The simple pendulum is made with a hollow sphere that has a hole at the bottom through which mercury that is filled in the sphere flows out gradually as the pendulum oscillates.
The time period of a simple pendulum made with a mass m attached to a string of length L is given by `T ~~ 2*pi*sqrt(L/g)` . It is noticed that the mass m is not present in the relation for time period. It has been assumed that the mass of the mercury flowing out is not significant enough to move the center of mass of the sphere attached to the string on which the sphere is suspended.
Here, length of the pendulum remains constant and only the mass of the sphere gradually decreases. As a result there is no change in the time period of the pendulum.
The time period of the simple pendulum is not affected by the mercury flowing out.
it increases then decreases and finally becomes constant