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Meteorology By Aristotle

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Author Topic: Meteorology By Aristotle  (Read 2782 times)
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Bathos
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« Reply #75 on: August 31, 2009, 12:04:43 am »

So the rainbow always appears opposite the sun whereas the halo is
round it. They are both reflections, but the rainbow is distinguished
by the variety of its colours. The reflection in the one case is from
water which is dark and from a distance; in the other from air which
is nearer and lighter in colour. White light through a dark medium
or on a dark surface (it makes no difference) looks red. We know how
red the flame of green wood is: this is because so much smoke is mixed
with the bright white firelight: so, too, the sun appears red through
smoke and mist. That is why in the rainbow reflection the outer circumference
is red (the reflection being from small particles of water), but not
in the case of the halo. The other colours shall be explained later.
Again, a condensation of this kind cannot persist in the neighbourhood
of the sun: it must either turn to rain or be dissolved, but opposite
to the sun there is an interval during which the water is formed.
If there were not this distinction haloes would be coloured like the
rainbow. Actually no complete or circular halo presents this colour,
only small and fragmentary appearances called 'rods'. But if a haze
due to water or any other dark substance formed there we should have
had, as we maintain, a complete rainbow like that which we do find
lamps. A rainbow appears round these in winter, generally with southerly
winds. Persons whose eyes are moist see it most clearly because their
sight is weak and easily reflected. It is due to the moistness of
the air and the soot which the flame gives off and which mixes with
the air and makes it a mirror, and to the blackness which that mirror
derives from the smoky nature of the soot. The light of the lamp appears
as a circle which is not white but purple. It shows the colours of
the rainbow; but because the sight that is reflected is too weak and
the mirror too dark, red is absent. The rainbow that is seen when
oars are raised out of the sea involves the same relative positions
as that in the sky, but its colour is more like that round the lamps,
being purple rather than red. The reflection is from very small particles
continuous with one another, and in this case the particles are fully
formed water. We get a rainbow, too, if a man sprinkles fine drops
in a room turned to the sun so that the sun is shining in part of
the room and throwing a shadow in the rest. Then if one man sprinkles
in the room, another, standing outside, sees a rainbow where the sun's
rays cease and make the shadow. Its nature and colour is like that
from the oars and its cause is the same, for the sprinkling hand corresponds
to the oar.
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