304 H. XAGAOKA. 



and the above expression for the vibration becomes 



( 3 ) Ida cos ( b -I ^ J 2-. 



The intensity of Hght at T is, therefore, given Ijy the expression 



or more simply by 



( I ) 1= MocUfda e ' ^ (-J^- ^«') 



Wlien the diffraction point is sitnated on the (_)ther side of the 

 surface from the source of light, and the phenomenon is seen projected 

 on a screen at I), ^ve must slightly modify the expression for the in- 

 tensity of light. 



Troceeding in exactly the same way as Ijefbre, the vibration at 

 I) due to a small element da at P ("Fig. 2j, will he proportional to 



, / t LO PV\ ,, 

 d(T cos {^Y^ J —\ 2-, 



which can be written 



/t _ LP , LO-L P OD-PD\^_ 



\T ~r^ I + I )- 



da cos 



Puttinii; as before 



LO - LP == JR, 

 OD - CD = JW, 



we get 



/t LP PD\,, /, . Jli + JP'\, 



Conse(piently, the total effect at I) is gi\'en by 

 I da cos la-] ^ j 2-. 



