Page:Popular Science Monthly Volume 7.djvu/520

504 will notice broken egg-shells in the water, and, on closer inspection, will observe wriggling nondescripts on the bottom, neither like fish nor eggs, but compounded of both. When they once begin to appear, they come in thousands, in millions, in myriads. The young need more water, at this time, but require less care; yet still they must be watched. The young fish may soon be turned loose into the stream.

If he is a salmon, after a few months' preparation to strengthen his sinews and test his power, he goes down to the sea, there to dwell, and feed, and grow, gaining wonderfully in size, drawing his sustenance from the exhaustless storehouse of the world, and coaling back to man, in a few months, a magnificent embodiment of strength and beauty, bringing to the lord of the universe five or ten pounds of as delicious food as ever delighted a gourmand's palate, or satisfied a hungry man's stomach. If he is only a trout, a younger brother of the glorious family of the Salmonidæ, he will lurk about the bottom of some pond, or graze some pebbly mountain-brook, and struggle up to a half-pound or more before twelve months shall have rolled over bis head.

Heat evolved by Friction of Ice.—Mr. A. Tylor, in a paper recently read before the Geographical Society of London—a synopsis of which was published in Nature—shows that heat evolved by friction of ice upon ice is an important element in glacial movement. By a simple apparatus he reduced ice to water in a temperature of 32°, at the rate of one and a quarter pound an hour, by friction only of ice upon ice, the pressure applied being but two pound to the square inch. By simple evaporation, the ice in the same temperature lost one-quarter of a pound in the same time.

In a temperature of 54° the production of water under friction was three and a quarter times greater than by simple melting when there was no friction.

The actual heat evolved by friction of ice upon ice is nearly the same as from oak upon oak, when well lubricated.

In the motion of glaciers great quantities of water are continually discharged, lubricating the bottom. Surface-melting of the ice Mr. Tylor considers insufficient to produce it. The bottom of a glacier, with its rasping under-surface of rock and sand, slides, to some extent, upon the bottom, and much heat is evolved in this way, but in innumerable fractures of the sides of the glaciers, of the surface-ice flowing on and over bottom-ice, there are friction and attrition, ice moving against ice, which melts it, and the water percolates through the fractures to the bottom.

In great glaciers. the pressure is enormous. With ice a mile thick it is half a ton to the square inch, and the quantity of water produced increased accordingly.

Economic Value of the Sunflower.—The common sunflower is a native of tropical America, and there it sometimes attains the extraordinary height, for an annual plant, of twenty feet. It thrives in nearly every region of the inhabitable globe. In the south of Europe and in the northwest provinces of India it is cultivated to a considerable extent. In the latter country, sunflower-plantations are said to have a very beneficial effect in promoting the healthfulness of regions infested by malarious fevers. The seeds are valued as food for cattle and poultry, and an oil may be expressed from them which is scarcely inferior to olive-oil. One acre of good land will produce about fifty bushels of seed, each bushel yielding a gallon of oil. The seeds are also used like almonds for making soothing emulsions, and, in some parts of Europe, a food for infants is prepared from them. In tropical America the Indians make bread of them. The leaves are used as fodder for cattle, and the stalks, when burned, yield large quantities of potash.

The plant called Jerusalem artichoke is doubly misnamed; it has as little to do with the Holy City as the soup made from its tuberous roots has to do with the Promised Land, and yet the former is called Jerusalem (from the Italian girasole—sunflower), and the soup is called "Palestine," because it contains "Jerusalem." It got the name of "artichoke" from a resemblance in taste between its tuber and the flower-receptacles of the true artichoke, but it differs totally from that plant in botanical characters. The Jerusalem artichoke is a species of the sunflower, and, like all sunflowers, a native of