Letter, from B. W. S. Vallack to Sir John Herschel, dated at St. Budeaux, near Plymouth Autograph letter signed by sender, with diagrams. Thanks John Frederick William Herschel for corrections to the mirrors of his telescope. Says the telescope finally gives 'a satisfactory view of Saturn.' Discusses the lenses for BV's binocular telescope. Thinks photography could benefit from binocular vision. 25 January 1866