If, for example, a
convex lens be moved back and forth between a candle and a screen in a
dimly lighted room, a position will be found where a picture of the candle
falls upon the screen. This picture, called the _image_, results from the
refraction of the candle light in passing through the lens.
[Fig. 158]
Fig. 158--*Diagram illustrating formation of images.* On the right the
image is formed by a double convex lens; on the left by the lenses of the
eye. The candle flame represents a luminous, or light-giving, body; but
light passes from the large arrow by reflection. (See text.)
In order to form an image, the light waves spreading out from the object
must be brought together, or focused. Focusing means literally the
bringing of light to a point, but it is evident in the formation of an
image that all the waves are not brought to a single point. If they were,
there would be no image. In the example of the candle given above, the
explanation is as follows:
The light from the candle comes from a great number of separate and
distinct points in the candle flame. The lens, by its peculiar shape,
bends the waves coming from any single point so that they are brought to a
corresponding point on the screen.
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