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PROCEEDINGS OF THE AMERICAN ACADEMY. 



In the following table the wave-lengths are given in the first column, 

 the fringe displacements in comparison with helium light in the second 

 column. These values, with the exception of those in the extreme red, 

 blue-violet, and ultra-violet, were obtained with the interferometer. 



In the third column are given the actual fringe shifts which would be 

 fourd for a layer of vapor 8 cms. thick (effective thickness 16 cms.), and 

 in the fourth column the refractive indices. The indices calculated from 

 the dispersion formula are given in the fifth column, for the sake of com- 

 parison with the observed values. More will be said of them in the next 

 section. 



