20 



Prof. A. Gray and Dr. W. Stewart. Radiation of [Apr. 27, 



Substance. 

 Helium. 



SAIL 



5016 (green) 1-61 x 10- 

 5876 yellow) 2-07x10-' 

 6678 (red) 2-90x10- 

 5461 (green) 2-12 x 10- 



6-41 x 10- J<1 



6-00x10- 11-3x10, 



6-49x10- 12-2 x 10, 

 7-12x10- 



Each result in the above table is the mean of several determinations ; 

 of three, seven, and five respectively in the case of helium, and of 

 seven in the case of the mercury line. 



FIG. 3. 



& of HeL 



= 6678* 



IOOO 20OO 



30OO 4-OOO 5OOO 6OOO 7OOO 

 Magnetic field in C.G.S. units. 



QOOO 9OOO IO.OOO 



When, with the green line of mercury under observation, the field 

 strength was increased to 13,000 C.G.S., the centre component of the 

 normal triplet was doubled, while each of the outer components was 

 itself tripled. The polarisation of the two triplets and of the central 

 doublet was the same as that of the lines from which they originated, 

 namely, that of the lines of the normal triplet. 



At all fields up to 13,000 the faint companion to the yellow helium 

 line D 3 was not tripled, but only doubled. 



For all the lines specified above, observations were made also along 

 the lines of force, one of the magnet cores being replaced for this 

 purpose by a core drilled from end to end with a hole about a 

 centimetre in diameter. The normal doublet was observed up to a 

 field of about 10,000 C.G.S., and the separation between the two 



