The torquetum or turquet is a complex and sophisticated instrument characteristic of Medieval astronomy and the Ptolemaic tradition. It was a product of Christian Europe in the late 13th century. It could be used to make measurements in the three sets of astronomical coordinates: horizon (alt-azimuthal), equatorial, and ecliptic. It also provided a mechanical means to interconvert between these sets of coordinates without the use of calculations (it served as an analog computer), and to demonstrate the relationships of these coordinate sets. Modern scholars attribute the torquetum's use largely for demonstration purposes and "conspicuous intellectual consumption."Nice phrase! In other words it was more entertainment than science. The torquetum combined the motions of the astrolabe and the qibla-finder, and added even more motions. Note the vertical and horizontal alidades, for sighting sun and stars: Here the torquetum runs through all of its possible motions: It certainly would have been impressive! Maybe not educational. = = = = = A smaller and perhaps more useful tool was the Horary Dial: This was made in Vienna around 1500. I can't find instructions for the usage of the triple-jointed arm or brachiolus, so Polistra will just wiggle it around. = = = = = The Navicula was more elegant and more useful. It was an artistic version of an astrolabe, designed to look like a ship. In other words it was both an analog computer and a literal computer. Naviculas were made in several European countries, from Venice to Colchester. I'm animating the Colchester version. The mast rotated from side to side, and carried a cursor sliding down a scale of latitude. A plumb dropped from the middle of the instrument so you could determine the angle of the entire navicula. Back view: The cursor had its own plumb, with a sliding bead. Here I'm simply rotating the entire instrument, pausing to show the alidade feature. You would sight between the slots in the end castles. Putting it through its paces, from the front: And from the back: Plenty of action, plenty of scales and moving parts. Now Polistra will follow David King's instructions. 1. To use the instrument, we first set the cursor on the mast to the latitude. 2 Then we rotate the mast to the solar declination on the lower scale. 3 Next we set the bead on the thread at the solar declination on the side scale. 4 When the instrument is tilted so that the rays of the sun pass through the hole on the upper sight and fall on the corresponding part of the lower sight, 5 ... the inclination of the horizontal axis of the instrument measures the solar altitude. The bead then falls on the appropriate marking of the hour-scale.
The current icon shows Polistra using a Personal Equation Machine.