Accession Number

1986.008.0082a

Alternate object names

Equinoctial Pocket Sundial;Pocket Sundial;Sundial Compass

Creation Date

circa 1620

Description

A sundial and compass device from Santa Margarita is an early version of a pocket watch. The compass was inside the cylindrical body of the piece and was visible through a piece of clear glass situated just under the sundial. The magnetic compass sat on a pin, which allowed it to spin and pivot. The device had to be set on a level surface to allow the sundial card to freely turn and find North. The body of the device was then rotated so the zero mark of the hour scale was in line with the compass and also pointing north. The sundial’s gnomon (the shadow caster) was then flipped up, and the sun's shadow would fall on one of the numeral marks inscribed on the bezel to indicate the local time.

The hinged, triangular gnomon was designed to lay flat for compact storage, and the device was covered by a removable lid when not in use. There is a remnant of a loop fixed to the side of the body, which would have allowed the device to be suspended by a chain or cord. An “Ro” monogram is inscribed below the hour scale, most likely the maker’s mark.

There are several reasons as to why this portable sundial would not have been terribly accurate, especially in the Caribbean. For one, the device was made for a particular latitude – in this case the gnomon is a 45-degree angle, meaning that it was designed to be accurate at the 45^th parallel north (i.e., southern Europe). Also, the dial also does not account for the declination of the sun (the angle of the sun above the horizon) which varied in slow-moving, 23.5-degree swings throughout the year. Tilting the device appropriately, though, could correct for any latitude and declination errors. Despite the limitations, this portable sundial/compass would have allowed the user to generally track the span of the day. See also 1986.008.0082b, c--g.

Exhibition Label

Case Caption (2023): 

The Pilot

Aboard a Spanish ship, the pilot was third in seniority and would have had over sixteen years’ experience. His training included mathematics and celestial navigation. He also had to be familiar with charts of the overall voyage and those of the fleet’s destination in detail. He needed to understand changes in cloud patterns, shifts in ocean currents, and the quality of the ocean floor along different coastlines.

Aboard the Nuestra Señora de Atocha, the pilot, Martin Jiminez, secured his chest carefully. It was still intact when it was discovered by Mel Fisher’s divers almost 400 years later. It held plotting dividers, a small sundial, a cross staff, a jar, gold and silver coins, and gold chains. Most importantly, it held the astrolabe shown here as well as four others. The astrolabe was used to determine latitude. Certainty about the ship’s latitude combined with the pilot’s other knowledge, meant that the ship would reach its destination safely and on time. 
Object Caption (2023):

Sundial Compass
Brass (c.1600)
Gift of Jamestown Inc.
1986.008.0082a-g

This sundial and compass combination, found on the wreck of the Santa Margarita, is an early version of a pocket watch. It would have been similar to the one found in Jiminez’ chest.