This principle is applicable not only to heat the most general and most widely diffused form of motion but to other forms as well. in every case it is always just the one term in the chain of the three interchangeable motions the character of the molecular work that is changed. Work of disgregation and mechanical work can be done e.g. by electricity as well as by heat. There are therefore various kinds of molecular work; but there is in the last resort only one work of disgre­gation as there is only one form of mechanical work. Disgregation is the name given in every instance to a permanent change of the distances separating the molecules no matter what cause has produced it