Earl of Macclesfield
Hornsby was especially concerned with the observation of the transit of Venus. In 1761, he observed the transit of Venus from Shirburn Castle, in Oxfordshire, the seat of the Earl of Macclesfield. George Parker, 2nd Earl of Macclesfield (ca. 1695–1764), celebrated as an astronomer, had spent most of his time conducting astronomical observations at Shirburn Castle; here he had built an observatory and a chemical laboratory.