Page:Popular Science Monthly Volume 25.djvu/880

862 the form of a duck, was observed to fill her capacious beak with from twenty to thirty grains of barley, with which she proceeded to the fowl-house, and there deposited her store immediately in front of the bantam." Another anecdote is given in evidence of the sagacity of the duck. "I had five Aylesbury ducks, with a number of fowls. The lord of the yard, a most despotic chanticleer, would never suffer the ducks to feed with his family and friends when, at the regular meal-times, the grain was scattered for their common use. Ferociously, and without pity, he drove them from the ground. This had been going on for many weeks; and one day, at the twelve-o'clock repast, the act of expulsion was performed as usual. I was present, and saw the discomfited ducks retire to a corner of the yard. There they evidently held a conference. Having been so engaged some five minutes, they proceeded with deliberate and resolute air, in single file, as is their wont, toward their oppressor. Having reached the tyrant, they surrounded him, each duck turning his posterior toward the enemy, and with concerted action fairly hustled him clean out of the yard. To see the surprise of the cock, as he jumped from side to side to avoid the pressure of the attacking party, was ludicrous in the extreme. The victory was complete; from that hour the ducks were never again molested."

Attractions and Repulsions of Dust.—Mr. John Aitkin has recently performed some experiments illustrating the formation of clear spaces in dusty air. His apparatus consisted of a dust-box blackened inside, having a glazed front, and provided with a window on one side. Condensed light was admitted through the window from a dark-lantern. Dusts were made by chemical processes or from calcined magnesia, lime, or charcoal, and were stirred up by means of a jet of air. A round tube was introduced into the box and the dust stirred up, when it was observed that the dust came in close contact with the top and sides of the tube, but that below it a space was clear. This disposition of the dust was found to be an effect of gravitation, under which the falling particles did not reach the space immediately under the tube. When a thin plate was inserted vertically in place of the tube, no clear space was formed. No increased effect was observed on lowering the temperature from the normal; but, if a little heat instead of cold was applied to the round tube, the dark space rose and encircled the tube, and the two currents of clear air united over the tube to form the dark plane in the upward current. Heat was furthermore found to exert a real repelling effect on the dust. On heating the vertical metallic plate, the dark plane was formed in the ascending current in front of the plate, beginning with the slightest increase, and growing thicker with the rise, of temperature. With very high temperatures, produced by heating platinum wire in a battery, every kind of dust was found to have a different-sized dark plane; and, as the particles could be seen streaming into the dark space under the wires, it was obvious that these large dark planes were not caused by repulsion, but by the evaporation or disintegration of the particles. The effect of electrification of the hot surface was found to be opposite to that of heat, and dust was attracted to the surface or repelled from it, according as electricity or heat was applied with more force. It was also found that after the dust-particles were electrified they tended to deposit themselves on any surface near them, and electricity proved to be capable of depositing the very fine dust of the atmosphere. The air in a flask was purified much more quickly by means of the electric discharge than it could have been by means of an air-pump and cotton-wool filter. It was shown that a hot and wet surface repels dust more than twice as strongly as a hot and dry one. From this it was concluded that the heat and moisture in our lungs exert a protecting influence on the surface of the bronchial tubes, and tend to keep the dust in the air from contact with their surfaces. It was also observed that dust was attracted to cold surfaces and attached itself to them.

Chinese Plants in America.—Dr. D. J. MacGowan has published some notes on Chinese plants which it may be profitable to acclimatize in the United States. Among the plants he has recommended are several bamboos, the coir-palm, banian,