  The Rayleigh-Benard theory by Grossmann and Lohse [J. Fluid Mech. 407, 27
(2000)] is extended towards very large Prandtl numbers Pr. The Nusselt number
Nu is found here to be independent of Pr. However, for fixed Rayleigh numbers
Ra> 10^{10} a maximum around Pr= 2 in the Nu(Pr)-dependence is predicted which
is absent for lower Ra. We moreover offer the full functional dependences of
Nu(Ra,Pr) and Re(Ra,Pr) within this extended theory, rather than only giving
the limiting power laws as done previously. This enables us to more
realistically describe the transitions between the various scaling regimes,
including their widths.
