EDITOR 771 riched (3 times normal) and the other impoverished (0.5 times normal) in the isotope O 17 . The pulses produced in the chamber were amplified and counted by a kicksorter or pulse amplitude analyzer. Differences between runs with the two samples showed a significant increase in the number of pulses between 1 and 2 Mev in the case of the enriched sample, with a peak at about 1.4 Mev. The effect proved to be caused by thermal neutrons, and has been attributed to the above reaction.With air in the ionization chamber, the pulses due to the reaction N u (n, p)C u were counted, thus permitting the cross section for the oxygen effect to be determined in terms of the nitrogen cross section. We found a value

No abstract

Annual means from continuous registration of cosmic‐ray ionization at four stations from 1937 to 1952 show a variation of nearly four per cent, which is similar at all stations and which is negatively correlated with sunspot numbers. This variation in cosmic‐ray intensity is quite similar for the annual means of all days, international magnetic quiet days, and international magnetic disturbed days, which indicates that it is not due to transient decreases accompanying some magnetic storms. Although the cosmic‐ray intensity at some stations is affected by meteorological conditions, it is shown that on the average the cosmic‐ray changes observed at Huancayo agree well with those at other stations. From an analysis of the variability of daily means at Huancayo and a sample comparison with Simpson's neutron data, it is concluded that the cosmic‐ray ionization at Huancayo is very little affected by meteorological effects. Through a comparison with Neher's balloon observations, evidence is provided to indicate the reliability of cosmic‐ray results at Huancayo over long periods of time. The relation between cosmic‐ray decreases and some measures of geomagnetic activity is indicated, and it is shown that the major transient decreases in cosmic‐ray intensity occur during magnetic disturbance. Graphs are included which depict the daily means of cosmic‐ray intensity at Huancayo for all available data, 1937–1953.

To facilitate the use of cosmic‐ray intensity data from ionization chambers which are being sent to International Geophysical Year World Data Centers, and of those which have appeared in two publications of the Carnegie Institution of Washington, an improved correction for instrumental drift at Huancayo is derived and the reliability of the corrections for seasonal variations is discussed. From ionization chambers, the decrease of intensity from its maxima (near sunspot minima) is shown to lag a year or more behind the increase of solar activity following sunspot minima. This lag does not appear in the results obtained by Neher at high altitude and high latitude, nor in those obtained by Rose from a neutron monitor at Ottawa. The variability of daily means of cosmic‐ray intensity (from monthly means) is in 1957 the largest observed during two complete solar cycles. Tables of monthly means corrected for seasonal wave are included, together with graphs of daily means at Huancayo for the period 1954–1957.