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Lewis and Clark, and the clocks and watches of their era.
From: George Huxtable
Date: 2004 Jan 1, 15:22 +0000
From: George Huxtable
Date: 2004 Jan 1, 15:22 +0000
I am putting together a little something about Lewis and Clark In taking equal-altitude observations of the Sun, with an artificial horizon, Lewis and Clark would group their observations into three a.m. times and three p.m. times. In the morning, the times were recorded when first the Sun's upper-limb coincided with its reflection as observed in the sextant; next, the Sun's centre: and finally, the Sun's lower-limb. In the afternoon, the corresponding times would be recorded, in reverse order, as the Sun fell. For all six measurements, the sextant setting would remain unchanged. The interval between successive measurements in each group of three should always be nearly the same, being the time that the Sun takes to rise (or fall) by a semidiameter on that day at that altitude. However, on occasions the recorded time intervals differ significantly from this equality, and it often appears to be an error of one whole minute in a single reading, or perhaps a few readings, in that set of six. This would not be very surprising, as the men would not be nearly so accustomed to reading a clock as we are today. Nowadays, when we read a clock, we do so without really thinking about it. If we just want the time to catch a bus, say, a glance at the minutes-hand provides time to the nearest minute, which is all that's needed. If we are timing to the second, however, using the seconds-hand, then we need to be much more careful about reading the minutes-hand. We need to observe which of the two minutes-divisions it lies between, and always choose the earlier, to which we then add the seconds. If it's very close to one of those divisions, then we choose which is the lower one according to whether the seconds-hand is nearing the top, or has just passed it. This is second-nature to us nowadays, so the mind-process involved was hardly worth describing in detail. But even for us, it's easy to get confused if (for example) the minutes-hand is badly aligned with the seconds reading. The evidence, from the Lewis and Clark journals, seems to be that right from the start of the expedition there were frequent misreadings of the chronometer, by just one whole minute, and it generally seems to be that the time was set down as 1 minute too late, rather than 1 minute too early. These errors recurred quite frequently in the early part of their journey, the only part with which I am familiar so far. Perhaps their team may have got better at reading the chronometer in the later stages, but I can't confirm this yet. When this problem occurs just once in a set of 6 timed equal-altitude observations, it can be rather easy to detect and correct, but it could easily occur in other timing contexts when it might well be much less obvious For example, if all 6 of the times were noted down as 1 minate later than they should have been, then the timing of the moment of midday would be 1 minute too late, but otherwise the error would not have been obvious. It seems that Lewis and Clark didn't review these observations later, as there are several occasions when such a 1-minute timing error is obvious in retrospect but has not been corrected. So, at long last, here are my questions, which are mainly addressed to American readers. Back in 1803, would the common soldiery, or even those at the level of Lewis and Clark, have been accustomed to reading the time, from any source? Would public clocks, such as village church clocks, have been common? Was it likely that an officer, or even a soldier, would possess a pocket-watch, with a seconds-hand, and know how to read it? Thanks for any advice. George. ================================================================ contact George Huxtable by email at george@huxtable.u-net.com, by phone at 01865 820222 (from outside UK, +44 1865 820222), or by mail at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. ================================================================