This part of the book contains all of Michell’s known letters. They are forty-four in number, not many. There are references to lost letters, but it does not seem that Michell maintained long correspondences. His closest colleague was probably Smeaton, whose Minute Book for 1782 and 1783, when he was largely in London, lists his many correspondents for those years; Michell is not among them. He often put off answering letters, as he acknowledged, and he spent a long time composing them. Several of his letters are very long; one of them he called a “paper.” Nearly all of his extant letters are about his main interest, science.