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I would like a copy.  Thanks.  -- Bob


glapook@pacbell.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


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