Published online by Cambridge University Press: 10 April 2014
We show that the weak limit of the maximal measures for any degenerating sequence of rational maps on the Riemann sphere   ${\hat{{\mathbb{C}}}} $  must be a countable sum of atoms. For a one-parameter family
 ${\hat{{\mathbb{C}}}} $  must be a countable sum of atoms. For a one-parameter family   $f_t$  of rational maps, we refine this result by showing that the measures of maximal entropy have a unique limit on
 $f_t$  of rational maps, we refine this result by showing that the measures of maximal entropy have a unique limit on   $\hat{{\mathbb{C}}}$  as the family degenerates. The family
 $\hat{{\mathbb{C}}}$  as the family degenerates. The family   $f_t$  may be viewed as a single rational function on the Berkovich projective line
 $f_t$  may be viewed as a single rational function on the Berkovich projective line   $\mathbf{P}^1_{\mathbb{L}}$  over the completion of the field of formal Puiseux series in
 $\mathbf{P}^1_{\mathbb{L}}$  over the completion of the field of formal Puiseux series in   $t$ , and the limiting measure on
 $t$ , and the limiting measure on   $\hat{{\mathbb{C}}}$  is the ‘residual measure’ associated with the equilibrium measure on
 $\hat{{\mathbb{C}}}$  is the ‘residual measure’ associated with the equilibrium measure on   $\mathbf{P}^1_{\mathbb{L}}$ . For the proof, we introduce a new technique for quantizing measures on the Berkovich projective line and demonstrate the uniqueness of solutions to a quantized version of the pullback formula for the equilibrium measure on
 $\mathbf{P}^1_{\mathbb{L}}$ . For the proof, we introduce a new technique for quantizing measures on the Berkovich projective line and demonstrate the uniqueness of solutions to a quantized version of the pullback formula for the equilibrium measure on   $\mathbf{P}^1_{\mathbb{L}}$ .
 $\mathbf{P}^1_{\mathbb{L}}$ .