Based on the object history of one of the earliest known metronomes made by Johann Nepomuk Mälzel, which is preserved in the collection of historical scientific instruments of the University of Regensburg, the article deals with the early history of this musical time-keeper and reconstructs its reception in a specific local context. It is argued that Mälzel’s metronome is a boundary object between physics and music and their respective cultures, and can be read as the mechanical realisation of one of the fundamental concepts of Enlightenment philosophy: namely, that the natural is at the same time the rational and that norms and values cannot be justified except by recourse to the authority of nature.