TIMHKU PHYSICS SOl'THKKN PINE. 



349 



KRLATION in- 1 STItKXliTH Til \VKKillT. 



The intimate relation of strength and specific weight ha* been well established liy tlio experiments. The :i\ n 

 age results obtained in connection with tint tests themselves were MM follows: 



Since in the determination of the specific gravity above given, wood of the K.-IIIIO per cent of moisture (as i.s (he 

 cane of (he, values of strength) was not always involved, and also since the test pieces, owing to sine and shape, can 

 not perfectly represent the wood of the entire stem, the following results of a special inquiry into tin- weight of the 

 wood represents probably more accurately the weight anil with it the strength-relations of the four species. 



WKIUHT RELATIONS. 

 [Tlu'st! data* refer to the averago specific weight for all the wood of each tree, only tr'jes of approximately the 8ame age being involved.] 



a The values of strength refer to all tests and therefore involve trees of wide range of age and consequently of quality, especially 

 thi-sr <f longleaf, involve much wood of old trees, hence the relation of weight and strength appears less distinct. 



From these results, although slightly at variance, we are justitied in concluding that Cuban and longleaf pine 

 are nearly alike in strength and weight and excel loblolly and shortleaf by about 20 per cent. Of these latter, 

 contrary to common belief, the loblolly is the heavier and stronger. 



The weake.st material would differ from the average material in transverse strength by about 20 per cent and 

 in compression strength by about 30 to 35 per cent, except Cuban pine, for which the difference appears greater 

 in transverse and smaller in compression strength. It must, of course, not be overlooked that these figures are 

 obtained from full-grown trees of the virgin forest, that strength varies with physical conditions of the material 

 and that, therefore, an intelligent inspection of the stick is always necessary before applying the values in practice. 

 They can only represent the average conditions for a large amount of material. 



DISTRIBUTION OF WEItillT AND STRENGTH THROUGHOUT THK TREE. 



In any one tree the wood is lighter and weaker as we pass from the base to the top. This is true of every tree 

 and of all four species. The decrease in weight and strength is most pronounced in the first 20 feet from the stump 

 and grows smaller upward. (See fig. 91.) 



This great difference iu weight and strength between butt and top tinds explanation in the relative width of 

 the summerwood. Since the specific weight of the dark suinmerwood band in each ring is in thrifty growth from 

 .90 to 1.00, while that of the spring wood is only about .40, the relative amount of summerwood furnishes altogether 

 the most delicate and accurate measure of these differences of weight as well as strength, and hence is the surest 

 criterion for ocular inspection of quality, especially since this relation is free from the disturbing influence of both 

 resin and moisture contents of the wood, so conspicuous in weight determinations. 



The following figures show the distribution of the summcrwood in a single.tree of longleaf pine, as an example 

 of this relation : 



