Letter, from Adolphe Quetelet to Sir John Herschel, dated at Brussels Autograph letter signed by sender. Still waits for the instrument that Edward Sabine had built. Wishes to make actinometer observations but has no instrument. Asks John Frederick William Herschel to have one made. Sends observations from Italy trip to Sabine to present to Royal Society [of London] Continues horary observations. 3 June 1840