According to Laplace, propagation of sound wave in air or gas is not in isothermal process as Newton assumed but it is an adiabatic process. The thermal conductivity of air is so small and the movement of compression and rarefaction in the air is so rapid that heat flows neither out of system nor into system, as a result, the change in volume and pressure of air are adiabatic gas equation is:
Where Cp and Cv at pressure and vol. constant sp. heat capacity.
Diff. we get,
This is good agreement with experimental value. Hence Laplace was able to correct Newton’s formula for velocity of sound in air by considering the propagation of sound in air gas an adiabatic process rather than isothermal.