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564 CURRENT ToPIcs. [J. F. I. in the majority of text books on chemistry." By the same method higher oxides of calcium and zinc were produced. G.F.S. The Origin of the Aurora Borealis. E. O. HURLBURT. (Ter- restrial Mag., March, 1928. ) "A theory of the aurora borealis has been developed by Birkeland, Stoermer, Vegard, and others on the assumption that the aurora is caused by charged particles emitted from the Sun which under the influence of the magnetic field of the Earth are diverted to the polar regions. There their energy is given to the atmosphere and by some process is converted partially or totally into the auroral light." There are objections to this explanation from the side of theory as well as from that of experiment. For instance no one has succeeded in reproducing the spectrum of the aurora in the laboratory. The author ventures to suggest a new theory. The energy that finally appears with auroral light comes from the sun in ultra- violet radiation. In the higher part of the earth's atmosphere it is absorbed with the production of ions and electrons. These particles diffuse but combine to only a slight extent. The ions drift along the magnetic field of the earth and concentrate in the polar regions. In lower levels there they recombine and the energy of combination appears in the auroral light. From observations made in Maine, August, 1927, the power of the auroral light then seen is calculated to have been Io 12 ergs/sec. This agrees sufficiently well with the results of another computation based on the rate of flow of ultra-violet light to the earth. The author wisely remarks "But here I must stop, partly to avoid being too rash, but mainly to admit that my contemplation of the aurora has been too limited to give that steadying of ideas which comes only from experimentation." G.F.S. The Application of Electrical Resistance Measurements to the Study of the Atmospheric Corrosion of Metals. J. C. HUDSON. (Proc. Phys. Soc., London, April I5, I928. ) The effect of atmospheric corrosion upon metals can be traced by a study of the weight of the specimen as time goes on. Vernon has done this "and the accuracy obtainable is well demonstrated by the fact that he was able to follow the development of tarnish films on lead and aluminium in cases where the final weight increment, after 25 days' exposure, was as low as o.28 milligrammes." Much labor is, however, necessary especially when the specimen is exposed in the open where the products of chemical action may be carried away by rain or otherwise lost. When, therefore, the Atmospheric Corrosion Committee of the British Non-Ferrous Metals Research

The origin of the Aurora Borealis

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Page 1: The origin of the Aurora Borealis

564 CURRENT ToPIcs. [J. F. I.

in the majori ty of text books on chemistry." By the same method higher oxides of calcium and zinc were produced. G . F . S .

The Origin of the Aurora Borealis. E. O. HURLBURT. (Ter- restrial Mag., March, 1928. ) "A theory of the aurora borealis has been developed by Birkeland, Stoermer, Vegard, and others on the assumption tha t the aurora is caused by charged particles emit ted from the Sun which under the influence of the magnetic field of the Ear th are diverted to the polar regions. There their energy is given to the atmosphere and by some process is converted partially or totally into the auroral l ight." There are objections to this explanation from the side of theory as well as from that of experiment. For instance no one has succeeded in reproducing the spectrum of the aurora in the laboratory.

The author ventures to suggest a new theory. The energy that finally appears with auroral light comes from the sun in ultra- violet radiation. In the higher par t of the earth 's atmosphere it is absorbed with the production of ions and electrons. These particles diffuse but combine to only a slight extent. The ions drift along the magnetic field of the earth and concentrate in the polar regions. In lower levels there they recombine and the energy of combination appears in the auroral light.

From observations made in Maine, August, 1927, the power of the auroral light then seen is calculated to have been Io 12 ergs/sec. This agrees sufficiently well with the results of another computat ion based on the rate of flow of ultra-violet light to the earth. The author wisely remarks " B u t here I must stop, par t ly to avoid being too rash, but mainly to admit tha t my contemplation of the aurora has been too limited to give that steadying of ideas which comes only from experimentat ion." G . F . S .

The Application of Electrical Resistance Measurements to the Study of the Atmospheric Corrosion of Metals. J. C. HUDSON. (Proc. Phys. Soc., London, April I5, I928. ) The effect of atmospheric corrosion upon metals can be traced by a s tudy of the weight of the specimen as time goes on. Vernon has done this " an d the accuracy obtainable is well demonstrated by the fact tha t he was able to follow the development of tarnish films on lead and aluminium in cases where the final weight increment, after 25 days ' exposure, was as low as o.28 milligrammes." Much labor is, however, necessary especially when the specimen is exposed in the open where the products of chemical action may be carried away by rain or otherwise lost. When, therefore, the Atmospheric Corrosion Committee of the British Non-Ferrous Metals Research