Page:Popular Science Monthly Volume 77.djvu/459

Rh theory. If one wishes to explain it by assuming the diffusion of ordinary gases through the glass walls of the tube, he must explain the fact that in many cases it was the heavy and least volatile substances that escaped fastest.

3. In the third place the element of time has been overlooked. Matter may be disintegrating, but at such a slow rate that in the limited time over which experiments have been extended the balance has failed to detect the change. As far as our experience goes the time of rotation of the earth is constant; but we know that it can not be absolutely constant. The moon has slowed down until it takes a month to make one turn. To an ephemeral insect almost everything would appear to be eternal.

With due respect for the balance and the wonderful work it has enabled chemists to do, it must be admitted that it is, comparatively, a very crude instrument. Let me prove it.

Suppose we fix the limit of sensibility of the chemical balance at one one-thousandth of a milligram. Our books on chemistry tell us that 1 c.c. of gas, say hydrogen, at ordinary pressure contains $$4 \times 10^{19}$$ molecules. The density of H being $$896 \times 10^{-7}$$, then 1 gm. of H would consist of $$(4 \times 10^{19}) \div (896 \times 10^{-7})$$ molecules. Taking 112 as the ratio of the molecular weights of radium and H, then 1 gm. of radium would consist of $$[(4 \times 10^{19}) \div (896 \times 10^{-7})] \div 112 = 4 \times 10^{22}$$ molecules. Therefore .001 mgm. of radium would consist of $$4 \times 10^{16}$$ molecules, and this would be the smallest possible number that our most sensitive balance could detect. If the gram of radium were disintegrating and its molecules escaping at the rate of a million per second it would require $$4 \times 10^{10}$$ seconds $$= 463,000$$ days $$= 1,270$$ years for that gram of radium to lose in weight only the one-thousandth part of one milligram, all the while its molecules trooping away at the rate of a million per second.

The population of the earth is about 1,500 millions. The smallest number of molecules a balance will detect is $$4 \times 10^{16}$$, or about 26,600,000 times the population of the earth. We wonder if Mars is inhabited. If a Martian were to come to the earth to make an experiment to determine whether or not the earth is populated and he had no better instrument "for the detection of the existence of a man" than is the balance for a molecule, he would be obliged to go back and report the earth uninhabited. In fact his instrument for the man test would need to be 26,600,000 times as sensitive as the balance to give him even a hint of the probability of an earth population.

Thomson says that the smallest quantity of unelectrified matter ever detected is probably neon, and this was discovered by the spectroscope—not the balance. But the number of molecules of neon required to give a spectroscopic effect is about ten million million, or about 7,000 times the population of the earth. It has been shown that the presence