Master lecturing while men observe a rainbow (Book 19: On colours, smells, tastes)
Seated at a lectern with an open book, the master instructs three men. While one faces forward, concentrating on the lesson, two turn away to observe a rainbow, a phenomenon discussed in the text. Apart from a slim band of red and a larger band of yellow, the individual colours of the rainbow are not distinguished. Figures in the border include hybrid creatures and a dragon.