i>:)4 Double Cross-Grain 



the tree a uniform left-handed or right-handed bias in inclination would 

 be given to the grain as a whole. In no case was there any appreciable 

 inclination between the radial board and the axis of the trunk and in 

 any case provided such inclination was not excessive, the comparative 

 value of the curves would not be influenced since each stick would be 

 equally affected. 



The sticks of the transverse series were subject to a similar type of 

 bias which was, however, of a two-fold origin; first to the possibility of 

 the disc not being truly at right angles to the longitudinal axis and 

 secondly to the sides of the sticks not being accurately perpendicular to 

 the transverse surface. 



The errors due to the first cause were considered to be negligible, 

 since, as far as could be judged, a disc was never inclined at more than 

 about five degrees to the transverse. The inclination between the sides 

 of the different sticks of a transverse series varied within a range of three 

 degrees at an outside estimation. 



As in the longitudinal series errors due to these causes will not affect 

 the comparative value of the curves so far as changes in inclination of 

 the grain are concerned and need only be borne in mind when comparing 

 the inclination of the grain at different points. 



As to the sense in which various terms are used the words " Period 

 length," "Amplitude"' and "Phase" are employed with meanings 

 analogous to those they possess when used in Physics for the description 

 of wave motion. 



The period length is the radial distance between the two maximum 

 inclinations which delimited the period. Amplitude is the angle included 

 between a maximum right-handed and left-handed inclination of the 

 grain. As each period comprises a right-handed or left-handed swing 

 of the grain which are only rarely of equal amount, the average of the 

 two swings is taken as the amplitude of the period. It was on this basis 

 that the ratio of period length to amplitude was worked out. 



SHOREA ROBUST A. 



The data regarding the width of the growth-rings and the inclination 

 of the grain at the various rings, from which the two series of curves 

 (Figs. 3 and 4) were constructed are tabulated for the sticks of the trans- 

 verse and longitudinal series in Tables I and II respectively. 



Although in both series the rings were counted from the centre, the 

 numbering of the rings in the two series does not correspond, there being 

 fewer rings in the longitudinal series. This discrepancy is due to two 



