12 Mr. A. A. Miclielson on the Application of 



When the distance between the sources is more than five or 

 six times the width, the periodicity of the second term alone 

 is of importance, the term A 1 representing the amplitude of its 

 variation. 



The fringes vanish whenever u= — ~ — a . 



z 



The general form of the visibility curve is given in fig. 8. 



Fie-. 8. 



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Ify>on the other hand, the two sources coincide the expression 

 reduces to that previously found for a single circular source. 



Table IV. exhibits the results of observations made upon 

 two circular apertures whose diameter is given under the 

 column a h and whose distance between centres under a, It 

 will be seen that the distance varies from eleven to five 

 diameters, and that the average error of one observation 

 (usually a single setting) is only 1J per cent. 



