the Black Spot in Liquid Films. 



Table VI. 



Polarized in plane of incidence ; angle of incidence 45°. 



19 



Obs. 



Intensity. 



o-i 



D. 



I 



II 



Ill 



IV 



V 



VI 



•00193 

 •00187 

 •00247 

 •00225 

 •00168 

 •00239 



2-53 

 249 

 283 

 2-74 

 2-35 

 2 39 



X 



77 



X 

 75 



X 

 69 



X 

 72 



X 

 £5 



X 

 83 



Mean 



10-6 mms. 

 71 



■ 



73 

 80 

 7 6 

 65 

 66 



7-2^ 



Table V. — In this table the plane of polarization made an 

 angle of 45° with the plane of incidence. The first two 

 observations were made April 22nd on a 1: 70 oleate-of-soda 

 solution that had stood in the vessel on the table of the 

 spectrometer exposed to the air of the room several days. 

 The last two were taken with a newly prepared solution. The 

 mean thickness is about 7 pp. 



Table VI. — This was taken with a similar solution, but 

 with the plane of polarization in the plane of incidence. The 

 mean thickness is about 7 fi/ju. 



Continuous readings were then made with a 1: 70 oleate-of- 

 soda solution at different angles of incidence. The results 

 are plotted in curves A, B, and C of figs. 6 and 7. Each 

 observation of the intensity plotted is calculated from the 

 mean of ten readings, taken alternately, on opposite sides 

 of the crossed positions of the nicols. A separate film was 

 used for each point. Readings were taken at intervals of 5°, 

 with angles of incidence varying from 22 0, 5 to 72°*5. 



Carve A (p. 520). — This was taken May 11th with a solution 

 that had stood one night exposed to the atmosphere of the room . 

 The intensity of the reflected light corresponds to that from a 

 film whose thickness is about 7 fx/n. The apparent increase in 

 the thickness at high angles of incidence may have been due 

 to the difficulty in matching the more intense images. The 

 temperature of the room was about 25° C. 



Curve B. — This was taken July 12th with a newly pre- 

 pared solution. Between these readings and those in A the 



2N2 ' 



