Volume 13, Issue 10, 01 October 1942
Index of content:
13(1942); http://dx.doi.org/10.1063/1.1714806View Description Hide Description
13(1942); http://dx.doi.org/10.1063/1.1714807View Description Hide Description
13(1942); http://dx.doi.org/10.1063/1.1714814View Description Hide Description
Large single crystals can be grown in ``218'' and similar tungsten wires by vacuum heating at a constant temperature in the range 1900°K to 2200°K. The growth can be followed by observation of the thermionic emission pattern, using a cylindrical electron‐projection tube with a fluorescent screen. The rate of growth is found to increase with temperature according to an exponential law. Crystal growth is slower in wires drawn to smaller diameter; this can be explained by the small grain hypothesis. The perfection of crystals is discussed.
13(1942); http://dx.doi.org/10.1063/1.1714815View Description Hide Description
The frequencies, frequency ratios, amplitudes of vibration, and mechanical constants of nearly‐complete circular rings of various diameters and cross sections were measured and analyzed. The first six modes of vibration parallel to the plane of the ring, and the first five modes transverse to the plane of the ring, were obtained for several rings. The positions of the nodal points are tabulated. For the parallel vibration the frequency ratio fn/f 1 is found to be independent of the cross section of the ring and for modes higher than the second are given accurately by the equation fn/f 1=0.628(n−0.200)2 where n is the mode. The frequencies of parallel vibration are found to be given by the equation, fn = (Kn/D 2) (B/m)½, where K 1=0.285, K 2=0.630, Kn =0.1795(n−0.200)2 (for n>2), D is the mean diameter, B the bending stiffness, and m the mass per unit length. For the transverse vibration the frequency ratios depend upon the type of cross section, but are of the general form, fn/f 1=K 2(A/C) [n+k(A/C)]2, for n>2. The values of K 2(A/C) and k(A/C) are given in graphical form. A/C is the ratio of bending to twisting stiffness of the cross section of the ring. The frequency of transverse vibration is given by the equation, fn = [ψ n (A/C)/D 2] (A/M)½. The values of ψ n (A/C) for a wide range of A/C values are given graphically for the first six modes. The distributions of amplitude of vibration around the rings for the first three modes of both parallel and transverse vibration are shown graphically.