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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@LISTSERV.WEBKAHUNA.COM]On Behalf Of Royer, Doug
Sent: Saturday, 14 February 2004 8:58 AM
To: NAVIGATION-L@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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