318 



Mr. R. B. Sangster on some Consequences of 



m fig. 2 the graphs, F(n) = q— s /p, and F(>i)=z^p are 

 shown for p = 2 ; and in fig. 3, the same graphs when //, =4. 



30 T 



^o■■ 



Fisr. 2. 



Fiff. 3. 



A numerical example of these formulae may also be of 

 interest. When p= 2 + ^/3 (approximately, 3' 7 32) , the normal 

 is the incidence of minimum reflexion. When /x== 4, minimum 

 reflexion occurs at i = 57°28', showing how quickly the mini- 

 mum moves away from the normal with increase of p ; but 

 when z = 65° 36', the light reflected is again equal to that 

 reflected at normal incidence. 



Doubtless, these high values of p are found only in the 

 region of metallic reflexion where metallic absorption has to 

 be taken into account and where FresnePs formula has to be 

 dealt with in a modified form, and it is only in order to 

 discuss the significance of + s/p that we are compelled for 

 the time to treat these high values of p as if they applied to 



