In 1775, Felice Fontana, director of the Museo di Fisica e Storia Naturale of Florence, published in Florence a work entitled Descrizione e usi di alcuni stromenti per misurare la salubrità dell'aria. One of the instruments he describes is this eudiometer—which he calls evaerometro—for measuring the purity of air. It was long believed that the instruments invented by Fontana had been lost, or even that they had been only designed and never built. This instrument, found in an incomplete state in the storerooms of the Istituto e Museo di Storia della Scienza of Florence, demonstrates the opposite.