In 1852, John Ransome St. John obtained an American patent for this mariner’s
compass designed to determine local changes in magnetic variation. Although the
instrument was complex and largely useless, it garnered a gold medal at the
American Institute fair of 1849 and a Prize Medal at the Crystal Palace
exhibition held in London in 1851.
Ref: Patent (#8,785) granted to John R. St. John on March 2, 1852.
"John R. St. John’s Variation Compass and Velocimeter," Transactions
of the American Institute (1851): 204-205.