MECHANICAL PHILOSOPHY. 



The strength of a beam increases from the centre towards 

 the ends or points of support, and the stress increases from 

 the. ends towards the centre; hence, a beam to be equally 

 strong at every point, should be eliptical, or the largest in the 

 middle and taper regularly towards both ends. 



The strongest form in which a given quantity of matter can 

 be disposed, is that of a hollow cylinder: this, however, is true 

 only when the transverse sections of the cylinder are perfectly 

 circular. In this way nature economizes material, avoids too 

 great weight, and at the same time augments strength. 



"A great column is in greater danger of being broken than 

 a similar small one ; an insect can sustain a weight many times 

 greater than itself, whereas a much larger animal, as a horse, 

 eould scarcely carry another horse of his own size." 



It is not regarded as safe to load a stone structure with more 

 than one-sixth the amount of pressure which it requires to 

 crush it: iron may be loaded to one-fourth that amount In 

 building bridges, <fec., which are to span considerable space 

 without as much support as might be desirable, it is important 

 to calculate accurately, both the strength and stress of the 

 beams : bridges apparently strong, and perfect in construction, 

 sometimes fall by their own weight: in such cases there is an 

 unnecessary violation of a philosophical principle of which no 

 mechanic should be ignorant For suspension bridges, the 

 strongest material for spanning a wide stream is cast steel 

 wire, the next strongest is malleable iron, and k-ast of all 

 metals, lead. A piece of cast steel wire one-eighth of an inch 

 in diameter will sustain a weight of 16,782 pounds; or 4,931 

 feet of its own length : malleable iron wire of the same size, 

 9,008, or 2,467 feet of its own length: lead wire of the same 

 size sustains only 228 pounds, or 42 feet of its own length. 



Of the different kinds of wood, the strongest are, the ash, 

 oak, teak, beech and larch, the strongest of these is the ash. 

 We see by these few facts in relation to mechanical philoso- 



