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Description: | Thomas Porthouse, London c.1820 No.233
1 day marine chronometer in mahogany box
Thomas Porthouse (c.1794-1860) gained a considerable reputation as a watch and chronometer maker in London. His origins are unknown, but it is possible he was related to the 18th century family of clockmakers by that name from Penrith in Cumberland (now Cumbria) in the North of England. The known facts about Thomas Porthouse suggest that sometime around the year 1815 he started his own business on High Street, Poplar, in London?s East End, near the city?s main docklands.The first city directory to include information about Porthouse as a tradesman, published in 1822 by the Manchester firm Pigot and Co, lists his premises at 210 High Street.
One year after the Royal Observatory announced its Premium Trials, Porthouse entered this chronometer, No.233 (see later for the details of the trial). No doubt recognizing the prestige to be gained by selling chronometers to the Royal Navy, Porthouse submitted a number of further chronometers for the Greenwich trials in the following years. Pocket chronometer No.6279 was entered in 1824 and purchased for the Admiralty in June 1825, and No.6281, also a pocket chronometer, was entered in 1825 and, after remaining on trial for three years, was finally purchased in October 1829. This chronometer, typical of these fine instruments, was still in use in 1916 when the ship it was on board was sunk by enemy action. No.6282 was tried at Greenwich in 1826, 1828 & 1829 but was withdrawn in 1830. Porthouse also submitted a number of eight-day chronometers for trial at this time. Nos 6291 and 6292, both eight-day instruments, were submitted in 1832 and Porthouse signed the declaration required that year (see page xxx). Porthouse was evidently considered a full ?maker? of chronometers, as he signed the Observatory?s somewhat tougher oath in 1835 declaring he made the instruments himself.
Porthouse also manufactured watches for sale to the public, and a fine gold, pump-winding pocket watch by him, hallmarked for 1829/30, is in the British Museum?s collection. It is also recorded (Ref: G. H. Baillie ) that Porthouse made turret clocks for the Admiralty, though it is much more likely he was a supplier who wholly sub-contracted such work, which is so very specialized and different from that of a watch & chronometer maker.
Under the address given for the years 1832 to 1835 in the Astronomer Royal?s records (Ref:1143/10) Porthouse is shown as at High Street Poplar, but this is then crossed through on all the entries and written next to it is: ?10 Northampton ? Goswell Street?. This was probably done retrospectively and it is likely he moved to Northampton Square about 1835; he certainly appears in Northampton Square in Robson?s London Directory for 1838.
Box/Mounting
Three-tier, brass-bound, mahogany box measuring 197mm high, 205mm wide, and 198mm deep. The lid of the box has butt hinges allowing it to open to 90� only, the hinges on lid and box marked on their underside with none, one, two and three notches, respectively, to identify their places. The straight grained mahogany lid, which is inlaid on top with a brass ?scalloped lozenge? tablet and a brass ?X? emblem, opens to a glazed panel retained with narrow half-round wooden beading. The front of the upper half has a push button brass lid catch with brass, ?flower petal? inlaid escutcheon, and a circular ivory tablet engraved: ?ONE DAY?. The lock on the lower half is inlaid with a brass, ?lozenge? escutcheon and a circular ivory tab let engraved: ?? / T.Porthouse / No.233?. Inside the back of the upper half 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 box fittings are 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 � turns) with a fine knurled edge at its base, and a thin convex glass over the dial. The interior fittings are otherwise of standard layout except that the rising ratchet winding key, which is probably a later replacement, is mounted on a shelf at the rear left corner, and the brass strut, limiting opening of the box to 90� (also probably a later addition) 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 underside of the box has a green baize covering.
Dial and hands
The 94.2 mm �, engraved and wax-filled, silvered-brass dial is inset into the brass edge, secured with two small screws at III and IX, a notch at VI in the brass edge allowing for a blade to lift off the dial. The pillar plate of the movement seats in the recess in the brass edge and is fixed from the front with three steel screws. The dial has roman hour numerals and there is a large seconds dial at IV o?clock having Arabic ten-second figures with straight batons at alternate five-second intervals and is marked: ??? below 60. The dial is signed below XII: ?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 pillars with flanges and fins at either end and one fin in the lower middle, the potence plate fixed with four blued steel screws, the barrel under a bridge on the potence plate. The blued steel set up click on this bridge originally had a 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. There is a four-wheel train and a great wheel, the fusee with Harrison?s maintaining power and a later bronze fusee pipe screwed to the potence plate. The train wheels are brass with 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, 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. Unfortunately, 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 from the arms (from above), are also blued. They extend to within 10� of the opposite arm and have Earnshaw-type wedge weights positioned (as found) at about 100� from the arms, and supplemental brass compensation screws in the rims at about 85� from the arms. Brass meantime screws are attached 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 indicates it being a later replacement. The jewelling, which is all pink stones mounted in brass settings (upper balance diamond endstone is in a blued steel setting), extends to the balance, escape wheel and upper fourth with endstones, the lower fourth and the escapement parts as mentioned.
Alterations/condition
The box probably originally had its upper half opening right over, and was converted to having the 90� strut in the mid 19th century. The wooden box is in sound and clean condition with a few small knocks and dents. The woodwork around the hinges on both box and lid show evidence of strain, and filling and gluing to strengthen in the past. There is a fracture at the front of the lid, repaired with six brass screws. The ivory tablet on the front of the upper half has a crack across the lower screwhole. There are areas of old (patinated) scratching on the lid and on the front of the box. The drop handles and outer brasswork are reasonably clean and sound and the inner brasswork is well preserved though the lacquer overall is slightly patchy with tarnish coming through in places.
The dial silvering is very clean, with one dark spot at V o?clock. The dial has probably been re-silvered several times in the past, as the engraving is now getting rather thin.
The movement is in generally sound clean condition, though it was found to be thick with old, solidified oil.. Light (old) rusting to some steel parts, and rust on the repaired detent spring (mechanically cleaned as best as possible). There are burrs raised under the cock foot suggesting the balance has had a new staff or has had it repivoted. The movement has only been very lightly cleaned, and has been re-oiled, during inspection.
Commentary, Provenance, etc
X emblem refers to Navigation training function
Bronze fusee pipe probably fitted with mainspring in 1867, possibly also when the box was strengthened inside.
and the instrument was to continue on test for two years, from April 1823 to March 1825. Its performance was sufficiently good to merit its immediate purchase, No.233 the beginning a period of Royal Navy service lasting a remarkable 112 years. It was finally sold off in 1937.(Alternately, ?. . .purchase by the Royal Navy, where it served for no fewer than 112 years before being sold in 1937.?)
Potence Plate �: 81.1
Pillar Plate �: 81.3
Plate distance: 18.8
Inside barrel �: 33.2
Arbor �: 11.8 steel, unsnailed.
Thickness: 0.38 ? 0.35
Height: 15.3
(5 full turns output from barrel)
Set up: (13 as found) 15 teeth, to line up click with spot on wheel
Signature: ?306 / 59210? & ?Meredith Son London July 869? (scratched on inside of spring, 26cms from end)
TRAIN COUNT
Wheel / Pinion (+ext dia) Comment: Crossings? Marks?Jewelled?
Fusee/Great: 75 / 37.5 No.of Turns:6 (Chain 54cms, 101 links)
Ratchet: 50 / 17.0 Brass, 2 steel clicks
Maintaining Power: 140 / 35.5 Brass
Centre/2nd: 96 / 30.3 + 14 / 7.4 Solid wheel. V.finely finished pinion
Third: 75 / 25.2 + 12 / 3.9 6 tapered crossings ?
Fourth: 80 / 21.0 + 10 / 3.6 ?
Escape: 12 / 13.8 + 8 / 2.4 3 curved crossings
Balance Frequency: 14,400 vbs/ hr (half seconds)
Hour: 60 / 16.2 Brass
Minute Wheel: 64 / 17.2 ?
Minute Pinion: 20 / 5.6 Highly polished steel
Cannon: 16 / 4.6 Grey-finished teel
Set up ratchet: 18 / 12.1 Blued steel
Impulse pallet tip �: 8.3
Discharge pallet tip radius: 1.4
Detent length: 30.0
Balance �: 31.8 Balance Mass (incl. b/spring & stud): 11.8g
Balance spring �: 13.0 Material: Blued steel
Turns incl. terminals: 9 � (c/w down)
AQN: Doyle (owner).
caption: Marine Chronometer - overall
caption: Marine Chronometer - movement | Publisher: | "http://collections.rmg.co.uk/" | Rights holder: | "Royal Museums Greenwich" | Subjects: | Marine chronometer chronometers | Source: | Royal Museums Greenwich | Identifier: | http://collections.rmg.co.uk/collections... | Go to resource |
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