438 MR.ANGUS R. FULTON ON EXPERIMENTS TO SHOW 
3. Rectangular beams of unequal sides are stiffer but not materially stronger when 
laid on the broad side of the section. 
4. When at the fracture point a rectangular stress diagram very slightly modified 
accurately represents the distribution of stress in a timber beam. 
5. For timber struts where the ratio of length to smaller dimension of cross-section 
does not exceed 12 to 15, a modification of the usual column formula is necessary. 
6. Fracture by shearing does not take place in timber beams of the commoner 
woods supported at two ends and loaded in the middle where the ratio of span to depth 
of beam exceeds, say, 7. 
The microscopic sections, micro-photographs, and photographs were prepared by 
Mr Gerorce West, University College, Dundee, to whom the author is greatly 
indebted for his assistance. The cost of these photographs was defrayed by a 
grant from the Carnegie Trust, which is here gratefully acknowledged. Thanks 
are also due to several of the students in University College, Dundee, especially 
Mr J. A. Hoop, for aid given in the experimental work, and to the Council of 
University College, for their very generous assistance. 
EXPLANATION OF PLATES. 
Puate I. 
Fig. 2. A block of Oak cut with the broad longitudinal sides tangential, and arranged so as to exhibit 
one of these sides. x {un.s. The fibres are displaced tangentially, local buckling taking place in two 
planes, more or less equally inclined to the direction of pressure. 
Fig. 3. A block of Ash cut with the broad longitudinal sides tangential, and arranged so as to exhibit 
one of these sides. x Zn.s. It has been fractured by crushing in a longitudinal direction, and the 
buckling has taken place in a single plane. This is the general case. 
Fig. 4. A block of Ash with the broad longitudinal sides radial, and arranged so as to exhibit one 
of these sides. x {n.s. The illustration shows that there is no movement in a radial direction. 
Fig. 5. A block of Boxwood cut with its broad longitudinal sides tangential, and arranged to show one 
of these sides. x {n.s. 
Fig. 6. A block of Boxwood cut with its broad longitudinal sides radial, and arranged to show one 
of these sides. x {%n.s. The stress is longitudinal compression and the displacement is tangential, 
irrespective of the proportions of the cross-section. 
Puate II. 
Fig. 7. Oak wood. A normal radial section, x 176 diams., showing a medullary ray (m) crossing 
wood-fibres (/), wood-parenchyma (p), etc. 
Fig. 8. Oak wood. A normal transverse section at the zone of demarcation between the autumn wood 
of one year and the spring wood of the next, x 240 diams., showing two narrow medullary rays (m), wood- 
fibres (f'), ete. ; 
Fig. 9. Oak wood. A normal transverse section at the line of demarcation between two annual zones 
of growth. x 88 diams. One large tracheide (¢) and a portion of another are shown. The size of this 
tracheide should be compared with that of Box. 
Fig. 10. Oak wood. A normal tangential section, x 240 diams., showing a portion of a broad medullary 
ray (M), narrow rays (m), wood-tibres (7), wood-parenchyma (p), etc. 
