Page:Popular Science Monthly Volume 14.djvu/711

Rh inference. The first experiment was rather surprising. A glass cylinder placed over an electric lamp (Foucault's regulator) for two minutes, and afterward examined, was seen to contain a perceptible amount of red fumes, due to peroxide of nitrogen (N2O4). The air surrounding the lamp was next drawn through a solution of potash, and the amount of nitric acid estimated; this gave ten to twelve grains of nitric acid produced per hour (it may eventually prove to be more, the difficulty being to collect the whole of it). The next step in the research will be to examine the various forms of electric light, with a view to determine the amount of nitric acid produced by each.

In an Ants' Nest.—The columns of the Popular Miscellany from month to month give evidence of the interest with which naturalists study the ways of ants. Indeed, the life-history of that interesting insect seems to be full of surprises for the persevering observer. Here is an account of a nest of Formica nigra, in which a number of Termites were kept as slaves. While entomologizing in Portugal in 1877, in the neighborhood of Cintra, Mr. Henry O. Forbes found a nest of F. nigra under a stone. On turning the stone over, he observed great consternation in the community, evidently caused by the fear lest a colony of Termes lucifugus, which the Formicas had enslaved, should escape. The Nigras instantly began seizing the Termites, driving them underground by the nearest orifices, in the mean time wrenching and pulling off their wings. In the nest there was also a large number of Termite larvæ, and the great object of the Nigras seemed to be to get these underground as speedily as possible. The ants fell on them with fierce impetuosity, seizing them anyhow and anywhere, dragging them against the most strenuous opposition into the nearest apertures of the underground home. Very often this opposition resulted in a long and savage fight, in which the larvæ were badly wounded, being deprived sometimes of their antennæ, sometimes of half their jaws, and not seldom killed outright. Occasionally, however, the larvæ were victorious, beating off the Formicas. The observer saw at the end of a long fight one larva drawn by its antennæ, while it strenuously held on to a small ball of earth which had proved a vain anchorage for its feet, for larva and clod together were dragged for a long distance through the grass. At last it seized one stalk so firmly that its enemy could not drag it farther; whereupon, after reconnoitering the ground for a little distance, the latter disappeared, but shortly returned with a companion, by whose aid the larva was detached. This done, the helper went his way, while the abductor proceeded with his captive till lost to view.

Pearls and their Origin.—People are still to be found who believe in the myth which ascribes to pearls a sort of animal nature—being born of other pearls, feeding like other animals, and growing larger by the conversion of food into their own substance. A glass tube purporting to contain some of these growing pearls and certain "grains of rice," on which they fed, was lately sent from Australia to Mr. Frank Buckland, who in turn placed it in the hands of a competent conchologist, Mr. Hugh Owen, for examination. Mr. Owen, honestly desirous of dissipating the crass ignorance which alone makes belief in such absurdities possible, takes the trouble to state briefly, in "Land and Water," the natural history of pearls, in substance as follows: Pearls are concretions found either attached to the interior of certain bivalve shells, or enveloped in the folds of the mantle of the animal that inhabits the shell; the latter are most valued. All pearls are formed of the same substance as that lining the inner surfaces of the shells in which they are formed. The peculiar luster is caused by alternate layers of thin membrane and carbonate of lime, and depends on very minute undulations of the layers. The most valuable pearls are found in the soft portions of the mollusca, and are believed to be originally a grain of sand, or some other irritating substance, which the animal covers with a nacreous deposit. That this is the correct theory is seen on cutting or slitting pearls, when each one is found to have a foreign body as a nucleus. Such being the natural history of pearls, the story of "young pearls feeding on rice"