4 (amdg_4.gif)] It is observed that it proceeds in a less oblique direction (towards the dotted line), and, on passing on through, leaves the liquid, proceeding in a line parallel to that at which it entered.

It should be observed that at the surface of bodies the refractive power is exerted, and that the light proceeds in a straight line until leaving the body.

The refraction is more or less, and in all cases in proportion as the rays fall more or less obliquely on the refracting surface.

It is this law of optics which has given rise to the lenses in our camera tubes, by which means we are enabled to secure a well-delineated representation of any object we choose to picture.
When a ray of light passes from one medium to another, and through that into the first again, if the two refractions be equal, and in opposite directions, no sensible effect will be produced.
The reader may readily comprehend the phenomena of refraction, by means of light passing through lenses of different curves, by reference to the following diagrams:-- [Illustration: Fig.

5, 6, 7 (amdg_5.gif)] Fig 5 represents a double-convex lens, Fig.