[12] See Eddington, Space, Time and Gravitation, p. 162ff.
[13] “Isotropy” means being similar in all directions—e.g., that a foot rule is as long when it points north as when it points east.
[14] Mathematical Theory of Relativity, p. 238.
[15] Mathematical Theory of Relativity, pp. 37-38. Italics in the original.
[16] For the definition of “structure,” see the present author’s Introduction to Mathematical Philosophy.
Transcriber’s Notes:
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The illustrations have been moved so that they do not break up paragraphs and so that they are next to the text they illustrate.
Typographical and punctuation errors have been silently corrected.