Astronomical Images : 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 overall composition of the holometer. It consisted of a square board, graduated at one edge, with a central compass and graduated circle. The arms, also marked with degrees, are hinged at the ends of the graduated side of the base and fold in on themselves. The hinges for this can be seen about halfway along the length of the arms. Each arm also bore a device called a rector, which stood out of the arm and carried sights for viewing distant points and measuring heights. However, owing to the difficulties of capturing perspective accurately, it is not immediately clear from this figure that the rectors were mounted on the vertical arms.</p>