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Considerable time has been spent by the author in studying, by experimental methods, the behavior of a bow while the arrow is being discharged. Some of the results of these investigations have been published in the magazine previously mentioned and in The Journal of the Franklin Institute (October, 1929). He has also had high speed pictures (one to three thousand frames per second) taken by Electric Research Products which, in addition to putting an end to all controversies regarding the “archers paradox” furnish an excellent means of studying the motions of the arrow and bow limbs. While these experimental methods are interesting and valuable, they are necessarily slow and expensive. An analytical method was therefore developed for determining the dynamical forces, the velocities and accelerations of the arrow and bow limbs. This method has been useful in improving the design and cast of bows. The method is briefly set forth in this paper. Since the dynamical treatment depends on the static conditions, a few of the static equations will first be given. Let us assume that the bow is made up of a short rigid middle section and two limbs, which, for all positions of the draw, bend in arcs of circles. This assumption is reasonable because

In this paper equations are set up which describe the behavior of a solid under the action of combined stresses when a steady state of creep is assumed to exist. A material is said to be in a steady state of creep if it yields with a constant speed under a given constant stress. In an ordinary creep test the steady state exists when the deformation has reached the point where the ``creep curve'' becomes a straight line. In mathematical language this can be expressed by saying that the stress is a function of the rate of strain and is independent of the amount of strain. Cases are worked out in which this stress vs. strain rate relation is a simple power function. Various types of flow including purely plastic flow and viscous flow can be discussed by changing the value of the exponent in the power function relation. Several specific examples which include the case of the thick walled cylinder with closed ends loaded by internal pressure and the case of a disk having a circular hole and loaded in its plane are worked out. Equations are developed which show the steady state stresses in such cases. Expressions for the stress concentration factors in creep are also obtained.

In this paper the principal results of experiments on the viscosity of lubricating oils under high pressure, other than mineral oils, have been reduced to the same units and collected for comparison. The investigations reviewed are those of the American Society of Mechanical Engineers; J. H. Hyde at the National Physical Laboratory of Great Britain; S. Kiesskalt at the Technische Hochschule, Karlsruhe, Germany; and Y. Suge at the Institute of Physical and Chemical Research, Tokyo, Japan. Viscosity‐pressure‐temperature data are given for eleven different oils.

This paper gives the results of an investigation of the voltage characteristic of the copper arc in air during the process of arc formation. A pair of copper electrodes, initially in contact and carrying current, were separated and the voltage arising across the arc gap was studied. Cathode‐ray oscillograms indicate that at the instant of contact separation there develops across the gap a voltage of about 12.2 volts. This voltage was attained in less than 10−5 seconds. This rapidly developed voltage was found to be independent of arc current for current values up to 100 amperes, which suggests that the rapidly developed initial voltage corresponds to the cathode fall of the arc.

Curves are presented from which it is possible to obtain the adiabatic compressibility of a petroleum oil in the range of 40°–200°F and up to 5000 pounds per square inch when only the specific gravity at 60°F and the kinematic viscosity at 100°F are known. A chart is given for obtaining the velocity of a pressure wave in an oil in which both the viscous drag and expansion of the containing tube are neglected. A table showing compressibilities and wave velocities for a number of Diesel fuel oils at 120°F and 1750 pounds per square inch pressure is given. The effects of viscosity and tube wall expansion on wave velocity are discussed and a chart is presented to aid in determining the wave velocity in steel tubes. The paper is concluded with a discussion of the effect of wave velocity on the point of injection of the fuel in the Diesel cycle.