Letter, from Henry Warburton to Sir John Herschel, dated at 45 Cadogan Place Autograph letter signed by sender, damaged. Glad for John Frederick William Herschel's renewed interest in mathematics. At 72, Henry Warburton expects to do no more. Reviewed John Frederick William Herschel's letter of 14 May [1856]. Fears John Frederick William Herschel misunderstood meaning of symbol Henry Warburton employed. Quotes explanation from Henry Warburton's paper on self-repeating series. 30 May 1856