STRENGTH OF MATERIALS. 45 



From these tatles we may ascertain the strength of 

 chains, rods, &c., when made of different, metals, and 

 of timhers, bars, levers, swing-trees, and farm imple- 

 ments, when made of woods. Wood which will hear 

 a very heavy weight for a minute or two will break 

 with two thirds of the weight when left upon it for a 

 long time. This explains the reason that store-house 

 and barn timbers sometimes give way under heavy 

 loads of grain, which have appeared at first to stand 

 with firmness. 



Although the preceding table gives the strength of 

 wood drawn lengthwise, yet the comparative results 

 are not greatly different when the force is applied in a 

 transverse or side direction, so as to break in the usual 

 way. 



The following table shows the results of several ex- 

 periments with pieces of wood one foot in length, one 

 inch sqviare, with the weight suspended from one end, 

 bending them sidewise. 



"White oak, seasoned, broke with 240 lbs. 



Chestnut, " " 170 " 



White pine, " " 135 " 



Yellow pine, " " 150 " 



Ash, " " 175 " 



Hickory, " " 2*70 " 



A rod of good iron is about ten times as strong as 

 the best hemp rope of the same size. The best iron 

 wire is nearly twenty times as strong as a hemp cord. 

 Hence the enormous strength of the wire cables, sev- 

 eral inches in diameter, which are employed for the 

 support of suspension bridges. 



A rope one inch in diameter will bear about 5000 

 lbs., but in practice should not be subjected to more 



