a Dielectric Normal to the Lines of Force. 347 



variation. Through the entire range the tint of the two halves 

 of the field did not change materially. After each turn of 

 the screw the analyser was set to equalize the intensities of 

 the two halves of the field. The readings of the circle are 

 given directly. The aperture was 3 mm, 



Rotations 



Readings of circle 



Angular deviation 



Differences or 



ofM. 



of analyser. 



from neutral plane. 



rotations. 











4216 



d-oo 



000 



1/40 



4247 



0-038 



o-oi 



1 



42-55 



1-5 



0-39 



2 



42-96 



30 



0-80 



3 



4337 



4-5 



1-21 



4 



43-80 



60 



1-64 



5 



44-23 



7-5 



207 



Current —5 



40-09 



-7-5 



-2-07 



reversed. +5 



44-25 



+ 7-5 



+2-09 



-5 



40-08 



-7-5 



-2-08 



+5 



4423 



+7-5 



+2-07 







4216 



000 



0-00 



Second Set of Observations. 



(In this set the magnetic field diminished 2 per cent, by the 

 end of the experiment.) 



Rotations 



Readings of circle 



Angular deviation 



Differences or 



ofM. 



of analyser. 



from neutral plane. 



rotations. 







42-16 



d-oo 



o-oo 



1 



42-55 



1-5 



0-39 



2 



42-98 



30 



0-82 



3 



43-37 



4-5 



1-21 



4 



43-81 



6-0 



1-65 



5 



44-22 



7-5 



2-06 



6 



4463 



90 



2-47 



7 



4502 



10-5 



2-86 



8 



45-41 



120 



3-25 



9 



45-78 



13-5 



3-62 



10 



46-13 



150 



3-97 



11 



46-50 



16-5 



4-34 







4216 



00 



o-oo 



These results show that Verdet's law holds up to 90°, the 

 Faraday effect changing sign for greater angles near the 

 neutral plane, as the law requires. 



To compare the intensity of the field calculated from this 

 formula with the direct measurement, a mean of several 

 observations on the rotation were taken for a given measured 



