A mass '$\mathrm{m}_1' is suspended from a spring of negligible mass. A spring is pulled slightly in downward direction and released, mass performs S.H.M. of period '\mathrm{T}_1'. If the mass is increased by '\mathrm{m}_2', the time period becomes '\mathrm{T}_2'. The ratio \frac{\mathrm{m}_2}{\mathrm{~m}_1}$ is