Sundial making tool

Horizontal instrument or sundial making tool, unknown maker, London, 1620-1635.

On the reverse is a stereographic projection for c. 52°, folded into a semicircle with arcs for sun’s declination and hour angle (to quarter hours) These arcs continue above the Cancer circle through the zenith (unusual). Path of ecliptic marked with months/days. Scale on edge gives declination and signs of zodiac. Rule delineated to give the sun’s altitude.

On the obverse is a protractor scale around circumference in the standard Elias Allen style. Inside, a number of arcs giving the angles of the hour lines on a horizontal sundial (to quarter hours) for a range of English latitudes with 1° steps. These are probably in a second, contemporary, hand.

While the maker is unknown, this instrument is likely to have been made in the workshop of Elias Allen.

This instrument is used for time telling and all the associated features (sunrise, sunset, day length, declination, sun’s altitude and azimuth as described in William Oughtred’s ‘The Horizontal Dial’.

It is also a very rare design template for the production of standard horizontal sundials for latitudes across England.