NavList:

   

Reply

Gary LaPook writes:


I now have a complete copy of "Certaine Errors In Navigation" in PDF
format and can email it off list to anyone who might want a copy. It
is a delightful book to read, Mr. Wright sounds like a thoroughly
modern man.


gl

On Dec 4, 8:03 pm, "Gary J. LaPook"  wrote:
> Gary LaPook adds:
>
> What I meant by: " I suspect that the method was just forgotten in the
> mists of time" was that in Wright's time there was no reason to publish
> a method to calculate altitude as that need did not develop until St.
> Hilaire invented the "new navigation" almost 300 years later. After St.
> Hilaire,  many methods were tried in an effort to  reduce the work
> needed to calculate altitude including different mechanical devices such
> as the Bygrave slide rule (and many more),  "short tables" and
> culminating in the precomputed altitude tables such as H.O 214, H.O.
> 218, H.O. 229 and H.O 249. I suspect that nobody thought to look back at
> a book that had been published in the dim and distant past, 1599, and
> that didn't even include a method for calculating altitude, only great
> circle distance.
>
> Gary LaPook wrote:
> > Gary LaPook writes:
>
> > You can look at his explanation yourself and you will see that is no
> > allowance for an elliptical earth so it uses the round earth
> > assumption used throughout celestial navigation.
>
> > I would think his method could produce better accuracy with either
> > modern printing of the form to use, larger scale or precision
> > machining of a mechanical device to do the computation. One tenth
> > minute precision is not needed for flight navigation and many methods
> > and devices were used that produced accuracy that was attainable by
> > the Wright method. I suspect that the method was just forgotten in the
> > mists of time.
>
> > gl
>
> > Fred Hebard wrote:
>
> >>Some naive comments/questions:
>
> >>First, how much of the discrepency between Wright's calculated
> >>distance and the modern digital calculator is due to the elliptical
> >>shape of the earth, or were you using the same assumptions?
>
> >>Second, one could guess that a graphical method would be good to 3
> >>decimal places (about what you got for question 1).  Five-decimal-
> >>place precision is needed to get 0.1 arcminute accuracy, more or
> >>less, so a graphical method would only be good to 10 arcminutes, more
> >>or less.  Perhaps it's the lack of precision that led to Wright's
> >>method not being adapted to standard sight reduction.  Certainly back
> >>in his time, simple reduction of noon sights for altitude was easy
> >>enough.  By the period when time sights for longitude became
> >>prevalent, and especially by the point when intercept methods took
> >>over, 3 decimal places wasn't close enough anymore.
>
> >>Fred
>
> >>On Dec 4, 2007, at 4:18 AM, Gary J. LaPook wrote:
>
> >>>Gary J. LaPook wrote:
>
> >>>It is not surprising that nobody ever noticed this before
> >>>(considering that Wright published in 1599 almost 300 years prior
> >>>to Marc St. Hilaire) that Wright's method of calculating the great
> >>>circle distance on the earth using only a strait edge and a compass
> >>>could just as easily be used to calculate the altitude of a
> >>>celestial body. The great circle distance is simply 60 NM times the
> >>>number of degrees of the great circle between two points and this
> >>>is exactly the same as the zenith distance to a body having the
> >>>geographical position represented by the second point.     The
> >>>formula is 90� minus zenith distance equals altitude.
>
> >>>Wright's example of calculation of the great circle distance
> >>>between London and Jerusalem resulted in his calculated distance of
> >>>2325 NM and a modern digital calculator comes up with 2316.8 NM a
> >>>difference of  only 8.2 NM or minutes of zenith distance or of
> >>>computed altitude for those coordinates! Using his method Wright
> >>>could compute altitudes to a precision of 8.2'. It is surprising in
> >>>light of the many devices invented later in an attempt to find a
> >>>mechanical method for this calculation that none (that I am aware
> >>>of) attempted to use Wright's method, a method that would seem
> >>>easily adapted to a mechanical device and that could provide much
> >>>greater accuracy using a larger scale and precise machining of the
> >>>parts.
>
> >>>I would really like it if someone could explain why Wright's method
> >>>works since I have not been able to find such an explanation
> >>>anywhere. I am attaching pages 45-52 of "Certaine Errors" in which
> >>>he lays out his method. I am also including the errata sheet
> >>>showing that the corrections of typos I identified in my previous
> >>>posts were correct.
>
> >>>gl
>
> >>>
> >>>
--~--~---------~--~----~------------~-------~--~----~
To post to this group, send email to NavList@fer3.com
To , send email to NavList-@fer3.com
-~----------~----~----~----~------~----~------~--~---

   

Reply