413 



ing the width of slit necessary for tlie appearance of tiie mentioned 

 polarisation phenomena. Then we can get an idea in how far we 

 mnst expect disturbances caused by the narrowness of the slit. 



With the arrangement shown in Fig. 1 the relative decrease in 

 intensity of the horizontal vibrations may easily be measured. 



Monochromatic green light falls upon a slit S, behind which a 

 calcite rhomb K is placed at such a distance that two adjacent images 

 of the slit are formed, one contaitiing the vertical vibrations, the other 

 the horizontal ones. By means of a nicol j.V the intensity of the 

 two images may be made equal. 







V'g. 1. Fig. 2. 



Let (fig. 2) op and OQ be the directions of the vibrations in the 

 two images. If the direction of vibration of the nicol is perpendi- 

 cular to /^(^, the condition for equal intensities of the two images 

 will be tg. a ^ OP : OQ. The ratio of the intensities of the horizontal 

 and vertical vibrations is then given by tg.'«. 



A first experiment was made with a slit (of platinoid) from a 

 spectroscope with constant deviation of Hilgkk. 



The results are contained in the following table : 



green light 



width of slit 

 in m.m. 



tang. « 



27' 



