All the results were now tabulated and reported to the students on mimeographed sheets in the form shown in the table. These results were then plotted by the students with respect to position of the test specimens in the plank, to exhibit more clearly the variations due to difference in the structure of the wood formed at different periods of the tree's growth (Fig. 15). On the whole these results are consistent, though but a single specimen represents each actual condition, and illustrate quite forcibly some of the variables in the strength of timber. There is another variable, however, which must be recognized before results like these can be used intelligently in designing, and that is the "time effect." The strength of timber for permanent loads is only about fifty to sixty per cent. of these values; or, in other words, the ultimate strength of timber for a permanent load is the same as the elastic strated to for a bomme bal This may be wice extent a text like that of the three cak specThere shown in Fig with Larns in Fig. 14. This, of mozne, vazort he varied at before the class on aecount of the bing time regained at if ery aired in offert and plan and kept going during the week, will arcase nach interest and densit. The mderlying notive in all this testing in wow tin with the class 824 Normal 227 wer FIG. 14. room work should be to arouse the student, to make him ee facts and relations clearly, to make him think. To this end also some simple problems in designing may be introduced from time to time, illustrating the practical use to be made of these test results. For instance, following the timber tests, the design of a low railroad trestle proves both interesting and instructive, requir |