ON NOVEMBER 20, 1931, in a lecture before a large audience gathered at the Institut Poincaré in Paris, there were presented the first direct measurements taken by Carl D. Anderson of the energies of cosmic-ray tracks made with an apparatus capable of measuring, by the method of magnetic deflectibility in air, energies of the order of magnitude to be expected in cosmic-ray photon-encounters with electrons and nuclei, namely, from 27×${10}^6$ volts up to at least 500×${10}^6$ volts. These same photographs were also shown on November 23rd at a physical seminar at the Cavendish Laboratories. Cambridge, England. The eleven cosmic-ray-track photographs shown and discussed on these ${\mathrm{occasions}}^1$ brought to light a certain number of new and important facts presented essentially as listed below in both of these lectures, and these facts have now been checked by three times as many successful exposures.

• Received 12 April 1932

DOI:https://doi.org/10.1103/PhysRev.40.325