Abstract: The influence of moment of inertia of a torsion bar on oscillation of the torsion pendulum is researched , and a new concept of equivalent moment of inertia of a torsion bar is introduced. The torsion oscillation of a columniform bar is discussed and a mistake on the correlative problem is corrected else.

Key words: torsion pendulum, equivalent moment of inertia, torsion oscillation, spring oscillator, analogical method