The first study of this type was made in May, 1948, at the Institute for Nuclear Studies of the University of Chicago (now the Enrico Fermi Institute). Scientists made radioactivity tests on samples of the Norton County meteorite donated for this purpose by the Institute of Meteoritics and air-expressed to Chicago because of the intense interest in the radioactivity question. In October, 1949, English investigators ran similar tests at the Londonderry Laboratory for Radiochemistry, Durham, England, on samples of the freshly fallen Beddgelert, North Wales, meteorite discussed on pp. 69-70. The results of these two pioneer studies were negative because the “Model-T” instruments available in 1948 and 1949 were not sensitive enough to detect the relatively low radioactivities present. [Illustration: The 6-blade meteorite gang-saw in the machine shop at the Institute of Meteoritics.] In 1955, however, scientists at Purdue University, using more refined counters, studied small nuggets of nickel-iron, also from the Norton meteorite. This time, the results of the radioactivity tests were positive. The investigators detected tritium (an isotope of hydrogen produced by cosmic-ray bombardment) in the samples. Furthermore, the _amount_ of this rare isotope present indicated that the intensity of cosmic radiation outside the earth’s atmosphere may be very much higher than had previously been thought possible. “Forewarned is forearmed,” and from the standpoint of future astronauts, this is as practical a result as one could wish for! In the relatively near future, men will certainly land on the surface of the moon. We know from radiometric studies that some degree of radioactivity is induced in meteorites by the full-intensity cosmic radiation to which they have been exposed during their motion through space. The nearly airless moon, like the meteorites, has also been exposed to very intense cosmic radiation for a long time. So those who are planning to land on our satellite are concerned about the radioactivities they will encounter when they begin their explorations of the lunar surface. Suppose that extra-sensitive instruments were designed to pick up and measure the radioactivities. Suppose further that these instruments were mounted in a space-probe put in an orbit circling closely about the moon. Plans for such a project are now under way. What types and intensities of lunar radioactivities might such probe-mounted instruments record? Until such a space-probe becomes available, earth-bound space-scientists are seeking at least a preliminary answer to this question. They are doing this by investigating the natural “probes” that have come to us from space—the meteorites.