396 



Lord Blythswood and Dr. Marchant on 



A double-image prism was employed to separate tbe outer 

 and inner components of the compound line. In the photo- 

 graphs^ components which are polarized parallel to the lines 

 of force form the top half of the line, and components 

 polarized perpendicularly to the lines of force are at the 

 bottom. 



Under a weak magnetic field the line appears as a triplet ; 

 as the strength of the field increases the lower or inner com- 

 ponent splits into a doublet, and the line becomes a quartet. 

 It should be noticed that in the double-order condition the 

 central line, which is composed of two outer components of 

 the two orders nearly superimposed, is very much brighter 

 than the outer components. 



In the single-order photograph with a slightly stronger field 

 (12,000), the side components of the orders on each side of 

 the original single order have come near enough to the centre 

 of the field to become bright, and are superimposed on the 

 components due to the original single order. In a still 

 stronger field the two outer components split into two com- 

 ponents each so that the resultant line becomes a sextet. It 

 is somewhat difficult to follow the final splitting of the outer 

 components. It may, however, best be done from the single- 

 order condition. 



Fig. 8. 



B'A'B' C'A' C 



B C 



Yvith 

 magnetism 



II 



VmV 



VwV 



Without 

 magnetism. 



A C 

 (1) 



B A C 



(2) 



3 A C 



/3) 



Starting from the condition (1) fig. 8, which is that shown 

 in the photograph with a field of 12,000 c.G.s. units, the line 

 C due to the order C is superimposed on the line A' due 

 to A ; and similarly B' is superimposed on the other com- 

 ponent of A, both lines being thick. As the field-strength 

 increases, the components of A get farther from the centre 

 of the field, and finally fail to show on the photograph; the 

 right-hand component of B and the left-hand component of 

 C gradually get nearer the centre of the field and become 



