MOMENT

(Lat.movere, to move.) A small but indefinite period of time. Sometimes the word instant is used synonymously with moment. Moment, Momentum. These terms have been used by writers on mechanics, in various senses. Galileo, in his Dialogues, uses the phrase momentum of a poioer, or of a weight, applied to a machine, to denote the action, energy, or impetus of the power to move the machine; so that an equilibrium subsists between two powers when their moments to move the macliine in opposite directions are equal: and he shows that the m.omcntum is f»roportional to the power multiplied into the virtual veocitv. This notion of momentum was also adopted by Wallis, in his j\/ •■- dm,; in which d m is the element of the ma , and r its distance from the axis. See Rotation. [s. 773]