7 



OF FOREST-TREES. 239 



and worthy friend Mr. Pepys (late secretary of the admiralty) has given CHAP. IV. 

 a just and profitable account in his Memoirs. 



Here farther, for the uses of timber, I will observe to our reader some 

 other particulars, for direction both of the seller and buyer, apphcable to 

 the several species : and first of the two sorts of laths allowed by sta- 

 tute, one of five, the other of four feet long, because of the different in- 

 tervals of rafters : that of five has one hundred to the bundle ; that of 

 four, one hundred and twenty, and should be in breadth one inch and a 

 half, and half an inch thick : of either of which sorts there are three, viz. 

 heart-oak, sap-laths, and deal-laths, which also differ in price : the 

 heart-oak are fittest to lie under tihng ; the second sort for plastering of 

 side-walls ; and the third for ceilings, because they are straight and even. 



Here we will gratify our curious reader with as curious an account of 

 the comparative strength and fortitude of the several usual sorts of tim- 

 ber, as upon suggestions, previous to this work, it was several times ex- 

 perimented by the lloyal Society, though omitted in the first impres- 

 sion, because the trials were not complete as they now thus stand in 

 our register ^ 



c The most accurate experiments upon the comparative strength of different kinds of 

 wood are given by P. Van Musschenbroek, in a work entitled, " Physicae Experimentales et 

 Geometricae Dissertationes." Mr. Emmerson, in his " Principles of Mechanics," is the 

 latest author upon the subject that I know of. " A piece of good Oak, an inch square, 

 ''and a yard long, suppoi'ted on both ends, will bear in the middle, for a very little time, 

 " about three hundred and thirty pounds avoirdupois. This is at a medium ; for there 

 " are some pieces that will carry something more, and others not so much. But such a 

 " piece of wood should not, in practice, be trusted for any length of time, with above a 

 " third or fourth part of that weight. For, since this is the extreme weight which the best 

 " wood will bear, that of a worse sort must break with it. For I have found, by expe- 

 " rience, that there is a great deal of difference in strength, in different pieces of the very 

 " same tree ; some pieces I have found that would not bear half the weight others would 

 " do. The wood of the boughs and branches ?s far weaker than that of the body : the 

 " wood of the great limbs is stronger than that of the small ones ; and the wood in the 

 *' heart of a sound tree is strongest of all. I have also found, by experience, that a piece 

 " of timber that has borne a great weight for a small time, has broke with a far less weight 

 " when left upon it for a far longer time. Wood is likewise weaker when it is green, and 

 " strongest when thoroughly dried. If Wood happens to be sappy, it will be weaker upon 

 " that account ; and will likewise decay sooner. Knots in wood weaken it very much ; 



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