Magic Transistor

The 1 megawatt Poulsen arc transmitter, one of the largest arc transmitters ever built, allowed shore radio stations to communicate with the United States Naval fleet worldwide, c. 1918.

This brass astrolabic quadrant, a Quadrans Novus or astrolabe/almucantar quadrant, was made for latitude 33 degrees 30 minutes (i.e. Damascus) from 1333-1334 by Muhammad Bin Ahmad al-Mizzi. An inscription on the front says that the quadrant was made for the 'muwaqqit' (literally: the timekeeper) of the Great Umayyad Mosque of Damascus. The earliest known description of an astrolabe reduced to a quadrant with no moving parts was in 1288 by the Jewish man Jacob ben Mahir ibn Tibbon (1236-1304), more widely known by his Latin name of Prophatius Judaeus or Profeit Tibbon from Montpellier. Tibbon's treatise was quickly improved by Peter Nightingale whose account received wide distribution. The instrument was quickly named the quadrans novus (new quadrant) to differentiate it from the traditional quadrant or quadrans vetus (old quadrant). The basic idea behind the idea of the quadrans novus is that the stereographic projection that defines the components of a planispheric astrolabe is just as valid if the astrolabe parts are folded into a single quadrant. The result is an instrument that can perform many of the functions of a standard astrolabe at much lower cost, but without the intuitive representation of the sky provided by the rotating rete. It is not clear how popular the astrolabe quadrant became as few examples survive. The arcs reproduce the ecliptic and horizons of a circular astrolabe folded over the East-West line and then folded again about the meridian. Additional arcs are provided to determine the unequal hours and to find the sines and cosines of angles. The astrolabe quadrant is equipped with with a thread (usually of silk) with one end attached at the north pole and a weight on the other end. A bead or pearl can be slid up and down the thread to mark positions on the face of the instrument. The thread can be moved to any position on the face of the quadrant to simulate the rotation of the astrolabe rete. [Brass Astrolabic Quadrant, Muhammad Bin Ahmad al-Mizzi, British Museum, London]