Newton assumed sound propagation is isothermal: $v = \sqrt{P/\rho}$, which gave 280 m/s (incorrect). Laplace corrected this: sound propagation is adiabatic because compressions/rarefactions are too fast for heat exchange. $v = \sqrt{\gamma P/\rho} = \sqrt{\gamma RT/M}$. For air at 20 degrees C: $v \approx 343$ m/s. Temperature dependence: $v \propto \sqrt{T}$. Humidity increases speed (moist air has lower effective molar mass). Pressure change at constant temperature has no effect (since $P/\rho = RT/M$ is constant).