Unpublished letter, regarding the northwest magnetic pole from John Macdonald to Sir Humphry Davy Macdonald details his process for calculating the approximate location of the northwest magnetic pole. Includes a diagram of the earth viewed from the South Pole, indicating a possible location for the southeast magnetic pole. He writes that he worries that if the British do not begin making concerted efforts to discover the true locations of these poles, the French or Russians might achieve it first. An ink inscription at top of first page reads '(JFWH [John Frederick William Herschel]. No 74)'. Subject: Geodesy Written by Macdonald in Summerlands, Exeter [Devon, England]. 19 October 1825