In a temperature-pressure ($$T$$-$$\mathit{\Pi}$$ diagram, an adiabatic curve $$\sim V^{1-\frac{1}{\gamma}}$$ was plotted. The product $$T_1 \, {\mathit{\Pi}_1}^{\frac{1}{\gamma}-1}$$ BEFORE the adiabatic process is equal to the product $$T_2 \, {\mathit{\Pi}_2}^{\frac{1}{\gamma}-1}$$ AFTER the adiabatic process.