If the conductor consists of a coil of wire the ends of which are connected with a suitable galvanometer, the integral electromotive force due to a sudden increase or decrease of the induction through the coil displaces in the circuit a quantity of electricity Q=SBns R, where SB is the increment or **decrement** of induction per square centimetre, s is the area of the coil, n the number of turns of wire, and R the resistance of the circuit.

The increment of this area (or the **decrement** of the negative area E--04) at constant temperature represents the external work obtainable from the substance in isothermal expansion, in the same way that the **decrement** of the intrinsic energy represents the work done in adiabatic expansion.

These functions do not, however, represent energy existing in the substance, like the intrinsic energy; but the increment of 90 represents heat supplied to, and the **decrement** of (E-04) represents work obtainable from, the substance when the temperature is kept constant.

Lord Kelvin has applied the principles of Thermodynamics to determine the thermal effects of increasing or diminishing the area of the free surface of a liquid, and has shown that in order to keep the temperature constant while the area of the surface increases by unity, an amount of heat must be supplied 275 to the liquid which is dynamically equivalent to the product of the absolute temperature into the **decrement** of the surface-tension per degree of temperature.