Page:Elementary Principles in Statistical Mechanics (1902).djvu/83

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The multiple integral which may also be written  and which, when taken within any given limits of phase, has been shown to have a value independent of the coördinates employed, expresses what we have called an extension-in-phase. In like manner we may say that the multiple integral (148) expresses an extension-in-configuration, and that the multiple integrals (149) and (150) express an extension-in-velocity. We have called which is equivalent to  an element of extension-in-phase. We may call an element of extension-in-configuration, and