Object Name: bowl of Ahaz refracting, scaphe sundial
Dimensions: 8.2 x 15.2 x 15.2 cm (3 1/4 x 6 x 6 in.)
Description: This bowl of Ahaz refracting, scaphe sundial is made of gilt brass and shaped as a footed bowl. The foot is damaged, having a chunk missing. The sundial is projected on the interior of the bowl and designed for latitude 43° 10'.
A small magnetic compass is set into the base of the bowl and is marked with an arrow for magnetic declination and 4 points of the compass labeled in Latin abbreviations. It has the original needle and glass. There are two drainage holes in the base.
The gnomon projects at a fixed angle from the meridian line inscribed on the inner surface. It is screwed to the bowl and marked, "POLVS GRA • 43 MI • 10." The meridian is divided 10°-90° every 5° with dots every 1°. It is labeled, "GRADVS ALTITVDINIS SOLIS: 1548."
Equal hours 5-12-7 are inscribed in the bowl at every hour, with lines of solar declination (or sun's zodiacal position) marked in symbols at each edge. The summer half of the year is on the left; the winter half is on the right. The hour scale is labeled, "HORE A MERIDIE ET SIGNA ZODIACI COGNOSCVNTVR EX REFRA[zodiacal symbols]CTIONE RADIORV~ SOLIS IN AQVA." The maker's signature is also here.
There is an inscription around the inner rim, with the first "D" engraved backwards. It reads, "[star] HYDRAVLICVM QVOD MIRABILI ARTIFICIO IMITATVR • HOROLOGIVM ACHAS IN QVO ESAIAS VMBRAM SOLIS RETRORSVM DVXIT DECEM GRADIBUS * QVARTO REGVM • 20 • CA: ESAIE 38 • CA:"
The underside of the base has two red, wax tags ("04" and "200") and "397" painted in red on the brass.
Signed: GE: HARTMAN NORNBERGE
Inscribed: along meridian line: GRADVS ALTITVDINIS SOLIS: 1548
by gnomon: POLVS GRA • 43 MI • 10
on hour scale: HORE A MERIDIE ET SIGNA ZODIACI COGNOSCVNTVR EX REFRACTIONE RADIORV~ SOLIS IN AQVA
around the inner rim: [star] HYDRAVLICVM QVOD MIRABILI ARTIFICIO IMITATVR • HOROLOGIVM ACHAS IN QVO ESAIAS VMBRAM SOLIS RETRORSVM DVXIT DECEM GRADIBUS * QVARTO REGVM • 20 • CA: ESAIE 38 • CA:
Function: This is a refracting sundial. When the bowl is filled with water, the refraction of light in the water moves the shadow of the gnomon back, so that it indicates the correct time on the hour scale.
Sundials inscribed inside bowls are known as scaphes. This type being refractive is often referred to as a "dial of Ahaz" or "bowl of Ahaz," because when the shadow moves backwards, it simulates the time-reversing miracle that the prophet Isaiah had shown to King Hezekiah on the sundial of Ahaz ((Isaiah 38: 7-8 and 2 Kings 20).
There are only several known examples of this instrument.
Curatorial Remarks: XRF analysis of the metals was done by Katherine Eremin and Sara Schechner in August 2007.
Provenance: Purchased from Mercator, Paris, in 1929 by Harold E. Gillingham, Philadelphia; purchased in 1949 by David P. Wheatland.