Planck’s estimate of the elementary charge: a bibliometric study on its limited reception (1901-1921)

Max Planck is widely recognised for founding quantum theory. In his 1900 seminal work on black-body radiation, he also provided a numerical estimation of the elementary charge. This result, however, was embedded within his broader theoretical development and was not presented as a primary result, so that his contemporaries likely approached it with caution. Planck himself acknowledged that the theoretical basis that led to this estimate was fragile and explicitly noted that further experimental work was needed to confirm it. Remarkably, despite these limitations, his estimate closely matched values later confirmed by precise experiments. In this study, we examine how Planck’s contemporaries received and cited this estimate. We first situate his work within the scientific context of black-body radiation, then we analyse primary literature from 1901 to 1921, covering journals from Europe and the USA, to trace patterns of citation and engagement with Planck’s elementary charge estimate. Finally, a statistical bibliometric analysis quantifies these trends, revealing the visibility and impact of Planck’s work across different journals, national contexts, and scientific communities.