1902.] 



Discharge from Metallic Poles in Water. 



35 



(2.) Broadened Bright Lines with Central Absorption. — This is well 

 shown in the central line of the violet triplet of iron at X 4063*76. 



(3.) Broadened Bright Line with Non-symmetrical Absorption (Maximum 

 of Emission towards Bed). — The best examples obtained of this type of 

 reversal are in the spectra of iron. The strong line at k 4260*64 in the 

 water-spark shows the most decided asymmetry, the less refrangible 

 component of the underlying bright line being 7 or 8 times stronger 

 than the part on the violet side of the absorption line. There appears 

 to be no suggestion, either, of the line being duplex, so that the 

 asymmetery cannot be explained as due to the interaction of two 

 neighbouring reversals of varying intensities. 



In the case of the absence of any line at 4481 '30 in the spark in 

 water, it may not be owing to the balance of absorption and radiation, 

 but to a special peculiarity of this line. From many considerations, I 

 regard 4481*30 as a high temperature line only, and therefore it may 

 be that the cooling action of the water envelope surrounding the water 

 spark entirely prevents the production of this radiation. 



From these considerations it appears evident that, if proper exposures 

 be given, lines may be photographed in the spectrum of iron, say, 

 which show all the phenomena described by Dr. Wilsing, but so re- 

 lated to each other and the complete stage — that of reversal, symme- 

 trical or unsymmetrical — -that it is impossible to regard them as 

 anything abnormal. A typical set of lines illustrating these points, 

 beginning with complete reversal with maximum of emission towards 

 red, is as follows : — 



Type. 



Example. 



Remarks. 



1. 



Complete reversal (strong) . . 



4415*29 (Fe) 



Both components of 

 bright line shown 

 strongly, red side 

 most prominent. 



2. 



Complete reversal (weak) . . 



4415*29 (Fe) 

 (another photograph) 



Both components of 

 bright line shown, 

 red side much the 

 stronger. 



3. 



Partial reversal (weak) 



4282-57 (Fe) 



Appearance of a bright 

 line with a dark 

 border on more re- 

 frangible side. 



4. 



Partial reversal (weaker) . . 



4282-57 (Fe) 

 (another photograph) 



Bright component pre- 

 dominant, dark line 

 only just visible. 



5. 



No reversal 



4315-26 (Fe) 

 and many other weak 

 lines. 





D 2 



