Cylindrus.

The astrolabe encoded the sky in geometry. The music box encodes a song in geometry. Both are mechanisms that take a continuous thing — celestial motion, melody — and freeze it into a hand-held object that plays it back on rotation. The pin is the note; the cylinder is the score; the comb is the instrument. Music without a performer.

Antoine Favre-Salomon was a watchmaker in Geneva. He filed the patent in February 1796 for a carillon sans timbre ni marteau — a chime without bell or hammer. The genius was the substitution: instead of bells struck by hammers, a steel comb whose tines vibrate when plucked by pins on a brass cylinder. Smaller, quieter, fits in a pocket watch. The mechanism that produced bell tones without bells.

The watchmaking valley of Sainte-Croix, in the Swiss Jura, picked up Favre's invention and industrialised it. By the 1820s the village ran a cottage trade pinning cylinders for export; by the 1860s, the big houses — Reuge, Bremond, Nicole Frères — were producing music boxes at scale. The math is the same as Favre's. The labour is the pinning: every melody is a pattern of brass-on-brass strikes that has to be hand-laid into a specific geometry.

Reuge has been making cylinder music boxes in Sainte-Croix since 1865. The mechanism hasn't changed: a brass cylinder with hand-pinned melodies, a tempered steel comb tuned by filing each tine, a clockwork spring barrel that turns the cylinder at a constant rate until the spring runs out. The newest pieces use the same techniques as the oldest. The substrate changed exactly once — in 1796 — and not since.

The astrolabe holds the celestial sphere in brass via projection geometry. The music box holds a melody in brass via pin geometry. Both replace a continuous calculation with a rotation. Both are the kind of object that doesn't argue with its constraints — they're built into the geometry. The instrument that came after — the player piano, the music ROM, the MP3 player — kept the idea and changed the substrate.