Copy letter, from Sir John Herschel to Friedrich Wilhelm Bessel, 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 Friedrich Wilhelm Bessel for letter in which Friedrich Wilhelm Bessel announces the discovery of annual stellar parallax; John Frederick William Herschel questions whether effects of temperature have been adequately considered. 24 October 1838