Added transmittance member

src/dielectric.hpp

@@ -15,6 +15,7 @@ public:
 
 private:
   double reflectance(double cos_theta_in, double cos_theta_out, double ir_in, double ir_out) const;
+  double transmittance(double cos_theta_in, double cos_theta_out, double ir_in, double ir_out) const;
 
   double ir_inside; //index of refraction inside material
   double ir_outside; //index of refraction outside material