Page:Outlines of Physical Chemistry - 1899.djvu/91

 ��Optical Properties. — Refraction of Light

The velocity of transmission of light through any medium depends on the nature of the medium and more particularly on its density.

When a ray of light passes from one medium into another it is refracted in obedience to SnelVs law. The incident ray, the refracted ray, and the normal to the boundary of the two media at the point of incidence, lie in one plane ; and besides, there is a certain ratio between the sine of the angle of incidence and the sine of the angle of refraction, which is constant and characteristic for the two media.

The wave theory of light teaches us that this ratio of sines is the same as the ratio of the velocities with which the light wave traverses the two media respectively. This ratio is termed the index of refraction f and is usually denoted by n. If i is the angle of incidence, r the angle of refraction, and v and v x the respective velocities of light in the two media, we have

__ sin i __ v sinr v{

If we consider three media such as air, a liquid and glass, and if we determine the index for any two pairs, such as :

n (air/glass) = n = v

and n (liquid/glass) = n x =--,

then we can find :

n (air /liquid) = - = — ^ = —.

v x n x v 2 n x

The limits of this book prevent us from going into a description of the various apparatus which may be used for the determination of the refractive index. A short account

�� �