248 Double Cross-Grain 



forms of the series of fractures obtained by the radial fracture of a series 

 of sticks sawn transversely from the radial board adjacent to the one 

 which supplied the data for the longitudinal series of curves (photo- 

 graph 1). 



It has already been pointed out that in a radial plane the positions 

 of the periods are not rigidly fixed with reference to the growth-rings, 

 and that there may be a considerable interval between the different 

 transverse levels as to the time of the inception of a period. There is 

 still a further inconstancy discoverable in the series. The actual inclination 

 of the grain at different transverse levels in the same radial plane is not 

 uniform at any ring, but varies in a very indefined manner from stick 

 to stick, and coupled with this is a corresponding variation in the rate 

 of change in the inclination of the grain. 



The following example will serve to illustrate these variations. 

 Between the 40th and 41st rings, Fig. 4. there is a maximum right-handed 

 phase in all the sticks of the longitudinal series. Now the inclination of 

 the grain at this point varies in a very irregular manner between 9 and 

 16 degrees, a range of variation far in excess of the probable error in 

 measurement which was estimated at one degree. 



Between the 42nd and 43rd ring the grain has become vertical, 

 hence the rate of change in inclination of the grain could not have been 

 uniform at the different transverse levels. 



From the 43rd ring onwards the direction of the change in the 

 inclination of the grain is still the same and reaches a maximum left- 

 handed inclination of five degrees between the 43rd and 44th rings at 

 the level of stick 1, after which the change in inclination of the gram 

 becomes right-handed. 



At other transverse levels, however, the grain is becoming still more 

 left-handed, reaching a maximum of 13 degrees at the 45th ring in the 

 13th stick and of 17 degrees at the 48th ring of the 18th stick. 



If the periodic changes in the inclination of the grain were simultaneous 

 with periods of growth and the amplitude of the periods was constant, 

 the grain would consist of a series of alternate left-handed and right- 

 handed spirals (double spiral grain), but on account of the irregularities 

 described above, the grain is composed of a series of superposed serpen- 

 tine curves grading one into the other which, for short lengths of the 

 trunk at least, tend to be arranged in the form of a double spiral. 



The transverse series of curves (Fig. 3) shows a complete parallel 

 correspondence in all points with the longitudinal series. At a transverse 

 level the periodic changes in the inclination of the grain are continuous 



