The wavelength of light as Thomas Young invented it

Abstract

This paper documents Thomas Young's invention of a concept which he alternately refers to as the ''magnitude'', ''breadth'', ''interval'' or ''length of an undulation'' of light. First, the paper highlights that Young was first to link some concept of a wavelength to a theory of optics and to assign a precise value to this length for each component of the colour spectrum. Then, it sets out an explanation of how Young made up these values. Finally, it examines the reasons why Young introduced an optical wavelength into his theory of light, insofar as these reasons might in turn shed light on why he was first to do so.