volvelle

As Elizabeth Bruxer correctly identified within a few short hours of its posting, this month’s crocodile mystery showed the inner disc of an unconstructed volvelle from a copy of the 1591 edition of Giambattista della Porta’s De furtivis literarum  notis (STC…

As three of you immediately identified in your comments, last week’s crocodile mystery was the fastening in the center of a volvelle, holding the various layers in place and allowing them to turn: volvelle from Cortes’s Breve compendio, leaf 37r…