Abstract Summary
Planetary automata, also called planetary clocks, were expensive and rare masterpieces of technical ingenuity designed to show the subtle motion of the heavenly bodies according to Ptolemaic theory. These automata may justly be considered mathematical instruments for a two-fold reason: they manifest a mechanical transposition of mathematical astronomy, and their conception and design required the mastery of practical geometry and trigonometry. They were almost exclusively the reserve of princes and emperors, and within the history of astronomy notice of about a dozen of them has reached us, of which four from the Renaissance survive (in Paris, Vienna, Kassel, and Dresden). This paper presents new research on these instruments, focusing on the two created under the explicit direction of Landgrave Wilhelm IV of Hesse-Kassel around 1560. Passing from the abstract geometrical models described by Ptolemy to a brass mechanism led Wilhelm, his chief “artifex” Eberhard Baldewein, and the roughly dozen craftsmen working under them to use eccentric axles, epicyclic gears, and cogwheels with deliberately uneven toothing. The research described, part of the ongoing project “Deus ex machina,” aims at deducing certain astronomical parameters implicit in Wilhelm’s mechanisms. In particular, the possibility of deriving parameters for the solar eccentricity will be explored in connection with Wilhelm’s own renowned program of astronomical observation. Could it be that a careful analysis of these machines (and the written sources once accompanying them) allows us to witness in their gearing the birth of a new astronomical theory?
