Article of the month August

Altitude dial 3

The ring dial

This is a replica of a 1721 Farmers’ Ring. It is just 35 mm (1.375 in) across and is sold in many bric-a-brac shops.

A small hole is set to the actual date using a scale on the circumference of the ring.
With the sundial hanging on a string, its hole is aimed at the sun. A light spot in the ring reads the time.

Do not expect great precision. Not only does the small size preclude it – this dial is not principally correct to begin with. It will tell time to the nearest half-hour, though, which used to be quite accurate enough in many case.

However, better ring dials were in fact made. These had a date scale on the inside of the ring, allowing for a correct hour line pattern.
The larger size also helped to improve accuracy.

This is a modern implementation of such a large sundial ring.
No longer a portable instrument, it is a fixed, pivoting sundial.
It has no movable hole. Instead, there is a (divided) slot.
The date scale is visible inside the ring.

The figure shows a plan for a farmers’ ring with movable hole and date scale, for 52 degrees latitude. This dial is principally correct.