tl^ 



XXIV. Notes on the Zeeman Effect. \j 



_%K A. Kent*. 



IT has been shown by H. M. Reese f that the separation of 

 the external components of the regular Zeeman triplet 

 or quadruplet, as seen perpendicular to the lines of force, 

 does not vary proportionally with the strength of the magnetic 

 field in which the luminous source is placed. This fact was 

 established for various zinc and cadmium lines up to a field 

 of about 26,000 c.g.s. units. 



Reese also states, in referring to certain lines in the spec- 

 trum of iron, that, u In comparing the separation of the lines 

 between 3900 and 4450 it was at once observed that the lines 

 could be broken up into two classes, in each of which the 

 separation of the various lines was of the same magnitude. 

 These two classes are identical with those for which Humphreys 

 found that the shift due to pressure was the same. On these 

 plates the separation is very small in all cases, owing to a 

 weak field, and no accurate measurements were taken of the 

 separation." 



It appeared then to be a matter of no little interest to 

 extend Reese's investigations on zinc using higher field- 

 strengths ; and also to make a more exhaustive investigation 

 of the spectrum of iron and measure the separation with care. 

 These two primary lines of study suggested others as given 

 below. 



The apparatus used was essentially that employed by 

 Reese:— A Rowland concave grating, radius of curvature 

 13 feet 3 inches, of 15,000 lines per inch, fitted with the 

 ordinary slit and camera box ; Seed's " Gilt Edge," ( Valuer's 

 " Isochromatic Fast/' and the International Colour Photo. 

 Co.'s " Erythro " plates ; an electromagnet giving a maxi- 

 mum field of 33,000 C.g.s. units for a 3 mm. gap; as luminous 

 source, a spark between terminals of, or containing, the 

 metals investigated — the spark being produced by an alter- 

 nating current, of 133 cycles per second passed through an 

 adjustable impedance and through a transformer, the secon- 

 dary circuit containing a condenser which discharged across 

 the spark-gap, the leads to which were short thick wires 

 (self-induction was used in the discharge circuit when it was 

 desirous to remove the air-spectrum or sharpen the lines of 

 the metal under investigation) ; and a dividing engine, whose 



* From the Johns Hopkins University Circulars, vol. xx. no. 152 

 (May-June 1901). 



t Astrophys. Journal, xii. No. 2, Sept, 1900, pp. 120-135. 



