An important enlargement of the field of nuclear research has been effected by the experiments of Lawrence. Lewis, and Livingstone,* who first used the ions of the heavy isotope of hydrogen to produce nuclear disintegrations. Their pioneer experiments showed that these ions, which will in future be termed “diplons,” produced disintegrations of considerably greater complexity than those produced by protons of the same energies. Thus, Lawrence, Lewis, and Livingstone reported that from most of the substances bombarded, one or more groups of protons were emitted, whilst a group having a range of about 18 cm. appeared to be emitted from every element investigated. This surprising result led these workers to the hypothesis that the “diplon” is unstable in a strong nuclear field and that it breaks up into a proton and a neutron with a liberation of energy of the order of 5 million volts, the neutron mass being taken to be 1·0006 to explain the observed proton energies. In addition to the emission of long-range protons, Lawrence, Lewis, and Livingstone ( loc. cit. ) reported the emission of α-particles from lithium, beryllium, boron, nitrogen, magnesium, and aluminium. The experiments of Rutherford, Oliphant, and Kinsey§ and the Wilson chamber photographs of Dee and Walton║ showed that tho 13·2 cm. α-particlcs from lithium originated from the dis-integration of Li 6 into two α-particles, and suggested that Li 7 disintegrated into two α-particles and a neutron. No detailed studies have been made of the disintegration of the other elements.