John Churchman’s “Magnetic Atlas”

4to. vii,[1],xxix,[2]32-82pp. plus 2 folding engraved maps and 1 folding engraved chart. Rebound to style in blue paper over boards.

A remarkable and very rare artifact of 18th-century American mapmaking and scientific inquiry.

John Churchman (1753-1805) was an American mathematician, surveyor and map maker who for many years held the official post of surveyor for Chester, Delaware and parts of Berks and Lancaster Counties, Pennsylvania. He first came to notice for his Map of the Peninsula between Delaware & Chesapeak Bays (1778), which he dedicated to the American Philosophical Society and which received the approval of that august body. He was also involved as an investor in a projected canal linking the Delaware and the Chesapeake, though construction did not start until 1804, near the end of his life.

Some time in the mid-1780s Churchman became consumed by the problem of finding longitude at sea, which had challenged navigators, scientists and inventors for centuries. The search was given impetus in 1714 by the creation in London of the Board of Longitude, charged with assessing proposals and empowered to award a staggering prize of £20,000 to whomever came up with the first viable method. This ultimately went to John Harrison for his extraordinary chronometers, but in late 18th-century America these were rare and expensive instruments, far out of the reach of ordinary mariners.

Churchman developed the theoretical underpinnings and methodology for an entirely different solution. His basic premises were that the northern and southern magnetic poles could be located precisely, that on any meridian linking those poles magnetic variation was the same at every point, and that over the centuries the magnetic poles rotated at a constant rate around the geographic poles. If these premises were true, a mariner would need know only his latitude and the local magnetic variation of the compass to ascertain his longitude with considerable accuracy.

Unfortunately for Churchman his method was theoretically unsound: the positions of the magnetic poles do not change at a predictable rate, and lines of equal variation do not run as straight lines between the opposing poles. Indeed they often tend in an east-west direction, as had been shown by Halley decades earlier.) Churchman’s method was also practically flawed, as change in magnetic variation is difficult to measure on an unstable vessel at sea.

An aggressive self promoter, Churchman communicated his method here and abroad to luminaries such as Benjamin Franklin, Thomas Jefferson and Joseph Banks and learned bodies including the American Philosophical Society, the Royal Academy of Sciences (France), and the Board of Longitude itself. The response varied, with some correspondents raising difficult objections. On August 8, 1787 for example, Thomas Jefferson wrote:

“… two difficulties occur; 1st, a ready and accurate method of finding the variation of the place; 2d, an instrument, so perfect as that (though the degree on it shall represent 160 miles) it shall give the parts of the degree, so minutely as to answer the purposes of the navigator.”

But Jefferson went on in a conciliatory tone, perhaps exhibiting his habitual aversion to conflict:

“I make no doubt but you have provided against the doubts entertained here; and I shall be happy that our country may have the honour of furnishing the old world, what it has so long sought in vain.” (Jefferson to Churchman, reprinted in The Magnetic Atlas, p. 66)

By 1790 Churchman felt emboldened to gloss over the objections and publish a remarkable map—the Magnetic Atlas—accompanied by an explanatory pamphlet. An expanded second edition of the pamphlet with newly-engraved maps of the northern and southern hemispheres appeared in London in 1794, and a third edition—that offered here—was issued in New York in 1800. A fourth and final edition was issued in London in 1804.

The Magnetic Atlas
Offered here is the very rare third edition of The Magnetic Atlas, “printed for the author, and sold by Gaine & Ten Eyck, No. 148, Pearl-Street” in New York. In fact, close comparison indicates that it was assembled from remaindered sheets of the 1794 London edition, with the substitution of a new title leaf, the addition of two leaves of notes after the Appendix (pp. 77-80), and the substitution of a new list of subscribers at the end (These sheets are on different stock and noticeably smaller than those printed in London.) The text begins with a long “History of Magnetic Discoveries,” followed by a short chapter of “Definitions and Corollaries,” chapters explaining the construction and use of the Magnetic Atlas, and a chapter speculating on the causes and effects of magnetic variation. These are followed by an Appendix reprinting correspondence that constitutes, if not an unalloyed endorsement of Churchman’s work, then at least a cautious recommendation thereof. The volume concludes with a short list of merely 51 subscribers, among them Aaron Burr of New York. The list is a far cry from the nearly 300 subscribers to the first edition, which had including representatives of America’s political, intellectual, religious and business elite, among them Adams, Jefferson, Hamilton and Franklin.

The pamphlet is illustrated by three plates, including two large folding maps depicting the northern and southern hemispheres on a polar projection. Each consists of eleven gores, which if assembled would yield a globe approximately 48” in circumference. On the map of the Northern Hemisphere the north “Magnetic Point,” or Pole, is shown at its supposed location in the Canadian Arctic, with the “Magnetic Orbit” a concentric ring around the geographic North Pole (Due to the lack of observations in the region, the location of the southern “Magnetic Point” is left imprecise.) Latitude and longitude are indicated by solid lines at one-degree intervals, while “magnetic meridians” emanate from the Magnetic Point as dotted lines intersecting the geographical meridians at angles corresponding to the magnetic variation. Though rather beside the point, the geography itself is relatively up to date and includes for example a reasonable depiction of the northern Pacific and Australia.

As with the text, close comparison indicates that these maps were printed from the same plates as those used for the London edition. However, the London imprint has been removed and the date changed to “1st July 1800, and numbers added to indicate compass variation along the magnetic meridians. These changes are in a different hand than that of the original engraver, but it is not known whether they were executed in London or New York.

This third edition of the Magnetic Atlas is extremely rare. Rare Book Hub lists no copies having appeared on the antiquarian market, while between them ESTC and OCLC locate but eight institutional holdings, of which only two are here in the United States (Boston Public Library and Princeton).

The fate of the Magnetic Atlas
Churchman’s correspondence with the Board of Longitude endured from 1787 through 1804 and is preserved to this day at the Royal Greenwich Observatory. Predictably, given the gaping flaws in this theories and methods, the Board never provided him the recognition he felt he deserved.

“Churchman must rank as the most persistent of all the investigators who studied the problem of finding longitude by variation: he devoted sustained attention to the problem for a period of at least seventeen years, and was encouraged to do so by many eminent men of science at the time. Yet his efforts were, from the outset, doomed to failure, and the Board of Longitude at no time seemed to be willing to grant him financial support…” (Cotter, 218)

Churchman does seem to have received considerable recognition elsewhere. The U.S. Congress repeatedly passed resolutions expressing strong approbation, though it rejected his petition for funding for a voyage to Baffin Bay to gather evidence confirming his theories. He received encouraging correspondence from as far afield as France, Germany and Russia, and in 1796 was even elected a member of the Imperial Academy of Sciences at St. Petersburg—an honor carefully noted on the title page of the present volume. However, reading between the lines one receives the strong impression that he was ultimately frustrated by the lack of financial recognition from either Congress or the Board of Longitude.

In early 1805, while in London on what seems to have been a mission to gain recognition from the Board of Longitude, Churchman suffered a debilitating stroke. He recovered somewhat, but died during a return voyage to Philadelphia on July 24 of that year.

Evans 37183. Sabin 13026. Wheat & Brun 6 (note to description of 1790 edition). ESTC W20710 (Boston Public, Cambridge University, Niedersachsische Staats- und Universitatsbibliothek, Princeton, Royal Society, St. Andrews University). OCLC gives copies at Boston Public Library, Danish National Library, University of Aberdeen, and University of St. Andrews University. Background on Churchman’s project from Charles H. Cotter, “John Churchman and the Longitude Problem,” in Navigation, vol. 27 no. 3 (Fall 1980), pp. 217-225. Biographical information on Churchman from Phillips, Virginia Cartography, pp. 58-59; Pritchard & Taliaferro, Degrees of Latitude, pp. 232-235; Smith & Vining, American Geographers, pp. 34-35.


Text washed and rebound, with some faint residual foxing. Some penciled calculations in margin of p. 43. Maps clean, each with a mended binding tear.