Scientific Serials

Abstract

American Journal of Science and Arts, February.—We have here two interesting papers on acoustics. Mr. Jacques has inquired into the velocity of loud sounds, measuring the velocity at different short distances from a cannon by means of a series of membranes electrically connected with a chronograph. He finds that the velocity of sound is a function of its intensity, and that experiments in which a cannon is used contain an error, probably due to the bodily motion of the air near the cannon. Immediately in the rear of the cannon the velocity was less than at a distance, but, going from the cannon, the velocity rose to a maximum considerably above the ordinary velocity, and then fell gradually to the rate usually received. When the cannon was pointed at right angles to its first position, the maximum velocity came nearer it, and had the cannon been pointed towards the membranes, the retardation would probably have become an acceleration.—Dr. Ihlseng has measured the velocity of sound in wood, both by Kundt's method and the graphic method, in which latter a blackened glass plate was drawn rapidly in a horizontal direction (across the direction of the rod's length), by a falling weight, and a pen attached to the rod wrote its vibration on the plate, which also registered those of a tuning-fork. This method was found one of considerable accuracy. Its results were slightly below those by Kundt's method, and (when the plate was moved in a different direction) it demonstrated the existence of transverse along with longitudinal, and gave their ratios.—Mr. Pumpelly writes on the relation of secular rock disintegration to lœss, glacial drift, and rock basins; Mr. Fontaine continues his notes on the mesozoic strata of Virginia; and Mr. Hawes describes a group of dissimilar eruptive rocks in Compton, New Hampshire.—In a method of determining dip, devised by Mr. Hodges, a compound bar is used consisting of two joined at right angles at a point near their ends; when placed so that the two branches make equal angles with the line of dip, the two joined poles neutralise each other, and any needle suspended near that point is unaffected. A slight turning of the compound bar renders the field round the needle a north or a south, and the needle moves correspondingly.—Some notices of recent American earthquakes are furnished by Prof. Rockwood, Jun.