Interference Methods to Astronomical Measurements. 9 



the value of the intensity of the maxima and minima in the 

 form I=l + B, whence finally we get for the visibility of the 

 fringes 



V = B (10) 



The values of V found from equation (10) are plotted in the 

 curve shown in fig. 6 *. 



The fringes disappear at the points for which— is 



1-33, 2-38, &c.; 



and the values of the successive (positive and negative) maxima 

 are: — 



V = +1-00 



V = -0-1 



V = +0-042 



V = -0-028 



On applying these results to the observations the accord- 

 ance is very satisfactory, as appears from the following 

 Table :— 



Table III. 



s. 



X. 



a. 



d. 



b. 



/• 



a. 



a v 



e. 



0. 



s. 



•550 



•231 



27,800 



84-75 



1-33 



1-74 



1-71 



+0-03 



+ 2 



,, 







•377 



)} 



55-25 



1-33 



2-72 



2-79 



- -07 



_2 





J 



, 





•933 



, 



22-65 



1-33 



6-66 



6-90 



- -24 



-3 





, 







•231 



21,200 



66-15 



1-33 



2-27 



2-24 



4- -03 



+1 





, 



, 





•377 





41-75 



1-33 



3-59 



3-66 



- -07 



—2 





' 



' 





•933 



>» 



16-65 



1-33 



9-04 



9-05 



- -01 







Case IV. — Double Source. 



Suppose next that there are two equal symmetrical sources 

 of light whose centres are at G and X (fig. 7) . 



Fiar. 7. 



* The curves corresponding- to Cases I., II., and III. are for con- 

 venience of comparison given together in Plate I. 



