The first person to carry out any reported experimental programme to investigate the heat produced as a result of plastic deformation was Henri Tresca in June 1878 Tresca forged a bar of platinum (as well as many other metals); at the moment of forging the metal had just cooled down below red heat. The subsequent blow of the steam hammer, which left a depression in the bar and lengthened it, also reheated it in the direction of two lines in the form of a letter X. So great was this reheating, the metal along these lines was fully restored for some seconds to red heat. Tresca carried out many forging experiments on different metals. Tresca estimated the amount of plastic work converted into heat from a large number of experiments, and it was always above 70%.