Contemporary Advances in Physics, XXIII - Data and Nature of Cosmic Rays

HE subject of this article is unique in modern physics for the minuteness of the phenomena, the delicacy of the observations, the adventurous excursions of the observers, the subtlety of the analysis, and the grandeur of the inferences. The effect which is studied, which may be described as the liberation of electrons from the molecules of the air by agents otherwise unknown, amounts at sea-level to the liberation of only about 1500 of these per cubic decimetre of air per second. It is not the whole of the observed effect; these 1500 electrons are those which are left over out of a quantity often much greater, after allowance is made for the actions of all known ionizing agents. The methods employed are ranked among the most ingenious and sensitive of science; yet the apparatus is not invariably set up in the calm seclusion of the laboratory. Physicists with their frail machines have gone to high mountain ponds in the Sierras and the Andes, to the distant wildernesses about the earth's magnetic poles; they have scooped out cavities in Alpine glaciers, they have lifted hundredweights of lead to the tops of peaks above the snow-line, they have cruised the arctic and the tropical oceans, they have descended into tunnels and deep mines, they have ascended into the sky in aeroplanes and balloons. As for the analysis of the precious data 148 CONTEMPORARY ADVANCES IN PHYSICS 149- obtained with so much labor, it will be evident from this article how intricate a process it now proves to be.