Once Upon a Time in Physics When Both Mathematics and Experiment Were Helpless: A Strange Life of Voltaic Contact Potential

Abstract.

This paper aims to answer the question of why the debate over the voltaic contact effect was so prolonged without a consensus during the nineteenth century. I propose that both experiment and mathematics were helpless to decide who was right. To demonstrate this, I will focus on the voltaic debates between James Clerk Maxwell and the Maxwellians, on the one hand, and William Thomson and the Thomsonians, on the other, and examine ten points: (1) the fundamental assumption, (2) the seat of the voltaic potential difference, (3) the role of the contact, (4) the magnitude of the potentials of two contacted metals, (5) the definition of potential, (6) the electrostatic measurement, (7) the thermoelectric measurement, (8) the physical interpretation of the same mathematical formula, (9) experiments in different media, and (10) experiments in the vacuum – all of which were in dispute between the Thomsonian and Maxwellian parties. I show that the two parties differed in theory, in the interpretation of measured data, in the physical interpretation of mathematical relationship, and in what they believed would constitute a crucial experiment. I assert that the Maxwellian and Thomsonian voltaic theories were incommensurable, but that this incommensurability was not exactly symmetrical because it mainly resided on the side of William Thomson.