‘200 
DR. BREWSTER ON REFLECTED LIGHT. 
II. Those in which periodical colours are produced at the confines of parti- 
cular kinds of glass, and various fluids and soft solids. 
From the first of these classes of facts the following conclusions may be drawn. 
1 . The reflective and refractive forces in media of the same refractive power 
do not follow the same law. This result is clearly established by the experi- 
ments with the prism B, which produced no orders of colours. Not only was 
there a strong reflected pencil when a perfect equilibrium was effected between 
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 obtained 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 represents the law of the reflective force 
were exactly the same in the prism B and the fluids combined with it, then the 
ordinates 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 re- 
flection 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 solid and fluid may be conceived to decrease in 
various ways. Fl S- 2 - 
J a 
1. They may extend to different distances from 
the reflecting surface, and decrease according to 
the same law. This relation is shown in Fig. 2, 
where MN is the reflecting surface, AB the limit 
of the sphere of reflecting activity in the solid, 
and C D that in the fluid , — a o b the curve which 
represents the reflecting force of the solid, and 
c n d that of the fluid. In this case there can be 
no compensation of opposite 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 mo is equal to no, the difference of the two forces mn, mo. 
In this case there will be a sphere of reflecting activity extending from AB to 
A IV, and such a combination must reflect light without refracting it. 
