Q. E. D. | Page 5

has said, most of these theories are so impossible as to be absurd, or so speculative that "they suggest no experimental tests for their validity."[2] Just at present Rutherford's theory of the structure of the atom is quite popular. This postulates a nucleus composed of a group of positive units and electrons, with an excess of the positive charges equal to half the atomic weight, with an equal number of electrons circulating about this nucleus in rings. Bohr's theory, which is not very different from this, has perhaps even more friends, and it is supported by the remarkable discoveries of the lamented Moseley. But we must not take such theories too seriously. As Kayser has said, any true theory of the make-up of the atoms must assume an absolutely full and perfect knowledge of all electrical and optical processes, and is therefore beyond our dreams. Or as Professor Planck said in his Columbia lectures, we are not entitled to hope that we shall ever be able to represent truly through any physical formul? the internal structure of the atom.
[Footnote 2: _Nature_, April 5, 1917.]
III
2. We must now take up the second phase of our subject, the problem of the origin of matter.
Before we knew anything of radioactivity we could have dismissed such a subject briefly by quoting the law of the conservation of matter, which says that matter can neither be created nor destroyed by any means known to science. By our knowledge of radioactivity we can make our answer a little more learned, a little less abrupt, but none the less discouraging to the advocate of the development hypothesis. We can tell how the elements of high atomic weight, such as uranium and thorium, are constantly giving off particles and are thus by loss or decomposition being changed over into other elements, such as radium, niton, polonium and lead. But our new knowledge compels us ultimately to give the same answer as before, namely, that _we still do not know how matter ever could have originated_, except that "in the beginning" it was called into existence by the fiat of Him whom we Christians worship as our God, the Creator. Thus we reach the conception of the universe as that of a great clock gradually running down, which is certainly the antithesis of that picture so long held before us by the advocates of the development theory.
Uranium is a rather rare element, though known for over a hundred years, and has an atomic weight of 238.5. In decomposing it gives off first a helium atom, weight 4; and after this action has been repeated three times the substance left is radium, atomic weight about 226.4. Thus radium is simply uranium after it has lost three helium atoms. Radium in its disintegration gives off three kinds of particles, namely, helium atoms (positively electrified), [Greek: b]-rays or electrons, and [Greek: g]-rays, the latter being identical with the X-rays, and having penetrating power sufficient to carry them through six inches of lead or a foot of solid iron. The final stage in this process of disintegration is the ordinary element lead, in which condition the atoms seem to have reached relative stability. Whether or not our stock of lead, with our other common elements that are not radioactive, was originally produced by the disintegration of these other elements, is merely a matter of conjecture. We know nothing at all about it.
The length of time it takes for half the atoms of an element to change is called its "life" or period. The periods of most of the radioactive substances have been calculated, that of uranium being very long. The calculated period of radium is 2,500 years, while that of polonium is only 202 days, and that of niton 5.6 days. These unquestioned facts, together with the enormous amount of heat evolved by the disintegration of these substances (that from radium being about 250,000 times the heat evolved by the combustion of carbon), have thrown a great deal of doubt upon the older estimates of the age of the earth.
The discussion of the details of these theories would be unprofitable. But through the mists of all these conflicting theories and probabilities two facts of tremendous importance for our modern world emerge in clear relief, namely, that the grand law of the conservation of matter still holds true, and hence that the matter of our world must have had an origin at some time in the past wholly different in degree and different in kind from any process going on around us that we call a natural process. These elements of high atomic weight that break down into others of lower atomic weight may be so rare because they have been about all used up in this process. At any rate, so far from