Page:Popular Science Monthly Volume 38.djvu/589

Rh dissolves in water, or into delicate, viscous, and somewhat tough superficial lamina?. Without using any Mordant, it produces very fast colors in wool, silk, cotton, and linen goods, varying, according to the application, from the clearest to the blackest brown. The corovillo affords a deep scarlet color, the preparation and application of which are a secret known only to a few families who keep it well. The acid extract from the lapacho—lapachic acid—appearing in greenish-yellow needle-crystals, affords, according to its treatment, rose-crimson, yellow, clear brown, and dark brown. The tree itself has some remarkable characteristics—in the impenetrable density of its inflorescence previous to the appearance of the leaves, the firmness and strength of its wood and its freedom from ash, the resistance of the wood to decay, and the intense induration of its wood when soaked for a considerable time in water.

Speed Of Insects.—"Flies," observes a writer in the London Spectator, "frequent the insides of our windows, buzzing sluggishly in and out of the room. But what different creatures are they when they accompany your horse on a hot summer's day! A swarm of these little pests keep pertinaciously on wing about your horse's ears; quicken the pace up to ten or twelve miles an hour, still they are there; let a gust of wind arise and carry them backward and behind, the breeze having dropped, their speed is redoubled, and they return to their post of annoyance to the poor horse. But this example gives only a partial proof of the fly's power of flight. The present writer was traveling one day in autumn by rail at about twenty-five miles an hour, when a company of flies put in an appearance at the carriage-window. They never settled, but easily kept pace with the train; so much so, indeed, that their flight seemed to be almost mechanical, and a thought struck the writer that they had probably been drawn into a kind of vortex, whereby they were drawn onward with little exertion on the part of themselves. But this notion was soon disproved. They sallied forth at right angles from the carriage, flew to a distance of thirty or forty feet, still keeping pace, and then returned with increased speed and buoyancy to the window." The same writer estimates that the dragon-fly, which passes and repasses as in instantaneous jerks, is capable of flying at a speed of from eighty to a hundred miles an hour.

Ambergris.—The word ambergris is French for gray amber, which is a misnomer, for ambergris is a very different substance from amber. The latter is fossilized resin, and is therefore of vegetable origin, while the former is a product of some disease in the sperm whale. Ambergris is sometimes found in the intestines of the whale, but most of the supply is picked up in masses which float on the surface of tropical seas. The best ambergris is soft and waxy, gray in color, and streaked with different shades. It is opaque, inflammable, and remarkably light. It is found in the largest quantities near the Bahamas, but it is a scarce article at best, being quoted in New York at thirty-four dollars an ounce, wholesale. Its use is in perfumery, its great value being due to its powerful odor, which somewhat resembles that of musk, but is much more lasting. It is so peculiar that it has never been successfully imitated. Ambergris is so costly that it is one of the most adulterated articles known in commerce. It is too costly to use alone, but a small quantity of its solution in alcohol is mixed with other perfumes, the blended odor of which it intensifies. A grain or two rubbed down with sugar is often added to a hogshead of wine, to which it gives a pleasing fragrance. A handkerchief perfumed with the famous Parisian compound perfume, extrait d'ambre, will retain the odor after several washings.

Strength of the Earth's Crust.—In estimating the strength of the earth's crust, Mr. G. K. Gilbert uses the term crust to indicate the outside part of the earth, without reference to the question whether it differs in constitution from the interior. The conditions of the problem are illustrated by supposing a large tank of paraffin with level surface. If a hole be dug in this and the material piled up at one side, the permanence of the hole or heap will depend on its magnitude. Beyond a certain limit, further excavation and heaping will be compensated by the flow of the material. Substitute for