NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: How Many Chronometers?
From: Brad Morris
Date: 2009 May 6, 19:26 -0700
From: Brad Morris
Date: 2009 May 6, 19:26 -0700
Hi Jim Your definitions are precise. Chronometer rate is the gain or loss of time per day, or whatever period you may chose to define. The assumption is that the rate is constant is fallicious. The rate of a chronometer varies with many factors. Take a close look at the chart recently provided by George. If the rate was constant, the line would be straight, independent of corrections at known longitudes. In fact, we see the converse. The line changes slope from correction to correction. We even see positive going slopes change into negative going slopes. The rate, therefore, is changing. The argument will be offered that modern mechanical chronometers are superior. In fact, they are. However, they are not perfect. The rate still changes with the viscosity of the lubricant with temperature. Hence the double box, to slow the transfer of thermal energy, with a glass top, such that you can see the chronometer without opening the box. The quartermaster is cautioned to wind the chronometer every day, at the same time, by the same amount, such that the chronometer utilizes the same spring region, independent of the wind down counter that provides the hours until unwound. All this attention to detail, and the rate still varies. If you remember other parts of the Royal Observatory, where H1 lives (hooray!), then you have seen the gradual transformation to other time pieces, away from the mechanical. And each time piece has been superceded by the next, each with dilemmas, problems and issues. Back to Greg's question though, which I understand to be the determination of when a chronometer has gone bad, we have offered the solution of solving for time when the longitude is known. If the longitude is not known, then you suffer from not knowing which one is wrong, the longitude or the chronometer! Bruce Stark, when he was contributing to the list, offered a wonderful exposition on how to recover GMT via lunars. The details are found in a NavList posting whose number I cannot remember. I did keep a file of it though, and link it herein. All the way from not knowing any time to GMT! I have not exercised the method and can offer no insight as to how accurately one can recover GMT from it. Based upon the source, however, I suspect it works quite well! Best Regards Brad --~--~---------~--~----~------------~-------~--~----~ Navigation List archive: www.fer3.com/arc To post, email NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---