CONTRIBUTION TO THE STUDYOF THE ELASTIC PROPERTIES OF TIMBERS - The study of the elastic properties of timbers which rest onthe mathematical theory of the elasticity, finaly aims the determinationof such a number of important quantities :1° The coefficient of longitudinal elasticity E1 either in thedirection of the axis of the stem, either in a perpendicular direction,radial E2 or tangential E3;2° The coefficients of POISSON, six in number;3° The coefficient of transversal elasticity G1, G2, G3.These different coefficients are deducted from tests of tension,compression, cleavage or torsion.Their determination has been done in several countriesspecially in England by CARRINGTON; in Germany by STAMERand SIEGLERSCHMIDT and SCHLUTER; in France also test havebeen carried out in the laboratory of the Ecole Nationale desEaux et Forêts at Nancy.After summing up the basis of the theory and exposing, theresearches of the different experimenters, the author give inhis study a comparative table of the whole abtained results.From there he deducts the general characteristics of the differenttimbers, about their elasticity. It is shown that the axialdirection — wood fibre direction — is, as to this property, aquite privileged direction whichever the timber may be. Thatproves the anisotropy of the timber in the mechanical pointof view.With the help of these results, the properties of the timber,about the resistance to tension, compression, and cleavage inthe three principal directions of strength are studied. Lastlypractical conclusions are drawn according to the use of timbersand their physical and mechanical properties. So the author is brought to distinguish three principal classesof timber :1° The very anisotropic timbers; like spruce, firs;2° The timbers of average anisotropy like pines, Douglasfir, birch;3° The slightly anisotropic timbers like ash, maple, beech,oak....