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REFLEXIONS IN SMOOTH WATER 9
word “inverted ’ in speaking of an image is there¬
fore used in a peculiar sense. Though the image is
upside down, every point in it is vertically beneath
the corresponding point in the object, and when
viewed so as to appear in the upright position, right
has become left, and left right. Thus it is sometimes
and perhaps more correctly spoken of as a “ per¬
verted " image.
Such reflexion, giving rise to the formation of an
image, is called regular. Inthe case of reflexion from
a rough or unpolished object, the incident light (a
part only of which is reflected) is very much scattered,
as if the surface on which the light falls were made
up of countless minute plane surfaces facing in every
possible direction. The law of reflexion still holds
good, but owing to the irregularity of the surface the
eye receives light from all directions and the forma¬
tion of an image is impossible. It is by means of this
surface-scattering, or so-called “ zvregular reflexion "
of light, that all objects which are not self-luminous
become visible to us. The perfectly polished mirror,
on the other hand, is invisible; we cannot distinguish
its surface at all, and are only made aware of its ex¬
istence by the images in it of neighbouring objects.
We have shown how the image is an exact repro¬
duction of the object. But the wzew we get of the
image is a different one from our direct view of the
object. In the language of perspective, the projection
on to the picture-plane of the image differs from that
of the object. In Fig. 3 the candlestick and its image
are drawn in perspective instead of in section in order
to show this difference, In the reflexion the under¬