# What is the difference between the Joule and Joule–Thomson coefficients?

Is there a difference between the Joule coefficient and the Joule–Thomson coefficient? Also, I am having a hard time understanding what they mean.

The Joule coefficient is $$\left(\frac{\partial T}{\partial V}\right)_U$$
Experimentally, Joule attempted to measure this value by expanding gas into an evacuated, insulated container, thus ensuring $$U$$ is constant.
The Joule–Thomson coefficient is $$\left(\frac{\partial T}{\partial P}\right)_H$$