Benjamin Thompson, Count Rumford, is best known for the cannon boring experiments that confirmed to him that heat was what we would call molecular motion. Some will also know him as the founder of the Royal Institution in London. He was, however, a much more colourful character than these details suggest. Born in Massachusetts in 1753, he had an unremarkable childhood. He married a wealthy widow, who bore him a daughter. In the American War of Independence he sided with the British, and spent some time in England. At the end of the war he moved to Europe and contrived to become an aide to the Elector of Bavaria. Munich was the scene of his most solid achievements and of most of his scientific work. It was here he was ennobled as Count Rumford. He founded the Royal Institution in 1799, during a lengthy interlude in London, but almost from the start there was friction between Rumford and other backers. He spent most of the rest of his life in Paris, contracting a second marriage to the wealthy widow of the chemist Lavoisier. Ironically, Lavoisier had been a supporter of the alternative, caloric, theory of heat. The couple soon divorced and Rumford became increasingly reclusive, dying suddenly in 1814. The book cover describes Rumford as `scientist, soldier, statesman, spy'. He was all of those but not first rate at any of them. He was also an adventurer, a womaniser and a self-publicist with a habit of exaggerating his own accomplishments and a talent for acquiring honours and permanent pensions. His work on the nature of heat was significant, but to claim, as the title does, that he was a scientific genius is excessive. He was the first to provide real evidence for the kinetic theory of heat, and his work did influence James Joule, who, with the help of Rumford's near-namesake William Thomson, succeeded in getting the equivalence of heat and mechanical work accepted, but Rumford himself made no fundamental discoveries. He was more of an inventor, devising improved oil lamps, an efficient fireplace known as the `Rumford stove', and a kitchen range to replace the traditional fire for cooking. He was a genuine philanthropist who used his gifts to benefit mankind but his relations with individuals were more difficult. He never saw his first wife again after leaving America, but after her death he was reconciled to his daughter. Brown's biography is a fast-moving, readable book, and the references, bibliography and index make it a good starting point for further study. It pulls no punches about the less attractive aspects of Rumford's life, and it is sufficiently discursive that it can be understood without prior background knowledge. It does fill in some details for those who only know that he studied the heat produced during the boring of cannon. That observation roused his interest, but his conclusions were derived from meticulously conducted experiments using a specially prepared cannon casting. There are minor flaws in the book. The sequence of events is not always easy to follow, so that, for example, the second wife of the aged Elector of Bavaria seems to remain 17 for at least two years. Teachers might wish that Brown had started rather than finished his discussion of heat energy where modern students begin, with the identity of all types of energy, measured in joules, rather than with calories and the now-alien concept of the mechanical equivalent of heat. These quibbles detract little from the book. It is to be recommended.