Hedonistic, pleasure-seeking, and hedonic, pleasurable (both from Greek hēdonē, pleasure), suggest that a hedonometer must be a device to measure happiness. It sounds futuristic but the future has now arrived, to judge from recent news stories containing the word. There's a website for that.
Researchers have developed a global happiness sensor and launched a website to display the results so we can all follow our communal progress towards paradise or the slough of despond. The latter is more likely, as the index has been sliding gently downwards since 2009.
The technique is linguistic and statistical. The researchers give numerical weights to significant words, assessing them according to their degree of pleasurableness — disaster has a low score, while Christmas has a much higher one. These weights are then applied to a large body of online texts, principally from Twitter posts, and the index is updated every day.
Hedonometer isn’t new. It’s usually said to have been coined — in a slightly different spelling — by the economist and statistician Francis Edgeworth. It appeared in his book, Mathematical Psychics: An Essay on the Application of Mathematics to the Moral Sciences, published in 1881. He developed the idea of a hedonical calculus:
To precise* the ideas, let there be granted to the science of pleasure what is granted to the science of energy; to imagine an ideally perfect instrument, a psychophysical machine, continually registering the height of pleasure experienced by an individual, exactly according to the verdict of consciousness, or rather diverging therefrom according to a law of errors. From moment to moment the hedonimeter varies; the delicate index now flickering with the flutter of the passions, now steadied by intellectual activity, now sunk whole hours in the neighbourhood of zero, or momentarily springing up towards infinity.
* This is the verb, to make definite, now rather rare.
However, we must grant the honour of invention to Samuel Taylor Coleridge, who wrote to his friend Thomas Allsop sometime in 1821: “A pleasure which, believe me, stands a good many degrees above moderate in the cordi [heart] or hedonometer”.
Hedonometer has several relatives, including hedonology, the study of pleasure and happiness (created in the late 1800s but recently given new life), and hedonomics, the study of the ways that consumers maximise their happiness in making economic choices. It was redefined in Ergonomics in Design in 2005 as the “branch of science and design devoted to the promotion of pleasurable human-technology interaction.” Everybody who has done battle with obstinate computers or obstreperous washing machines will want some of that.