Book excerpt: The study is one of a series undertaken as part of a continuing investigation of the properties of tropical woods. In this study, panels representing 27 tropical American hardwoods and three control species, white oak, Central American mahogany, and teak, were exposed to the weather for 18 months on the roof of the Yale Forestry School building at New Haven, Connecticut. The species tested were selected to represent a wide range of both density and tangential shrinkage. Quite often wood which is exposed to the weather is painted. Therefore, a set of matched specimens which had been painted on the weather surface was exposed with the unpainted panels. In so far as possible heatwood was used in all specimens. The period of exposure was from late November 1948 through May 1950. The weathering characteristics of a species demonstrate its ability to resist many forms of deterioration. (Author).