Copy letter, from Sir John Herschel to William Henry Smyth, dated at Slough Copy of letter, copied as part of the correspondence project led by Colonel John Herschel FRS following the death of his father. Thanks William Henry Smyth for excerpt from Niccolo Cacciatore's letter; comments on the awarding of medals for merit, and points out some necessary conditions which must be considered if the observations of the satellites of Jupiter are to be used in determining the constant of aberration. 27 May 1830