Soon after his return to Lancashire, Horrocks began a scientific correspondence with William Crabtree a merchant in Broughton, near Manchester. Chapman suggests that John Worthington of Manchester, who had been an undergraduate at Cambridge at the same time as Horrocks, probably introduced Horrocks and Crabtree.
Sa lalong madaling panahon pagkatapos ng kanyang bumalik sa Lancashire, Horrocks nagsimula ng isang liham na pang-agham na may William Crabtree isang merchant sa Broughton, malapit sa Manchester. Magtitingi nagmumungkahi na ang John Worthington ng Manchester, na naging isang undergraduate at Cambridge sa parehong panahon bilang Horrocks, marahil nagpasimula ng Horrocks at Crabtree.