# NavList:

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

**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@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