Analysis of the Ionosphere

HE very title of this article embodies the assumption that in the upper reaches of the atmosphere there is a host of ions. By " u p p e r reaches" here is meant, a region of the atmosphere so high that no man ever entered it, nor even a balloon with instruments. The ions therefore have never been observed by normal electrical means. They are postulated as the explanation of two things mainly: the echoing of radio signals from the sky, and that small portion of the earth's magnetic field which fluctuates with time. The idea that these things require explanation, and the idea of the sort of postulate that is required to explain them, can both be followed back for m a n y years. W h a t was lacking in the early days was the notion of mobile electrified particles, that is to say, of " i o n s , " in the air. T h a t notion did not even exist, when in the eighties Balfour Stewart desired to imagine a conducting layer in the upper air for explaining magnetic fluctuations. It was only just being formed, when in 1902 Kennelly and Heaviside independently desired to imagine a conducting layer in the upper air for explaining why wireless signals can travel around the world. To speak of a conducting layer in the * This paper, in abbreviated form, appears in the current issue of Electrical Engineering.