"I. Deductions from the principle of the equivalence of heat and work. We shall forbear entering... on the nature of the motion... supposed... within a body, and shall assume... a motion of the particles... and that heat is the measure of their '. Or... more generally... lay down one maxim... founded on the above assumption: — In all cases where work is produced by heat, a quantity of heat proportional to the work done is consumed; and inversely, by the expenditure of a like quantity of work, the same amount of heat may be produced."