
Meteorology
order. When sight is strained to a great distance the appearance of
the distant object is affected in a certain way: and the same thing
holds good here. So the reflection from the outer rainbow is weaker
because it takes place from a greater distance and less of it
reaches the sun, and so the colours seen are fainter. Their order is
reversed because more reflection reaches the sun from the smaller,
inner band. For that reflection is nearer to our sight which is
reflected from the band which is nearest to the primary rainbow. Now
the smallest band in the outer rainbow is that which is nearest, and
so it will be red; and the second and the third will follow the same
principle. Let B be the outer rainbow, A the inner one; let R stand
for the red colour, G for green, V for violet; yellow appears at the
point Y. Three rainbows or more are not found because even the
second is fainter, so that the third reflection can have no strength
whatever and cannot reach the sun at all. (See diagram.)
5
The rainbow can never be a circle nor a segment of a circle
greater than a semicircle. The consideration of the diagram will prove
this and the other properties of the rainbow. (See diagram.)
Let A be a hemisphere resting on the circle of the horizon, let
its centre be K and let H be another point appearing on the horizon.
Then, if the lines that fall in a cone from K have HK as their axis,
and, K and M being joined, the lines KM are reflected from the
hemisphere to H over the greater angle, the lines from K will fall
on the circumference of a circle. If the reflection takes place when
the luminous body is rising or setting the segment of the circle above
the earth which is cut off by the horizon will be a semicircle; if
the luminous body is above the horizon it will always be less than a
semicircle, and it will be smallest when the luminous body culminates.
First let the luminous body be appearing on the horizon at the point
