Copy letter, from Sir John Herschel to William Wallace, dated at Collingwood Copy of a letter. Gratified by William Wallace's volume. Recalls John Frederick William Herschel's catenary theorems. Writes function to complete theory of exponential transcendents. William Wallace's applications have greater practical bearing than John Frederick William Herschel's early efforts, which John Frederick William Herschel now finds difficult to decipher. Sorry that William Wallace declared Mr. Gilbert's tables defective. 16 December 1840