DR. BREWSTER ON REFLECTED LIGHT. 



201 



2. The reflecting forces may extend to different distances, and vary ac- 

 cording to a different law. Two cases of this kind are shown in Fig. 3 and 4. 



Fig. 3. Fig. 4. 



a 



In the case of Fig. 3. the curves expressing the law of the forces have a com- 

 mon ordinate m n where the reflections are compensated ; but from a to n the 

 reflecting force of the solid will predominate over that of the fluid, and from n 

 to d the force of the fluid will predominate over that of the solid ; so that in 

 such a combination there will be two spheres of reflecting activity, one of whicli 

 begins where the other ends. 



In the case of Fig. 4, where the curves have the same maximum ordinate m b, 

 we shall have a sphere of reflecting activity commencing at a, reaching its 

 maximum at c, and its minimum at b. 



3. The reflecting forces may be conceived to extend to the same distance, 

 and to vary according to different laws. Two cases of this kind may occur ; 

 one, as in Fig. 5, where the maximum of unbalanced force is distant from the 

 surface, and another, as in fig. 6. where the maximum takes place at the re- 

 flecting surface. 



Fig. 5. 



Fig. 6. 



M- 



A'- 



-B 



-N 



-B' 



In the conclusions which we have drawn respecting the independence of the 

 reflecting and refracting forces, it was supposed that the latter follow the same 



MDCCCXXIX. 2 D 



