Highlights of the Past and a Challenge for the Future

Abstract

I am of course deeply gratified to have my name assigned to this laboratory, which is to be devoted to a field in which I have worked for so large a part of my life. Laboratory work has always fascinated me because of the unexpectedness of what may be found and of the application which may be made of the discoveries. No more important example of the unexpected can be found than Roentgen's discovery of the x-rays. This was nearly fifty-three years ago and was one of the great steps leading up to the present atomic age. This discovery enlarged tremendously the known spectrum of radiant energy, which had previously been carried only from what we now call radio waves to heat and light, including the ultraviolet. The nature of the new radiations, at first unknown, was found also to be electromagnetic, thus joining them to the short-wavelength end of the previously known spectrum, that is, to the ultraviolet. Prior to Roentgen's discovery we had talked of a hypothetical indivisible and indestructible atom, and had recognized in the various chemical elements 88 different kinds of atoms. We had long been aware of a certain periodicity in the properties of these atoms but could only wonder why this was so. X-ray research showed the reason—that the atoms of the various elements all consist of the same building blocks and differ only in the number and arrangement of these particles, which we now recognize as electrons, protons, and neutrons. Our hypothetical atom, that indivisible particle of matter, was found to consist of a whole swarm of smaller particles, more than 300 in the case of the heaviest elements. We have thought that there were only as many kinds of atoms as there are chemical elements, but we know today that each chemical element may occur in several different atom forms (isotopes) and we now list some seven hundred different kinds of atoms. In the year following Roentgen's discovery, radioactivity was first observed. It was in the case of uranium, whose atoms proved to be unstable and spontaneously to undergo a series of internal changes until they finally become lead, thus exploding the idea of inherent permanence of the atom. We had felt very sure of the conservation of mass. If you burned a weighed piece of wood, weighed the remaining ash, and took account of the gases which came off, you found no diminution in total weight. We know now that mass may disappear as such, reappearing as energy, and that the two are mutually interchangeable. Were our measurements sufficiently precise, we would find, when we burn a piece of wood, that there is a loss in weight and that it corresponds exactly to the heat energy liberated. The weight loss would, however, in this case be relatively too small to show on even our most delicate balances, as it would amount to only about a ten thousandth of a millionth of the weight of the wood. We are here dealing with a chemical reaction in which nuclear changes are not involved.