FORCE OF NATURE--"What holds the nucleus of the atom together? In the past quarter century physicists have devoted a huge amount of experimentation and mental labor to this problem--probably more man-hours than have been given to any other scientific question in the history of mankind. By all the laws of known forces, the particles in an atom's nucleus should flee from one another, instead of clinging together so strongly that we must build enormously energetic machines to pry them apart. The glue that holds the nucleus together must be a kind of force utterly different from any we yet know. Japanese physicist Hideki Yukawa, as early as 1935, suggested a new particle for the nucleus, whose emission and absorption is supposed to transmit the nuclear forces. This particle, when Yukawa invented it, was of course purely hypothetical. Today it is known as the meson. --Hans A. Bethe"