The real significance of recent developments is in the fact that they change—in a way revolutionize—some of our ideas of things. And here let me say that proved facts and proposed theories should not be confused. A theory is simply a working hypothesis, invented for the purpose of explaining facts, to be discarded when facts are discovered with which the theory is not in harmony. A theory may explain many facts, it may be generally accepted, it may have survived for generations, and be false. The phlogiston theory, the corpuscular theory, are two examples. Shall we say that the theory of the indestructibility of matter, and of the conservation of energy, are two others?
The usual chemistry text-book would have us believe in the indestructibility of matter because the chemist can change the form of matter almost at will, and in all the chemical reactions there is no loss of weight. In replying to this argument I wish to make three points:
1. The balance, notwithstanding the statement of text-books, compares weights and not masses, and it is only because weight is assumed to be proportional to mass that we say we determine mass by the balance. What we really compare is the gravitational force which the earth exerts on two masses, and we have no a priori right to assume that this gravitational force is absolutely independent of the state or molecular arrangement of the attracted body. Why, for instance, should we expect an absolutely uniform field of force about a crystal when that same crystal will, if placed in a proper solution, continue to grow symmetrically, and perhaps replace a broken-off corner before beginning its growth?
It is conceivable that there should be a loss of weight in chemical reactions and yet no destruction of matter. It is possible that mass and weight are not strictly proportional. If J. J. Thomson were not disposed to question the equation m.g. he would not have experimented with a pendulum of radium, and he would not now be experimenting with a pendulum of uranium oxide.
2. In the second place there is an apparent change of weight in chemical reactions as has been shown by several experimenters—notably by Landolt,[1] who found a loss in forty-two out of fifty-four cases. The chemical reactions were brought about in sealed glass tubes which generally weighed less after the reactions than they weighed before. Later[2] it was found that some of these losses might be attributed to temperature and volume changes. Whatever the testimony of the balance may have been, some of the reactions must have been accompanied by a loss of weight, for it has been proved by chemical means that such reactions are frequently attended by the escape of something through the walls of the glass tubes.[3] This loss is readily explained by the disintegration
