Instrument invented by Marsilio Landriani (1751-1815) c. 1775 to measure the "healthiness" of an air sample: "With such a name," Landriani wrote in his Ricerche Fisiche intorno alla salubrità dell'aria (Milan, 1775), "I call my small machine after Eudios, a Greek word meaning 'goodness of the air'." In 1772, Joseph Priestley (1733-1804) had discovered a "nitrous air" that could be used to measure the "goodness" and "respirability" of a sample of ordinary air. In modern terms, this process is based on the fact that nitrous air (NO, nitrogen oxide), in a hydraulically sealed vessel, removes oxygen from regular air, turning itself into water-soluble higher nitrogen oxides.