A Geographic Study of Cosmic Rays

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Abstract
Data are given from measurements of the intensity of cosmic rays by 8 different expeditions at 69 stations distributed at representative points over the earth's surface. Each set of apparatus consisted of a 10 cm spherical steel ionization chamber filled with argon at 30 atmospheres, connected to a Lindemann electrometer, and shielded with 2.5 cm of bronze plus 5.0 cm of lead. Measurements were made by comparing the ionization current due to the cosmic rays with that due to a capsule of radium at a measured distance, the radium standards used with the several sets of apparatus having been intercompared. The method of detecting and correcting for the following disturbing effect is discussed: insulation leak and absorption, local gamma-radiation, radioactive contamination of the ionization chamber, and shielding from cosmic rays by roof and horizon. Intensity vs. barometer (altitude) curves are given for various latitudes. These show not only the rapid increase with altitude noted by previous observers, but also the fact that at each altitude the intensity is greater for high latitudes than near the equator. At sea level the intensity at high latitudes is 14±0.6 percent greater than at the equator; at 2000 m elevation, 22 percent greater; and at 4360 m, 33 percent greater. This variation follows the geomagnetic latitude more closely than the geographic or the local magnetic latitude, and is most rapid between geomagnetic latitudes 25 and 40 degrees. Consideration of the conditions necessary for deflection of high-speed electrified particles by the earth's magnetic field indicates that if the cosmic rays are electrons, they must originate not less than several hundred kilometers above the earth. The data can be quantitatively explained on the basis of Lemaitre and Vallarta's theory of electrons approaching the earth from remote space. Acknowledgment is made of the cooperation of more than 60 physicists in this program, 25 of whom are named.