James's observation that "in most of us, by the age of thirty, the character has set like plastic" 1 applies to Cavendish, if we take his "character" to include a narrow focus on science. His earliest known extended series of experiments were in chemistry and heat, specifically on arsenic and on specific and latent heats. This was around 1764, 2 twelve years after he had left the university and four years after he had been elected to the Royal Society. His first publication came two years

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... on the chemistry of air, when he was thirty-five; this was rather late for a scientific researcher to begin, but in this as in other ways he was not typical. Never in a hurry to bring his work before the world, he was concerned to perfect it before communicating it. Cavendish's Correspondent The earliest contributions to the Philosophical Transactions were letters to its founder, Henry Oldenburg. Over time, the pretense of letters was dropped, and the genre of the scientific paper emerged as authors increasingly wrote for their readers instead of to the editor. With the introduction of a committee of papers in 1752, the editor withdrew further. 3 Still, during the time Cavendish was a student and beyond, publications in the Philosophical Transactions commonly took the form of "letters" addressed to the president of the Society or to a member who was knowledgeable about the subject. Sometimes a letter by an author would be published as a preface to a paper. The practice of sending letters to the journal is the background of Henry Cavendish's papers written to be read by a person referred to as "you." Given Cavendish's habits of privacy, a correspondent draws our interest. "You" might have been his father, who was convenient, though here an informal way of communicating would have been more natural. Among other possibile correspondents is the longtime family friend William Heberden, who having lectured on chemistry at Cambridge would have been a competent reader; Cavendish's first published chemical research was carried out at Heberden's request. Another possibile correspondent is another family friend William Watson, who together with Heberden signed Cavendish's certificate at the Royal Society. Others are the London apothecary Timothy Lane, the London schoolmaster John Canton, and the Cambridge fellow and Anglican minister John Michell.