A rare group of 'Saxby's patent spherograph' marine navigational error calculator panels Printed by George Smith, Watts and Company for S.M. Saxby and H. Wood and Company, Liverpool, 1856-57 Comprising SAXBY'S SPHEROGRAPH No. 2, FOR GREAT CIRCLE SAILING AND THE MEASUREMENT OF NAUTICAL DISTANCES WITHOUT ANY CALCULATION, Drawn and Engraved by Edward Powell of the Hydrographic Office, Admiralty incorporating rotating panel pierced with pair of lunettes inset with calibrated tracing paper within a surround annotated for Northern and Southern Hemispheres, the upper margin with Royal coat of arms and inscribed By Her Majesty's Royal Letters Patent and signed in ink S.M. Saxby opposing issue No. 6 over Date 16th Feb 1857, the verso with Directions For Use, together with KEY TO SAXBY'S PATENT SPHEROGRAH No. 2 and KEY TO SAXBY'S PATENT SYSTEM OF GREAT CIRCLE SAILING, each with matching signatures, issue numbers and dates; SAXBY'S SPHEROGRAPH No 3, LATITUDE, TIME &c. similarly constructed, signed, numbered No. 18 and dated 20 July 1857 together with another identical unsigned and undated; SAXBY'S SPHEROGRAPH No 4, FOR CORRECTING LUNAR DISTANCES WITHOUT THE AID OF LOGARITHMS AS ACCURATELY AS IT CAN BE DONE AT SEA BY CALCULATION again similarly constructed, signed, numbered No. 1 and dated 13 July 1857; a KEY TO SAXBY'S SPHEROGRAPH signed, numbered No. 2 and dated Nov 24 1856; and two further panels No. 1 KEY TO SAXBY'S PATENT SPHEROGRAPH plus No 4 CORRECTION OF LUNAR DISTANCES both unsigned and undated, each panel 32cm (12.5ins) by 29cm (11.375ins) and contained in an original mahogany protective box (9). The current lot was developed during the 1850's by Stephen Martin Saxby in order to assist mariners to calculate inherent errors in magnetic compass reading without having to resort to calculations in complex spherical trigonometry (which were possible with the knowledge of the approximate latitude and date). Saxby's design was devised as a representation of the celestial sphere onto which projections of the same both in the 'Horizon System' and the 'Equinoctial System' can be superimposed and correlated by rotating the latter until the polar axis pointed to the correct latitude indication in the projection of the Horizon System. The resultant device which essentially comprised of two diagrams rotating around a common centre and was given the name 'Spherograph'.