A hedonometer or hedonimeter is a device used to gauge happiness or pleasure. Conceived of at least as early as 1880, the term was used in 1881 by the economist Francis Ysidro Edgeworth to describe "an ideally perfect instrument, a psychophysical machine, continually registering the height of pleasure experienced by an individual."
More recently, it has been used to refer to a tool developed by Peter Dodds and Chris Danforth to gauge the valence of various corpora, including historical State of the Union addresses, song lyrics, and online tweets and blogs. A version of the tool is available at hedonometer.org, which they call a sort of "Dow Jones Index of Happiness", and hope will be used by government officials in conjunction with other metrics as a gauge of the population's well-being.