James Joule was the son of a Sale ford brewer and became interested in the subject of energy at a very early age. He spent many years making careful experiments to show that mechanical and electrical energy could be transferred to internal energy in water which produced a rise in temperature.
His best-known apparatus is illustrated in Fig. 18.1. Two heavy lead weights were attached to string wound round the spindle of an eight-vaned paddle wheel which rotated inside a copper vessel containing water. Inside the vessel were four fixed vanes which prevented the water from being carried round bodily. The work done by vthe paddle against the resistance offered by the water was transferred to internal energy in the water and copper. By means of the handle the weights could be wound up and allowed to fall several times. The internal energy acquired by the water and copper was calculated from their masses and temperature rise and Joule was able to show that this was exactly equivalent to the transfer of potential energy from the falling weights.