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. Suggests that phenomenon in observing Jupiter satellite was an optical illusion. Asks William Henry Smyth to observe spots on Mars to confirm observations of William Pearson. Asks William Henry Smyth to contribute to W. S. Stratford memorial. 11 July 1828