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.

NOTES ON ANIMALS. — The insect effects its breathing, not as men and animals do, by the lungs, but through openings in all sides of the body. It has an intricate system of tubes running through all parts of its person, through which the air is brought in contact with the legs, wings, and so on. These tubes are each protected by delicate membranes. In the fly there exist certain air pouches in addition to the tubes, which serve as reservoirs of air.

It is generally supposed that instinct unerringly teaches birds and insects the best way in which to build their homes or nests, and also to provide for their offspring. The following incident, recently under personal observation, will show that instinct is not always infallible, says the Scientific American: "A friend placed three small empty vials in an open box on a shelf, in an upright position in close contact, and they were uncorked. A short time afterward it was a matter of surprise to find that these had been appropriated by a female mud wasp. She had placed a goodly number of spiders in the center vial, doubtless intended to serve as food for her future brood; then proceeded to deposit her eggs in those on either side. She next closed tightly the mouths of all three receptacles with a hard lime cement. Having finished her work, she then doubtless went on her way, satisfied all had been done for her offspring that a thoughtful mother could do. But just think of the sensations of those little wasps when they come into existence, for, while starving in their sealed cages, they can plainly see, through the impenetrable glass walls, the bountiful supply of food which was provided for their use."