Sold !Sold! Sold! – Thos Earnshaw Chronometer – Spring Detent Escapement – “Z Balance” – sn 427/2658 – Silver Pair Cases – 1798c

General Description:

This is a very nice and extremely rare 18th Century Pocket Chronometer by Thos. Earnshaw, which has a Spring Detent Escapement (Under the plate), a “Z” balance with trapezoidal weights and a Helical hairspring, which is Freesprung. It comes in Matching Silver Pair Cases, dated 1798 and bears sn 427/2658.

It has a 46mm Enamel Dial with Roman Numerals and a large flush sub-seconds dial, which is signed as shown in the pics.

The 50mm diameter Inner Case is 75mm incl. the ring and the outer case is 60mm in Diameter. It bears London Hallmark for 1798c and weighs 153 grams

The movement is in very good working condition and was overhauled some years ago in the UK  (The seconds hand moves in 1/2 sec steps).

Our ref is ACC 405 and this watch comes to you directly from a large Irish Watch Collection, which was assembled over the past 40-50 years.

Priced at €6,500 or nearest Offer.

Payment Methods for this item are by :

– Bank Draft / Cashiers Cheque
– Direct Payment of Funds by Electronic Transfer to my Bank Account ( The Payments Page is Preloaded with this information).

Dial:

Type: Enamel
Signed:  Thos. Earnshaw – Inv’t et Fecit : No 427
Width (mm): 46mm (Note:25.4mm=1inch)
Numerals: ROMAN
Hands: Gold Spade Hour and Gold Minute ( Original – see #429 in pics on internet)
Crystal: Glass
Condition: Excellent – a few marks and light chips at the bezel on the 3 & 7 Minute markers

Cases:

Metal Content: SILVER – London 1798c
Serial Number:      –
Maker: T G under a hatchet ( Thomas Gooch ?, Clerkenwell – see Priestley)
Diameter (mm):50 inner and 60
Condition: Very Good – no dings, light wear marks.

Movement:

Calibre: Earnshaw Spring Detent Escapement as described above.
Model:  Fully Jewelled Fusee Chronometer
Serial Number :  427/2658
Condition: Beautiful Cosmetically
Timekeeping: Not fully Tested at time of listing, but running very well and keeping good time.
Overhauled: Yes. Some years ago, by a Watchmaker in the UK.

Notes on Thomas Earnshaw – extracted from Wikipedia for which see addition information):

See also extracts on the web from Jonathan Bett’s “Marine Chronometers at Greenwich” – published in 2017.

Thomas Earnshaw (4 February 1749 in Ashton-under-Lyne – 1 March 1829 in London) was an English watchmaker who, following John Arnold‘s earlier work, further simplified the process of marine chronometer production, making them available to the general public. He is also known for his improvements to the transit clock at the Royal Greenwich Observatory in London and his invention of a chronometer escapement and a form of bimetallic compensation balance.^[1]

In 1780, he devised a modification to the detached chronometer escapement, the detent being mounted on a spring instead of on pivots. This spring detent escapement was patented by Thomas Wright (for whom he worked) in 1783. Whilst initially the design was crude and unsuccessful, with modifications it later became the standard form in marine chronometers,^[2] following the invention of the detent escapement by Pierre Le Roy in 1748.^[3] John Arnold also invented a similar escapement in 1782.

In 1805, Earnshaw and Arnold were granted awards by the Board of Longitude for their improvements to chronometers; Earnshaw received £2500 and John Arnold’s son John Roger Arnold received £1672. The bimetallic compensation balance and the spring detent escapement in the forms designed by Earnshaw have been used essentially universally in marine chronometers since then, and for this reason Earnshaw is generally regarded as one of the pioneers of chronometer development.^[4]

Although he was principally a watchmaker, he did not shy away from building clocks. When asked by Nevil Maskelyne, he produced a clock for the Armagh Observatory. This clock incorporated Earnshaw’s new design of escapement and had a number of novel features, including an airtight case (designed to reduce dust and draughts). It was highly praised by John Thomas Romney Robinson in the 19th century, who at that time believed it to be the most accurate clock in the world. In 1794, its purchase price was £100 and Earnshaw charged £100 to travel with it to Armagh and set it up in the new Observatory.^[5]

The Observatory also purchased Earnshaw’s second clock ^[6] which was operated at sidereal rate with Edward Troughton’s Equatorial Telescope.