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Movement for clock

ca. 1730
Origin: England, London
OH: 18 1/8"; OW: 14 7/8"; OD: 6 1/4"
Brass, silvered brass, iron, steel, and oak
Gift of Richard Gump
Acc. No. 1964-56,B
One piece brass arched dial measuring 12 1/8” W x 18” H with seconds dial centered in arch with Arabic numerals (5-60) and a recessed 12-pointed star in center. Below to the right and left are two smaller dials: at right is strike-silent dial with foliate engraving; at left is dial with Arabic numerals (5-60) for pendulum regulation; below, large chapter ring with Roman hour numerals interspersed by half-hour fleur-de-lis marks. Minute divisions in outer circumference of chapter ring with Arabic numerals. All dials silvered, with black numerals and matted brass centers. In center of chapter ring is segmented triangular aperture: upper part with engraving "WM/ Scafe/LONDON"; lower part with annual calendar and equation of time table dial; both engraved on silvered surface. Cast spandrels missing.

Movement Description:
The eight-day brass time, strike, and calendar weight-driven trident shaped movement measures 15 15/16” H x 10” W. Plate thickness is 0.120” and clearance between front and back plates is 2.375”. Clock has an anchor-recoil escapement regulated by a seconds beat pendulum. A rack-and-snail strike sounds the hours on a 3.85” diameter cast bell mounted inside the movement. The trident shaped movement is required to support the upper left pendulum regulation dial, the upper right strike-silent dial, and the seconds dial at the center of the arch. The anchor-recoil escapement is very high in the movement and is driven by a vertical contrate wheel.

Eight brass pillars are riveted into the back plate and pinned at the front plate. The movement is fastened to the seat board by steel seat board screws threaded into the bottom pillars. The brass time and strike barrels are grooved for the weight cords. Both main wheels are .255” thick. All time and strike train wheels have four-arm crossings. The conventional motion work is uncrossed. The round steel crutch-rod has a closed-end fork with a triangular projection.

There are standard cast-brass pulleys with riveted brass stirrups.
Label:Some London clockmakers produced extremely complicated clocks. William Scafe, who was master of the London Clockmaker’s Company in 1749, created this elegant clock, for which
• the large center dial indicates the hours and minutes
• the top center dial indicates seconds
• the left small dial can be manipulated to regulate the speed of the pendulum

Temperature and humidity can affect the metal in the pendulum shaft, causing it to expand or contract. Since the length of the pendulum and the weight of the bob are specifically calibrated for a specific time to the swing (usually one second), changes in temperature and humidity can alter the length of the rod thereby affecting the clock’s accuracy. This dial allows the owner to compensate for those changes. Turning the hand to lower numbers slows the pendulum; higher numbers speed it up. Clocks without this feature on the dial could be regulated by tightening or loosening a nut at the bottom of the pendulum.

• the right small dial indicates whether the clock will strike the hours (chime) or be silent
• the large opening in the center of the large dial indicates (from bottom to top) the days, the months, and the equation of time (a chart indicating whether the solar time for a certain date is faster or slower than the solar mean time kept by the clock). The equation of time was used to help set the clock accurately.

The solar day (based on the earth’s rotation with respect to the sun, as indicated on a sundial) is either slightly more or less than 24 hours depending on the time of year. The equation of time is the difference between the apparent solar time (indicated on a sundial) and the solar mean time (indicated by a clock that runs for exactly 24 hours per day). “Sun Faster” indicates that the solar time is faster than the solar mean time by the number of minutes shown below on the chart for the date. “Sun Slower” indicates that the solar time is slower. This calculation assisted the clock’s owner in setting the clock at noon, using apparent solar time (when the sun was directly overhead). He then could compensate using the equation of time to set the clock for solar mean time.

This clock originally had cast brass spandrels covering all of the shiny brass areas on the dial.
Mark(s):Engraved on dial "WM/ Scafe/ LONDON"