HOW FAILURE UNDER STRESS OCCURS IN TIMBER. A425 
ASH. 
Greatest dimension tangential :— 
A.— Beam on Radial Face. igen ee nm Tangentral 
ace. 
No. | Span. | =e 
Breadth.| Depth. EK, Breadth. | Depth. | E 
B. 
33 36 1°65 3-625 565 3°625 1°65 628 1-11 
31 36 1°65 3°63 736 3°63 1°65 868 1:18 
Mean 1:145 
Greatest dimension radial :— 4 
12 36 3°55 1:87 948 1:87 3°55 894 “945 
15 36 3°6 1:65 961 1°65 3'6 842 875 
Mean ‘91 
Box. 
Greatest dimension tangential :-— 
oleae 208 | 630 | 208 | 11s | 915 || 145 
| i bose be ro7 | 2-00 725 || 2-00 | 107 | 875 || 1-21 
Mean 1:33 
Greatest dimension radial :— 
2 | 36 | 2-65 | 1-16 808 | 116 2-65 | 604 15 
10, 96 | 939) | ihre 930 | 114 232 | 782 84 
Mean “795 
In the Ash and Box experiments, whether By is greater or less than 1 depends 
Ky 
mainly on whether the broad face of the beam is vertical or horizontal; but, making 
allowance for this, there still remains an advantage in stiffness in favour of laying the 
tangential side horizontal, of about 6 or 7 per cent. 
Two conclusions may be drawn from these results :— 
(a) In each case an advantage, though it may be slight, exists in placing a timber 
beam on a tangential face, due probably to the medullary rays being now vertical, and 
therefore not affecting the stiffness. 
(b) For beams of given proportions of section, say 2 to 1, the effect of placing the 
beam on a broad or narrow face, and using the ordinary formula to make them 
comparable, seems to be decidedly in favour of placing them on the broad side. The 
advantage ranges from 3 per cent. in Oak, 9 per cent. in Ash, to 20 per cent. in Box. 
Evidently the explanation of this lies in the anti-clastic curvature of the beams. In 
addition to the bending which takes place in the vertical plane parallel to the axis of 
TRANS. ROY. SOC. EDIN., VOL. XLVIII., PART II. (NO. 21). 64 
