Progress during the nineteenth century
During the years which followed Rumford’s experiments the concepts of work and energy began to emerge in scientific thought. Moreover, the rapid development of steam power, which was then taking place, played its part in stimulating a general interest in the transfer of internal energy from steam into mechanical work. At first the discussion was confined to the theoretical level. In England Thomas Young drew attention to the confusion which existed between force as such and the work which is done when a force is exerted through a distance. He was also the first to use the word energy to refer to the capacity of a moving body for doing work. This was in 1807. The German physicist, Robert Mayer, calculated the work done when a gas is compressed and assumed that the whole of this work became transferred to internal energy which increased the temperature of the gas.
Generally speaking, the main body of scientific opinion was hostile to the new ideas. Eventually, however, during the period 1840-50 a series of experiments was carried out by James Joule which established that, when the temperature of a body was raised by doing work on it, there was an exact equivalence between the work done and the internal energy acquired.