"Those terrible cosmic rays!" Is there nothing they can't do?
In 1925, the confirmation of highly-penetrating radiation from “finite space” announced by Robert A. Millikan, calling them “cosmic rays”, was reported in the newspapers. He spoke to the National Academy of Sciences at Madison, Wisconsin. Earlier tests with high-altitude balloons, or atop mountains, remained inconclusive as to extra-terrestrial origin.
The rays, he thought then, could be of local origin from radioactive materials. However, in 1925, measurements he made up to 27-m below Muir Lake (altitude 3540-m) and Lake Arrowhead (alt. 1530-m) showed rays reached given depths in each by comparable amounts.
Thus the atmosphere difference of 2-km did not originate the rays, they had 18 times the penetrating power of any known gamma rays, and possibly were the “birth cries” of infant atoms from fusion or electron capture. link
