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.