428 Prof. Carl Barns on Interferometry 



There is another feature of importance which must now 

 be accentuated. In case of different colours, and stationary 

 mirrors and grating, y is not constant from colour to colour, 

 whereas 



2N = 2y- 2efx sin B tan B 

 is constant for all colours, as has been shown above. Thus 

 the equation to be differentiated for constancy of adjustment 

 but variable colour loses the variable y and becomes 



?i\=2£/xcosR-2N. 

 !N here is the difference of perpendicular distances to the 

 mirrors, M and N, from the ends of the normal in the glass 

 plate, at the point of incidence of the white ray. Performing 

 the operations : 



?i 2 cosR . 



2D cos defi(l + a) -y cos B* * " ^ ' 



Hence maximum d0/dn = yD at the centres of ellipses which 

 occur for 



J ~ cosB 

 The value of ddjdn for the different Fraunhofer lines above, 

 if a ='015 is still considered constant and e= '68, is given 

 in Table III. 



Table III. 



Values of dOJdn and displacements of mirror, N . e — 'QS cm. 



N c and y c , etc., refer to centres of ellipses. 



cW 

 dn 



Spectrum lines... 



= 



B. 



D. 



E. 



F. 



a. 



Equation 17 : 



dBJdn = 



1'27" 



r 5" 



53" 



46" 



35" 



16: 



dBJdn = 



3' 4" 



V 52" 



1' 20" 



59" 



38" 



» IS: 



dBJdn = 



-6' 53" 



-10' 38" 



CO 



+8' 47" 



4-3' 51" 





-dfi/dX = 



281 



445 



623 



793 



1140 



„ 19: 



dBJdn = 



-1'54" 



-1'50" 



CO 



4-2' 21" 



4-40" 



„ 20: 



dQ/dn = 



-1'44" 



-1'44" 



CO 



4-2' 11" 



4-36" 



21: 



y c = 



1-1779 



1-1811 



1-1921 



1-1981 



1-2090 





A V C = 



- -0142 



-•0110 



±•0 



+•0060 



4- -0169 





N c = 



•9235 



•9274 



•9391 



•9156 



•9578 





AN = 

 c 



-■0156 



-•0117 



±-o 



4-0065 



+ •0187 



(observed) 



AN = 

 c 



-•0153 



-•0098 



±•0 



+ •00.^7 





Equation 20 : * 



! 



dBJdn = 





-r 54" 



CO 



2' 21" 



48" 



* Interpolated between D and Gr by p=a-\- i\+c\ 2 , where b~ 

 c= 0000197. 



•00273, 



