1851 Great Exhibition: Official Catalogue: Class X.: Edward John Dent
55. DENT, EDWARD JOHN, 61 Strand, 33 Cockspur Street, and 34 Royal Exchange — Inventor and Manufacturer.
1. Gold "tac" watch. The term "tac" implies that the time is ascertained by turning round the large external gold hand until it is stopped. The time is then known by determining the place of the hand with reference to the twelve projecting nibs on the edge of the case by the touch. The interval of time can be thus determined to about a minute. This description of watch supersedes the usual striking repeater, is less liable to derangement, and is less expensive. It is wound up and the hands set without the usual detached key.
2. Similar watch, with hunting-case, and small opening in the centre to know the time without opening the cover.
3. Hunting cased watch, with case-springs outside, and to wind up and set the hands without a detached key. For use in India, and may be considered air-tight, by which arrangement frequent cleaning is avoided.
4. Gold open-faced watch, with compensation-balance, etc. A specimen of the best description of English watch.
5. Gold watch, with compensation-balance, etc., and two seconds' hands in the centre. The under one (as shown stationary at the 45 seconds or minutes) drops instantly on pressing a nib at the end of the pendant of the watch. This auxiliary hand remains still as long as required. Intended for delicate experiments where small intervals of time are required to be noted.
6. Chased watch, with compensation-balance, etc., having a drop seconds' hand. It is wound up, and the hands are set, without the usual detached key; made for the son of the Viceroy of Egypt.
7. Engraved watch, with compensation-balance, etc.; a specimen of watches intended for the Spanish market.
8, 9. Watches, with compensation-balances, as specimens for the Turkish market.
10. Watch, with compensation-balance, etc., as a specimen for the Persian market.
11. Watch, with compensation-balance, English style.
12, 13. Ladies' watches, with compensation-balances, etc.
14, 15. Ladies' gold watches of the usual construction.
16, 17. Gentlemen's gold watches, with compensation balances, etc.
18, 19, 20. Gentlemen's watches of the usual construction, without compensation-balances.
21. Marine chronometer, with a glass balance-spring, glass balance, and compensated, for temperature, by means of platinum and silver. This glass balance-spring has been tried at the Royal Observatory, and on board
H.M. surveying ship, "Fairy" (for official rates, see "Nautical Magazine," xxix).
22. Patent marine chronometer, having the steel balance - spring, gilded by the electro-metallurgic process.
23. Patent marine chronometer, having a secondary compensation, by which the compensation weights are made to move so as to counteract the effect produced by the changes of temperature.
24. Marine chronometer of the ordinary construction.
25. A compass which can be inverted; the magnetic needles are placed on a vertical axis, and the divisions are engraved on both sides of the silver ring (or compass-card), so that one reading can be made before, and the other after, inversion. The mean between these two readings gives the error of the zero on the card; therefore the true magnetic bearing of any observed object can be determined.
[The ordinary way of fixing the card and needle of a compass is upon an inverted cup resting on a fine point. The application of the chronometer suspension to compasses, as above, is with the view of avoiding the great friction upon the fine point, caused by great vertical oscillations.— J. G.]
26. An azimuth and altitude compass. The principle is the same as in the former, with the addition of a telescope carrying cross wires, and a divided arc for altitudes; the rays from the observed object pass through the telescope, whilst those from the card, reflected by the prism, pass to the eye of the observer.
27. A steering compass, with the needles gimballed on a vertical axis, by means of which, the effect of the violent motions of the ship on the compass-card, and the effect of variation of dip, are neutralized. The superiority of this over the ordinary compass, in which the point of suspension of the card is higher than the centre of gravity, is most evident in steamers where the speed is great, and where the motion occasioned by the sea, as well as that from the vibration of the engine, disturb the usual compass-card, which obeys the laws of a pendulous body; whilst the compass-card placed on a vertical axis is not disturbed from any such causes.
28. An eight-day quarter striking turret clock, with compensated pendulum, 8 feet long, and weighing above 2 cwt.; vibrating half seconds, with pin-wheel, and dead escapement, but with a small recoil. All the wheels in the clock are of cast-iron, except the 'scape-wheel, which is brass, of only 4 inches diameter, containing 40 pins, and turning in 2 minutes.
The 'scape-wheel is driven by a small spiral spring fixed to a pinion, which turns on a stud set in the same line as the 'scape-wheel arbor, and carrying one of the pivot-holes of that arbor. This spring is wound up a quarter of a turn by the clock, at every quarter of a turn of the 'scape-wheel.
The dial-work is all driven by the great wheel, without the intervention of any pinion, and it is consequently very strong, and capable of working four very large dials. The dials in the great avenue of the Exhibition are 7 feet in diameter. The hands are adjustable by means of hand-screws, and a small regulating-dial set on the clock; this dial is reversed, in order to provide for the case of the external dial being on a level with the clock, and the hands driven directly by the prolonged arbor of the regulating-dial. The hands are counterpoised outside the dials; because, when the counterpoises are within, the force of the wind on the hands is not counterpoised at all; and the weight of a large hand, when unbalanced, tends to loosen the hand on its arbor, and so make it point behind the true time from 6 to 12, and before it from 12 to 6.
The maintaining power for keeping the clock going while winding, is of a new construction. Before winding, the maintaining weight must be raised sufficiently high to keep the clock going about seven minutes, and when wound up, it can be thrown out of action immediately.
All the great wheels are set in the great frame, and the small triangular frames can be taken off without moving the great wheels and barrel, or the pendulums, which may also be suspended from the wall. The smaller wheels will also take out separately. The weights are hung by wire' ropes, and they require a fall of about 40 feet, with a single pulley. The pulleys are 1 foot in diameter.
The hammers are raised by cams cast on the great wheels, of such a shape as to raise them with the least friction. They are strong enough for an hour-bell of several tons weight, and quarters to correspond, though the great wheels are only 18 inches in diameter. The hammers all stand ready to fall as soon as they are discharged by the going part. The 1st, 2nd, and 3rd quarters begin exactly at those quarters; the 9-th begins half a minute before the hour, and the hour-hammer falls exactly at the hour.
The object aimed at in this clock, is to combine the greatest accuracy of time-keeping with great strength, and the cheapest mode of construction which is consistent with good work.
29. A patent dipleidoscope, to be used as a fixed meridian instrument. The optical arrangement consists in two silvered parallel reflecting glasses placed at an angle of about 60° behind the front glass. The image of the sun is reflected from the front glass, and the sun's rays which pass through, impinge first on one plane, and are reflected to the other, they then pass out through the front glass. By this optical arrangement, two suns are visible to the eye of the observer moving in opposite directions, and when they coincide, it is the instant of apparent noon. The time can be ascertained by this instrument with considerable precision. The dipleidoscope allows of three observations of the sun: 1st, when the limbs touch; 2nd, when the images coincide; and 3rd, when the limbs separate.
[The dipleidoscope was invented, a few years since, by G. M. Bloxem, Esq., and, when accurately fixed, the time of apparent noon can be determined by it within one or two seconds. Two bright and sharp images of the sun are seen, which approach each other, and exactly coincide at apparent noon.— J. G.]
30. A dipleidoscope fitted up equatorially, which admits of observations being taken from 9 A.M. to 3 p.m., and is rendered portable by having a magnetic needle. When the instrument is set by the needle, the magnetic declina,• tion of the place requires to be allowed for.
31. A superior astronomical clock, with a remontoire dead-beat escapement, invented by G. B. Airy, Esq., Astronomer Royal (see paper in "Royal Astronomical Society's Monthly Notices," Nov. 11, 1842, by Mr. Airy.)
A large church clock. (Main Avenue.)