Abstract
THERE are many points of resemblance between the movements of the. molecules of a gas and the movements of those corpuscular radiations with which we have become acquainted in following up the discovery of radio-activity. In both cases we find that things of extremely minute dimensions are darting to and fro with great velocity, and in both cases the, path of any one individual is made up of straight portions of various lengths, along which it is moving uniformly and free from external influence, and of encounters of short duration with other individuals, when energy is exchanged and directions of motion are altered. There is even a resemblance in the universality of each movement. The motion of molecules is a fundamental fact throughout the whole of our atmosphere, and, indeed, in all material bodies; the motion of the radiant particles emitted by radio-active substances is also widely distributed, and of great importance. Taking Eve's estimate of the usual ionisation of the air, we can calculate that in this room, in every second, some thousands of α and β particles enter into existence, complete their paths through all the atoms they meet, and sink into obscurity; some of them, viz. the α particles, as atoms of helium. These last move through definite and well-known distances in the air. For example, a third of those which are due to radium products move through a range of just above 4 cm., an equal number have a range of just below 5 cm., and again an equal number move through 7 cm., and the speed is so great that the life of each α particle as such is completed in about a thousandth-millionth of a second. They leave their mark behind them in the ionisation of the air through which they have passed, and in the heat into which their energy has been commuted. The former effect is easily detected by the sensitive measuring instruments which we now possess; the latter is too small to measure, and must be greatly increased by the aid of radium itself, before it can be investigated. - But on a large scale, which, takes into account the distribution of radio-active material, through the earth, the sea, and the air, the effects are of first-rate importance to the physical conditions of our earth.
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Discourse delivered at the Royal Institution on Friday, January 27, by Prof. William H. Bragg, F.R.S.
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Radio-activity as a Kinetic Theory of a Fourth State of Matter 1 . Nature 85, 491–494 (1911). https://doi.org/10.1038/085491a0
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DOI: https://doi.org/10.1038/085491a0