Book review: H. Kranz, W. Oberschelp, Mechanisches Memorieren und Chiffrieren um 1430 : Johannes Fontanas Tractatus de instrumentis artis memorie, Stuttgart, 2009.

Note: This book contains a critical edition, with German translation, of a short Latin treatise which the authors call Tractatus de instrumentis artis memorie. It is the third part of the Secretum de thesauro experimentorum ymaginationis hominum by Johannes (or Giovanni) Fontana (ca. 1390--ca. 1455), who was born in Venice and studied in Padua. The text exists in a unique manuscript in Paris, where it is written in a simple code in which each Latin letter is represented by its own symbol. In the Tractatus de instrumentis artis memorie, Fontana describes twelve simple instruments which can be used as memory aids. For each instrument, the manuscript provides a figure which is photographically reproduced in the book under review. For example, Fontana's first instrument is called the speculum (mirror); it consists of five concentric rings which can be rotated around a central axis. On each of the rings, the letters of the alphabet are inscribed in order. Fontana suggests that an arbitrary combination of five letters (such as XROTA) can be remembered by turning the rings such that the letters X, R, O, T, A are on the radius of the instrument from the central axis to the left side.