Mean cosmic-ray intensities have been measured with much precision both at Pasadena, California (latitude 34) and at Churchill, Manitoba (latitude 59), the latter a distance of 730 miles from the North magnetic pole.

(1) The observed equality in these intensities indicates that these rays enter the earth's atmosphere as photons rather than as streams of electrons.

(2) Evidence is presented that the incoming rays are of a uniform intensity in all directions and in all latitudes, the small and apparently erratic fluctuations found by many observers at different stations arising simply from eruptions, waves, or ripples which change the thickness of the atmospheric blanket interposed between the source and the observer.

(3) The cosmic-ray electroscope thus acquires significance as a meteorological instrument.

(4) The influence of these rays in the maintenance of the earth's charge is considered.

• Received 23 October 1930

DOI:https://doi.org/10.1103/PhysRev.36.1595