The formation of a paper tool: intensity schemes in the old quantum theory

Abstract This paper studies the development of intensity schemes within the framework of the old quantum theory. It investigates how these schemes emerged in a complex process involving empirical observation, data analysis and conceptual reconfiguration and became essential tools for predicting the intensities of multiplets in the absence of a well-formed quantum theory of radiation. By applying the concept of paper tools, the study shows how intensity schemes became theoretical representations allowing both the classification and interpretation of observations and the formulation of theoretical predictions. It thereby highlights the importance of representational tools and empirical regularities within the development of the old quantum theory.