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    Re: Magnetic Variation. (has been: Magnetic Declination) Version 11
    From: Kieran Kelly
    Date: 2004 Feb 14, 09:33 +1100

    Sorry about this. Tables are very difficult in plain text:
    
    1) Alt 7dd 30' is the sun's alt shot with the sextant. He used the symbol
    not the words
    
    2) 1/2 sum is half the total of PD and Lat and Alt ie 62dd 30'
    
    diff is the difference between the 1/2 sum and the pd i.e. 37dd 00'
    
    77dd 25' is the anti log of the Log Sin Sq 9.592280. In his notebook the
    diff figure of 37dd has a double  underline to indicate it is not part of
    the sum. Impossible to show this in plain text.
    
    Kieran Kelly
    
    
    
    -----Original Message-----
    From: Navigation Mailing List
    [mailto:NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM]On Behalf Of Royer, Doug
    Sent: Saturday, 14 February 2004 8:58 AM
    To: NAVIGATION-L{at}LISTSERV.WEBKAHUNA.COM
    Subject: Re: Magnetic Variation. (has been: Magnetic Declination)
    Version 11
    
    
    Thanks Keiran.
    I have a few questions concerning the below notations.
    1.Alt sun symbol  dd 30' ??? please explain
    2.I understand the haversine column.Where I get lost is:
    1/2 sum 62dd 30'
    diff    37dd 00'
            77dd 25'
    Please explain the above.
    Yes,do post other techniques.However,let's explore this one 1st so I
    understand it.
    
    
    The Australian explorer Augustus Gregory used several techniques for finding
    variation (i.e. difference between true and magnetic north. I will quote one
    here using an early morning sun altitude. This is verbatim from the field
    books:
    
    28 AUGUST 1856 at Camp LVII
    Alt sun symbol  dd 30'          az N 279dd 30' e mag
    
    
    
    Polar Distance          99dd 30'
    Lat                     18dd 00'           sec .021794
    Alt                      7dd 30'           sec .003731
                         2)125dd 00'
    
            1/2 sum         62dd 30'          cos 9.664406
            diff            37dd 00'          cos 9.902349
                            77dd 25'   log sin sq 9.592280
                           360
                           282dd 35'
                           279dd 30'
                             3dd 05'   var E
    
    So there you have it. Mag var with a compass, sextant and log tables. In
    this case he did not use amplitude tables. Also because he is on land with
    no ship nearby, deviation is presumed to be zero (I think). This was only
    one technique he used and is based using haversines for a solution of the
    celestial triangle originating at his visible pole i.e. the south pole.
    
    I can post some of his other techniques if you are interested..
    
    Regards
    
    Kieran Kelly
    Sydney
    Australia
    
    
    

       
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