Copy letter, from Sir John Herschel to Wilhelm Struve Copy of a letter. Sends Wilhelm Struve John Frederick William Herschel's 'Light' published in the Encyclopaedia Metropolitana. Mentions recalibration of his magnitude measurements of small stars near other small ones. Comments on results in Wilhelm Struve's paper concerning Saturn's ring. Confirms sighting of 'well defined, equable, planetary disk.' 6 July 1828