At the age of nineteen, he invented an electro- Joint

—1. The point at which a junction is magnetic engine. He was the first to ~ made. {; f ascertain the mechanical equivalent of 2. The junction by which any two parts heat, working for forty years in its deter are united. min at i on. In 1847 he stated the doctrine of the conservation of energy. He made many imp or- A good electrical joint should have conductivtant researches in electricity and thermodynamity, mechanical strength, durability, and facility ics, discovering the law known as Joule’s law for insulation. In making a joint it may be for determining the relation between the heat and brazed, soldered, welded, or as usually made, the the current pre ure and time in an electric cirtwo ends of the conductors are brought into close cuit. His name has been given to the unit of metallic contact and secured in position by twisting the ends. This is known as a dry joint. electric work, the joule.