Prout's hypothesis was influential in - if not necessary for - the establishment of the atomic weight of oxygen, a figure conclusively demonstrated in 1895. Ironically, the successful determination of oxygen's weight also led to a final refutation of the hypothesis ( at least the hypothesis in the classical sense). But more than this, the end of Prout's hypothesis via the determination of oxygen's atomic weight was due to three fundamental changes that characterized the way chemistry was practised and communicated in the late nineteenth century. First, encyclopaedia-like presentations of past atomic-weight investigations became the focus in numerous and influential studies. Second, there was a dramatic change in the way professional publications presented investigations and experiments, characterized by experimental detail and apparatus design at the expense of theoretical discussion. Finally, the production of hydrogen became the focus of research, as it was one of the principal components of any investigation into atomic weights. Here I present Prout's hypothesis in its historical context by focusing on these three developments and their influence on the research of Edward Williams Morley. While doing so I also illustrate the way marginalized scientists were able to take advantage of their otherwise dubious position and participate in an active and important role in atomic-weight investigations.
