Wednesday, November 23, 2011

The Sundial Compass

The sundial compass was a unique and clever instrument conceived in the early 17th century. It simply consisted of a mechanical compass with a sundial affixed to it, but being "pocket" sized it was used in the same convienent way as having a pocket watch and GPS navigational device today. Something your every-explorer of the 1600s probably didn't have with them.

John Smith demonstating his compass

Edward Wright - a mathematician - had developed the "sea ring" in 1610, a magnetic compass with a universal dial attached on top, which gave mariners an opprotunity of determining TIME and PLACE at the same time. By the mid-1600s these "sundial compasses" were gaining popularity throughout Europe and many variations were invented by French, German, Dutch, and later English designers.

The most popular known sundial compass today is called the "equinoctial" compass, and was first brought to use around 1630. It looks like a pocket watch with a compass at its base while a folding lid containing the Gnomon ( the blade ) and the clock dial lays atop. This is a standard compass that can be used anywhere within the latitude range of Canada to Mexico. Although, if an explorer was to travel more southernly or northernly they would need to make some adjustment to the angle of the blade before they'd get an accurate time reading. Even in the standard range, adjustment has to be figured depending on the time zone you are in. Otherwise your "clock" can be off by a few minutes to more than an half hour.

On second thought, maybe just carrying a pocket watch and a compass would be a smarter choice for the modern mariner.


  1. Wow. What a fascinating tribute to the sundial compass! lol. I miss talking to you absent-minded buccaneer. :)

  2. Oh, how wonderful to have you visit again Beatle! I missed you too matey.