function debye,m1,m2,f2

;-----------------------------------------------------------
;
; routine uses the Debye relation to 
; find the refractive index of a mixture of two substances.
;
; Input:
;   m1......refractive index of substance 1
;   m2......refractive index of substance 2
;   f2......volume fraction of substance 2
;
; Output:
;   result..refractive index of mixture
;
; source:  Mark Hervig
;
;-----------------------------------------------------------

;- dialectric function e = index^2

   e1   = m1^2
   e2   = m2^2

;- Debye mixing rule

   term  = f2*(e2-1.)/(e2+2.)+(1.-f2)*(e1-1.)/(e1+2.)
   e3    = (2.*term + 1.) / (1. - term)
   result = sqrt(e3)

   return,result
   end