1851 Great Exhibition: Official Catalogue: Class X.: Charles Frodsham
57. FRODSHAM, CHARLES, 84 Strand — Chronometer Maker.
1. Astronomical clock, with mercurial pendulum, and Graham's dead-beat escapement.
[Mercurial pendulums, and Graham's dead-beat escapement, are now used in nearly all astronomical clocks. The number of such clocks now in London exceeds 200; about 60 of these, chiefly the property of eminent chronometer makers, are rated on Greenwich mean time, and it is found that their performance is such as to adapt them for astronomical uses. They certainly reflect great credit on the various artists engaged in the science of horology.
The mercurial pendulum is so called from the circumstance of the bob being of mercury enclosed in a cylinder, screwed to the bottom of a steel rod. Gridiron pendulums were in use before mercurial pendulums were adopted: they consisted of an assemblage of brass and steel rods so arranged, that, owing to the difference in the expansion of brass and steel, the brass rods carried the bob up, while the steel ones let it down. The shape of pendulum bobs is important. Until lately they were of the form of a double convex lens, this form offering but little resistance on passing through the air, when its edge was always in the plane of motion; but, as it was liable to be a little twisted, a varying resistance was offered; and which is not the case in the adoption of the form of the cylinder, which probably is the best shape for the bob.
It is usual to call those clocks astronomical which are used in observatories for determining the right ascension of the heavenly bodies, and they are such, including every appendage which contributes to accuracy in the measurement of time under all the changes of atmospheric temperature.—J. G.]
2. Marine chronometers, on a new calibre, with Arnold and Earnshaw's detached escapement; the compensation balance is of the ordinary kind, with Arnold's bar as auxiliary compensation. This new calibre is based upon the plan of the diameter of barrel, fuzee-wheel, and extreme diameter of the balance being the same, namely, one inch and five-tenths. The total weight of the compensation balance is 5 dwts., being as the contents of the barrel. Thus if a barrel, one inch in diameter, by three-tenths of an inch in depth, will carry a balance weighing 20 grains, a barrel of the same diameter, and of double the depth, will carry a balance weighing 40 grains. The balance-spring is 15 inches long; the diameter 45/100, the thickness of wire 10/1000 by 18/1000 broad, and the number of turns 10 to 12. The wheels (escape-wheel included) are each five times the diameter of their respective pinions—that is, the pinion upon which the wheel revolves. The fuzee-wheel has 90 teeth, centre wheel 90, centre pinion 14, third wheel 80, third pinion 12, fourth wheel 80, fourth pinion 10, and scape pinion 10, scapewheel 15.
3. Specimens of gold pocket chronometers and lever watches, reduced from the calibre of the chronometer; with improvements in the form of the teeth of wheels and pinions, in the balance-springs, and in the mode of attaching the spring.
4. The double rotatory escapement. This is a specimen of a new calibre movement, by which a powerful watch may be made in a flat case; a method which might have been adopted at the period when flat watches were first introduced, as it has all the advantages of a thick watch, by taking the contents of the barrel in diameter and depth as the basis of power.
5. Day of the month watch, with lever escapement and double rollers. The calibre of this watch may be called more simple than the preceding one, only because it more closely resembles that which is daily made. The number of the teeth of the wheels is peculiar. The centre-wheel is much enlarged, with 100 teeth working in a pinion of 10, whilst the third wheel is diminished, which has 60 teeth working in a pinion of 10; the fourth wheel 63 teeth in a pinion of 7. Although this is a good working calibre for a superior watch, yet if power is admitted to be a principle in watch-making, it is impossible to get the same depth of barrel in this watch, unless the calibre of No. 1 is used.
In producing the foregoing calibres all technical sizes have been rejected, and the common measurement of inches, tenths, hundredths, and thousandths adopted; so that from one calibre, a watch of any size may be made by proportion.
6. Specimen of gold lever watches, with the split- centre seconds-hand movement. This watch, being a complete time-keeper, is capable of determining the precise time of any observation to a quarter of a second, by means of an extra seconds' hand, with which it is provided, and which in the ordinary state of the watch, lies under the principal seconds' hand, and travels with it.
In taking an observation, the observer keeps his eye steadily fixed upon the object, and his finger in readiness to touch a spring, which allows the registering hand to fall simultaneously upon the face of the watch, where it may be allowed to remain upwards of 40 seconds for reading off the time; this being done, the finger is to be immediately removed in order to free the register, which instantly returns to its place ready for the next observation, without having in the least degree interfered with the correct performance of the watch.
7. Specimen of railway watches.
8. Specimen of English pinions for astronomical clocks, showing the true curve of the teeth.
9. Specimen of carriage clocks.
10. Specimen of portable chime clock.
11. Specimen of chronometer and watch movements.
12. Diagrams of calibres of chronometers and watches.
13. Gauges for admeasurement of watch-work to the thousandth of an inch.
14. Specimens of gold watch cases.
15. The new calibre, by means of which the manufacture of watches and chronometers is greatly improved and facilitated, and the expense considerably reduced. The cut represents this new calibre.
16. Five stages of the process of manufacture hi the compensation balance.
17. Auxiliary compensation for the adjustments of the extremes of temperature.
[Power being an indispensable element in time-keeping, it is of the utmost importance that the motive force should be transmitted with a constant velocity-ratio from wheel to pinion throughout the train, without its being absorbed by the increased friction and wear consequent upon improper curves.
The correct forms of curve were described, a century ago, by Camus, and recently in a work on the Principles of Mechanism, by Professor Willis, of Cambridge, 8vo, London, 1841.
In watch-work, the wheel is the driver, and the addendum to the tooth beyond the pitch-line is of the epicycloidal form, which, to the general eye, may be familiarly explained as resembling a Gothic arch, or a bishop's mitre. The pinion is the follower, and has the two flanks of its leaf formed by radial lines direct to the centre; and the addendum upon the pitch-line is a semicircle whose diameter is the breadth of the leaf. The specimen will explain the rest.
The new calibre by the exhibitor is shown as a general improvement in chronometers and watches.]