Notation on back, "Unshielded Ionization Chamber, containing Argon Gas under high pressure and sensitive photographic film which automatically records ionization produced by cosmic rays, is here shown beneath 45 feet of limestone about a quarter of a mile within the Endless Caverns of New Market, Virginia. This chamber was subsequently shielded with 625 pounds of lead 11om (about 4 inches) thick, which then recorded frequent bursts of cosmic rays energetic enough to penetrate the overlying limestone and also the thick covering of lead. Left to right: Professor L.B. Snoddy, Professor E.P. Ney, Mrs. L.B. Snoddy, and James L. Young, III, all of the University of Virginia."