Early Time and Distance Measurement at Sea

Abstract

The discussion following Captain C. V. Sølver's claim to have discovered an early Norse bearing-dial incidentally raised the question of what was the ‘dyoll’ referred to in English ship inventories of the fifteenth century. There are various practical reasons for doubting the theory that it was a compass-dial, that is to say a sun-dial with an inset compass, which for a particular latitude would, when correctly orientated, indicate the time of day. However, the idea that the ‘dyoll’ indicated time rather than direction seems to fit the evidence, and G. P. B. Naish's note on fifteenth- to seventeenth-century ship inventories leaves little doubt that it was an instrument for measuring equal intervals of time, and probably a sand-glass. This conclusion, which to some extent casts the early history of the compass card once more into the melting-pot, prompts a number of questions. Some are stated here and are answered either wholly or in part. Others remain to be answered.