MOST ILLUSTRIOUS

MATHEMATICIAN, IOANNIS

DE MONTE REGIO original: "DE MONTE REGIO" (Regiomontanus) ON THE TORQUETUM

An Astronomical Instrument, addressed to the Reverend Lord Ioannes, Archbishop of Esztergom, 21 Problems.

A woodcut depicts a decorative initial letter V containing a profile portrait of a man.Those who study astronomical exercises are accustomed to using a twofold genus of instruments. They have a certain portable genus, which is to say, it can be handled wherever one pleases, now under the open sky, now in any enclosed place to which the rays of the stars cannot penetrate. Such is the work of the Albion an astronomical instrument invented by Richard of Wallingford, the solid sphere, the equatorium, the saphea, the common astrolabe, the horary quadrant, the cylinder, and others of this kind, and finally the rulers of Hipparchus, by which he measured the diameters of the luminaries, just as his follower Ptolemy commemorates and Proclus relates in his astronomical suppositions. To these may be added the instrument of Archimedes, which he briefly explains in his little book on the sand-reckoner. The other genus shall be rightly called "stationary," which, unless it has a firm seat, is of no or very little use, such as the annular astrolabe of Ptolemy, to which the name has commonly been given from the rings armillae. Likewise, his great rulers and the other two instruments, the fabrication and use of which he handed down at the beginning of the Great Construction the Almagest. Such also is the collective machine of Geber of Seville, constructed with great industry, for it wonderfully embraces all the instruments of Ptolemy in a pleasing compendium. Finally, the sundials which are presented for the use of the common people do not escape the limits of this genus. To these and others of this kind we add the instrument which will be handled by us, the composition of which I intended to commit to letters elsewhere,