272 



Sir James Dewar 



[Jan. 16, 



Similarly with the alcohol : assuming the same refractive index 

 as for ice, the transmission by each plate is 88 * 1 per cent. : then 

 since 54 per cent, emerges in this case, the proportion transmitted 

 by the alcohol alone is 



— Y= 69 '6 percent. 

 88-1/ * 



54 



Several other liquids were similarly studied, such as methylene 

 iodide and chinoline. (See Fig. 17.) 



A chinoline film gave observed transmission of 54 per cent. 

 With a refractive index at each silver chloride-chinoline surface of 

 1*268, the reflected proportion will be 1*4 per cent. ; this with the 

 6 • 7 per cent, at each silver chloride-liquid air surface would result 



AgCII 



2. 2 



Films between 

 Successive Plates 



2 3 4-56 



I a 3 4 5 



No of Plates & Films 



Fig. 17. 



in a corrected transmission of 65 per cent, for the chinoline film alone. 

 By the same method of taking a fractional diminution at successive 

 surfaces, based on the refractive index through each surface, the 

 transmissions were worked out for three films of alcohol and four 

 films of methylene iodide, enclosed respectively by four and five silver 

 chloride plates in succession. The transmissions were observed at 

 each step as the piles of plates and solidified films were built up. 

 The results are given in Fig. 17. The calculated transmissions 

 through the successive alcohol films were 72*7 per cent., 65*2 

 per cent., and 65*1 per cent. ; and through the methylene iodide 

 films, 76 • 5 per cent., 79 ■ 1 per cent., 80 ■ 6 per cent., and 78 • 9 per cent. 

 These values were deduced on a transmission factor of 0*9345 for 



