294 ^- ^- Spaiilding 



substituted. For this, it is evident, the empirical law, according to 

 which the maximum amount of work is given, must be known. 



It is indeed just this method, the practicability of whose appli- 

 cation to segmentation furnishes the experimental data or values 

 for substitution in, and, therefore, for the computation, in accord- 

 ance with, our epitomizing formula, of the energy-transfer involved 

 in that event. The result is that this event, even with all its spe- 

 cific qualitative characteristics as a vital phenomenon, is brought 

 under the Four Laws. 



Now to determine W, it is necessary to knovv the conditions under 

 which the change in state will take place reversibly, /. e.^ to know 

 the value of the intensities or resultant intensity, within the system, 

 that must be compensated by an externally applied intensity in 

 order to produce equilibrium and thereby reversibility. Then 

 the product of this value, into the value of the change in the cor- 

 responding capacity factor, gives the value of the maximum amount 

 of work produced by the change in state under consideration. 



But, furthermore, if, during the occurrence of the change, the 

 intensity-factor also varies, as does, for example, the pressure of 

 a gas in expanding, then ^is to be calculated from the correspond- 

 ing integral, in this case, 



-I 



W=\ pdv 



To evaluate this, and corresponding integrals, the law of the varia- 

 tion of that intensity with the capacity-factor, that is, the func- 

 tional relation between the intensity and extensity, during the 

 change, must be known. This can be found only empirically and 

 yet also, I think, only in accordance with and as implying the gen- 

 eral principles expounded. 



On the other hand, U2 — Ui, is, if possible, to be determined by 

 direct calorimetric or some other mode of measurement in calorie- 

 equivalence units. But in some cases it is impossible to keep the 

 two quantities W and U^ — Ui distinct, and the measurements 

 made (by compensation methods) furnish the basis for the com- 

 putation only of the energy-transfer, E, as equal to W-\r{U.^ — U^\ 

 that which is determined is, therefore, the excess of the maximum 



