Unlike “summing to zero” in simple arithmetic, however, the disappearance of mass, technically called its annihilation, results in a release of energy, as was long ago observed in the case of electron-positron annihilation. Where considerable masses are annihilated, as in an A-bomb explosion, the amount of energy released is tremendous, as is now well known to everyone. [Illustration: A. Representation of the structure of an atom of ordinary terrestrial matter. The nucleus is positively charged and around it circle negatively charged electrons. B. Representation of the structure of an atom of contraterrene matter. This is the reverse of the situation in (A). The nucleus here is negatively charged, and around it revolve positively charged electrons, also called positrons.] The effect of such an energy release as would accompany the infall of a contraterrene meteorite would be a _natural_ nuclear explosion of vast power. Such an explosion would account for all the sensational phenomena observed at the time of the Podkamennaya Tunguska incident; and, furthermore, would explain why the Russian investigators have never succeeded in recovering meteorites from this fall. (Further details, p. 102.) If the Podkamennaya Tunguska meteorite was contraterrene, then the soil in the impact area must have been made radioactive in the same way that the earth around the “ground zero” of a nuclear explosion is contaminated by radioactivity. After the senior author had repeatedly urged Russian scientists (who are the only ones that have been permitted to visit the site of the Podkamennaya Tunguska fall) to try to detect any long-lasting radioactivities that might still be present in the ground at Podkamennaya Tunguska, such a radioactivity survey was finally carried out in the summer of 1960. According to an official report of the Soviet news agency TASS, the investigators obtained “abnormally high radioactivity readings” which the Russians tentatively considered to be the result of “a natural nuclear explosion” occurring in the Podkamennaya Tunguska area on June 30, 1908. Science-fiction fans in the U.S.S.R. would like to believe that this “nuclear explosion” resulted from the impact of a Martian spaceship rather than a contraterrene meteorite. Reputable Russian scientists, however, have shown how completely absurd this “fable” of a Martian landing really is.