Page:Elementary Principles in Statistical Mechanics (1902).djvu/108

84 or Setting $$u=1$$ in this equation, we get  and substituting this value, we have  or

If we differentiate equation (250) with respect to $$a$$ (which may represent any of the external coördinates), and write $$A$$ for the force $$-\frac{d\epsilon}{dA}$$, we get or  Setting $$u=1$$ in this equation, we get  Substituting this value, we have  or

Repeated applications of the principles expressed by equations (252) and (255) are perhaps best made in the particular cases. Yet we may write (252) in this form