The Grimthorpe Brock No 1209, c. 1852 A mahogany wall regulator with four legged gravity escapement

The Grimthorpe Brock
No.1209, Circa 1852
An important mahogany wall regulator with a very early example of Denison’s four-legged gravity Escapement by James Brock, London
Height
6 feet 2 inches (1880 mm)
Case
The arched top mahogany glazed case with substantial concave base and finial below. The base and backboard combined and wall fixed, with a massive cast iron movement bracket and integral pendulum suspension block, the long glazed removable hood locking to the backboard on both sides. The glazed front door, running the full height of the hood, with carved mahogany Gothic tracery decoration, shaped and mounted below the dial.
Dial
11½ inch circular silvered brass dial, incorporating an angled silvered bezel, engraved with ‘reversed’ seconds and hour rings, the standard layout for a gravity escapement due to its positioning at the bottom of the plates. Counter-balanced second and hour hands with protective brass dust shutter, through the front door glass, to the winding square.
Duration
7½ days
Movement
The single train rectangular plated movement with semi-circular cut to the base for the four-legged locking ‘wheel’, with four cylindrical pinned pillars and signed to the backplate Brock, 21 George St., Portman Square, London. No.1209. The train with large anti-friction rollers supporting the great wheel arbor, the two steel gravity arms with ivory impulse rollers at the ends, acting on the substantial steel pendulum rod. This mounted lower centre with a ‘tray’ for fine regulation weights above the mercury filled, ceramic lined, adjustable iron pendulum jar. The triple line with a solid top pulley mounted on the cast iron bracket and a 6-spoked pulley holding the 28lb weight.
Escapement
Very early version of Denison’s four-legged gravity with mercury compensated pendulum
Provenance
Said to have been made in 1852 for E B Denison, later becoming Sir Edmond Beckett and finally Lord Grimthorpe, designer of the great clock (Big Ben) at the palace of Westminster;
Private collection UK, sold by Derek Roberts in 2000, for £53,500;
The John C Taylor Collection, inventory no.53
Exhibited
1986, Tonbridge, Precision Pendulum Clocks Exhibition, exhibit no.17
Literature
Derek Roberts, English Precision Pendulum clocks, 2003, (illus.) p.192-193;
Erbrich, Präzisionspendeluhren, 1978, (illus.) p.220-221;
Antiquarian Horology, June 1983, Martin & Roberts, ‘Lord Grimthorpe and his Experimental Regulator’, (illus.) p.157-168
Comments
The anti-friction rollers supporting the great wheel arbor are needed for the heavy driving weight required to power the gravity escapement, particularly on ‘unlocking’, while the triple line for the double-pulley is to compensate for lack of drop and increase duration to over 7 days.
James Brock (1826-1893) was Edward Dent’s foreman and oversaw the construction of the ‘Big Ben’ clock for the Houses of Parliament, Westminster. He probably left Dent’s in 1855 to take over the business of his father, who died in that year. He was held in great esteem by Dent, and therefore allowed to produce clocks under his own name while employed by Dent’s, for whom he seems to have made the majority of their regulators, including for E J Dent’s successors after he had left their direct employ. As their outworker, his serial numbers therefore fell within Dent’s own series, and can be dated by reference to the records of Dent’s production. Brock was also held in high esteem by Lord Grimthorpe, the designer of the Westminster clock and its escapement, and for whom Brock made the present clock.
To obtain the required accuracy for such a large-scaled clock, Grimthorpe designed his four-legged gravity escapement, which he subsequently modified to a three-legged escapement as installed in the Westminster clock. For the first working model of his gravity escapement, Grimthorpe employed the skills of James Brock, the workshop foreman in the business of Victoria London’s leading precision clockmaker, Dent’s. It is clear that Grimthorpe had great respect for Brock as a clockmaker, seconding Dent’s own opinion, who as his employer appears to have allowed the two to work directly together, rather than through Dent’s business. Brock then went on via Dent’s own shop to supervise the construction of the parliamentary clock and its eventual installation in the clock tower at the Palace of Westminster. Dent clearly allowed Brock to sign his work for Grimthorpe in his own name, while the serial numbers of such clocks remained within the general sequence of Dent’s workshop numbering.
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