Volume 7, Issue 10, 01 October 1936
Index of content:
7(1936); http://dx.doi.org/10.1063/1.1745344View Description Hide Description
Photographs of lightning taken with rotating film cameras near Albuquerque, New Mexico, in the summer of 1935 show three different types of electrical breakdown. In the first type the first flash starts at the cloud, proceeds about 1 km and stops abruptly in air. This was followed in 0.008 sec. by a second flash traversing the same path but extending it about 0.22 km. The third similar flash 0.01 sec. later extended the path 0.5 km. The fourth flash extended the path clear to earth 0.0098 sec. later. The second type showed the well‐known ``leader'' type of breakdown of Schonland and others. The third type of breakdown consisted of only the main violent discharge between cloud and earth. The results are briefly discussed and a new possible mechanism for lightning breakdown pointed out.
7(1936); http://dx.doi.org/10.1063/1.1745345View Description Hide Description
Some diffusion problems arising in biophysics are discussed for simple two‐body cases. The steady state concentration field is determined, by a method of images, for cases of constant inflow over the surfaces of two external spheres, or two long parallel cylinders; both when the bodies are in an inactive environment, and when they are aligned with an external gradient. As an application, there is calculated the resultant force on each body arising from a normal surface pressure proportional to the concentration. The numerical value of these forces is of the same order of magnitude as that approximately estimated previously by N. Rashevsky.3
7(1936); http://dx.doi.org/10.1063/1.1745346View Description Hide Description
A series of observations of the atmospheric potential gradient have been made over a period of six years and have been correlated with positions of the sun‐spots and weather conditions. Maxima or minima of the potential gradient and storms appear to recur at intervals of approximately 27 days and at the same time that sun‐spots appear near a plane through the axis of the sun and the earth. The supposition is made that the variations of the potential gradient and the storms are associated with radiation which travels approximately with the velocity of light from the sun. Since the light received from the sun‐spot group cannot change rapidly as the group passes its position of nearest approach to the earth it seems more reasonable to suppose that a radiation not distributed according to Lambert's cosine law is involved.
7(1936); http://dx.doi.org/10.1063/1.1745347View Description Hide Description
The problem here treated is that of finding the longitudinal motion of a long coil spring suspended vertically from a rigid support: the spring being sufficiently ``soft'' and long that it stretches appreciably under its own weight. Thus the tension and linear density each vary from top to bottom of the spring. A general solution involving displacements from the stretched static position is obtained and applied to three specific sets of boundary conditions; first, the lower end free, second the lower end rigidly fixed and lastly with a weight attached to the lower end. The natural periods corresponding to the first three fundamental modes of motion for each of the three conditions mentioned above have been determined experimentally for a long coil spring of piano wire and the results compared with the theoretically computed values. Before experimental results are given it is shown, by a second form of the equation of motion, that the natural frequencies of a spring are not affected by stretching.