THE POPULAR SCIENCE MONTHLY.
heard a rumbling sound and felt a quaking of the earth, which they took to be a veritable earthquake. But, as the sound was not repeated, they soon forgot the occurrence, and continued their chase till they came to the vicinity of the Bear Tooth. What was their surprise to find that the stupendous mass of the eastern tusk had been dislodged, sweeping for a quarter of a mile through a forest of heavy timber, and overwhelming with its débris the ground round about! Virginia City, in the same State, is gradually slipping down the mountain-side on which it is built. The movement is gradual, and imperceptible at the surface. A water-main recently uncovered was found telescoped for the space of one foot, and otherwise injured. A fissure has been traced in the ground on the western side of the town; on one side of this the ground is three feet higher than on the other.
The Death of a Generation.—A writer in an English magazine studies from birth to death the march of an English generation through life, basing his remarks on the annual report of the registrar-general. The author singles out, in imagination, a generation of one million souls, and finds that of these more than one-fourth die before they reach five years of age. During the next five years the deaths number less than one-seventh of those in the first quinquennium. From ten to fifteen, the average mortality is lower than at any other period. From fifteen to twenty the number of deaths increases again, especially among women. At this period, the influence of dangerous occupations begins to be seen in the death-rate. Fully eight times as many men as women die violent deaths. The number of such deaths continues to rise from twenty to twenty-five, and keeps high for at least twenty years. Consumption is prevalent and fatal from twenty to forty-five, and is responsible for nearly half the deaths. From thirty-five to forty-five the effects of wear and tear begin to appear, and many persons succumb to diseases of the important internal organs. By fifty-five the imagined million has dwindled down to less than one-half, or 421,115. After this, the death-rate increases more rapidly. At seventy-five, there remain 161,124, and at eighty-five, 38,565. Only 202 reach the age of one hundred. At fifty-three, the number of men and women surviving is about equal, but from fifty-five onward the women exceed the men.
Setting Tires with Hot Water.—The use of hot water in place of fire for expanding tires may not be new, but it is less common than it ought to be, if we are to accept as accurate the results said to be obtained in the workshops of the Moscow-Nizhni Railroad, in Russia. There an iron tank, one-fourth filled with water, is fixed near a stationary boiler, from which a steam-pipe is led through it, capable of heating the water to 212° Fahr. Into this the tire is plunged by means of a portable crane, and, after an immersion of from ten to fifteen minutes, is taken out and immediately placed on the wheel. The allowance for shrinking—in other words, the difference between the diameter of the skeleton and that of the tire—is 0.75 millimetre to a metre. This is ascertained by gauges of great accuracy; and, if it be deviated from, the tire will either be loose after cooling, or too small to get on the wheel. When fire is used, the tire can never be heated equally or cooled equally in all parts, and, in consequence, is sure to be more or less oval in form, which is not the case when hot water is employed. The officials of the railroad named above made a comparison of the two methods, from which it appears that, during a six years' trial of fire-shrunken tires, 37 per cent, ran loose, and 5 per cent, were broken; while, during a three years' trial of water-shrunken tires, less than one per cent, ran loose, and only a single tire was broken.
Distribution of Prairie and Forest.—Many are the theories which have been offered to explain the distribution of prairie and forest. The continued existence of the prairies of the West has been attributed to the annual fires; to the nature of the soil and its underlying rock; to deficiency of rainfall; finally, to deficiency of winter rains and snow. The contrary conditions would, according to these theories, favor the production of forests. Prof. J. E. Todd, who, in the American Naturalist, discusses this problem with special reference to South-