Mr Mercator's Logarithmotechnia - the Demonstration Promised at the end of the foregoing discourse Wallis's own method of finding the sum of a logarithm (demonstration promised at end of RBO/4/1) Written in a letter to the Lord Brouncker and read before the Society in 1668 Figure 1 - ink drawing, height 700mm x 500 mm Figure 2 - ink drawing, height 450 mm x 800mm 5 August 1668