The text of this paper has been published during the absence of Professor Abbe and the proof read by comparison with two complete manuscript left by the author. All illustrations not absolutely essential to the main topic were necessarily omitted, but Professor Abbe failed to make the corresponding correction in the text. It is impossible to delay the publication. Hence, reference is made in this paper to the following figures which are not reproduced: Nos. 1, 2, 12, 13, 14, 15, 16, 17, 20, 21, 22, 25, 26, 27, 32, 33, 34, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48 53, 54, 57, 58, 59 60, 61, 62, 63, 64, 65, 66, 68, 69, 70, 71, 72, 73, 74, 78, 79, 80, 81, 82.
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