The past couple of years have seen the celebration of a number of key developments in the history of physics. In 1913 Niels Bohr, perhaps the second most famous physicist of the 20th century after Einstein, published his iconic theory of the atom. Its main ingredient, which has propelled it into the scientific hall of fame, was it’s incorporation of the notion of the quantum of energy. The now commonplace view that electrons are in shells around the nucleus is a direct outcome of the quantization of their energy.
Between 1913 and 1914 the little known English physicist, Henry Moseley, discovered that the use of increasing atomic weights was not the best way to order the elements in the chemist’s periodic table. Instead, Moseley proposed using a whole number sequence to denote a property that he called the atomic number of an element. This change had the effect of removing the few remaining anomalies in the way that the elements are arranged in this icon of science that is found on the walls of lecture halls and laboratories all over the world. In recent years the periodic table has even become a cultural icon to be appropriated by artists, designers and advertisers of every persuasion.
But another scientist who was publishing articles at about the same time as Bohr and Moseley has been almost completely forgotten by all but a few historians of physics. He is the English mathematical physicist John Nicholson, who was in fact the first to suggest that the momentum of electrons in an atom is quantized. Bohr openly acknowledges this point in all his early papers.
Nicholson hypothesized the existence of what he called proto-elements that he believed existed in inter-stellar space and which gave rise to our familiar terrestrial chemical elements. He gave them exotic names like nebulium and coronium and using this idea he was able to explain many unassigned lines in the spectra of the solar corona and the major stellar nebulas such as the famous Crab nebula in the constellation of Orion. He also succeeded in predicting some hitherto unknown lines in each of these astronomical bodies.
The really odd thing is that Nicholson was completely wrong, or at least that’s how his ideas are usually regarded. How it is that supposedly ‘wrong’ theories can produce such advances in science, even if only temporarily?
Science progresses as a unified whole, not stopping to care about which scientist is successful or not, while being only concerned with overall progress. The attribution of priority and scientific awards, from a global perspective, is a kind of charade which is intended to reward scientists for competing with each other. On this view no scientific development can be regarded as being right or wrong. I like to draw an analogy with the evolution of species or organisms. Developments that occur in living organisms can never be said to be right or wrong. Those that are advantageous to the species are perpetuated while those that are not simply die away. So it is with scientific developments. Nicholson’s belief in proto-elements may not have been productive but his notion of quantization in atoms was tremendously useful and the baton was passed on to Bohr and all the quantum physicists who came later.
Instead of viewing the development of science through the actions of individuals and scientific heroes, a more holistic view is better to discern the whole process — including the work of lesser-known intermediate figures, such as Nicholson. The Dutch economist Anton den Broek first made the proposal that elements should be characterized by an ordinal number before Moseley had even begun doing physics. This is not a disputed point since Moseley begins one of his key papers by stating that he began his research in order to verify the van den Broek hypothesis on atomic number.
Another intermediate figure in the history of physics was Edmund Stoner who took a decisive step forward in assigning quantum numbers to each of the electrons in an atom while as a graduate student at Cambridge. In all there are four such quantum numbers which are used to specify precisely how the electrons are arranged first in shells, then sub-shells and finally orbitals in any atom. Stoner was responsible for applying the third quantum number. It was after reading Stoner’s article that the much more famous Wolfgang Pauli was able to suggest a fourth quantum number which later acquired the name of electron spin to describe a further degree of freedom for every electron in an atom.