THE ABSOLUTE INTENSITY OF INTERFERING LIGHT. 



i .3 



/T- T -/T " + 27i 



r 



The coefficient of m r between brackets is 



r 1.3...(2r-l) f 1 i 



- -~' ~ 



whlch 1S e( l ual to 



_ 

 2.4...2r ' /2r " 



2 r 2 r 1.2...r 



a 



Let *%r=*r 



By squaring- -s, we obtain, coefficient of m r in ( 



'^ TT a<? \7T 



&C> t0 r+ rtepm8 



H & c ) 



J 



. 



1 2' "(/I) 2 3 



(-l) r f r + l r+l (r + iy (r + l)r (r + l)(r)(r-l) 

 ~(fr+T) 2 { ~T~ ~T~ ~T72~ 1.2 1.2.3 C ' 



( l) r 

 = 7/r + 1)* x coefficient of the products two and two of the consecutive terms 



of the expansion of (1 + *) , i. e. 1st coefficient x 2 d + 2* x 3 d + &c. 



VOL. XV. PART II. 4 S 



