| THE LAW OF SUBSTANCE. |
By Professor R. H. THURSTON,
CORNELL UNIVERSITY.
IN Haeckel's new and remarkable monistic book, 'The Riddle of the Universe at the Close of the Nineteenth Century/ which has just been translated by Joseph McCabe and published by the Harpers, the accepted laws of the persistence of matter and the persistence of energy are enunciated and their unity insisted upon; the union constituting what is denominated 'The Law of Substance/ Substance, 'Stoff' in other words, being in fact what we are familiar with as matter, including all its physical attributes, as essential parts of it, as a person's character and his material parts are one and, failing either of those attributes, is no longer the same. It is only by these characteristics that we can recognize or define either the person or the molecule; without them, so far as we can see, there would be neither person nor matter.
The principle and the law of substance are unquestionably now incorporated into the scientific code permanently and positively; but the time of recognition and the dates of discovery of the two elements of that law are not, in the opinion of the writer, precisely as stated by Haeckel; the discoverers are not given credit by this author in correct proportion. He accords to Lavoisier the discovery of the persistence of matter and the proof of that principle, undoubtedly, as generally believed, correctly. He gives Robert Mayer (1842) credit for the discovery of the principle of the persistence of energy and assigns to Helmholtz (1847) its more general application.
It was, in fact, Benjamin Thompson (Count Rumford), the American philosopher, who, in 1796-97, experimentally proved the equivalence of the two forms of energy, thermal and dynamic. He read the paper describing his work in 1798, before the Royal Society of Great Britain; while Sir Humphry Davy confirmed it and added further proof immediately afterward.
It must be carefully noted that there are at least three quantities to be observed, studied and quantitatively measured: (1) substance or matter; (2) the forces which affect matter; (3) energy. Matter can perhaps be conceived of as destitute of any designated force and possibly even of any known attributes, such as the physical forces; forces can possibly be conceived apart from any specific matter; energy involves both matter and motion, and infers the action of forces in its production or variation. Nevertheless, our only method of acquiring a knowledge of mat-
