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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.

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