Astronomical Images : Surveying with astronomical instruments: triangulation with Fullon's holometer

Abel Fullon

Astronomical Images

<p style='text-align: justify;'>Abel Fullon (1513-1563/1565) was Director of the Mint for Henry II of France and also succeeded Leonardo da Vinci as the engineer to the king of France. His holometer was an instrument that could be used to make angular measurements in surveying. In 1551, Henry granted Fullon a ten-year patent monopoly on the holometer in exchange for Fullon's publishing a description of the instrument. This written account did not appear until 1561, after the patent had expired, and was translated into both Italian and Latin from the original French. This figure shows the holometer in use. Its construction demanded that observations were made from two stations, with a known distance and orientation between them. This requirement is expressed visually with the scale shown between stations A and B. With measurements from these two stations and knowledge of the distance between the stations, the distance to the object of interest could be determined.</p>