224 Dr Brewster on the reflection and decomposition of 



reflected pencil when a perfect equilibrium was effected be- 

 tween the opposite refracting forces, but there was not even an 

 approximation to evanescence, as the forces advanced to their 

 point of compensation. The same result was obts^ined with a 

 prism newly ground and polished. 



2. The force which produces reflection varies according to 

 a different law in different bodies. If the curve which repre- 

 sents the law of the reflective force were exactly the same in 

 the prism B and the fluids combined with it, then the ordi- 

 nates which represent the intensity of the force at any given 

 point would be exactly equal, and consequently there would 

 be a perfect equilibrium of opposite actions, and no reflection 

 of the passing light. But as a copious reflection takes place 

 even when the opposite forces are balanced, we are entitled to 

 infer that the law of the two forces is different. 



The reflective forces in the sohd and fluid may be conceived 

 to decrease in various ways. 



1. They may extend to different distances from the reflect- 

 ing surface, and decrease according to the same law. This 

 relation is shown in Plate III. Fig. 2, where MN is the reflect- 

 ing surface, AB the limit of the sphere of reflecting activity 

 in the solid, and CD that in the fluid, — a o h the curve which 

 represents the reflecting force of the solid, and end that of 

 the fluid. In this case there can be no compensation of op- 

 posite reflections, and an unbalanced reflecting force will exist 

 at almost every point of the sphere of reflecting activity. From 

 a to c the light will be acted upon by the undiminished force 

 of the solid. At c the force of the fluid begins to oppose that 

 of the solid, and the unbalanced force at any other line w o is 

 equal to n o, the difference of the two forces m n, m o. In this 

 case there will be a sphere of reflecting activity extending from 

 AB to A'B', and such a combination must reflect light without 

 refracting it. 



2. The reflecting forces may extend to different distances, 

 and vary according to a different law. Two cases of this kind 

 are shown in Fig. 3 and 4. 



In the case of Fig. 3, the curves expressing the law of the 

 forces have a common ordinate m n, where the reflections are 

 compensated ; but from a to n the reflecting force of the solid 



