Unpublished letter, on the variation of the magnetic needle from John Jas [James] Rorie to [John Frederick William] Herschel Rorie reports on his observations of magnetic variation in the west and east, providing data relating to latitudes and variations from his own observations. He then posits about the reasons for the variation, and provides a list of further stations where observations of variation should be made. Subject: Geodesy Written by Rorie at No. 12 College Street, Southampton [Hampshire, England]. [1820s]