An ornithologist, having investigated the question of at what hour in summer the commonest small birds wake and sing, says the greenfinch is the earliest riser, as it pipes as early as 1:30 in the morning, the blackcap beginning at about 2:30. It is nearly 4:00 o'clock, and the sun is well above the horizon before the first real songster appears in the person of the blackbird. He is heard a half an hour before the thrush, and the chirp of the robin begins about the same length of time before that of the wren. The house sparrow and the tomtit occupy the last place in the list. This investigation has ruined the lark's reputation for early rising. That much-celebrated bird is quite a sluggard, as it does not rise until long after the chaffinches, linnets, and a number of hedgerow birds have been up and about. THE YOUNG NATURALIST. TESTING THE CLEANNESS OF THE AIR.--Professor Dewar has recently devised a new method of testing the contamination of the air. A short time ago he exhibited before the Royal institution two samples of liquid air in glass tubes--one was made from air which had been washed to purify it from dust, soot, carbonic acid and other impurities. This, when condensed, was a pale blue liquid. The other sample was made by condensing the air of the lecture-room in which the audience was assembled, and was an opaque, blackish fluid, resembling soup in appearance. THEIR WONDERFUL EYES.--When a fly comes from an egg, one of a family of thousands, it is soft, pulpy, white, eyeless, legless. When mature it affords the student one of the most marvelous fields in all nature, with its nerve clusters and brain, its feet like the hoofs of a rhinoceros, a thousand hollow hairs on each footpad, the wings, which make 15,000 vibrations a second, and the eyes. There are 8,000 of these, each a perfect lens. A fly's eyes are hard, immovable and retain their form after death. As a fly cannot turn its head it has eyes in all directions. So small are these eyes that 1,000,000 would not cover the surface of a square inch. Each eye measures a thousandth part of an inch and the color is almost always red. Each of these eyes is a lens and photographs have been taken through them. The lenses are of varying kinds--some suitable for looking off at a distance, others for things close at hand. Occasionally with his thousand eyes a fly is deceived. This is evidenced when a blue-bottle inside a room heads for the open country. He does not see the window glass and the thump with which he strikes and the angry buzz which shows his discomfiture show how mistaken he was. To prove there is nothing extraordinary in a fly's having 8,000 eyes it is known that a certain beetle owns 50,016 eyes; a certain butterfly 34,710, a common dragonfly 25,088, and a silkworm moth 12,500.