From the March 19, 1932, issue


A beautiful explosion, so large that the camera could only catch a part of it with sufficient clarity to detail its streaked and billowing effects, is reproduced on the front cover of this week’s Science News Letter. It is one of hundreds of such blasts that have located valuable new oil fields along the Gulf coast of Texas and Louisiana.

Several hundred pounds of dynamite buried about 20 feet deep is detonated. It explodes with terrific force, sending miniature earthquake shocks out in all directions. Some of the earth vibrations travel smoothly and swiftly through uniform materials; the paths of others are broken by irregular underground formations. Portable seismographs record the waves, and from a study of these records, remarkably accurate knowledge of the physical properties and structure of the underground rocks is obtained.

In this manner a number of salt domes have been located beneath which drills found profitable stores of oil. Along the Gulf coast of Texas and Louisiana, where salt domes deep in the earth often indicate the presence of oil, more than 50 proven domes have been found since the successful introduction of geophysical prospecting in 1924.

The success of the earthquake recorder in locating oil on the Gulf coast focused worldwide attention on this method of studying the structure of the earth thousands of feet below the surface. It has been applied to many forms of geological research. From the Gulf coast it spread to the midcontinent and California and to other parts of the world, chiefly Argentina, Venezuela, Russia, Romania, Persia, North Germany, and the Dutch East Indies.

The photographer of the striking cover illustration is O.C. Petty of San Antonio, Texas.


Television to be shown on a large screen in the theatre is a step nearer reality following the invention in the laboratories of C. Francis Jenkins in Washington, D.C., of a new type of projector for the receiving set.

In the new apparatus a fixed lantern slide on which the objects move instead of being stationary, as they are on common still slides, takes the place of the flying light-spot system of reproducing the picture. This electrical rather than photographic scanning is accomplished by the substitution of a transparent scanning disc, which contains wires running out radially from its center like the spokes of a wheel, for the common metal disc containing a ring of pinholes near its edge, Mr. Jenkins explained.


The mechanical brains and fingers of the dial telephone system have reduced the number of jobs for telephone operators in the United States by more than 69,000. This is the estimate reported by the U.S. Bureau of Labor Statistics, which has surveyed the progress of the dial telephone and its industrial effects.

Complete conversion to the dial system means an average displacement of about two-thirds of the operators, the report states. And as the telephone-using public grows more fully accustomed to spinning the dial, even fewer operators will be needed to help out in emergencies. In addition, the trend now is toward automatic handling of simpler types of toll calls, a fact that may further reduce the number of operators employed.

In 1921, less than three percent of the telephones in the United States were of the dial type. By the end of 1930, very nearly one-third of the phones were dial-equipped.

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