| Summary: | In: Pam. 538.7:C47e. John Churchman, An explanation of the magnetic atlas or variation chart. Philadelphia: James Johnson: 1790. Front. Churchman was an American who was devoted to his own theories of the variations of the magnetic needle and other things. He had presented his scheme to the Society in 1787 and was given mild encouragement. He founded his belief on the hypothesis of two bodies (besides the moon) revolving round the earth, in small circles parallel to the equator; one near the north pole, and the other was near the south pole; and the needle, being wholly governed by the attraction of these magnetic satellites, will, in whatever part of the world, always rest in the plane of the circle, passing through them and the given place. [The American Museum, Sept. 1789: p. 218]. He persevered in his work and at the 17 September 1790 meeting his "Navigation Chart, or Magnetick Atlas" was presented. It disappeared, but another copy was given by Johann Rodolph Valltravers on 19 May 1797. The Valltravers copy is the one now at the Society. Wheat: 6; Presented by the author to the Society, 17 September 1790, with a description. Another copy presented by Johann R. Valltravers, 19 May 1797.
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