NO LONGER DEAD

Evening Star, Issue 21319, 25 January 1933, Page 10

NO LONGER DEAD

THE ELUSIVE ATOM

WIDENING KNOWLEDGE

MODERN CONCEPTIONS

Physical science is moving toward or already has arrived at the position of doubting if it be possible to frame “ material ” images corresponding in any way with tho mathematical interpretations and inferences which have carried observation into theory ._ Kinks in space, “ events ” in which time is a fourth dimension, mass which changes with velocity, particles which jump from one orbit to another instantaneously in the strictest sense of the word “ instantaneous,” things which are simultaneously particles and waves, waves that are waves in nothing and of nothing, can be no more than metaphors, probably dangerous evpn to those who understand bow flimsy they are, and certainly completely misleading to all others. Physical science is full of the ghosts of dead hypotheses, says the scientific correspondent to ‘ The Times.’ Those of us who are of middle age or upwards were taught to believe that atoms were the ultimate constituents of matter, each element consisting of atoms of unique qualities. But the possibility of arranging them in an orderly periodic table, their position, which had a definite relation to their qualities, suggested that they might not ho entirely independent entities. The prophetic speculation of Crookes carried the suggestion further, on the lines that they might be a common primitive substance, a “ proteii,” the different qualities of the elements depending on the quantities and arrangements of the proteii in each. Then came J. J. Thomson’s discovery and naming of the “ electron,” a unit of negative electricity, very much smaller than the atom, and the even more revolutionary discovery of the spontaneous disintegration of "the radio-active elements, and the successes of the Cavendish Laboratory in Cambridge in artificially disintegrating some of the elements, and in the process producing predicted transmutations. The atoms, once thought indivisible and indestructible, became ghosts, honoured only because of tbeir past. SOLAR SYSTEM ATOM.

Next, due mostly to the wonderful experimental and theoretical work of Rutherford and Bohr, the dead atom was replaced by a kind of solar system. Each chemical element had its own system, consisting of a central nucleus, surrounded by revolving satellites. The units were protons, particles charged each with a unit quantity of what by a historical accident was called positive electricity, and electrons, with an equal unit charge of negative electricity. All protons, wherever found, were supposed to be identical, and so also all electrons. A proton and an electron, having equal and opposite charges, formed an electrically neutral system. The nucleus of each atom consisted of protons in close spatial ahd physical linkage with a smaller number of electrons, so that it carried a balance of positive electrical charges depending on the number of protons unsatisfied by electrons. The satellites of each system consisted of negative electrons much more loosely attached spatially and physically, but sufficient in number to neutralise the positive charge of the excess of protons.' THE SIMPLEST SYSTEM. The simplest of these systems was that of the hydrogen “atom,” its nucleus consisting of one proton with a unit-charge of positive electricity, with a single electron as its satellite, so that when the electron was detached the system had the single positive charge of the proton. Practically all the mass was assumed to be in the proton, which was calculated to have about 1,850 times the mass of the electron, but the dimensions of the proton and the electron were assumed to be roughly identical. The proton or hydrogen nucleus was therefore regarded as a particle of unit mass, carrying a unit charge of positive electricity. But with the arrival of the conception of protons and electron as waves, as well as particles, the solar system model is also well on the way to be litte more than an honoured ghost. The next most simple system was the helium atom, consisting of a nucleus of four protons and two electrons very intimately bound together, and two loosely held satellite electrons. The helium nucleus, known also as the “ alpha ” particle, which appears in many forms of radiation, had a positive charge of two units and a mass four times that of the hydrogen nucleus, the mass of the electrons being taken as relatively negligible. The helium nucleus appeared to be a system of extreme stability, and it was a useful supposition that all the elements in the periodic table had nuclei consisting of the greatest possible number _of helium nuclei with hydrogen nuclei to make up the difference. Thus phosphorus, with the atomic weight 31, could be built up of seven helium nuclei giving 28 of its mass, and three hydrogen nuclei to bring up 28 to 31. But this attractive picture may be only another ghost. Already in 1920, in a Bakerian lecture to the Royal Society, Rutherford suggested the possibility of a proton or hydrogen nucleus having intimately associated with it, in the fashion of the electrons of other nuclei, a single electron. Such a combination would form a new kind of body having mass 1 and no charge. For such a body he proposed the name •“ neutron ” and predicted that it would have properties of a novel kind. As its external field would be practically zero, it would be able to move freely through any kind of matter, and it might be impossible to retain it in any sealed vessel. During the last year Dr Chadwick, working in the Cavendish Laboratory, has shown that it is possible to excite from Beryllium a radiation of great penetrating power. The most probable interpretation of this is that it consists of particles of mass 1 and of zero charge, that is to say, of Rutherford’s “ neutrons.” Thus a third arrangement of matter, the neutron, may have to be added to the proton and the electron in future models of atomic systems.