Dynamical Theory of Diffraction. 233 



dde of the zero position the d 



cos i + cos (i + 0) . [I , . . 



On either side of the zero position the disturbance will 

 therefore be 



sin i + sin 6 



sin / - (sin i ± sin 6) J, 



which accounts for the want of symmetry observed by 

 Mr. 0. V. Raman (Phil. Mag. Jan. 1909) when a diffraction 

 band is produced at oblique incidence. 

 15. Finally, to solve 



(&-*?)+ = *(;**,*) 



we have only to find the particular integral. 

 Proceeding in the usual way, 



* = D^T?P F ' where D ^c4 



= i-r- J — +-±-1* 



21) LD + cA D-cAj 

 = ~ \e~ ctA £e-*' A F'dt' + e° tA |V rt " A FW 



= -i fccosh c(t-t')A}F'Jt' = ~ (cosh (t-t^Fdt 



attending to the meaning of the operation cosh {(.'(£ — Ov^} 



[art. 8], 



= ttt n ?,,F 0"D jn ^' since °^~* 



[art. 10] 



- 2 1 dv, 



17T 



where <£t> is an element of volume, which is Lorentz's 

 result. 



