A steam engine is a device by means of which heat is transfor­med into work. Work may be defined as the result produced by a force acting through space, and is common-ly measured in fo­ot-pounds; a foot-pound represents the work done in raising 1 pound 1 foot in height. The rate of doing work is called power. It has been found by exper-iment that there is a definite relati­on between heat and work, in the ratio of 1 thermal unit to 778 foot-pounds of work. The number 778 is commonly called the heat equiv-alent of work or the mechanical equivalent of heat.