This 17th-century treatise on music shows a mechanical, water-driven organ. Water enters on the right side of the diagram, turning a gear mechanism that animates a cylinder roll and keyboard. Musical notation cut into the cylinder roll determines the keys depressed for any given time. This is similar to the many organ rolls still preserved at the American Organ Institute at OU. On the far left, blacksmiths strike hammers upon an anvil, recalling the story of Pythagoras discovering the mathematical ratios of the musical scale from the chance hearing of blacksmiths at work.