An ionospheric investigation concerning the Lorentz polarization‐correction

Some years ago considerable discussion took place concerning the relation between the constitution of the ionosphere and its refractive index for radio waves. The question at issue was whether the force per unit‐charge exerted by the electric field of a radio wave upon an elementary charged particle In the ionosphere should be taken simply as the Maxwellian electric intensity E (the Sellmeyer theory), or whether there should be added a contribution (4π/3)P (the Lorentz theory). The discussion culminated in a theoretical treatment of the subject by Darwin which seemed to point to the conclusion that the Sellmeyer theory should hold good in the ionosphere at radio frequencies. For reflection from the ionosphere of radio waves of frequency less than the gyromagnetic frequency there is in middle latitudes a clear‐cut distinction in the behavior of the extraordinary wave according to the two theories. Over the past year a large number of records showing magneto‐ionic splitting of ionospheric echoes at these wave‐frequencies have been obtained. We are led to believe that it is impossible to interpret these observations in terms of the Sellmeyer theory but that no objection exists to their interpretation in terms of the Lorentz theory. On the basis of the Lorentz theory the observations indicate that there is in the E ‐region of the ionosphere a level of maximum atomic and molecular ion‐density somewhat below the level of maximum electron‐density.