utterly imperceptible to the most delicate weighing until after the lapse of millions of years; so that for all practical purposes, and for times such as are dealt with in cosmic history, they are permanent, even as the solar system and stellar aggregates appear to us to be permanent. Yet we know that all these systems are in reality transitory, as terrestrial structures like the pyramids or as the mountains and the continents themselves are transitory: of all these things it may be said that in any given form they have their day and cease to be. But whereas geological and astronomical configurations pass through their phases in a time to be reckoned in millions of years, the active life of a solar system covering perhaps no very long period, it is probable that the changes we have begun to suspect in the foundation stones of the universe, the more stable elemental atoms themselves, must require a period to be expressed only by millions of millions of centuries. For in such a time as this, at the rate of a hundred atoms per second, a bare kilogram—a couple of pounds only—of matter, even of heavy matter, would have drifted away; not so much indeed—a couple of ounces more likely. And yet this period is a million times the estimated age of the earth.
16. If we allow ourselves to speculate, on the strength of the slender experimental evidence as yet forthcoming, instead of waiting, as to be wise we must wait, for confirmation and thorough examination of the facts, we should say that the whole of existing matter appears liable to processes of change, and in that sense to be a transient phenomenon.
Somehow, we might conjecture, by some means at present unknown, it takes its rise: electrons of opposite sign crystallizing or falling together, perhaps at first into a manifestly unstable form; these forms then pass on from one into another, going through a series of transitional states, and abiding for a long time in those configurations which are most stable; giving a process of evolution inconceivably slow in its later stages, comparatively rapid in its early ones: and yet not so rapid, even in a substance like radium, but that its life as such may be reckoned by thousands of years.
If such a transitory existence is ever established for the forms of matter as we know them, it by no means follows that the process goes on in one direction only, or that the total amount of matter in the universe is subject to diminution. There may be regeneration as well as degeneration.
The total amount of radio-activity in a substance is singularly constant. If the radio-active portion is removed, a fresh supply makes its appearance at a measured rate, that rate being expressible by a decreasing geometrical progression, and being precisely equal to the rate at which the power of the removed portion decays.
