We propose a Log N-Log S distribution of close-by cooling isolated neutron stars as an independent test for models of the thermal evolution of compact objects. We discuss advantages and problems of the method and give some illustrations basing on population synthesis calculations of Log N-Log S for different cooling curves. It is shown that the Log N -- Log S test can be used to reject models of cooling which successfully passed the test confronting data on the temperature - age plot. However, population synthesis models have their own uncertainties which are complementary to the ones of the temperature -- age test, so that for higher efficiency these two approaches should be used together.