The penetrating radiation in the atmosphere at Hobart

If a gas be enclosed in a thick-walled vessel and protected from all external disurbances a few of its atoms are still found to be ionised during every second. It can be shown that this residual ionisation cannot be due to the heat energy of the gas itself (1), the atoms must therefore be broken up by a radiation coming from without. This external radiation must. arise in the walls of the vessel itself, or penetrate them. If the former is the case we may say with fair certainty that it is due to radio-active matter in_ the walls, and if the latter it must be a radiation of extremely great penetrating P!JWer, as shielding the vessel -with several feet of water has little effect on the ionisation.
The residual ionisation is now known to be due to both these causes, and they may 1be distinguished from one another experimentally. The origin of at any rate a part of the radiation is still in doubt, and measurements made at different parts of the earth's surface may be expected to provide evidence indicating what factors are concerned.
Recenti experiments by ~various workers have given -curiously contradictory indications as to the nature of the penetrating radiation, leaving the matter in a condition most stimulating for further research.
Millikan (2) and others (3, 4, 5) have shown that the radiation increases in intensity with the height above sea level at which the measurement is made, and, further, that it varies with meteorological conditions (6). This would seem to show decisively that it is an external radiation, and that it probably arises in the upper atmosphere.