In it he showed that the wide pendulum swings of verge clocks caused them to be inaccurate, because the period of oscillation of the pendulum was not isochronous but varied to a small degree due to circular error with changes in the amplitude of the pendulums swing, which occurred with unavoidable changes in drive force.
22.
So we can see that the effective mass of the spring added to the mass of the load gives us the " effective total mass " of the system that must be used in the standard formula 2 \ pi \ left ( \ frac { m } { k } \ right ) ^ { 1 / 2 } to determine the period of oscillation.
