Page:Popular Science Monthly Volume 27.djvu/593

Rh with the earth, could not have any material influence in attracting the lightning from the clouds; if it had, then the houses with tin roofs, many of them without lightning-rods, now so common, would be in great danger, whereas they are not struck oftener than houses with tile roofs. The presence of iron, however, might increase the danger of fire after the house had been struck; for, if we place a combustible substance between two conducting surfaces, it is generally sure to take fire when an electric current is passed through it from one of the conducting surfaces to the other. So, if lightning should strike a house, it would find its way to any masses of metal within the building and ignite whatever combustible matters it passed. In view of this fact, and of the present very extensive use of metal in house-construction, the provision of suitable conductors to divert electrical currents from the combustible parts of the building has become more important than ever.

Was it Volcanic or Cosmic Dust?—Mr. W. Mattieu Williams is of the opinion that the long continuance of the glowing twilights tells against the validity of the volcanic-dust theory; for that dust must have settled by this time, or, if so much of it has continued to float in the atmosphere, it should have shown its presence more palpably than it has done. The two alternative hypotheses to this one, worthy of serious consideration, are: 1. That the earth, and possibly the whole or a large portion of the solar system, has, in the course of its journey through space, passed through a region unusually rich in meteoric dust; or, 2. That an unusually large amount of aqueous vapor has been raised to the upper regions of our atmosphere by increased solar activity. Apparently in favor of the meteoric theory is the statement of F. Mangini, that on three days in February and March, 1885, when the glows, accompanied by rain, were especially remarkable, he collected at Reggio, in Calabria, some new-fallen red dust, which, when examined under the microscope, seemed to consist of mica, quartz, and irregular polyhedric crystals. Analysis brought out magnetic iron oxide, sulphuric and phosphoric acids, silica, calcium, magnesium, aluminum, nickel, and arsenious, ferric, and manganous oxides. The dust did not come from Etna, because the wind was blowing in the opposite direction, and Etna dusts are black; nor from the Sahara, because Sahara dusts contain no iron.

Oranges in Palestine.—The climate and soil of Palestine are well adapted to the cultivation of the orange, which, according to Consul Merrill, there suffers from no diseases or parasites of any kind. The trees appear to flourish best near the sea, and the orange-groves are for the most part near Jaffa and Gaza. In Jaffa there are five hundred gardens, of which one hundred and fifty are ranked as first class, all the gardens together containing about 800,000 trees. The trees are set about fifteen feet apart, while the ground between them is planted with small fruits or vegetables. The sweet lemon is used as the stock, and the variety of orange desired is grafted upon it. The trees are watered every week in the summer, at a cost per season of about one fifth the value of the crop in gardens of the first class. The Jaffa oranges proper, the only kind exported, are oval, or lemon-shaped.



has summarized the results of forty-six years of observations on earth-quakes in Chili. They are more frequent in the northern part of the country, where there are no volcanoes, and the Andes are fifteen thousand feet high, than in the southern part, where there are volcanoes, and the mountains are only a third as high. The effects of the shocks on buildings depend more on the nature of the soil than on the violence of the spasms. The sea-phenomena are of two kinds: local, or oscillating, when the waters retire to beyond the lowest-water mark, to return in waves a hundred feet high beating upon the coast and destroying everything they reach; or, when the shocks occur at a distance, the water runs along the coast in a grand wave without previously retiring. In the more severe earthquakes, when there are several shocks in the same day, it is generally the second or third one that produces the greatest destruction. The destructive effects of an earthquake are never as considerable in the interior of a mine as at the surface.

of the Physical Section of the French Academy of Sciences, died after a very short illness, about