NavList:

Geoffrey,

I have read much on Thompson in Canada and Lewis and Clark. I agree that Thompson's work was much better.

Lewis and Clark were Army officers and were shown how to use the sextant, AH, the almanac, etc. before leaving Washington but were told, in effect, that the math computations for clearing the luners was too much so just bring your sight data back to Washington and we will hire professonal computers to find your longitude.

I agree with Frank Reed that sea Navigators did Lunars without much trouble but I would think not right away without standing with an experienced navigator to show them.  I also know that land based astronomers took great pains setting up heavy transit telescopes to get their longitude but even there they were not working to the crude level of precision that navigators work to.

If a navigator gets a cel-nav fix to within 1.5 NM of his true ( GPS ) that is not bad but to an astronomer a fix 500 feet off is BAD.

My thinking was, on land, to get your longitude to a navigator's precision using land based instruments - telescopes, tripods, plum bobs, transits.  The math involved would be addition and subtraction, no paralax and no refrraction problems.  I all my study and reading over the years I have not  found anyone that has done that.  Now I know surveyors use the meridian to get time checks and other things ( my sin-in-law is a surveyor ) but I have not found any ( land ) navagator or early explorer to use land based instruments - a sextant and bowl of mercury, yes.

I know there is a reason but like Hanno Ix's beatuiful haversign method, why did the not think of that, it is so simple?

John H.