﻿Resonance Radiation of Mercury Vapour. 1111 



Increased the spectral range of the frequencies to which the 

 mercury molecules could respond, in other words broadened 

 the 2536 absorption line of the mercury vapour, which was 

 thus able to divert as resonance radiation more energy from 

 the exciting beam. In vacuo, the mercury vapour abstracts 

 only the "core" of the very narrow 253b' line ; in helium 

 or argon practically the entire energy of the line may be 

 diverted. This was tested in the following way. 



The 2536 light from the monochromator was passed 

 through a highly exhausted quartz tube containing a drop 

 of mercury. This removed the " core" of the line, the light 

 •emerging from the tube causing no resonance radiation in a 

 second exhausted mercury tube, though still nearly as intense 

 as the original beam. Helium was now admitted to the second 

 tube, and intense resonance radiation immediately observed, 

 proving that the mercury vapour in helium will resonate to 



Fig:. 2. 



the frequencies to the right and left of the core of the 

 exciting line, as indicated in fig. 2. Here we have the 

 intensity curve of the 2536 exciting line represented by an 

 unbroken line, the portion abstracted by mercury vapour in 

 vacuo by a dotted line, and the portion taken up by mercury 

 in argon or helium by the line of dashes. 



