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Low‐energy nucleonic cosmic‐ray data from stations at Lincoln, Mt. Washington, Sulfur Mountain, and Deep River were studied with regard to onset times, time and magnitude of maximum increase, and decay characteristics. The decay behavior underwent a definite transition that is clearly related to the termination of the optical flare. The first part of the decay is clearly exponential, with a time constant in the neighborhood of 17 minutes, whereas the latter part is not distinctly established either as exponential (with a possible time constant of 78 minutes) or as following a t−1.5 law. Ordinary impact zones do not seem to fit the pattern of increases observed at various stations in the northern hemisphere.

This communication presents some experimental results that seem to indicate that the barometric pressure coefficient customarily employed to correct terrestrial neutron monitor intensities is subject to variations in magnitude that are apparently related to changes of atmospheric water vapor content above the site of measurement. An aluminum container was placed above one section of the IGY standard neutron monitor at the University of Denver, Denver, Colorado (1600‐meter altitude, 2.93 Gv/c Quenby‐Wenk threshold). The container was filled to different depths of water for various intervals of time, and the corresponding attenuation of the nucleonic intensity was determined. Preliminary results of a statistically reliable nature have been obtained for four different water levels. The results are indicated m the table below.

To investigate the relationship between solar activity and cosmic ray modulation, time series of the nucleonic flux and of solar plages, sunspots, centimeter radio noise, and the brightness of the white light corona at 1.1 and 1.5 solar radii from the center of Sun are cross-correlated. Data pertain to the years 1964-1967 during the ascending phase of the current solar cycle. The amplitudes and phases of correlation functions for filtered and unfiltered indices are discussed. The existence of a superior solar index for relating solar activity to long-term modulation is not yet demonstrated conclusively, and the time lag of modulation is too poorly determined to permit its use in estimating the radius of the modulation region.

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