[The Horological Journal. Vol. ??, No. ?? (April, 1878): 120-122.]
(Continued from page 105.)
JOHN HARRISON'S TRAIN REMONTOIRE.
THE chronometer which obtained Harrison the £20,000 prize from Government differed in many important respects from the marine timekeepers now in universal use. It was, in the first place, simply a large silver watch in a pair of cases kept from shocks by lying on a soft cushion, not brass cased and suspended on gymbals like our modern ship's chronometer.
The compensation for temperature was derived from a long bimetallic curb acting on the spring; but "Harrison, himself, was dissatisfied with it, and suggested that the compensation ought to be done in the balance." 1
The going-spring of the fusee was a spiral, the "brass" being hollowed out to receive it, and there were other minor differences, but the chief and grand difference was in the escapement, which was a "verge" with the escape-wheel driven by an auxiliary spring (the maintainer), the spiral, fig. 2, rewound by the train eight times a minute.
The pallets were not at an angle of about 95 [degree sign] as in the ordinary form, but were parallel, and were jewels set in brass collets; there was, therefore, a good deal of "set" and not so much recoil, and as a result the impulse came very near to a double chronometer action (see fig. 9). In order to prevent the maintainer spring running down, there was a brake arranged to come into action on the balance, and so stop the watch when the chain reached the largest part of the fusee.
The accompanying figures, studied in connection with the previous articles, will render clear the details of the remontoire arrangement.
Former explanations taken from Harrison's description are necessarily unsatisfactory, as his was very obscure, probably purposely so.
These drawings have, by the kindness of the Astronomer-Royal in permitting the necessary facilities, been made2 direct from a Harrison watch by Larcum Kendal, date A. D. 1769, belonging to the Royal Obervatory at Greenwich.
[Note: Figs. 1 through 9 originally were all contained on, and constituted, page 121.]
[Figs. 1 through 6 are given first in smaller versions, for ease of reference in the text.]
Fig. 1. [smaller version]
The same letters are used in all the figures.
Fig. 1 is a section of the 4th wheel arrangement.
Figs. 2, 3, 4 and 5, are details of the same. Fig. 2, contrate wheel and barrel containing maintainer. The projections P, P', are in this position in the middle of arming.
Fig. 2 [smaller version]
Fig. 3, 4th wheel, hollow pinion, and arbor, through which passes loosely the spindle T of contrate wheel. Pipe B, has a small notch at the end r, on which the barrel centre (fig. 4) is pushed, and the pin at G, fitting into it, connects the two.
Fig. 3. [smaller version]
Fig. 4, maintainer barrel, having a hook h, inside to catch outer end of spring. The projections P', P', pass through the arms of contrate wheel to keep the spring from running down.
Fig. 4. [smaller version]
Fig. 5, T the arbor of S (the seconds wheel) is thinned as far as the bottom of c c. Q, eight pins fixed on collet of contrate wheel; they release the train by their action on hook H (fig. 7), discharging detent D off locking pin p, c c contrate wheel, m drum with hook t to catch eye of srping.
Fig. 5. [smaller version]
Fig. 6 shows arrangements of cocks, S S, seconds wheel, c b cock screwed on to bar to hold the lower pivot. The lower pivot of the 4th wheel is pivoted into the bar; p b, bar on counter potence to hold upper pivot of seconds wheel, the upper pivot of 4th wheel runs in a potence.
Fig. 6. [smaller version]
[Figs. 1 through 6 full sized.]
[Figs. 3, 4, 5 repeated in a single image to demonstrate their collinearity in the original text.]
[Figures 3, 4, and 5 repeated together]
[Figs. 3, 4, 5 repeated yet again, smaller so as to be more readily visible on a screen.]to demonstrate their collinearity in the original text.
[Figures 3, 4, and 5 repeated together]
Fig. 7 and fig. 8, details of locking and discharging the re-winder. L, locking wheel (it drive the fly v), on which is a pin p, stopped against detent D of the five-fingered piece c 1, c 2, D R H, whose axis is at J. c 1, c 2, counterpoise weights. R, friction roller, on which the excenteric [sic] X acts to release hook H off the eight [page 120 ends here; page 121 is comprised entirely of figs. 1-9, the text resumes on page 122] pins at Q. The five-fingered piece is kept always pressing R against X by the action of the spring s s on nib e. Hook H is pivoted at i in the arm of the five-fingered piece that carries it, and is kept in the position shown in fig. 8 by the spring K. The discharging is effected by the pins at Q, on the contrate wheel as it goes on, impelled by the maintainer.
The locking pressure is reduced to a minimum, the wheel L making a whole turn at each escape. The fly turns each time of the arming 8 2/3 times, making the action easy and steady.
O, the contrate wheel; the major portion is omitted to avoid confusion in the parts; W is the crown wheel.
Fig. 7. [smaller version]
Fig. 8. [smaller version]
Fig. 9 is a perspective view of the pallets.
Fig. 9. [smaller version]
1 Denison's Fourth Edition, page 290.
2 By my chronometer foreman, R. E. Burrett.
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