We always suppose these external coördinates to have the same values for all systems of any ensemble. In the case of a canonical distribution, i. e., when the index of probability of phase is a linear function of the energy, it is evident that the values of the external coördinates will affect the distribution, since they affect the energy. In the equation
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(105)
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by which
may be determined, the external coördinates,
,
, etc., contained implicitly in
, as well as
, are to be regarded as constant in the integrations indicated. The equation indicates that
is a function of these constants. If we imagine their values varied, and the ensemble distributed canonically according to their new values, we have by differentiation of the equation
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(106)
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or, multiplying by
, and setting
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(107)
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