. Elements of geology : a text-book for colleges and for the general reader. Geology. Fig. 74. Fig. 75. 1° for every 53 feet. This very important fact has been determined by numerous observations on the temperature of mines and of Artesian wells in almost every part of the earth. All the facts thus far stated are graphically illustrated in the accompanying figure (Fig. 74), in which the line a b represents depth below the surface, and the diverging line c d the increasing heat; m the invariable stratum; n the line of no daily variation; the curves p e, c e, o e, the temperatures in summer, aut
. Elements of geology : a text-book for colleges and for the general reader. Geology. Fig. 74. Fig. 75. 1° for every 53 feet. This very important fact has been determined by numerous observations on the temperature of mines and of Artesian wells in almost every part of the earth. All the facts thus far stated are graphically illustrated in the accompanying figure (Fig. 74), in which the line a b represents depth below the surface, and the diverging line c d the increasing heat; m the invariable stratum; n the line of no daily variation; the curves p e, c e, o e, the temperatures in summer, autumn, and winter, respectively; the space ceo the annual swing of temperature; and the smaller curves meeting on the line n9 the daily variation or swing of temperature. We have given the rate of increase as about 1° in 53 feet. It varies, however, in different places, from 1° in 30 feet to 1° in 90 feet. Except in the vicinity of volcanic action, this difference is probably due to varying conductivity of the rocks. The lines, or rather surfaces, which join places in the interior of the earth, having equal tempera- tures, may be called isogeotherms. If the rate of increase were every- where the same, the isogeotherms would be regularly concentric; but, as this is not the case, they are irregular surfaces (Fig. 75), rising nearer the earth-surface and closing upon one another where the con- ductivity is poor, and sinking deeper and separating where the con- ductivity is greater. Constitution of the Earth's Interior.—From the facts given above it is probable that the temperature of the interior of the earth is very great. A rate of increase of 1° for every 53 feet would give us, at the depth of twenty-five or thirty miles, a temperature, sufficient to fuse most. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original w
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Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1892
