Astronomy and the art of clockmaking in the fourteenth, fifteenth and sixteenth centuries

Abstract

It has been established that the geared clock only became an astronomical measuring instrument after a rather lengthy period of development. Only from the end of the sixteenth century could the determination of the coordinates of the stars with the help of time-measurements compete with direct angular readings. The relation between astronomy and the art of clockmaking covered during the period from the fourteenth to the sixteenth century quite a different field: the clock was then not an instrument for measurement, but one for demonstration. This aim was achieved by large astronomical clocks of artistic design, in which clockmakers and astronomers collaborated, and which were sited in churches and on other public buildings. In the period under investigation, we recognize the existence of three distinct types of such clocks, which are distinguished by the design of their dials: 1. (1)|Clocks, found in Italy and England, having a dial with concentric rings and showing besides the hours also the revolution of the stars, the Sun and the Moon around the immovable Earth. The dial thus represents a kind of small planetarium. The other two types utilize the principles of stereographic projection, namely, 2. (2)|the older type, which uses as the centre of this projection the North Pole, and 3. (3)|the more recent type, which employs as this centre the South Pole of the celestial sphere, so that the projection covers the Northern sky. It has been shown that type 2 was constructed essentially up to the first decade of the fifteenth century, while type 3 came in existence only from the end of the fifteenth century onwards. There are, in addition, some hybrid types—(1 and 2) and (1 and 3)—the analysis of which supports the above chronological pattern. These astronomical clocks have been of importance for the development of astronomy proper in at least two directions: they led to a remarkable spread of fundamental astronomical knowledge, and their theoretical basis contributed to the improvement of the planetary theories current at this period.