Abstract
IN connexion with Prof. Størmer's interesting letter on this subject in NATURE of Nov. 3, it may be of interest to inquire whether by purely terrestrial agencies such long temporal retardations of short wave signals may be explained. Abnormally long retardations of such signals, returned from the upper atmosphere, were first announced by A. H. Taylor and L. C. Young (Proc. Inst. Radio Eng., vol. 16, May 1928), who, in experiments carried out between Rocky Point and Washington, obtained retardations corresponding to a distance of transit of 2900 km. to 10,000 km., although the great circle distance between the stations was only 420 km. In discussing these experiments in a paper at the Brussels meeting of the Union Radio Scientifique Internationale in September last, it was pointed out that wireless waves, meeting the ionised layer at vertical incidence, would travel upwards until they were ‘reflected’ at a point where the group velocity was reduced to zero, and that if the ionisation gradient in this region was not large, the waves might be appreciably retarded before and after reaching the critical value of ionisation. Put quantitatively, the retardation of any signal sent up from the ground and received there again is (where c is the velocity of radiation in vacuo, ds an element of path, and µ. the refractive index), and this quantity may greatly exceed if µ is very small for an appreciable part of the path.
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APPLETON, E. [Letters to Editor]. Nature 122, 879 (1928). https://doi.org/10.1038/122879a0
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DOI: https://doi.org/10.1038/122879a0
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