802 



PROCEEDINGS OF THE AMERICAN ACADEMY 



added to tlio.se of the readings, and thus the readings of any set are 

 rendered equivalent to those taken when the screen is at a distance from 

 the lens equal to its principal focus. This being done, the greatest 

 variation of any of the readings from the standard was found to be 

 a little over one per cent. 



The result of these measurements of the vertical slit are given in 

 Table L, and of the horizontal slit in Table II. Column 1 gives the 



TABLE I. 



TABLE IL 



