THE CONSERVATION OF ENERGY
This principle puts physics in its relation to energy where chemistry has long been in its relation to matter. If matter were not conservative, if it could be created or destroyed at will, chemistry would be an impossible science. Physics is put upon a solid foundation by the assumption of a like conservatism in energy; it can neither be created nor destroyed, although it may appear in many different forms which are, in general, mutually interconvertible.
Many men have contributed to the establishment of this great principle, but it was actually discovered and proved by the labors of three or four. Although it was practically all done before the middle of the nineteenth century, its general popular recognition did not come until a quarter of a century later. The doctrine was first distinctly formulated by Robert Mayer, a German physician, who published in 1842 a suggestive paper on “The Forces of Inorganic Nature,” which, however, attracted little or no attention. Mayer had not approached the problem from an experimental stand-point, but at about the same time it was attacked most successfully from this side by a young Englishman, James Prescott Joule, son of a wealthy brewer of Manchester, England. Joule made the first really accurate determination of the mechanical equivalent of a given quantity of heat, a physical constant which Rumford had tried to measure, reaching only a rough approximation. Substantially Joule’s result was that the heat energy necessary to raise the temperature of any given mass of water one degree Fahr. is the equivalent of the mechanical energy required to lift that mass through a height of seven hundred and seventy-two feet against the force of the earth’s attraction; and, conversely, if a mass of water be allowed to fall through a distance of seven hundred and seventy-two feet under the action of gravity, and at the end of its motion be instantly arrested, the heat generated will suffice to raise its temperature one degree Fahr. Of such vast importance is this numerical coefficient that it has been called the golden number of the nineteenth century. Since Joule’s time it has been redetermined by several physicists, notably by Professor Rowland, of Baltimore, the general conclusion being that Joule’s number was somewhat, but not greatly, too small.
The first clear and full exposition of the doctrine of the conservation of energy was given by Joule in a popular lecture in Manchester in 1847, but it attracted little attention until a few months later, when the author presented his theory at a meeting of the British Association for the Advancement of Science. Even among scientific men it would have passed without comment or consideration had it not been for the presence of another young Englishman, then as little known as Joule himself, who began a series of remarks, appreciative and critical, which resulted in making Joule’s paper the sensation of the meeting. This was William Thomson, who had been, only a year before, at the age of twenty-two years, appointed professor of natural philosophy at the University of Glasgow, now known as Lord Kelvin, the most versatile, brilliant, and profound student of physical science which the century has produced. From that day to the death of Joule (1889) these two men were closely associated in the demonstration and exploitation of a great principle of which they were at first almost the sole exponents among English-speaking people.
By an interesting coincidence, in the same year in which Joule announced the result of his experiments, the Physical Society of Berlin listened to a paper almost identical with Joule’s in character and conclusions, but prepared quite independently, by a young German physician, Herman von Helmholtz, destined to rank at the time of his death, in 1893, as one of the very first mathematicians of the age, doubtless the first physiologist of his time, and as a physicist with whom not more than one other of the nineteenth century may be compared. Helmholtz’s paper was rejected by the editor of the leading scientific journal of Germany, but his work was so important that he must always share with Joule and Kelvin in the glory of this epoch-making generalization.
Even a brief sketch of the history of the doctrine of the conservation of energy would be incomplete if mention were not made of the work of Tyndall. Although by original research he contributed in no small degree to the demonstration of the theory, it is mainly through his wonderful skill in popular presentation of the principles of physical science that he becomes related to the great movement of the middle of the century. His masterful exposition of the new theory in a course of lectures at the Royal Institution, given in 1862 and published in 1863 under the title Heat as a Mode of Motion, was the means of making the intelligent public acquainted with its beauty and profound significance, and the history of science affords no more admirable example of the possibilities and wisdom of popular scientific writing than this book. As for the principle of the conservation of energy itself it is not too much to say that during the last half of the century it has been the guiding and controlling spirit of all scientific discovery or of invention through the application of scientific principles.