James T. Wilson

Quantitative Studies on Thermal Expansion and Contraction of Lake Ice

Field observations during the winter of 1951-1952 on Wamplers Lake in southeastern Michigan included measurements on the movement of the sheet of lake ice in response to air-temperature fluctuations. The following generalities resulted from the study: (1) A temperature rise of 1° F. per hour prolonged over a period of 12 hours on an 8-inch sheet is sufficient to cause thrust on a shore composed of unconsolidated glacial outwash containing some boulders. (2) The direction of ice thrust against the shore is not everywhere orthogonal to the trend of the shore line on an elongate lake but may be oblique at certain points. (3) Tensional fracturing of the ice due to rapid cooling results in one set of cracks that radiate from the central part of the lake and another set roughly concentric with the shore line.

Elastic Waves in Lake Ice Produced by Impact of Falling Weights

Experimental studies of the propagation of elastic waves in lake ice were made at Lake Margrethe, Michigan, and Garrison Dam, North Dakota. These studies were designed to investigate, in particular, flexural waves in the ice‐water system produced by hammer drops, cylinder drops, and sledge hammer impacts on lake ice and nearby land. A method similar to the standard seismic‐refraction techniques was employed for the wave studies. Flexural wave dispersion curves obtained from records of mechanical impulses on ice are, in general, consistent with theoretical curves based on the “layer” theory of Press and Ewing (1951) for the observed ice thickness and elastic parameters. Three groups of points on the observed dispersion curves obtained from Lake Margrethe data are flexural waves with frequencies from 2 to 8 cps, 13 to 25 cps, and 40 to 140 cps. The first and third groups exhibit dispersion consistent with the combined thickness of a two‐layer floating ice sheet. The second group follows dispersion for a wav...

Plant Resonance of Seismometers

A seismometer resting on an elastic medium can be regarded as a simple damped oscillator. Methods for measuring the “plant” resonance of seismometers are discussed along with the various parameters affecting the resonance. Laboratory measurements on sand and rubber, and field measurements on different types of soils were made using an electromechanical oscillator to generate elastic waves. The results are tabulated and the correlations with resonances observed in machine foundations are discussed.