NOVEMBER 1 1937 PHYSICAL REVIEW VOLUME 52 LETTERS TO THE EDITOR addressing the to this department, Closing dates for this department are, for the first issue of the month, the eighteenth of the preceding month, for the second issue, the third of the month. Because of Che late closing dates for the section no proof can be shown to authors. The Board of Editors does not hold itself responsible for the opinions expressed by the correspondents. Communications should not in general exceed 600 words in length. New Evidence for the Existence of a Particle of Mass between those of the proton and electron. If this is true, Intermediate Between the Proton and Electron it should be possible to distinguish clearly such a particle Anderson and Neddermyer' have shown that, for energies from an electron or proton by observing its track density up to 300 and 400 Mev, the cosmic-ray shower particles and magnetic deflection near the end of its range, although losses in lead pl res corre it is to be expected that the fraction of the predicted by theory for electrons. Recent studies of range? which the distinction can be made is very small, To and energy lossa indicate that the singly occurring cosmic- examine this possibility experimentally we have used the apparatus of Fig. 1. The three-counter are more penetrating than showe telescope consisting of tubes 1, 2, and 3 and a lead filter L for removing shower particles, selects penetrating ra ing magnetic deflection, Thus the natural assumptions directed toward the cloud chamber Cwhich is in a magnetic heir energy losses is sa field of 3500 and the singly occurring particles are electrons. The near the end of its range as it enters the chamber that here is no chance of emergence below. In order to reduce of the specific ionization that the penetrating rays are not the number of photographs of high energy particles, the protons. The suggestion has been made that they are tube group 4 was used as a cut-off counter with a circuit particles of electronic charge, and of mass intermediate so arranged that the chamber would be set off only in of the cloud chamber valve was delayed about one sec.to facilitate determination of the drop count along a track. Because of geometrical imperfections of the arrangement 20 ○3 C FIG. 1. Geometrical arrangement of apparatus FIG. 2. Track A