( s^fi ) 



any cliaiip;e in wavelength of line 5791, that of the otlier line 

 remaining- coiiislant, ninst manifest itself in a relative displaeement, 

 determined by et] nations (1) and (2). 



Taking two negatives with the smallest possible interval of time 

 anv change of position of line a' can be made out by measurement. 

 A small displacement of line a.' to a position n" , was noticed. 



4. The annexed table gives* in detail the results of measnremejits 

 on negatives, taken according to the method of § 3 on different 

 days and under somewhat different circumstances. 



The echelon used, was described on a former occasion ^) ; it lias 

 30 plates 7,8 m.m. thick, the depth of the steps being 1 m.m. 



The distance of line a to line b is measured in m.m. and indicated 

 as distance n — h and so on. H denotes the strength of tield in Gauss. 



It appears from this table that the position of line a' relatively 

 to a and h is changed by magnetization and that the displacement 

 increases with the field intensity. 



It is not less clear however that the observed displacement is due 

 not only to a change of wavelength of line 579J, but to a super- 

 position of change of frequency of the two lines considered. Indeed 

 the distance n — />, i. e. the distance of the adjacent orders of line 

 5771, is always smaller in the first section of the table than in the 

 second one. Hence we must conclude to a change of wavelength of 



1) Zeeman. These Proceedings 30 November 1901. 



