IN the mathematical development of the problem of radio propagation over plane earth, Sommerfeld1 expressed his solution in the form of three terms, one of which he identified with the surface wave of Zenneck2. Curves calculated from Sommerfeld's formula have been given by Rolf3. Weyl4, approaching the problem in a different manner, obtained a solution which did not explicitly contain this term. A formula given by Norton5 gives values agreeing with Weyl. It appears that Weyl was of the opinion that his result was numerically equivalent to that of Sommerfeld. The purpose of this letter is to point out that this is not true, that the evaluation of Sommerfeld's formula by Rolf differs from the formulæ of Weyl and Norton by exactly the surface wave component, and to give the results of a recent experiment showing the Weyl-Norton values to be the correct ones, which raises a question as to whether surface waves do or do not physically exist.
A. Sommerfeld, Ann. Phys., 4, 28 665 (1909); Jahrb. drahtl. t.u.t., 4, 157 (1911).
J. Zenneck, Ann. Phys., 4, 23, 846 (1907).
B. Rolf, Proc. Inst. Rod. Eng., 18, 391 (1930).
H. Weyl, Ann. Phys., 4, 60 481 (1919).
K. A. Norton, NATURE, 135, 954 (1935).
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