There are a few things at sea that one can usually rely on as constant: the sun rises in the east and sets in the west; valves and screws obey the lefty-loosy, righty-tighty rule; and a compass is divided into 360 degrees. Imagine the surprise, then, when sailor Dennis Ross discovered that a compass from the estate of his departed sea-going grandfather was divided into 400 increments. “The 400° compass is marked 1922, Lemaire, Paris, and No. 15741 is engraved above the hinge and M.G. on the top,” Ross said.
A crafty French ploy? Perhaps. “The 400 division replacing the 360° scale was introduced at the time of the French Revolution as part of the decimalization process,” said Willem Mörzer Bruyns, senior curator at the Sheepsvaartmuseum, a maritime museum in Amsterdam. “However, it did not catch on, nor did the attempted decimalization of time. Nevertheless, the 400 (‘parts’ or ‘grades’) division was in use during the 19th century, especially by the French military engineering service. Decimalization was the subject of an international conference in 1900, and a number of decimally divided instruments were produced at that time.”
In Europe, compasses incremented in 400 divisions are still available, mostly for surveying purposes, according to an engineer at the Finnish compass manufacturer Suunto.
Bruyns doubted whether Ross’s compass was intended for nautical use. He also thought the compass might predate 1922, since compasses are rarely dated; rather, the “1922” is possibly the manufacturer’s mark. Perhaps 360° on a ship’s compass can be considered constant after all.