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Doug wrote after an earlier posting of mine:

>Kieran stated he has a way to find local variation using " a
>sextant, compass and amplitude". How can this be done? Am I missing
something
>or are my thoughts to confined i.e.. ship board application only?

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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