Abstract
American Journal of Science, December.—A microsclerometer, for determining the hardness of minerals, by T. A. Jaggar. This instrument depends upon the energy required to make a boring of a certain diameter and depth under a given weight and by means of a diamond point of a cleavage tetrahedron of perfect shape. The hardness is measured by the number of turns required to make the boring, or by the depth reached after a certain number of revolutions. The depth is measured by a microscope attached to the boring point, by bringing successive divisions of a slanting micrometer scale into focus. The values found for the hardness of Mohs's scale-minerals show even greater gaps than those obtained by Pfaff and Rosival. Taking corundum as 1000, topaz is 152, quartz 40, orthoclase 25, apatite 1˙23, fluorite 0˙75, calcite 0˙26, and gypsum 0˙04.—On the sapphires from Montana, by G. F. Kunz. Sapphires were first found in transported gravels along the bars of the Upper Missouri, then in the earthy products of decomposed dikes, and lastly further down in the unaltered igneous rock itself. Much beautiful material has already been obtained, but little of high value.—On the corundum-bearing rock from Yogo Gulch, Montana, by L. V. Pirsson. The dikes of igneous rock containing sapphire and corundum are of a dark grey, basic appearance, and have an uneven fracture. In thin sections it appears as a dark lamprophyre, consisting mainly of biotite and pyroxene. There is a little iron ore present, but much less than is usually seen in rocks of this class.—Electrical measurements by alternating currents, by Henry A. Rowland. Gives some twenty-four methods of measuring inductances, capacities and resistances by means of alternating currents. Some of these depend upon a new principle in the shape of an adjustment of two currents to a phase difference of 90°. This is done by passing one current through the fixed, and the other through the suspended coil of an electrodynamometer. The fixed coil may then be made to carry a heavy current, and the sensitiveness of the apparatus is greatly increased. Inductances can be compared to within 1 in 10,000, but care must be taken not to twist the leads, as their electrostatic action is then very great. The question of standard inductances is thus practically solved.
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Scientific Serials. Nature 57, 189 (1897). https://doi.org/10.1038/057189a0
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DOI: https://doi.org/10.1038/057189a0