A model of the remontoire action on John Harrisons longitude watch H4 

Thank you Tommy, prise indeed. I guess you have seen my H1 model video

Hi Joseph You are correct, mine does just that when the motive power is removed. Harrison recognised that and added a lever operated by the fusee that applied a brake to the balance wheel rim half an hour before the main spring ran out. Thus the remontoire spring was left in a fully wound state. It should never get that far when wound regularly and would have been a skilled job to pre tension the remontoire spring if it did run down. My model has has not got that sophistication but has got a manual brake on the balance wheel. My remontoire spring needs 3 eights of a turn which equals 3 full rotations of the 5 th wheel to pretension it. Hope this helps.

@@MrParamount3 Thank you for that. I was curious to see if Harrison had come up with a different solution. It sounds like both he and Daniels (who made a couple of watches with a remontoire) used effectively the same solution.

Good plan. Done

@@MrParamount3 Thanks!

Hi. The answer to your question is complicated, but here goes. The aim is to keep the balance wheel, which is the timing part of the watch, swinging regularly and invariably which will give accuracy and good timekeeping.. Remember this was the 18th century and they didn't have the modern materials we had. They were groping towards solutions. The big mainspring has a lot of power when fully wound and much less when it is wound down. The balance wheel would see variable force which is not ideal. In this remontoire a small spring is wound by the mainspring every 7.5 seconds and it is this spring that powers the balance giving regular and almost constant torque. As long as the mainspring can wind the remontoire spring the watch will work with constant force. My blog www.woodenclockspot.blogspot.com has a little more detail on this point.

@@MrParamount3 Thanks so much for that explanation. That was actually very clever. We moderns tend to look down at the past, (atomic clocks, quartz, etc) but early achievements like this should be recognized and celebrated. Cheers.

@@MrParamount3 Thank you, brilliant design

The answer is that technology moved on very rapidly. Within a few tens of years they developed better escapements for chronometers, see Earnshaw spring detent escapement, and worked out how to manage balance hairsprings so that the differences in frequency between large and small swings of the balance were much reduced. The remontoire was thus banished to history for chronometers. The fusee was still retained. Together with temperature compensation at the balance the chronometer then stayed essentially unchanged for 200 years until quartz took over. Harrison's work was effectively a magnificent dead end, the important bit being that he proved a chronometer could keep accurate time at sea and that he inspired others to produce chronometers better and cheaper, leading to mass adoption.

ofc this is not the best solution by today's standard. This was made in 1759.

Remontoirs are actually very effective especially when you are constrained with space in watches and cant use a fusee or where you have a escapement with larger lift angles like any lever escapement (swiss lever etc like the one shown). There isnt much “wasted” energy in a modern remontoir and that isnt really an issue you are concerned with as the gear trains only job now is to charge that spring. There were some very acurate competition watches made with remontoirs and derek pratt made some of the most stunning toubillon remontoirs that are really worth checking out

Great answer and lovely to Derek's name being mentioned. @@felixarbable

It doesn't matter that energy is 'wasted'. All the mainspring has to do is re-wind the remontoire. Again it doesn't matter that the remointoire may not be the best means of achieving constant force, what is worth considering here is the spring that drives the escapement is re-wound every 7 1/2 seconds so escapement error effectively becomes invisible. Once you have Arnold's terminal curves on the balance spring and isochronism is approached, the remontoire can be done away with.