polarisation of light by reflexion from transparent bodies. 133 
Prop. vir. 
Every ray of light polarised by reflexion has been acted upon by the 
refracting force before it has suffered reflexion. 
This follows from the light not being polarised at 45®, but 
at various angles increasing with the refracting force. 
Cor. It results from this Proposition, that light suffers a 
partial refraction before it is reflected ; and that the refractive 
force extends to a greater distance than the reflecting force 
from the surface of transparent bodies. This result is not only 
consistent with the most extensive analogies, but affords an 
explanation of phenomena, which have hitherto been unex- 
plained. 
Bouguer, for example, observed that at 8j~° of incidence, 
a surface of water reflected 614 rays, while glass reflected 
only 584. Now supposing the light to be refracted by the 
water and the glass, before it suffers reflexion, the real angle 
of incidence upon the glass will be only 57 0 44', while the 
angle of incidence upon the water will be 6i° 5'; so that the 
pencil being incident more obliquely upon the water, ought 
to be more copiously reflected. 
Prop. viii. 
When a ray of light is incident at the polarising angle upon any 
substance whatever , it receives such a change in its direction , by 
the action of the refracting force, that the real angle of incidence 
at which it is reflected and polarised is 45° 
Let MN,Fig. 2, be the refracting and the reflecting surface, 
and OP the termination of the sphere of refracting activity. 
Let a ray RG be incident at G, at the polarising angle, and 
