Energy and engineers at the turn of the XX century

Physicists of modern age adopted a model of nature called mechanistic: matter is made up of particles interacting by central forces, which were pictured as hands pulling ropes. In the second half of the XIX century this vision underwent a deep crisis because of its difficulties in explaining the already known thermal phenomena and the new electro-magnetic and chemical phenomena. Thus, many scientists looked for a primitive concept that could be more suitable than that of force. Such a concept seemed to be that of energy, yet the idea of force was not completely rejected, like for instance Green did in its theory of transmission of light in aether. A stronger, not to say radical, position was that by Wilhelm Ostwald (1853-1932), who won the Nobel Prize for chemistry in 1909. Indeed, at the same time he strongly promoted the philosophical vision of an entire natural world founded on the concept of energy. He started from considering that the conservation of energy is commonly accepted as a principle in physics. Thus, he suggested that energy, though immaterial, has the same role of a natural substance, and is as real and enduring as material substances. Although the emergence of energetism was largely a German phenomenon, it spread also through Europe. This work considers how energetism influenced the engineers’ vision of mechanics and thermodynamics of the time, especially in Italy. Indeed, engineers more than physicists, were interested to physical theories grounded on concrete objects. Energy, as conceived by Ostwald, represented then for sure good heuristics. In particular, we will carry out a scrutiny of textbooks on thermal machines adopted in some schools of engineering.