XXVII.] DANTZIC FIR. 319 



true tensile strain could be reached. The results given 

 in Table CXXVI. were, therefore, only obtained after 

 much perseverance and not a few failures. The five 

 pieces subjected to the strain bore respectively 2,240, 

 2,800, 3,220, 3,416, and 4,480 lbs., giving an average of 

 3,231 lbs. as the direct cohesion per square inch. Their 

 specific gravities varied from 512 to 639, the average 

 being 603, which is very near the average specific gravity 

 of the pieces tried for the transverse strength.* 



A great many experiments were made to ascertain 

 the resistance of this wood to a vertical or crushing 

 force, the details of which are given in Tables CXXVI I. 

 to CXXXI, From Table CXXVIII. it may be deduced 

 that the proportion of length to section best adapted for 

 carrying the greatest weights is when the sectional area 

 in inches is to the length in inches as 4 : 5 or v-^L = 

 side of square for the base. This confirms the opinion 

 before given as regards English Oak ; but the rule must 

 rather be considered approximate than absolute, for in 

 the experiments on pieces 3" x 3" (Table CXXIX.), 

 the maximum strength lay in that of 12 inches in 

 length, making the proportion as 9:12 {^/-^ L = sec- 

 tional area). If, however, the area of the base (or the 

 sectional area) be too small for the length of the pillar, 

 it will be liable to bend or buckle up under the load, 

 showing that stiffness is an important element in the con- 

 dition of strength. 



Specimens were also tested measuring 4" x 4" (Table 

 CXXX.), but the results obtained were scarcely so 



* The results of nearly all my experiments on the tensile strength of 

 woods are lower than the values given by Rankine, Tredgold, and some 

 others. But as the specimens 2" x 2" x 30" were each tested by hydraulic 

 machinery most carefully applied, the tabular values here given may, I 

 consider, be depended upon. 



