AN INTERFEROMETER STUDY OF RADIATIONS 

 IN A MAGNETIC FIELD.- 



By Professor J. C. Shedd. 



In the historical development of this subject two well 

 marked experimental methods have been developed. The 

 first of these is the Spectrophotographic method used by Dr. 

 P. Zeeman and the majority of those who have followed. This 

 method is found to be limited, (1) in range by reason of the 

 small resolving power of the ruled grating, so that good 

 results are only obtained by using strong magnetic fields. It 

 is also limited, (2) in accuracy, by reason of the wide mar- 

 gin of error in the settings of the micrometer, especially when 

 nebulous lines are to be measured. 



The second method is due to Professor A. A. Michelson 

 and consists in the use of the interferential refractometer as 

 devised by him. This method is found to have a resolving 

 power greatly in excess of the photographic method, and hence 

 is applicable to low values as well as to high values of 

 magnetic field strength. The results so far accomplished 

 may be briefly summarized as follows: 



I. By the Spectrophotographic Method. 



(1) A classification of spectral lines according to the type 

 of line produced by the action of the magnetic field. 



(2) The measurement of the change in wave-length pro- 

 duced by the magnetic field, and a determination of 

 the ratio of ionic charge to ionic mass (e/w). 



II. With the interferometer method Professor ]\Iichelson 

 has presented three well-marked types of lines with a possible 

 fourth type. 



The experiments now to be briefly described have sought 

 to determine : 



'See also Physikalische Zeitschrift, Vol. 1, Xo. 24. 



