Page:Popular Science Monthly Volume 9.djvu/534

 concrete floor, in the green or wet state, of a room say twelve and a half by twenty-five feet, may be struck in a week after the completion of the floor, if the concrete be only six inches in uniform thickness, and gauged in such proportions that every cubic yard when in situ contains four bushels of Portland cement, and six bushels of clean, sharp, siliceous sand. One month after the concrete has set, the floor would be capable of sustaining an equally-distributed load of 112 pounds to the foot superficial, and, twelve months after, an equally-distributed load of 450 pounds per foot superficial. If the thickness of the flooring be increased to twelve inches, and the concrete gauged as before, a room nineteen and a half feet in width by any length may be covered with the same results as to strength, as those given above for the room twelve and a half feet in width. A wall of concrete is impervious to water, and fire-proof.

A Relic of the Mound-Builders.—Through the kindness of Prof. A. E. Dolbear, of Tufts College, Massachusetts, I am enabled to present to the attention of archæologists a brief notice and figure of an unusually interesting specimen of carving in stone, the work of the mound-builders of Ohio. The history of the specimen, as given me by Prof. Dolbear, is briefly this: "It was ploughed up in a field a few miles from Marysville, Union County, Ohio."

The relic is a small pebble of bluish-gray slate, highly polished, and ground to a moderately sharp edge. The front or carved side is oval and of a uniform surface; the back is sloped from a central flat oval space, about one-fourth of an inch in its long diameter. Had the specimen not the carving of a face upon it, it could properly be classed with that form of implement known as the "celt," although these very seldom have an edge extending along the entire margin. Circular celts or "skinning-knives," of about the same size, with a cut-ting-edge along the whole margin, have been found by the writer, in New Jersey. The remarkable feature of the relic here described is the human face carved upon one side. As a representation of a woman's face, it is certainly artistically executed. As has been remarked of a mound-builder's smoking-pipe, having a somewhat similar carving, "the muscles of the face are faithfully rendered, and the forehead is finely moulded. The eyes are prominent and the chin open, and full and rounded." The nose and mouth are distinctly cut, but not as accurately finished as the other features.

Although the labor expended upon the stone to bring it to so well defined an edge, about its margins, was so considerable, the specimen can scarcely be considered an ornamented cutting-implement. Celts, such as we have referred to, are never marked by carvings, even of plain lines, so far as we have collected them in New Jersey; although some other forms, as plummets (?) and pestles, were occasionally carved. What, indeed, this relic really was, when the aborigine who carved it had it in possession, it is useless to-conjecture. Its value now consists in its being a well-preserved specimen of the work of a stone-age savage; and possibly a characteristic delineation of the features of a woman of the race known as the mound-builders.

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The Loan Exhibition in London.—The exhibition of scientific instruments at London was opened with an address by Mr. W.