Clément Juglar (1819-1905) was credited by Joseph Schumpeter as the founder of modern business-cycle theory. Schumpeter praised Juglar for identifying the cyclical character of economic fluctuations and for having been seminal in the combination of theoretical, statistical and historical analysis, and also named the classical business cycle after the French economist. Strikingly, the latter's pioneering work is hardly known today. The paper reexamines Juglar's explanation of cyclical fluctuations and compares it with Schumpeter's one. One important difference is that for Schumpeter the classical business cycle is driven by technological innovations of medium size, whereas for Juglar the cause for an overheated boom is speculation fuelled by easy credit.