Page:Popular Science Monthly Volume 43.djvu/152

142 of sand were formed, several feet deep in favorable places, packed as snow-drifts are packed by a blizzard. In parts of the Western plains the fine, loose sand has been blown away at times, leaving every pebble and large bowlder standing out in bold relief. The loose material often gathers in the form of drifts or dunes, which travel across the country with frequent changes of outline. A few miles north of Winnemucca Lake, in western Nevada, is a belt of these drifting sand hills, described by the geologist Russell as some seventy-five feet in thickness and about forty miles in length by eight miles in breadth. Another range of sand dunes, at least twenty miles long, and forming hills some two or three hundred feet high, is on the eastern end of Alkali Lake in the same State. Dunes of equal height have been formed on the eastern shore of Lake Michigan, and at Grand Haven and Sleeping Bear have drifted over the woodlands, so as to leave only the dead tops of trees exposed. The erosive power of these drifting sands is often an important agent in wearing away the rocks upon which they strike. Carried along by the force of the winds, they work effectively in undermining cliffs, scouring down mountain passes, and giving curious and fantastic forms to prominent rocks.

The Whistled Language of the Canary Islands.—As a result of his studies of the whistled language of Gomera, in the Canary Islands, M. J. Lajard affirms that it is not a special idiom or a whistle which tries to imitate the Spanish language; but it is the Spanish language strengthened by the aid of whistling. "The Gomerian, while he is speaking, puts one, two, or four fingers in his mouth, as we sometimes see done in the street in order to make shrill sounds, and at the same time he whistles with force. There results a mixture of words and whistle, unintelligible to ears not accustomed to it, but in which can be distinguished the words of the language. . . . The whistling, then, is only an artifice employed to carry to a distance the sound of the voice, to the detriment of its distinctness and tone-quality. This last inconvenience is so great that up to this time travelers have been unable to understand the whistled language. To be able to understand it, you must know how to whistle yourself." It is, however, very limited in its compass, and whistled conversations are of short duration. It exists in other of the Canary Islands than in Gomera, and there is reason for believing that it was formerly more widespread and more prevalent than now. Rudiments of a whistled language, the mechanism of which is like that of the Canaries, exist even in Paris; it is employed by butchers and by thieves.

What constitutes a Polluted Water.—A water is said to be polluted, according to Prof, von Pettenkofer, when it is no longer clear and inodorous, when fishes and plants perish in it, and when it contains more organic matter and less oxygen than are to be found in the unpolluted portions of the flow of the stream. Such contamination is essentially different from the transient turbidity due to heavy rains or to melting snow. Still, even the permanent pollutions disappear in the further course of the river bed, by deposition and other agencies. Here the rapidity of the stream and the quantity of the water exert a preponderating effect. The most formidable impurities are supposed to consist of the putrescent refuse which flows out of sewers of cities, and quickly produces an offensive odor at the places where it accumulates. Prof, von Pettenkofer has for many years given his attention to the question of the extent to which rivers are polluted by such agencies, and has had researches conducted by his pupils. But nothing has hitherto altered the opinion which he expressed long ago, that sewage may be safely permitted to flow into a river if its volume is not more than one fifteenth that of the river water, and its rate of flow is decidedly greater than that of the current. Taking the city of Munich, which has 280,000 inhabittants, he computes the pollution of the Isar by its sewage as amounting to only of the discharge of the river—a pollution so inconsiderable that it can not be detected by the eye when a corresponding mixture is made up experimentally. But it is also not permanent, for at Ismaning, seven kilometres below Munich, the sewage influx is no longer to be detected; and at Freising, thirty-three kilometres below, the chemical and bacteriological