Marvels of Heat, Light, and Sound

An excerpt from the Introduction: THE discovery in recent times of the intimate connection between all the great manifestations of energy, which we call the physical forces, has been one of the most fruitful results of modern thought. Formerly it was believed that the forces in action around us - of gravity, heat light, sound, electricity - were so many distinct powers not directly connected with one another, and certainly not interchangeable. Little could it be guessed...
More Description

An excerpt from the Introduction:

THE discovery in recent times of the intimate connection between all the great manifestations of energy, which we call the physical forces, has been one of the most fruitful results of modern thought. Formerly it was believed that the forces in action around us - of gravity, heat light, sound, electricity - were so many distinct powers not directly connected with one another, and certainly not interchangeable. Little could it be guessed that we should now be teaching that energy, the power of doing work, is in its essence one thing, which may have many manifestations; that all these manifestations are but temporary, and that they never disappear without a quantity of some other force appearing or becoming active ; that, in fact, no form of energy ever disappears without giving rise or being converted into an equivalent quantity of some other force or forces.

But by the experiments of Joule and Mayer, followed by others, it has been proved that this is the case; and the grand principle of the convertibility of energy into different and equivalent forms, which can be reckoned, has been established.

From this has been deduced the great generalisation of the conservation of energy, which asserts that the sum total of energy in the universe is constant, and that it simply varies in the situation and form of its manifestations. Now it is evident that this, theory cannot be absolutely proved, because it is impossible for us to measure the total quantity of energy in the universe at different times, and see whether it is always the same. So that we must be content to have made this great assumption without absolute proof, and to gain from its use some advantage as to the phenomena with which we are brought into contact.

Certain observations, however, do give strong support to this view. For instance, in every case in which we can trace the appearance or the changes of the forms of energy, either an exact equivalent is found to have appeared and disappeared, or something so near, that we may well consider that the difference is due to our imperfect observation. The more nearly we are able to approach to a completely accurate mode of estimating energy, the more closely do we find that the quantities of energy disappearing and appearing are equal. By studying different changes we are enabled to reckon absolutely what is the equivalent between energy in one form and in another, and it is possible to predict to a large extent what changes will take place when we transform one force into another. And thus the assumption that ho energy entirely disappears or is created anew, but simply that it changes its manifestation, allows us to predict new results from new combinations of force and material, by assuring us of the absence of such disturbances as must vitiate our calculations if they occurred, and throw worldly events into confusion. Such a principle as the conservation of energy is as valuable to us for practical purposes as the certainty that two and two make four, and will always make four.