## Tito Gonnella’s coplanar adding machine with tooth lock washers from the year 1859

In 1859, Florentine professor of mathematics Tito Filippo I. B. Gonnella (1794-1867) published the “Descrizione di due Macchine Arithmetiche per l’addizione”. In this work, he describes a coplanar adding machine with tooth lock washers and a second adding machine with key input. The latter is in Florence in the Museo di Storia della Scienza. Gonnella’s original book is part of the ArithmeumLibrary. We happened to discover the corresponding coplanar adding machine with tooth lock washers in a private collection. It is now also a part of the Arithmeum collection.

Gonnella, a natural scientist who obtained his doctorate in Pisa, belonged to a Florentine committee in 1818 that - at the request of Leopold II, Grand Duke of Tuscany - was to write the new land register of Tuscany. Between 1829 and 1850, Gonnella taught Pure Mathematics and Mechanics at the “Accademia di Belle Arti” in Florence, afterwards until 1854 he taught Pure Mathematics. In 1851, he presented his planimeter at the World Fair in London and received a medal, first class for it. Gonnella’s name cannot be found anywhere on the machine, there is only the engraving “I.P.C. Firenze” which probably indicates the workshop that realized Gonnella’s design by his order. Since the machine is so unique, its number 59 might be a hint towards the year it was built, as the paper about the machine was published this same year.

The extraordinary mechanics of Gonnella’s adding machine are clearly shown in the 3D animated video that Nils Dohmen, student of Computer Science, made as a part of his bachelor’s thesis for Professor Dr. Ina Prinz’ series of lectures about the history of mechanical calculation. The tens carry is solved in a very original way, but unfortunately does not work flawlessly over all positions in succession. Gonnella found a pragmatic solution for this problem – you will see it in detail in the video. Enjoy!