Inventory no. 44225 - Epact entry
Epact number: 24439
Equinoctial Dial
Signed by Charles Whitwell
Dated 1606; London
Gilt brass; 62 mm in diameter
Main text
In addition to its universal equinoctial dial, this instrument has calendrical tables and a lunar volvelle with an aspectarium. The compass needed to orient the dial in use has a hand-coloured compass card printed from an engraved plate. The instrument's cover is in the form of a ring to enable the compass to be seen even when the instrument is closed.
This compact design of equinoctial dial was used by a number of English makers of the early 17th century.
Source museum: Museum of the History of Science, Oxford
Museum number: Inventory no. 44,225
Detailed text
The dial consists of a circular compass bowl with a hinged cover. The cover has a circular aperture so that the compass can be seen when the instrument is closed.
The outside of the cover has a catch and a circular calendar scale in which each month is named and is divided and numbered to 10, 20 and the last day of the month, along with subdivisions to every 2 days. The inside of the cover has a circular table of primes and epacts and the date '1606'.
Fixed to the same hinge as the cover is the equinoctial dial, which is held by a decorated support and recesses into the compass housing. The upper face of the hour ring has hours I to XII, I to XII, divided to half hours. The lower face has VI to [XII] to VI for winter hours, again divide to half hours. In the vacant half of this lower face is the signature 'Carolus Whitwell fecit'.
The folding gnomon has an integral quadrant to set the latitude, running from 10 to 90°, divided to 10, 5 and 1 and numbered by 10. There is a hole to attach a (missing) plumb bob.
The compass has a hand-coloured printed card with an outer scale of degrees, 0 to 90 to 0 to 90 to 0, divided to 10 and 2 and numbered by 10. The inner wind rose names 32 directions. The blued needle appears to be a modern replacement.
On the underside of the compass bowl is a lunar volvelle. There are two fixed outer scales, one of hours I to XII, I to XII, divided to half hours, and the other a wind rose with 32 directions marked, of which the 16 most important are identified by letters. There are two rotating discs with pointers: the larger has a scale for the age of the moon 1 to 29|1/2|; the smaller has an aspectarium with symbols for trine, quadrature and sextile, and an aperture to reveal the phases of the moon.
Provenance: Lewis Evans Collection 220.
Stephen Johnston