Introduction

Abstract

Heat was considered to be an invisible fluid, called caloric until late into the eighteenth century. It was believed that a hot piece of material contained more caloric than a cold one and that an object would become warmer by transferring caloric into it. At the mid 1800s, Mayer, Helmholtz, and Joule discovered independently that heat is simply a form of energy. They realized that when two bodies have different temperatures, thermal energy is transferred from the hotter to the colder one when brought into contact. Count Rumford discovered, by observing the boring of cannons, that mechanical work, expended in the boring process, was responsible for the creation of heat. He concluded that mechanical energy could be transformed into heat energy. This observation lead eventually to the concept of a mechanical heat equivalent.