Astronomical Images : Astronomical ring: annulus Boneti

Johann Dryander

Astronomical Images

<p style='text-align: justify;'>Johann Dryander (1500-1560) was an anatomist and physician as well as a mathematician and astronomer. He taught for a time at Paris and performed several dissections there, before being appointed Professor of Medicine and Mathematics at the University of Marburg in 1535. His astronomical publications, which include a work on astrolabes, as well as this treatise on astronomical rings, suggest that he was interested in the practical aspects of astronomy. The astronomical rings consist of three rings fashioned into one instrument. The instrument was invented by Gemma Frisius, who published a work on the rings in 1534, and so is sometimes known as Gemma's rings. The instrument could be used to tell the time and had the advantage that no further instruments were used to orientate it, since the meridian could be identified as the line of orientation at which the shadows of the instrument's rings align. It also had applications in surveying. Around two thirds of Dryander's work was devoted to describing the parts of his new version of the instrument and its markings, and there was a lengthy section on measuring the heights of objects. Following this section came a series of short treatises on different forms of the rings, listed on the <i>verso</i> of the title page, so that the whole work acted as a comprehensive guide to astronomical rings of all sorts. This page opened the second treatise collected by Dryander, which treated an instrument of a rather simple form. The instrument shown is a kind of ring dial, which could be used to measure altitudes and determine time when a beam of light passed through a small hole in the ring, falling on the scale inscribed on the inside of the ring. The author of this treatise, which was divided into chapters according to the function of the instrument under consideration, was Bonet de Lattes, a Jewish physician living in the latter part of the fifteenth and beginning of the sixteenth centuries.</p>