Welcome to the NavList Message Boards.

NavList:

A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    Re: Certaine Errors in Navigation Corrected
    From: Gary LaPook
    Date: 2007 Dec 10, 11:50 -0800

    Gary adds:
    It is interesting to compare Wright's almanac with the modern one. The
     sun's declination today, December 7, 2007 at noon in England is 22�
     35.7' south. If we were using Wright's almanac for the same day,
    which
     would be November 27th in the column for 1607 (found on page 118), we
     get his value of 22� 38' south and a modern almanac program gives it
    as 22� 39.0', only one minute differece!
    
    gl
    
    On Dec 10, 11:44 am, glap...---.net wrote:
    > Gary writes:
    >
    > It is interesting to compare Wright's almanac with the modern one. The
    > sun's declination today, December 7, 2007 at noon in England is 22�
    > 35.7' south. If we were using Wright's almanac for the same day, which
    > would be November 27th in the column for 1607 (found on page 118), we
    > get his value of 22� 38' south which is close enough for government
    > work. In comparing Wright's almanac with the modern one you must
    > subtract 10 days from his tabulation since England did not change to
    > the Gregorian calendar until September 25, 1752 while most Catholic
    > countries changed on October 5, 1582. (This caused me much confusion
    > when I first looked at his almanac almost thirty years ago since I
    > assumed that Wright was also using the Gregorian calendar since he
    > published 17 years after that calendar went into effect.)
    >
    > Also, comparing his value for the declination of the sun at the summer
    > solstice of 1597, he gives it as 23� 30' north while a modern almanac
    > program gives it as 23� 29.6' north, a difference within the limit of
    > precision of Wright's table!
    >
    > Remember that the letter "s" was printed in 1599 with a character that
    > looks like the modern letter "f" and that the letters "u" and "v" are
    > often interchanged.
    >
    > On Dec 8, 5:14 am, RS Peterson  wrote:
    >
    > > I would like a copy.  Thanks.  -- Bob
    >
    > > glap...---.net wrote:
    > > >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
    >
    > > >>>>>
    > > >>>>>
    >
    > > --
    > > Robert S. Peterson
    > > Great Lakes Compass
    > > 31 N Alfred, Elgin IL  60123  USA
    > > 847/697-6491
    > > Compass Adjusting & Repair for Lake Michigan Navigators Since 1985
    > > e-mail: rspeterson(at)wowway(dot)com
    --~--~---------~--~----~------------~-------~--~----~
    To post to this group, send email to NavList@fer3.com
    To unsubscribe, send email to NavList-unsubscribe@fer3.com
    -~----------~----~----~----~------~----~------~--~---
    

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    Join NavList

    Name:
    (please, no nicknames or handles)
    Email:
    Do you want to receive all group messages by email?
    Yes No

    You can also join by posting. Your first on-topic post automatically makes you a member.

    Posting Code

    Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
    Email:

    Email Settings

    Posting Code:

    Custom Index

    Subject:
    Author:
    Start date: (yyyymm dd)
    End date: (yyyymm dd)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site