THE OAK. 11 



at the height of its own diameter is generally reduced 

 by an elegant curve, concave to the eye, to a diameter 

 less by at least one-third, and sometimes to half its 

 original base. From thence its sides, tapering more gra- 

 dually, assume a perpendicular direction, and for some 

 height form a cylinder. After that a greater circumference 

 becomes necessary for the insertion and establishment of 

 the principal boughs, which produce a swelling of its 

 diameter. Hence may be deduced an idea of what the 

 proper shape of a column of the greatest stability ought to 

 be to resist the action of external violence, when the 

 quantity of matter is given whereof it is to be composed. 

 Upon this model, therefore, on the 25th of August, 1759, 

 Mr. Smeaton completed his lighthouse, being the third 

 structure of the kind which had been raised on the dan- 

 gerous rock from which it derives its name." How wisely 

 he acted in choosing Nature for his instructress may be 

 inferred from the fact that it has now stood upwards of a 

 hundred years, without requiring any essential repairs. 



The trunk of the Oak, thus perfectly adapted as it is by 

 its form to resist the most violent action of the wind, 

 derives additional strength from the slow rate of growth 

 of its timber. A very small quantity of woody fibre is 

 deposited every year, but it is proportionately dense and 

 solid, and the concentric annual layers are very firmly 

 united. Hence it is admirably prepared to withstand 

 lateral violence, as well as to support its enormous super- 

 incumbent weight of branches ; while its tap-root, de- 

 scending perpendicularly to a great depth, and its tortuous 

 underground arms proceeding horizontally at a greater 

 depth beneath the surface than those of most other trees, 

 are equally efficacious in resisting any upheaving force to 

 which its spreading and abundant foliage might otherwise 

 render it peculiarly liable. 



Were it not for this wonderfully massive structure of 

 the main trunk, the Oak would be unable to bear up the 

 ponderous weight of its enormous limbs, which, each a 



