Page:Popular Science Monthly Volume 21.djvu/440

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serted in it, and a conical steel needle-drill is introduced into the central hole of the metallic cylinder thus formed. The piston-head of the perforator is then made to strike upon the head of the needle, so as to drive it in like a wedge and cause it to force the two segments apart and split the rock. As many holes may be made as are necessary to break the rock up, and this depends much upon its hardness. Fig. 5 represents a section

PSM V21 D440 Coal mine preparation for fracturing rock.jpg

Fig. 5.—Section of a Gallery under a Coal-Mine, indicating the Holes to be bored by the Perforator, so as to break up the Sterile Rock in Four Successive Operations.

of the chamber of a coal-mine, and indicates the position of the holes that have to be drilled to break up the rock in four successive operations. The inventors of this apparatus claim that rock can be broken up with it in veins of the average thickness almost as fast as with gunpowder.

Transmission of Vibrations.—The Transactions of the Seismological Society of Japan contains an account of experiments by Professor H. M. Paul, in Washington, D.C., on the transmission of vibrations from railroad-trains through the ground. Cups containing mercury were fixed at four stations, at distances of from 0·29 to 0·93 of a mile from the railroad, in which the amount of disturbance caused by vibration was ascertained by noticing the displacements of the reflected image of the pole-star. The character of the effects varied according to the distance of the station from the train, the nature of the ground at the station, and the kind of train, but they were distinct. At I one of the stations the communication of vibrations, which were limited to a shallow depth, appeared to be interrupted by the intervention of a ravine. The effect of carriage-driving on a public road was also observed. A hack carrying four persons and drawn by two horses, about four hundred feet away, caused a temporary shaking of the mercury whenever a wheel struck a stone or hollow; and a similar effect was produced while the carriage was crossing a small wooden bridge at about five hundred feet; but no serious continuous disturbance was perceived till the carriage approached within two or three hundred feet of the instrument.

The Systematic Position of the Brachiopoda.—In the "Jenaische Zeitschrift für Naturwissenschaft," Jena, 1881, Dr. Oscar Hertwig and Dr. Richard Hertwig, the eminent embryologists, recognize the work of