Voyage of Discovery — Knowing their location?

[Naphtali]

Prior to beginning the Voyage of Discovery, Captain Lewis was trained to use a sextant (with necessary acoutrements) for navigation and map creation. One essential for identifying location was to maintain uniformly accurate time, using chronometer. How did Lewis maintain the accuracy of mechanical chronometer for the duration of the exploration? Chronometers, circa 1803, were delicate and large, when properly boxed for protection. And the voyage's logs report boats/canoes overturning into rivers more than once.

Nowadays quartz and [some] mechanical watches/clocks essentially guarantee chronometer-level time accuracy. And maintaining nearly perfect accuracy is guaranteed with a few mouse clicks on the Internet. Identifying a specific time for use in navigation occurred in Great Britain with Greenwich Mean Time being basis location. Greenwich is several thousand miles from Washington, D.C., from which I anticipate Captain Lewis' chronometer (did he include a back-up?) was adjusted.

How did Lewis maintain the accuracy of mechanical chronometer for the duration of the exploration?

 

[Daveboone]

Ships usually had several so they at least could use an average.
A ship also usually got a fix on the sun at first day light....As I recall exactly one minute after the sun cleared the horizon, which would be challenging on land as well as at high noon.

 

[mhb]

Good question. Most mechanical chronometers were and still are housed in sealed cases which would protect them from most incidental exposures to moisture, though probably not immersion for any amount of time. They were also mounted in gimbals inside a wooden box to further protect them from the environment and help with rate stability with changes in orientation and movement of the assembly. It seems likely that, knowing of the upcoming uncertainties of the projected voyage, the chronometer might have been housed in a more resistant case than normal, possibly external to the chronometer case and box. It would certainly be a real problem, given the difficulties encountered over the course of the Corps' travels, and would have required extraordinary care of the chronometer, if it were to be relied on.

mhb - MIke

 

[mhb]

Later:

Lewis is known to have purchased an Arnold chronometer in Philadelphia - for $250, plus 75 cents for the winding key (!). He had it regulated before the expedition embarked. No one seems to know what the chronometer looked like, or whether it still exists. It is on record that Lewis and Clark forgot to wind the chronometer more than once, which would completely nullify any chance of accuracy with reference to Greenwich (or any other) standard meridian time. They did have a fairly complete array of other survey instruments, but, without an accurate, working and reliable chronometer, could only estimate their longitude.

mhb - MIke

 

[Dale Lilly]

Good question. Most mechanical chronometers were and still are housed in sealed cases which would protect them from most incidental exposures to moisture, though probably not immersion for any amount of time. They were also mounted in gimbals inside a wooden box to further protect them from the environment and help with rate stability with changes in orientation and movement of the assembly. It seems likely that, knowing of the upcoming uncertainties of the projected voyage, the chronometer might have been housed in a more resistant case than normal, possibly external to the chronometer case and box. It would certainly be a real problem, given the difficulties encountered over the course of the Corps' travels, and would have required extraordinary care of the chronometer, if it were to be relied on.

mhb - MIke

Would that problem not apply to all travelers and map makers when going into unmapped territory? I am also a sailor and using a sextant on a pitching small sailboat is always difficult. Polecat

 

[Old Hawkeye]

A sextant can only measure latitude. I don't know if the Corps of Discovery had a working chronograph with them during the entire three years. They may have "estimated" longitude as many explorers did in pre-chronograph times. I don't believe any other instrument is needed to determine longitude other than the difference in local time & GMT & figuring out when noon local time was. I think a stick in the ground is all you need. One hour is 15 degrees of longitude. Lots of good "dead reckoning" navigators back in the day that were surprisingly accurate, as many of the old maps attest to. One degree longitude is around 70 miles. So, if you estimated you traveled 15 miles west & kept track of each days "estimate" you could get a approximate longitudinal fix.

 

[mhb]

Dale:

Yes, particularly in the pre-GPS past. As to the use of the sextant for determining altitude, the Corps was on dry land, or near it, most of the time, so could make their celestial observations from a more stable position - also, they had several versions of an artificial horizon to assist with the levelling issue. As to the time issue, they could determine the local 'high noon' by making several post-and-shadow observations around the expected time, but that would help but little without knowing the exact time difference from a known meridian. Compass direction and duration of march would be somewhat useful, but the accurate time would again be needed.

mhb - MIke

 

[Coot]

Prior to beginning the Voyage of Discovery, Captain Lewis was trained to use a sextant (with necessary acoutrements) for navigation and map creation. One essential for identifying location was to maintain uniformly accurate time, using chronometer. How did Lewis maintain the accuracy of mechanical chronometer for the duration of the exploration? Chronometers, circa 1803, were delicate and large, when properly boxed for protection. And the voyage's logs report boats/canoes overturning into rivers more than once.

Nowadays quartz and [some] mechanical watches/clocks essentially guarantee chronometer-level time accuracy. And maintaining nearly perfect accuracy is guaranteed with a few mouse clicks on the Internet. Identifying a specific time for use in navigation occurred in Great Britain with Greenwich Mean Time being basis location. Greenwich is several thousand miles from Washington, D.C., from which I anticipate Captain Lewis' chronometer (did he include a back-up?) was adjusted.

How did Lewis maintain the accuracy of mechanical chronometer for the duration of the exploration?

Records show that while at Fort Mandan, they used lunar observations to calculate longitude and time. The most complex use of a sextant is to use OLD or observed lunar distance (the angle between sun & moon), a nautical almanack and a lot of higher order math to determine longitude (and therefore time (by use of observing LAN or local apparent noon - fairly simple by comparison)) without a chronometer. This could then be used to check or if needed, reset a chronometer. Captain Cook navigated the Pacific without a chronometer using the lunar observation method.

 

[tenngun]

A sextant can only measure latitude. I don't know if the Corps of Discovery had a working chronograph with them during the entire three years. They may have "estimated" longitude as many explorers did in pre-chronograph times. I don't believe any other instrument is needed to determine longitude other than the difference in local time & GMT & figuring out when noon local time was. I think a stick in the ground is all you need. One hour is 15 degrees of longitude. Lots of good "dead reckoning" navigators back in the day that were surprising accurate, as many of the old maps attest to. One degree longitude is around 70 miles. So, if you estimated you traveled 15 miles west & kept track of each days "estimate" you could get a approximate longitudinal fix.

Time gives you a quick measurement, GPS of the day. Noting time of moon rise relative local noon, or rise of bright stars. Against an almanac one could get longitude and easier job on dry land then at sea.
Before clocks longitude of coast and cities were well known. Chronometers gave officers at sea a chance to get longitude fast enough to avoid before one piled up on the rocks.
I don’t know how L&C did it, just that one can work it out with a pia of math made easier with a good almanac

 

[Gun Tramp]

Wow, what a fascinating discussion. For me, this is The Muzzleloading Forum.

 

[Whitworth]

A chronometer is known to lose or gain precisely X amount of seconds or minutes per 24 hours. By knowing this amount time can thus be corrected. The was a great series on PBS about Harrison's development of the chronometer finally adopted by the Royal Navy. I think it was called "Longitude".

 

[Whitworth]

Would that problem not apply to all travelers and map makers when going into unmapped territory? I am also a sailor and using a sextant on a pitching small sailboat is always difficult. Polecat

Whenever I see a Navigator's Plexiglas bubble for shooting the sun or stars in something like a DC-3 or B17 I think how far we have come since those days. I got one of the first aviation GPS units to hit the market, it was giant leap from flying zigzag from one VOR radio beacon to the next to get to your destination. GPS allowed you to fly direct, point to point just like the big boys had been with their inertial guidance systems.

 

[Rod Man]

Another thing, Lewis & Clark most of the time had no idea where they were longitudinally but they had a reasonable Idea as to the time based off of there observations. They would make many observations write them down in there notes. Then once they got the info back to civilization they “astrologist and math savants” were able to back calculate the position. To their credit their written notes and assumptions were very close to where the points plot. It’s all very amazing!!! Exciting times they were.

RM

 

[tenngun]

A chronometer is known to lose or gain precisely X amount of seconds or minutes per 24 hours. By knowing this amount time can thus be corrected. The was a great series on PBS about Harrison's development of the chronometer finally adopted by the Royal Navy. I think it was called "Longitude".

Based on the boom by same name It was one of those books that were a dull as watching paint dry but fascinating enough you couldn’t put down

 

[andy52]

Most of the timepieces of the time were not highly accurate and very expensive.
Most common people really couldn't afford one. I have a 1797 English-made watch that's accurate to about 5 minutes in a 24 hour period which was pretty good for the time.

 

[Whitworth]

Beautiful watch, makes my Dad's Hamilton Railway Special look rather pedestrian. When Dad hired on after the War a railroad man had to have his watch cleaned and regulated every 30 days, using a "loaner" while his was being cleaned and regulated. Time was serious then.

 

[Old Hawkeye]

A chronometer is known to lose or gain precisely X amount of seconds or minutes per 24 hours. By knowing this amount time can thus be corrected. The was a great series on PBS about Harrison's development of the chronometer finally adopted by the Royal Navy. I think it was called "Longitude".

My understanding was the difference between a regular clock & a chronograph was that the chronograph DIDN"T lose or gain time & was accurate to an extreme degree. Wasn't it this precise time keeping that allowed navigators to accurately fix their longitude by noting the difference between local time & GMT? I was taught that Harrison's great hurdle was developing a clock that didn't lose or gain time on broad a swaying & pitching ship. I have never heard of a chronograph that has a known built in error, but I haven't heard of a lot of things & I'm sure that mechanical chronographs weren't as perfect as today's atomic clocks. Can you elaborate?

 

[Whitworth]

My understanding was the difference between a regular clock & a chronograph was that the chronograph DIDN"T lose or gain time & was accurate to an extreme degree. Wasn't it this precise time keeping that allowed navigators to accurately fix their longitude by noting the difference between local time & GMT? I was taught that Harrison's great hurdle was developing a clock that didn't lose or gain time on broad a swaying & pitching ship. I have never heard of a chronograph that has a known built in error, but I haven't heard of a lot of things & I'm sure that mechanical chronographs weren't as perfect as today's atomic clocks. Can you elaborate?

A chronometer wasn't corrected everyday, it's precise loss or gain was noted, true time calculated and the ship's clock corrected accordingly. Same with a land journey. This is my understanding of the method used, if I'm wrong someone chime in.

 

[Dave James]

Reading all this gives me a greater appreciation for my father, a Naval Aviator, who flew the Black Cat missions, he always joked about being glad it was a seaplane, as they were lucky to see the stars most nights

 

[French Colonial]

Beautiful watch, makes my Dad's Hamilton Railway Special look rather pedestrian. When Dad hired on after the War a railroad man had to have his watch cleaned and regulated every 30 days, using a "loaner" while his was being cleaned and regulated. Time was serious then.

There is nothing pedestrian about a Hamilton Railway special