till. Thai the strciiL'th ami .stiffness ro also dependent upon ihc pro- 

 portion i>( >nmiii!T In sprint: uiowth ; 



ijth. Tluil irregularity id readings, bolh with the c.TlcnsoiiKtcr and 

 wilh the rule. ate chiefly din> In tin- presence of a knol, or to curly or 

 oblique grain caused hy a knot. 



in, some of t ho Tables give the effect* on ruriotu specimens, of 

 alternately loading them :ind relieving them (Votn their load, :ind from 

 the experiments carried out. up to dale the foil, .win- inferences 

 may (irrliajis lie drawn : 



If the specimen is clisiir, free from knot-, ami .straight in the grain, 

 and it'no interval <'\' re-t, is allowed, then for any given rani,": of loads : 



The total extension is greater. during the first loading ; 

 (6) The extensions due to the successive loadings continually 

 diminish, tending to a minimum limii. sn tl at the co-efficients of elas- 

 ticity increase, and therefore so ,ilsn dm'- !!,. -lilin 



(e) By the successive unlnadin_ ia produced, which con- 



tinually increases, l)iit at a diminishing rate, and which tends to a 

 maximum limit ; 



(a) When lhi> spei -linen is allowed an interval of rot under ihe 

 minimum load, the first total extension, when the loading i> ivsumod, 

 is uivater than at the comme.iiccme.it, but continually diminishes, tend- 

 ing to a minimum limit, which possibly coincides with' the maximum 

 limit, reached previous to the int-rval ol' iv-t. 



So idso, after the inteval of rot, when the first set produced the spe- 

 eimen is from load, is iMv-iter than that previously [irodueed, but gra- 

 dually diminishes, in tln> Miceoodini; releases from load, tending proba- 

 bly to a minimum limit coinciding with the maximum limit reached 

 before the interval of rest. 



These inferences arc also in accord with simihir experiments carried 

 out by Mr. Kerry, li.A.Sc. 



Special attention may be directed to tin: ti-.-t ol' specimen 4, beam XXI. 

 This specimen failed simultaneously at two sections, the wood seem- 

 ing to be very brittle, an I tlie character of the failure pointed to some 

 inherent weakness in the timlx-r itself. After a microscopic examina- 

 tion of the fractured sections, Professor Penhallow described the fractures 

 as li.'ing " very regular anil devoid of any fibrous character, having the 

 ' exact appearance of a piece of glass. The lines of fracture followed 

 " the variations in thickness of structure longitudinally and trans- 

 vci-scly with great reg dariiy. The peculiar brittlcness can only be 

 " referred to some local molecular condition of unknown origin, possibly 

 " to a deficiency in the element of water." 



The simultaneous failure at two sections of spccimans '1 an 1 S from 

 White L'inebaaui XljVIII may probably be referred to a similar cause, 

 and, as Professor Ponhalluw s.iys, a le^uata expla-i itions of such 

 failures are still to be sought. 



In the Tables the extensomcter measurements are given in hundred- 

 thousandths of an inch, and the rule measurements in hundredth.-) of an 

 inch. 



\\iih eacli table a diagrammatic section is also given, showing the 

 part of the stick from which the several specimens have been taken. 



IHAGRAMETIC 



