inflowing of waves on the sea beach, he can verify this for himself. Consequently when the more rapid etheric waves overtake the slower ones, they combine to form a larger wave, and it is at these points that the zones of sensation occur.

If the reader will draw a diagram of two waved lines traveling along the same horizontal line and so proportioned that the crest of each of the large waves coincides with the crest of every third wave of the small ones, he will see what I mean: and if he then recollects that the fall in the larger waves neutralizes the rise in the smaller ones, and that because this double series starts from the interior of the body the surface of the body comes at just one of these neutralized points, he will see why sensation is neutralized there; and he will also see why the succeeding zones of sensation are double the distance from each other that the first one is from the surface of the body: it is simply because the surface of the body cuts the first long wave exactly in the middle, and therefore only half that wave occurs outside the body. This is the explanation given by De Rochas, and it affords another example of that principle of mathematical sequence of which I have spoken. It would appear tha