- Museum number
- 1894,0623.4
- Description
-
Mechanical universal equinoctial dial; silver and gilt brass; vertical brass ring frame; scrolled feet with levelling screw; engraved compass well inset in base with windrose and two spirit levels; compass needle missing; who;e instrument rotates within rim of base; fixed vertical ring with silvered ring within; pivoted sighted system; signature; time-indicating system in form of watch dial.
- Production date
- 1718-1748 (Dates of maker being active, dial not dated)
- Dimensions
-
Length: 200 millimetres
-
Width: 153 millimetres
- $Inscriptions
-
- Curator's comments
-
A very similar instrument is in the Greenwich Maritime Museum, reg. no. AST0391, although that dial is engraved in French. A third instrument by Deane in the Oxford MHS, inv. no. 71015, is very similar to these except for the type of bubble levels used. A sundial by Deane’s master John Rowley in the Cambridge Whipple Museum, acc. no. Wh: 676, is also similar. See H. Higton, Sundials at Greenwich, Oxford 2002, no. 167, pp. 183-4.
-
Ward 1981
An exceptionally fine instrument. The frame of the instrument consists of a vertical brass ring, diameter 160 mm, supported by two flanking engraved leafy scrolls, each developing from a mask; base; diameter 130 mm with three ornate, scrolled feet, each provided with a levelling screw. Screwed to the top of the fixed ring is an engraved piece surmounted by a folding shaped handle.
Inset in the base is a finely engraved compass well, diameter 73 mm, with a silvered scale 0°•-360°• clockwise from north on a raised shelf, the degrees numbered every ten; a silvered scale 0-90-0-90-0, marked and numbered in tens of degrees, in the well; within this, a windrose with eight points marked with initials, and some decorative engraving. Inset in the well are two spirit levels at right-angles, one with the glass and contents missing. The compass needle is also missing. Surrounding the well is a silvered scale of the equation of time, with zero at 23½ December, 16 April, 15½ June and 31 August, agreeing with the Gregorian calendar.
The whole instrument can be rotated within the rim of the base with the aid of a geared knurled knob. Sliding within the fixed vertical ring is a silvered ring graduated 0- 90-0-90-0 for latitude setting: this is divided to half-degrees and numbered every ten degrees. Pivoted within this ring, in polar bearings, is a sighting system, the main part of which is a thick brass ring, diameter 121 mm surrounding a central portion, pierced and engraved with leafy scrolls, which carries on one face a centrally pivoted index arm moving over a scale of dates near the rim which extends from 20 December through January to 24 June and, in the reverse direction, back through July to 20 December; the equinoxes are at 20½ March and 22½ September. This arm is geared to a sector on the opposite face to which is attached a shaped alidade arm pivoted near the edge of the ring and with an index traversing a silvered scale - 23½-0- + 23½ degrees for the sun's declination; this scale is divided to quarter-degrees and numbered every ten degrees. The neighbouring part of the ring is signed: Wm. DEANE FECIT. The alidade carries a convex lens mounted near its outer end, but the corresponding screen is missing.
Also mounted within the pivoted ring but at right-angles to it and attached to the fixed ring is the time indicating system. This is in the form of a watch dial, diameter 55 mm, with glazed bezel and silvered ring of Roman hours I- XII, I-XII surrounded by a minute-ring divided to one-minute intervals and numbered every five minutes. The steel hour-hand rotates with the pivoted ring, and the minute-hand is geared up from this, as with other mechanical equinoctial dials.
The sequence of operations in obtaining a time reading from this instrument is :
1. Orient it by means of the compass, using the knurled knob for final adjustment.
2. Level it, using the three screws and the two spirit levels.
3. Adjust for latitude of use, by moving the sliding ring within the fixed vertical ring.
4. Adjust for the date of use by turning the index on the pivoted system. .
5. Rotate the pivoted system until the lens throws the sun's image on to the centre of the screen.
6. Read off the true solar time in hours and minutes.
7. Add or subtract the equation of time for the date of use, if mean solar time is required
- Location
- Not on display
- Condition
-
Latest: 2 (Jul 2015)
-
3 (Mar 1996) Compass-needle missing. This object is on display in HSR.
- Acquisition date
- 1894
- Department
- Britain, Europe and Prehistory
- Registration number
- 1894,0623.4
