The intensity 

 curves for the above lines of gold are of this nature 



whereas those for the copper lines investigated are more of this character 



Copper 



DUFFIKLD, -Phil. Trans.,' A, vol. 209, p. 20 5, 1908. 



