Stranica 30 [30]
kő ." LIGHT AND WATER
surface of the candlestick is visible, whereas, looking
directly at the object, it is out of sight. Anyone look¬
ing from E would get a view of the candlestick and
its image very similar to that drawn in the figure.
The lines ADE, BFE and CGE represent the paths
of the rays from A, B and C respectively, which
reach the eye after reflexion at the surface of the
mirror. And if the straight lines BF, AD and
CG are produced downwards they will be found all
to meet at a point e, as far beneath the glass in a
vertical line as the eye is above it, so that the view
of the image seen from E is the inversion of the
view of the object that we should get if we were to
remove the mirror and look at it from e. It is neces¬
sary to note this difference, because the word “ re¬
flexion” is used to denote ¢he observer's view” of the
image, and not the image itself. The image always
remains the same, being, as we have said, the exact
inversion of the object; but the reflexion, or view we
get of it, varies with our position.
In considering the reflexions seen in a sheet of water
we will assume in the first place that its surface is per¬
fectly smooth and unruffled. Reflexion takes place
therefore exactly as in the case of the plane mirror."
" The line OD, produced both ways, marks the intersection of
the plane of incidence of the ray AD with the surface of the mirror.
For the sake of simplicity in the figure, the points B and C are
chosen in this same plane, so that F and G also lie on the same line
OD produced. This line bisects the vertical Ee in L.
" Or, projection of the image on to the picture plane.
" For the present we ignore the fact that the reflective power
water is different for light at different angles of incidence. This
fact is, however, taken into account in the third chapter.