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Re: Harrison chronometer no. 4 (1891 article)
From: Ken Muldrew
Date: 2008 May 12, 09:40 -0600
From: Ken Muldrew
Date: 2008 May 12, 09:40 -0600
On 12 May 2008 at 1:49, frankreed@HistoricalAtlas.net wrote: > > http://articles.adsabs.harvard.edu/full/1891Obs....14..122P > > In this article, the author says of H4: > "although popularly styled a 'chronometer,' is really only a verge > watch". > > He then desctribes the "tremulous" motion of the seconds hand. What is a > "verge watch"? A verge watch is one with a verge escapement (and I suppose size and the use of a balance spring defines it as a "watch", though it was a pretty big watch). It's true that Harrison used a verge escapement although he put diamonds with a cycloidal curve on the pallets. I've restored a couple of old verge pocket watches and one feels an immense sense of accomplishment if they can be brought within 5 minutes/day. That Harrison could make a verge with such accuracy is just slightly short of miraculous. > Is it connected to the tremulous motion (which makes it > difficult to read H4 to the nearest second)? When he implies it's not a > chronometer, is he speaking of some fairly specific contemporary > definition > of a chronometer, c.1891? He was probably just defining "chronometer" by the escapement rather than the helical balance spring and thermal compensation mechanisms. I don't know the period of the balance in H4 but if it was typical of a verge watch then the second hand would have advanced in several small increments for each second (I think mine go 5 but I may be confusing them with my old lever watches). Earnshaw's chronometer escapement only moved after two full oscillations of the balance so it may have had a second hand that ticked out whole seconds. Ken Muldrew. --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---