When swallows fly low, just skimming the ground, it is supposed to be a sign of rain. During the frequent intervals of heavy, overcast weather which have marked this summer, they might have been observed flying low for a week together without a spot of rain falling. Chilly air drives insects downwards, and, indeed, paralyses a great many of them altogether. It is a fall of temperature, and not wet, that makes the swallows chase their prey low down. Insects are not much afraid of rain if it is warm and soft, so that in the midst of showers, if there is sunshine too, you may see the swallows high in the atmosphere. It is when they fly low, but just missing the grass, that their wonderful powers of flight appear. In the air above there are no obstacles, and if you shoot an arrow it travels to the end of its journey without let or hindrance; there are no streets there to turn corners, no narrow lanes, no trees or hedges. When the shallow comes down to the earth his path is no longer that of the immortals, his way is as the way of men, constantly obstructed, and made a thousandfold more difficult by the velocity of his passage. Imagine shooting an arrow from the strongest bow in such a manner that it might travel about seven inches above the ground--how far would it go before it would strike a tall buttercup, a wiry bennet, or stick into a slight rise of the turf? You must imagine it given the power to rise over hedges, to make short angles about buildings, slip between the trunks of trees, to avoid moving objects, as men or animals, not to come in contact with other animated arrows, and by some mysterious instinct to know what is or what is not out of sight on the other side of the wall. I was sitting on a log in the narrowest of narrow lanes, a hedge at the back, in front thick fir trees, whose boughs touched the ground, almost within reach, the lane being nothing more than a broader footpath. It was one of those overcast days when the shelter of the hedge and the furze was pleasant in July. Suddenly a swallow slid by me as it seemed underneath my very hands, so close to the ground that he almost travelled in the rut, the least movement on my part would have stopped him. Almost before I could lift my head he had reached the end of the lane and rose over the gate into the road--not a moments pause before he made that leap over the gate to see if there was a waggon or not in the way; a waggon-load of hay would have blocked the road entirely. How did he know that a man or a horse would not step into his course at the instant he topped the bar?