The story
Widely attributed to British philosopher Jeremy Bentham (1748-1832), but apparently used only by his successors.
Etymology from Wiktionary, CC BY-SA 4.0.
felicific calculus
Today it means: A quasi-mathematical technique proposed by 19th-century utilitarian ethical theorists for determining the net amount of happiness, pleasure, or utility resulting from an action, sometimes regarded as a precursor of cost-benefit analysis. Full definition →