Should the dried stem of a tree, of considerable length, be laid hollow, supported at each end, the outside layer being stretched almost to breaking by the longitudinal contraction being greatest in the outermost part, a very small weight, aided by a slight jerk or concussion, may be sufficient to burst the outside layer on the lower side, the outside layers on the upper side not standing out as a support above, but combining their contractile force with gravity to rend the lower. As the outer layer gives way, the strain is thrown concentrated upon the next outermost, which also gives way, and the beam is broken {224} across in detail. In like manner, when the direct longitudinal strength is tested, the external circles being in greater tension than the internal, the tightest parts of the log will give way in succession, like a rope with strands of different degrees of tightness; yet the lateral adhesion of the layers will have considerable effect in strengthening the mass. The above explains the fallacy of estimating the longitudinal strength of a thick piece of timber from experiments with small shreds; it likewise explains how a large unbuilt mast is so easily sprung; wherefore a beam round as grown will be rendered stronger as a beam by being formed into a hollow cylinder, by boring out the central part; and also how a square log will be strengthened as a beam, by cleaving it up the middle, and placing the two pieces on edge, with their outside or backs together. In the latter case, the middle, by being turned outside, and exposed to the air, will contract more than what it would do shut up and covered by the exterior wood, especially if resinous pine timber, which continues to contract for many years, owing to the resin, when exposed to the air, gradually drying or undergoing some change, by which it is diminished in size, and rendered similar to amber. {225} Consideration of the difference of tension of the concentric layers, from the difference of disposition to contract by drying, modified by the difference of position in which these layers may stand, when supporting weights and bearing strain, with the various qualities of timber of the same kind of tree, from variety, age, soil, climate, or from being taken from near the outside or heart, or butt or top, will, we think, account for the contrariety of results which unphilosophical experiments have afforded. {226} VI.—STEWARDS PLANTER’S GUIDE, AND SIR WALTER SCOTT’S CRITIQUE. We have noticed that a sensation has been produced in a certain quarter, particularly among persons of a certain age, by a publication of Sir Henry Steuart of Allanton, on removing large trees, eked out by a very clever article in the London Quarterly, on Landscape Gardening, ascribed to Sir Walter Scott.