276 ffutchms - Absorption and Thickness of thin Films. 



firsi order interference color of about wave-length •000057°"'. 

 Taking the index of refraction of the material as 1-5, we have 

 for the film thickness : 



•000057 



= •000005!) n " 

 4X2X1-5 



The thickness was also found thus : A loop was made at the 

 end of a fine platinum wire. Three films whose diameters 

 were 12, 14, and ir5 cm respectively were gathered from the 

 water on which they were formed into a small ball on the 

 wire loop, the water pressed out, and the remaining material 

 dried to constant weight. 



The wire alone weighed 0-021 8e m 



Wire with film " 0-0231 



Weight of film 0-0013 



Area of film 372 c '" a 



The density of a sample of the toothbrush handle from which 

 the film was made was 1*136. From the above we get for the 

 mean thickness of the film : 



0-0013' 



— = 0-0000026 cm 

 372X1-136 



equal to one-twentieth the wave-length of green light. 



Bowdoin College, July 1st. 



