863 



THE POPULAR SCIENCE MONTHLY. 



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 chanti- 

 cleer, would never suffer the ducks to feed 

 with his family and friends when, at the reg- 

 ular 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 re- 

 tire to a corner of the yard. There they 

 evidently held a conference. Having been 

 so engaged some five minutes, they proceed- 

 ed 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 at- 

 tacking party, was ludicrous in the extreme. 

 The victory was complete ; from that hour 

 the ducks were never again molested." 



Attraetions and Repulsions of Dnst. — 



Mr. John Aitkin has recently performed 

 some experiments illustrating the forma- 

 tion of clear spaces in dusty air. His ap- 

 paratus 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 mag- 

 nesia, 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 ver- 



tically in place of the tube, no clear space 

 was formed. No increased effect was ob- 

 served 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 up- 

 ward 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 heat- 

 ing 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 at- 

 mosphere. The air in a flask was purified 

 much more quickly by means of the elec- 

 tric discharge than it could have been by 

 means of an air-pump and cotton-wool fil- 

 ter. It was shown that a hot and wet sur- 

 face repels dust more than twice as strongly 

 as a hot and dry one. From this it was con- 

 cluded that the heat and moisture in our 

 lungs exert a protecting influence on the 

 surface of the hronehial 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 at- 

 tached 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 sev- 

 eral bamboos, the coir-palm, banian, piano- 



