﻿580 Mr. Karl T. Compton on Contact Difference of 



any portion of the ultra-violet light from striking B. The 

 exit-hole in B is 3 rain, in diameter. By looking in through 

 the window E and adjusting the levelling-screws shown in 

 the figure, these holes may all be put in the line, abc, of the 



j'is:. 1. 



To Electrometer 



-TbPoteutiflLl Cells 



Fi<r. 2. 



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light. Several perforated metallic boxes C were prepared. 

 One set, as nearly similar to each other in dimensions as 

 could be made, was prepared by simultaneously drilling holes 

 as near together as possible in the foils of aluminium, zinc, 

 lead, iron, and copper. One was also made of platinum foil' 



