
Meteorology
are equal, the points where they form an angle will always lie on a
circle.
Let AGB and AZB and ADB be lines each of which goes from the point A
to the point B and forms an angle. Let the lines AG, AZ, AD be equal
and those at B, GB, ZB, DB equal too. (See diagram.)
Draw the line AEB. Then the triangles are equal; for their base
AEB is equal. Draw perpendiculars to AEB from the angles; GE from G,
ZE from Z, DE from D. Then these perpendiculars are equal, being in
equal triangles. And they are all in one plane, being all at right
angles to AEB and meeting at a single point E. So if you draw the line
it will be a circle and E its centre. Now B is the sun, A the eye, and
the circumference passing through the points GZD the cloud from
which the line of sight is reflected to the sun.
The mirrors must be thought of as contiguous: each of them is too
small to be visible, but their contiguity makes the whole made up of
them all to seem one. The bright band is the sun, which is seen as a
circle, appearing successively in each of the mirrors as a point
indivisible to sense. The band of cloud next to it is black, its
colour being intensified by contrast with the brightness of the
halo. The halo is formed rather near the earth because that is calmer:
for where there is wind it is clear that no halo can maintain its
position.
Haloes are commoner round the moon because the greater heat of the
sun dissolves the condensations of the air more rapidly.
Haloes are formed round stars for the same reasons, but they are not
prognostic in the same way because the condensation they imply is so
insignificant as to be barren.
4
We have already stated that the rainbow is a reflection: we have now
to explain what sort of reflection it is, to describe its various
