32 Total Reflexion at Second Surface of Parallel Plate. 



can be obtained using the theory of the plane-parallel homo- 

 geneous plate. When the silver film is as thin as one-twentieth 



Silver Films. 



Angle of 



Observed Deviation. 



Calculated Deviation. 



incidence. 



! (1) 



o 

 2 

 1 

 



o 



_2 



+3 

 +2 

 -2 



o 



-1 

 -1 



(2) 



... 



o 





 



1 



o 



1 



3 



i 



(3) 



o 



1 



3 

 1 

 3 



o 

 4 

 6 

 9 

 4 



o 



5 

 1 







1 



(4) 



"o 



2 



4 

 6 



T 



12 



11 



9 



° 

 8 



(5) 



o 



S 



4 



15 



25 



o 



35 

 39 

 41 

 32 



o 



30 

 25 

 18 

 16 



10 

 3 

 1 

 1 



(6) 



o 



2 

 1 



12 



23 



o 

 36 

 39 

 42 

 39 



o 



37 

 34 

 32 

 24 



o 



19 



10 

 5 



i (- = 0-055. 



A 



~ = 0-07. 



V- 



1 



39 50 



41 



42 30 

 44 



o 



4 



1 



-3 



—7 



o 



27 

 18 

 15 

 12 



o 



5 

 2 



-4 

 -9 



2-8 

 2-8 

 2-8 

 2-7 



0-85 : 

 0-89 ; 

 1-00 

 2 32 



45 30 



47 



48 30 

 50 



o 



60 

 41 

 36 



26 



2-7 

 2-7 

 2-6 

 26 



4-85 

 3-61 

 321 



2-69 



51 30 



53 



54 30 



56 



o 

 10 

 10 



I 



o 



24 

 20 

 18 

 16 



o 



15 

 14 

 13 

 12 



25 



2-5 

 2-4 

 24 



2-56 

 240 

 226 

 2-15 



57 30 

 59 



GO 30 

 62 



o 



8 



7 

 6 



2-3 

 2-3 

 22 

 2 - 2 



2-08 

 1-99 

 1-96 

 1-93 ' 



of the wave-length of sodium light, as in the above experi- 

 ments, then we can no longer consider it homogeneous ; and 

 apparently cannot expect an agreement with the formula 

 derived on that supposition. 



The values of d s and r s " are very striking, particularly the 

 value of r s ". In the ordinary case of total reflexion d s can 

 large as 2 ; but r s " can have much larger values than 

 If we write af/ 2 =m + ip, and a 3 y 3 = —is, where m, p, 

 are real positive quantities, then 



+ i(p + s) I 



be as 

 that, 

 and s 



s I m-\-i(p — 



is small in comparison with p for the 



metals gold, silver 

 the maximum value of rJ'. i 



and sodium. Consequently 



-^-. -^ is the ratio of the imaginary to the real part of x.-,y 2 > 

 m m 



or the ratio of the imaginary to the real part of a 33 since <y t 



is approximately veal. Now a. 2 is given by 



