Influence of a Magnetic Field on Radiation Frequency. 413 



The entries of "all cases" and of " tricolours observed" in 

 Table V are deduced from Table I, by combining the appropriate 

 columns. The letters at the top show which columns are combined. 



Seven other observed cases, disposed in three groups, are 

 scattered beyond the limits of Table VI ; two of these seven cases 

 are tricolour. 



" Further Note on the Influence of a Magnetic Field on Radia- 

 tion Frequency." By Oliver Lodge, F.R.S., assisted by 

 Mr. Benjamin Da vies. Received May L9, — Read June 3, 

 1897. 



Referring to a former communication of mine, on the subject of 

 Zeeman's discovery, printed on page 513 of the 1 Proceedings of the 

 Royal Society ' for February 11 this year, vol. 60, No. 367, I wish 

 to add an observation to those previously recorded, as I have recently 

 acquired a concave Rowland grating (3-J- X lj-inch ruled surface, 

 14,438 lines to inch, 10 feet radius of curvature, being the one used 

 by Mr. George Higgs), of which the spectra of the first and third 

 orders on one side are very satisfactory. 



It is said on page 513, " If the focussing is sharp enough to show 

 a narrow, dark reversal line down the middle of each sodium line, 

 that dark line completely disappears when the magnet is excited." 

 With the greater optical power now available the dark reversal line 

 is often by no means narrow, and though in some positions of the 

 flame it does still tend to disappear or become less manifest when 

 the flame is subjected to a concentrated magnetic field, the reason of 

 its partial disappearance is that it is partially reversed again — i.e.., 

 that a third bright line, as it were, makes its appearance in the 

 midst of the dark line, giving a triple appearance to each sodium 

 line. 



More completely stated the phenomena are as follows: — After 

 obtaining each sodium line with a prominently double aspect by 

 manipulating the flame, the magnet is excited, and the dark band in 

 the midst of each sodium line is then seen to widen out considerably 

 in the region of most intense magnetisation, while a bright intrusion 

 line makes its appearance. On closer examination this new line is 

 seen to be double, by reason of a dark division down its middle ; and 

 I apprehend that with still more magnetic power this dark band 

 might itself open out into two ; but this last phenomenon I have not 

 yet observed. 



The whole sodium group is thus seen as if it were octuple. The 

 effect is not due to a mere mechanical disturbance or rearrangement 

 of the gases of the flame by the agency of magnetism ; because a 



