( n 



extremely small displacement under rather unfavourable circumstances. 



The failure of all attempts hitherto made to observe an electric 

 spectral effect ^), induced me to try a new w^ay for attacking the 

 problem. I have imagined a method which would reveal an action of 

 the electric field by an asymmetrical change of a magnetic triplet, 

 or by a remarkable variation of a magnetic doublet. 



I shall prove that tlie mentioned asymmetry must change its sign 

 if the direction of the electric field is rotated through an angle of 

 90°. In some of my experiments the electric field existing between 

 metallic electrodes during the passage of the spark is used. 



The spark passes across an air space, in a longitudinal or in a 

 transverse magnetic field as the case may be. [In more recent experi- 

 ments the absorption lines of a xenotime crystal were studied]. 



Besides the mentioned asymmetries different, delicate particularities 

 of triplets originating under the simultaneous influence of magnetic 

 and electric forces can be predicted. 



Th3 observation of tlie whole of these particularities would give 

 almost as strong evidence for the existence of the electric effect as 

 a direct observation of the effect in an experiment made with electric 

 forces alone. 



There is one particularity, which, if it could be observed, would 

 prove by itself most strongly the existence of an electric spectral 

 effect. I shall show (see § 10) that the components of the magnetic 

 doublet, observed along the horizontal magnetic lines of force cease 

 to be completely circularl}^ polarized, but must become slightly 

 elliptically polarized, if the vibrating electrons are at the same time 

 under the influence of a vertical electric field. The ellipticity hinted at 

 must be much more easily observable than a change of frec|uency 

 under the sole action of electric forces. 



For some time I privately held the opinion that the asymmetry 

 of some magnetic triplets, first studied in detail by myself and after- 

 wards by Gmelin, Dufolr, Nagaoka, and others, could be explained 

 by a cooperation of electric and magnetic fields. 



I shall show, however, experimentally that such cannot be tlie case. 



A description of the experiments hitherto made seems to be of 

 some interest, although at the present moment the question of the 

 existence of a specific action of electric fields on the emission of 

 light cannot yet be answered affirmatively. 



The experiments certainly are of some value for our understanding 

 of the asymmetry of triplets, and may show tlie way to better 



1) Gf. Hull. Proc. R. S. p. 80. Vol. 78. 1907. 



