If the cluster formation rate is constant and the disruption time of clusters depends on their initial mass as t _ { dis } = t _ { 4 } \times ( M _ { cl } / 10 ^ { 4 } M _ { \odot } ) ^ { \gamma } , the values of t _ { 4 } and \gamma can be derived in a very simple way from the age and mass histograms of large homogeneous samples of clusters with reliable age and/or mass determinations .
We demonstrate the method and derive the values of t _ { 4 } and \gamma from cluster samples in selected fields of four galaxies : M51 , M33 , SMC and the solar neighbourhood .
The values of \gamma are the same within their uncertainties in the four galaxies with < \gamma > = 0.62 \pm 0.06 .
However , the disruption time t _ { 4 } of clusters of 10 ^ { 4 } ~ { } M _ { \odot } is very different in the different locations .
It is shortest in the inner region of M51 ( t _ { 4 } = 4 \times 10 ^ { 7 } yrs ) and highest in the SMC ( t _ { 4 } = 4 \times 10 ^ { 9 } yrs ) .