With integers, besides adding and subtracting, it was easy to double and to multiply by 10:
- The change of intrinsic energy E along any path is found by subtracting the work pdv from either of the expressions for dH.
P. 211, Paris, 1869) proposed an equation of the form (p+po)(v - b) =RO, in which the effect of the size of the molecules is represented by subtracting a quantity b, the " covolume," from the volume occupied by the gas, and the effect of the mutual attractions of the molecules is represented by adding a quantity po, the internal pressure, to the external pressure, p. This type of equation, was more fully worked out by van der Waals, who identified the internal pressure, po, with the capillary pressure of Laplace, and assumed that it varied directly as the square of the density, and could be written a/v 2 .
The year of the era, therefore, will be found by subtracting the number of the Olympic year from 776.
Since five Olympic periods have elapsed, the third year of the sixth Olympiad is 5X4+3=23; therefore, subtracting 23 from 776, we have 753, which is the year before Christ to which the foundation of Rome is referred by Varro.