Author: WALKER (Ralph), of Jamaica:
Title: A Treatise on Magnetism, with a Description and Explanation of a Meridional and Azimuth Compass, for ascertaining the Quantity of Variation, without any calculations whatever, at any time of the day, also improvements upon compasses in general. With Table of Variation for All Latitudes and Longitudes.
Description: London: Printed by R. Hindmarsh...Sold by George Adams..., 1794. Large 8vo, 208 x 124 mms., pp. 9 [10 blank, 11 - 12 Contents], [9] - 226, 7 folding engraved plates, recently rebound in quarter calf, marbled boards, gilt spine, red leather labels; lacking the final leaf with the directions to the binder, but a very good copy. "In 1794 Ralph Walker 'of Jamaica' travelled to London 'for the purpose of laying my meridional and azimuth compass, and improvements upon compasses in general, before the Board of Longitude. Although Walker was a seaman and his inventive capacities were directed towards navigational problems, he included in his Treatise on Magnetism an appendix on land surveying. He felt it his duty to Jamaica and the West Indies, he said, 'to point out what advantage this improvement in compasses may be of, respecting the surveying of lands, and fixing the boundaries of estates and new settlements.' The burden of Walker's advice rested on his calculation of magnetic variation over time" (Higman: Jamaica Surveyed). The work was noticed in The Critical Review for 1794, but with only a cursory assessment of Walker's book. The British Critic, and Quarterly Theological Review for 1795 was sympathetic to Walker's undertaking: "Some faults might be pointed out in Mr. Walker's style, but he must be a very ill-natured critic who should notice a few blemishes in a work written principall for those whose minds are very little cultivated, and which conveys information of very general importance."

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