On the theory of the Matthews and the Russell-Léonard photometers for the measurement of mean spherical and mean hemisperhical intensities
A 1905 technical paper from the National Bureau of Standards on the theory of the Matthews and Russell-Léonard photometers, written for physicists and lighting engineers measuring lamp intensity. The figures are spare line diagrams: circles and ellipses crossed by axes, with radial vectors labelled I and angles marked θ and ω, usable as geometric marks, angle notation, or diagram scaffolding.
