and Poissoris Ratio for Spruce. 



877 



the points lie sufficiently near to the straight lines except 

 those corresponding with a sy and a y2l hut it should be 

 observed that these values were obtained from pieces which 

 were cut with their thicknesses in the direction XOX, that 

 is in the direction of the widths of the rings. The thicknesses 

 of the pieces were thus often comparable with widths of the 

 rings, so that the ratio of Autumn wood to Spring wood 

 usually varied from piece to piece. 



Fi< 



Relation bt-taeen 



5tj 1 



.L Sx_ Sx_ a Sm _ . ._ 



100 







10v 













• s 



BO 







2 sc 













s / 





• \^< 



t 



to 











/* 





60 



^ 



\ 



J.N 60 















+ 



*■* 





^0 









r *y 









oTF 



^>- 



"ll 



v 



V 



y 







• 





£0 











/ 



















&fr a 



/ 



^-^N., 



.,"?s. 









Deni,t 3 d™ (fcjwwfh) 



Jjensifj dry (fcspercu Pi") 



It is significant to note in connexion with these curves 

 that they all obey the symmetrical relations of n, an seolo- 

 tropic body having three planes of elastic symmetry *. 

 These relations are : 



v z _ 



°ZV 



E*' 



&ZX 



El' 





E/ 



'y ^>z -^z E. r Ea; 



From an examination of the curves it will be found that 

 approximately these equalities are equal respectively to 



700 Sy, 700 S* and ^, 



The degree of accuracy aimed at throughout all the 

 experiments was an error of less than one per cent. It 

 should, however, be noted that in all cases except where the 

 length of the pieces was in the direction of the grain, 

 incipient creeping was evidenced at comparatively small 



* Love's Elasticity, Art. 73. 



