302 POPULAR SCIENCE MONTHLY. 



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 terres- 

 trial structures like the pyramids or as the mountains and the conti- 

 nents 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 uni- 

 verse, 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 kilo- 

 gram — 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 to- 

 gether, perhaps at first into a manifestly unstable form; these forms 

 then pass on from one into another, going through a series of transi- 

 tional 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 con- 

 stant. 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. 



