Thomas Porthouse, London c.1822 No.233

One-day marine chronometer ZAA0057

Box/Mounting Three-tier, brass-bound, mahogany box of concealed dovetail construction, measuring 197mm high, 205mm wide, and 198mm deep. The lid of the box has stop-hinges allowing it to open to 90° only, the hinges on the lid and box marked on their underside with one, two and three or ‘no’ notches, respectively, to identify their places. The straight grained mahogany lid, which is inlaid on top with a brass hollowed-lozenge tablet and a brass “X” emblem, opens to a glazed panel retained with narrow half-round wooden bead. The front of the upper section has a push button brass lid catch with brass, inlaid petal escutcheon, and a circular ivory tablet engraved: ONE DAY. The lock on the lower half is inlaid with a brass, ‘hollowed-corner rectangle escutcheon and a circular ivory tablet engraved: ↑ / T.Porthouse / No.233. Inside the back of the upper section is pasted a label marked: [ FORM No.213] / Issued from / Royal Observatory, Greenwich / 191 , (the 191 crossed out) and stamped in ink: 16 JAN 1917. The underside of the box has a green baize covering.

The box furniture is standard, with brass drop handles on the sides. There are thin rectangular brass plates for the gimbal screws on the sides, with integral threaded brass sockets inside the full width of the box sides. The inside of the box is strengthened at the base with thick mahogany quadrant fillets down both sides, fixed with three brass screws from the outside. The deep and thin, lacquered brass gimbal ring is of a large diameter in relation to the bowl, which has a narrow brass screw-down bezel (2 ¾ turns) with a fine knurled edge at its base, and a thin convex glass over the dial. The later brass strut, limiting opening of the box to 90°, is on the right hand side in the box. The straight-sided bowl has two turned rings on the sides and a small thick brass winding shutter on the flat base. The rising-ratchet winding key, which is probably a later replacement, is mounted on a shelf at the rear left corner.

Dial and Hands The 94.2 mm Ø, engraved, silvered-brass dial is inset into the brass edge, secured with two small screws at 15 and 45 minutes, a notch at 30 in the brass edge allowing for a blade to lift off the dial. The pillar plate of the movement seats in the rebate in the brass edge and is fixed from the dial side with three steel screws. The dial has roman hour numerals and there is a seconds indication below the dial centre, marked within: ↑. The main dial is signed above the centre: Thos Porthouse / London / 233 / ONE DAY. The dial appears to have been scratched: Porthouse on the back, the mark almost completely obliterated. Blued-steel open-spade and poker-hands with a fine, blued-steel pointer seconds hand with a counter-poised tail.

Movement Full-plate fusee movement with four flanged and finned pillars, the potence plate fixed with four dot-marked blued-steel screws, the barrel under a bar. The blued-steel set up click on the bar originally had a return spring which is now missing. The general level of finish of the movement is fine, with a high polish. The potence plate is engraved on its upper surface: Thos Porthouse Poplar ↑ LONDON. The underside of the balance cock foot is stamped: WN.

The later signed blued-steel mainspring has a round hooking with a steel hook in the barrel wall, the original rectangular hooking hole in the barrel being neatly plugged. There are also neat circular brass plugs in the barrel wall, one within that rectangular plug and one for an earlier chain hooking position, and the barrel cap has been turned slightly on its underside to accommodate a slightly higher spring. The fusee has Harrison’s maintaining power and a later bronze fusee pipe screwed to the potence plate.

There is a four-wheel train and a great wheel, the third, fourth and escape wheels run on a bar on the pillar plate and the lower fusee pivot run on a small bridge. All train holes have been plugged and re-pitched from new, as well as the maintaining-power detent, which has also had its position moved from a place very close to a pillar.

Escapement, Balance, Spring and Jewelling Earnshaw-type spring detent escapement with grey-finished, dovetail detent screwed to a gilt brass foot, incorporating the banking piece, and mounted on the potence plate. The well made and finished steel detent has a steel passing spring running alongside the detent blade, and with a light pink jewelled locking stone. The blade is now joined to the dovetail foot with a poor replacement steel spring, lead-soldered to both. The impulse roller has a radially mounted pink stone and the discharge roller also has a pink stone inset.

The Earnshaw-type, two-arm bimetal balance has narrow, straight blued-steel arms. The rim segments, which, unusually, run clockwise (as seen from above) from the arms, are also blued. They extend to within 10° of the opposite arm and have Earnshaw-type segmental weights positioned at about 100° from the arms. There are also supplemental brass compensation screws in the rims at about 85° from the arms. Brass meantime screws are attached in the rims at the end of the arms, and small steel meantime screws are attached on short pieces of rim segment extending on the other side of the arms. The blued-steel helical balance spring has terminals on both ends, the upper terminal with a brass stud fixed to the cock. A plugged hole under this stud suggests it is a later replacement. The upper balance pivot has a rose-cut diamond endstone in a blued-steel setting, and the remainder of the jewelling, which is all in pink stones mounted in brass settings, includes the balance, escape wheel and upper fourth wheel pivots, with endstones, the lower fourth and the escapement parts as mentioned.

History Porthouse No.233 was submitted by the maker for the Greenwich chronometer trials in 1823 and the instrument was to remain on test for two years, from April 1823 to March 1825. Its performance was sufficiently good to merit its immediate purchase by the Royal Navy, where it served for no fewer than 112 years before being sold in 1937. Amongst other issues to Navy ships, the chronometer was employed by Commander E. Belcher in the steam paddle vessel Lightning during his survey of the Irish Channel in 1835, and was sent to HMS Gorgon in August 1839. The Gorgon was a steam paddle frigate which in 1840 took part in the bombardment of the city of Acre in the Mediterranean. In the 1840s it also served on the wooden paddle sloops, Styx & Hydra, and the 5th rate Curacoa. In the early 1860s it served on Tartar and in the 70s Rinaldo, and the gun vessel Seagull. In 1896 it was on board the cruiser Thetis, in 1898 with the torpedo cruiser Porpoise, and in 1899 with the cruiser Minerva. Between 1912 and 1916 the chronometer was in the possession of the Royal Naval College at Dartmouth, used for training, and in 1917 it joined the brand new battle cruiser HMS Glorious on which it would certainly also have been used for training only. Finally, in April 1937, it was sold to the antiquarian dealer Percy Webster along with 26 other chronometers, for a price of £45 for the lot. It was then acquired by the NMM as part of the Doyle bequest in January 1959.