192 ME. WILLIAM FAIEBAIEN ON 



plates, it must be observed that the commissioners had no 

 experience, nor were they acquainted with the strength, 

 rigidity, and other properties of girders composed of wrought- 

 iron riveted plates. In these, the deflection due to the 

 passing load is nearly the siame at all velocities; and unless 

 there exist irregularities and inequalities on the rails, so 

 as to cause a series of impacts, we may reasonably conclude 

 that the deflections are not seriously, if at all, increased at 

 high velocities. 



The questionable security of a great number of horizon- 

 tal bridges which, of late years, have been introduced for 

 the support of railways, or common roads, has not only 

 called for legislative interference, but the appointment of a 

 commission to watch over the public interests and public 

 safety in railway constructions. This commission, or the 

 inspectors under their direction, I believe, have instructions 

 to pass no bridge or other structure upon any line of rail- 

 way, until carefully tested as to its security, and other 

 conditions calculated to meet all the requirements of general 

 traflSc. These inspectors are employed for the exclusive 

 purpose of examining every new Une of railway, and report- 

 ing upon its efiiciency before it is opened to the public; and, 

 in Older to assure themselves of the security of the bridges, 

 cuttings, tunnels, embankments, &c, upon the line, these 

 are generally submitted to severe tests, in order to ascertain 

 their condition and fitness for securing to the public a 

 safe and agreeable transit from one end to the other. 

 Bridges, above all other structures, are regarded with sus- 

 picion, and, in order that the lives and limbs of the public 

 should be duly protected, are submitted to a certain proof, 

 which generally consists of a double train of locomotive en- 

 gines and tenders being run over the bridge at diflerent 

 velocities. A train of locomotive engines is considered the 

 greatest load that can be placed upon a bridge; and, having 

 ascertained the deflection of the girders fi-om their own 



