The late Sir Humphrey Davy, one of the most successful modern explorers of the secrets of nature, was not above attending to, and explaining the, “weather-omens” which are derived from popular observation. In his ‘Salmonia’ he has the following dialogue between Halieus (a fly-fisher), Poietes (a poet), Physicus (a man of science), and Ornither (a sportsman):-- “_Poiet_. I hope we shall have another good day to-morrow, for the clouds are red in the west. “_Phys_. I have no doubt of it, for the red has a tint of purple. “_Hal_. Do you know why this tint portends fine weather? “_Phys_. The air, when dry, I believe, refracts more red, or heat-making 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 foretel 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; and as 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.