A New Concept

This chapter begins with the question that arises among experts in the theory of heat in the late 1840s: how to make this theory compatible with the new findings. Clausius resolved this issue. Thomson adhered then to the thesis that heat is motion and created the concept “mechanical energy”. This concept not only covers what was properly mechanical, but also the activity due to heat, which had become a kind of motion. This is how the term energy appeared in the heat theory. A year later, Thomson distinguishes between static and dynamic reserves of mechanical energy, which led to the distinction between potential and kinetic energy. It is, finally, shown how the different theses on energy that had appeared since the 1840s emerge as characteristics of energy in the 1870s. This accumulation of meanings of the term energy made it more difficult to understand the concept.