THE ABSOLUTE INTENSITY OF INTERFERING LIGHT. 329 



Now, by formula (1.) Prob. Ill, we can obtain the value of each of the integrals of 

 these expressions by writing/ v^ for a, and putting for q its corresponding va- 

 lue: thus, 



TT e 



/ 

 co __ ,____ 







r co 



/ 



X 



sin sn cos 



A 6 A 



{_^ 2ir(y + 2/)/V 1 4 <r/V 1 4y C7+Q/V 1 \ 



2 cos 2>7r f ff e - e * * 



A6 



/v- 



^ f 27T/ff/ 2-7T , - T 



= == J 2 cos , y , ( cos -- v "? . y x V 1 sin 

 f,J-l\ 



, -- . 



b \ \b 



,. , 4-7T/ 2 4-7r(^+/)/ 4 TT(^ + /)/-! 



- cos ^ ; + V 1 sin -=T-T -- cos - ^ , J ' J + V - 1 sin - ^ ' ' } 

 Ao A6 A6 A6J 



7T 



cos - > A + cos ^T7 -- V sm 



> A ^T7 -- - -\ L 



A 6 A 6 A 6 



4-7T/ 2 4lT/ 2 , 5 . 4-7T/ 2 



- V-l sm -^- cos ^ ; + V 1 sin ^ ; - cos 



^ ^ - -- . 



A6 Ao Ao 



\ Q 



-sm -^4-- } ' 



jjo^ig 27 / " ~\ '' 2 



Hence the expression for the total intensity is reduced to - a ff = - ^-- x 



sum of areas of the mirrors estimated perpendicularly to the line which bisects 

 the angle between ; or which is the same thing, 



2 ^2 a 2 



total intensity = jp x effective aperture. 

 But it ought to be, 2 x effective aperture 



