  We report measurements of the critical exponents of the classical
three-dimensional Heisenberg model on simple cubic lattices of size $L^3$ with
$L$ = 12, 16, 20, 24, 32, 40, and 48. The data was obtained from a few long
single-cluster Monte Carlo simulations near the phase transition. We compute
high precision estimates of the critical coupling $K_c$, Binder's parameter
$U^* and the critical exponents $\nu,\beta / \nu, \eta$, and $\alpha / \nu$,
using extensively histogram reweighting and optimization techniques that allow
us to keep control over the statistical errors. Measurements of the
autocorrelation time show the expected reduction of critical slowing down at
the phase transition as compared to local update algorithms. This allows
simulations on significantly larger lattices than in previous studies and
consequently a better control over systematic errors in finite-size scaling
analyses.
