Can Measure Angles Interpolated To A Single Minute

360 Degree Spinner View

This is a wonderful example of a rare instrument - a Hanks Minute Compass. Minute Compasses were the high precision compasses from 1760 until roughly 1830. Please see my Minute Compass Webpage to fully appreciate how special and rare these instruments are.

Julius Hanks, the inventor of the Bow Compass, made this Minute Compass in 1821. This compass could measure angles to the nearest minute of a degree. The Minute Compass feature is made possible by a shifting south sight vane that has a vernier scale attached to it. See the pics below. The shifting sight vane approach was first articulated by Robert Patterson in an article published in 1785. Julius Hanks is the only maker known to have used the shifting sight vane approach.

In use, looking thru the South sight vane, you line up the N-S sights on the target. You then read the magnetic needle, which likely sets between two degree marks (say 17 and 18 degrees NE. You then rotate the sight vanes so that the needle is exactly lined up with the nearest degree mark (say 17 degrees). Next, using the thumbscrew on the side of the South sight vane, you move the south sight vane until you can look thru the sight vanes and see the target again. The Vernier Scale at the base of the South Sight vane tells you the number of minutes away from the 17 degree mark the target is. And there you have it!

The Hanks Minute Compass is good size - 6 inch needle and about 15.25 inches in length. The compass comes out of Western NY (Eden and North Collins) - the Circa 1900 owner of the Compass surveyed some lots there. I have his name and field book (with only a few pages filled out). I also have his Jacob staff with original adapter and 66ft Gunter Chain. The box is a replacement box that apparently is a near copy of the original box.

The sight arms are slightly bent, as a pic below shows.

As I said above, this is a wonderful example of a very rare instrument. Perfect for display, especially since it comes with its Jacob Staff and a partial known history.