Since the mid 1700's people thought that hot objects contained an abundance of a fluid called caloric.  An object feels hot because of the caloric it holds (much like a sponge feels wet because of the water it holds).  When we bring hot and cold objects together caloric flows between (much like water form the wet to the dry sponge).
 
 
 

Joule showed that the temperature change of water/ beer was related to the amount of mechanical energy put into the system (via falling weights).  He measured the amount of gravitational energy and the change in the waterís temperature very precisely.

He showed that for many different conditions the amount of caloric inputted to the water was proportional to the amount of gravitational energy.  He also looked at chemical and electrical energies
 

Joule showed that the model of calorics was incorrect, that temperature increases were simply due to transfers of energy.