( '^74 ) 



from vvhicli the followiiif>- e.\tiiu'ti(jiis with rospccl 

 bisectrix are calculated : 



1o tlie acute 



TABLE II. 



The values for //' found by calculation with .?; = 90°, which 

 accordingly represent the limit of extinction with regard to the acute 

 bisectrix on the plane making i-ight angles with the lalter, give a 

 measure for the exactitude of the values found. The errors successively 

 amount to + i8", +11", 0", - 4", —1". 



The greatest extinction for different values of .r with the corresponding 



angle [ «1 are now to be calculated from the formulas (7) and 



(8) ; we come to the following result : 



To calculate from 



mï^ V sin x cot '2i/' 



the V 



As 



cot ((mad — • 2 T7- i 1 Tr 8 



SUV V -\- co.s' V cos" .V 



aluo of t(,n„x when sin .r = 0, we eliminate y' . 



