ABSTRACT
The most general formula for this principle can be stated in these terms: in every modification of an isolated system the total energy of the system conserves an invariable value. (1) If no account is taken of the condition of isolation, whose importance we shall see later, this formula resembles that of the conservation of matter. There is this difference that the concept of matter, which originates from common sense, is vast and without precision whereas that of energy, created ad hoc by science, seems to present all the desired precision. We shall see, however, in a later chapter that this is not absolutely so.
