One of the preeminent natural philosophers of the Enlightenment, Benjamin Thompson started out as a farm boy with a practical turn of mind. His inventions include the Rumford fireplace, insulated clothing, the thermos, convection ovens, double boilers, double-paned glass and an improved sloop. He was knighted by King George III and became a Count of the Holy Roman Emperor. Thompson's popularity with women eclipsed his achievements, though. He was married twice and had affairs with many other prominent women, including the wife of Boston printer Isaiah Thomas and that of a doctor who would crew the first balloon to cross the English Channel. He even fathered a child by the court mistress of the Prince Elector and had affairs with several other German noblewomen. Drawing on Thompson's correspondence and diaries, this book examines his friendships and romantic relationships.