ABSTRACT
The power that a steam engine could exert, i.e. the horse-power or rate of doing work, was a practical consideration with every possible purchaser and such a method of rating engines grew up as early as 1785. The output of energy in an engine was seen to depend on the limits of temperature between which the engine works, and to increase the energy, the limit must be extended; hence the necessity of higher and higher pressures. The position of the steam engine has not been materially altered by the advent of the steam turbine. At the end of the eighteenth century the accepted view about heat was the caloric or material theory. Caloric was supposed to be a “subtle elastic fluid which permeated the pores of bodies and filled the interstices between the molecules of matter.
