tint of purple.

_Hal_. Do you know why this tint portends fine weather?

_Phys_. The air, when dry, I believe, refracts more red or heating
rays; and as dry air is not perfectly transparent, they are again
reflected in the horizon. I have generally observed a coppery or
yellow sun-set to foretell rain; but, as an indication of wet weather
approaching, nothing is more certain than a halo round the moon,
which is produced by the precipitated water; and the larger the
circle, the nearer the clouds, and consequently the more ready to
fall.

_Hal_. I have often observed that the old proverb is correct--

'A rainbow in the morning is the shepherd's warning;
A rainbow at night is the shepherd's delight'

Can you explain this omen?

_Phys_. A rainbow can only occur when the clouds containing or
depositing the rain are opposite the sun,--and in the evening the
rainbow is in the east, and in the morning in the west. As,
therefore, our heavy rains in this climate are usually brought by the
westerly wind, a rainbow in the west indicates that the bad weather
is on the road, by the wind, to us; whereas, the rainbow in the east
proves that the rain in these clouds is passing from us.

_Poiet_. I have often observed that when the swallows fly high, fine
weather is to be expected or continued; but when they fly low, and
close to the ground, rain is almost surely approaching. Can you
account for this?

_Hal_. Swallows follow the flies and gnats, and flies and gnats
usually delight in warm strata of air; and as warm air is lighter,
and usually moister than cold air, when the warm strata of air are
high, there is less chance of moisture being thrown down from them by
the mixture with cold air; but when the warm and moist air is close
to the surface, it is almost certain that, as the cold air flows down
into it, a deposition of water will take place.

_Poiet_. I have often seen sea-gulls assemble on the land, and have
almost always observed that very stormy and rainy weather was
approaching. I conclude that these animals, sensible of a current of
air approaching from the ocean, retire to the land to shelter
themselves from the storm.

_Orn_. No such thing. The storm is their element, and the little
petrel enjoys the heaviest gale; because, living on the smaller