L'étude du spectre énergétique des particules α sortant d'une couche plane et d'épaisseur faible devant le parcours a montré que l'introduction brutale de la valeur de la masse superficielle du dépôt dans la correction de l'autoabsorption conduit à des résultats incorrects. On décrit une méthode permettant de déterminer avec précision cette correction. L'incertitude sur la valeur du terme de correction dû à la rétrodiffusion des particules α par le support de la couche ne permet pas de déterminer les activités absolues α avec une erreur inférieure à 0,5 ou I pour I00 suivant les cas
M EASUREMENTS made on the penetrating component of cosmic radiation near sea level for a period of 45 days have been utilized for statistical correlation with data from the daily ascents of two nearby radiosonde stations. The measuring equipment consisted of three trays of G-M tubes mounted as a vertical telescope. The telescope was operated under 12 inches of concrete in floors and roof, and a 10-cm Pb absorber was placed between trays 2 and 3. The pulses from the trays were fed into pulse amplifiers and into a coincidence circuit employing pulse shaping prior to the coincidence measurement. Threefold coincidence pulses were applied to a sealer-pen recorder arrangement which recorded the coincidence through a scale of eight. This allowed continuous monitoring of equipment performance.To account for the fluctuations of the penetrating intensity at the ground, Duperier 1 introduced the temperature of the /x-meson production layer to be used in addition to the atmospheric pressure and the height of the production layer, the effects of which were already known. 2 According to Duperier's model, the probability that a 7r-meson will decay into a /u-meson is dependent on the density of the region in which the ir-meson finds itself. Therefore, the ju-meson intensity at the ground depends on the temperature of the production region.The telescope was arranged to have approximately spherical symmetry over the solid angle subtended, so no zenith angle correction was applied. The maximum angular aperture of the arrangement was 17°7' from the vertical. Hourly counting rates were obtained from the observed data, and the mean rate for each day was computed for the 45 days extending from October 9 to November 22, 1950, which were free from electronic failures.The mean hourly counting rate, the daily average of the tempertture and height of the 100-millibar level, and the daily mean barometric pressure obtained from the filed radiosonde observations of the Portland, Maine, and Nantucket, Massachusetts, Weather Bureau Stations were analyzed for statistical correlation. A linear regression equation aJ c =aSr-r-j35B-h
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