JOURNAL 



OF THE 



WASHINGTON ACADEMY OF SCIENCES 



Vol. V APRIL 19, 1915 No. 8 



PHYSICS. — Some notes on the theory of the Rayleigh-Zeiss inter- 

 ferometer. By Leason H. Adams, Geophysical Laborator3^ 

 Communicated bj^ Arthur L. Day. 



In the course of some work on the freezing point of dilute 

 aqueous solutions in which a Zeiss interferometer was employed 

 as a means of determining the concentration of the equilibrium 

 solutions, 1 some trouble was experienced at first in obtaining 

 thoroughly concordant readings; this was found to be due to 

 an alteration of the achromatic reference fringe produced by 

 differences in optical dispersion. In order to guard against 

 error from this source it proved necessary to investigate the re- 

 lationships in order to derive formulae from which the exact 

 amount of shift of the achromatic fringe could be predicted. 

 The appropriate formulae for this type of instrument have 

 apparently not been worked out heretofore ;2 consequently it 

 has seemed worth while to call attention to these relationships 

 and to put the formulae on record so as to save trouble to future 

 users of this most useful type of instrument. 



1. The optical path-differences resulting from the tilting of a 

 plane-parallel glass plate. In the form of interferometer under 

 consideration the difference in optical path-length of the two 

 interfering beams of light is compensated by tilting one of two 



1 L. H. Adams, J. Am. Chem. Soc, 37, 481 (1915). A paper dealing with the 

 use of this form of interferometer in the analysis of solutions is in course of 

 publication in the J. Am. Chem. Soc. 



^ Except, possibly, in part by Siertsema in 1890 in a Groningen dissertation, 

 a copy of which I have been unable to secure. 



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