MECHANICS. 159 



The beams he subjected to trial were of oak, from 

 seven to twenty-eight feet in length, and from four 

 inches square to eight inches. 



It appears from them, that the quantity called s in 

 the above formulas, or the strength of the ligneous 

 fibre, is nearly proportional to the specific gravity, 

 or to the weight of a given bulk, for example, a cu- 

 bic foot of the timber. The weights required to 

 break the beams were found to be very nearly as 

 the quantities b c 2 , the length remaining the same. 

 The real strengths, however, fell a little short of 

 the computed, and the more, the longer the beam. 

 In beams of different lengths, the variation of 

 strength did not follow the inverse ratio of the 

 lengths near so exactly as it did that of the other 

 quantities included in the formula. Histoire Natiir- 

 relle par M. DE BUFFON : Supplement, torn. in. 

 p. 255., &c. l&no edit. 



238. In a beam, of which the section is a tri- 

 angle, having the base &, and the depth or perpen- 



dicular p, when the base is uppermost, Wzz ^--; 



J / 



but when the vertex of the triangle is uppennost, 



or the edge of the prism, W = *; . 



o / 



The strength of a prismatic beam is therefore twice 

 as great when a face is uppermost, as when the op- 

 posite edge is uppermost. 



2 In 



