Page:Popular Science Monthly Volume 45.djvu/878

856 left them to wander around the garden, only returning to give them suck She at length escaped from the garden to Neuilly, but returned of her own accord. For fear of losing her entirely, she was separated from her young and fastened up. The young are very familiar, and play all day long with the other young dogs.

Thrifty Birds.—A curious illustration of the industrial instincts of animals, given in M. Frédéric Houssay's book on that subject, is afforded by the California woodpecker, which, though an insect eater, stores away for its winter supply food of an entirely different character, not so subject to decay. It collects acorns, for which it hollows small holes in a tree—a hole for an acorn—into which the acorn is exactly fitted, ready to be split by the strong beak of its owner, but too tightly held to be stolen by other birds or squirrels. Another woodpecker, in Mexico, stores against droughts, selecting the hollow stem of a species of aloe, the bore of which is just large enough to hold a nut. It drills holes at intervals in the stem and fills it from bottom to top with nuts, the separate holes being probably made for convenience of access to the column of nuts within. The common ants of Italy store oats and other kinds of grain in chambers which they make of about the size of a watch. They have a way of keeping the grains from sprouting with which we are not acquainted; and if they are removed, the seeds sprout. When they wish to use their store, they allow the grains to germinate till the chemical change takes place in the material that makes its fermenting juice suitable for their digestion. They then arrest the process of change by destroying the sprout, and use the stock of glutinous sugar and starch as their main food in winter.

Atmospheric Dust and Air Colors.—Having continued his observations on dust particles in the atmosphere in connection with other meteorological phenomena, Mr. John Aitken has now exceeding fifteen hundred observations, to produce which required the testing of fifteen thousand samples of air. The list includes, besides Great Britain, observations made in the south of France, at Hyères, Cannes, and Mentone, and at the Italian lakes. At none of the places in these districts was pure air ever met with. On the slopes of Monte Motterone, at Baveno, with the wind blowing up the slopes and carrying up the impure air, the amount of dust at two thousand feet was reduced only to 0·64 of the number at low level, while if the wind was from other directions it was reduced to 0·3. The conclusion that the descriptions given by many writers of the beauty of the coloring on earth and sky seen at high level at sunrise and sunset are much exaggerated is confirmed by the observations on the Rigi Kulm. During five years no coloring at sunrise or sunset was witnessed from this point equal to what is frequently seen at low level. The sunset colors are shown to depend very much on the amount of dust in the air. When the atmosphere is comparatively free from dust the coloring is cold, but the lighting is clear and sharp; and when there is much dust, there is more color on the mountains and clouds and in the air itself, and the coloring is warmer and softer. At high level the coloring is more feeble and of shorter duration. A thick veil of haze seemed to hang in the air between the observer and the mountain on all days when the number of particles was great, and it became very faint when the number was small. The condition of the air on the occasions of the different visits to the Rigi varied greatly. The clearest days, with the lowest numbers of particles, were when the wind blew from the Alps. The daily maximum on the Rigi did not appear on all days. Winds from pure directions generally prevented it, either by checking the ascent of the valley air, or by the valley air being pure, or by the pure valley air not being much heated by the sun and therefore having but little tendency to rise. It was very marked when the wind was from the plains. The hour at which the rise in numbers began and the hour of maximum were very irregular. The amount of the daily maximum varied greatly; sometimes it was only two or three times the morning number, while it at other times exceeded it eightfold. In the observations at Kingairloch, in Argyllshire, certain abnormal readings of dust particles were always accompanied by certain conditions of weather. If the sky remained clouded all day, the numbers were always low during the whole of