RAIL-ROADS. 551 



that iron rails were first used, the weight came to be di- 

 rided into moderate loads upon several cars. 



We shall only notice those in present use, the form of 

 which varies according to the nature of the load. The 

 four wheels are of cast iron and of one size, generally 

 about three feet in diameter, but varying from eighteen 

 inches to four feet. The rims of the wheels are now 

 usually case hardened, by which the friction and wear 

 are much reduced, and a true circular form more readily 

 preserved. On the ' plate rail' the wheel is plain, but 

 on the ' edge rail' a flange or rim is required on the inner 

 side of each wheel to preserve the carriage in its track. 

 The axle-trees are universally of wrought iron, the square 

 ends being fixed into the wheels for steadiness, and the 

 axles, therefore, revolve either on cast iron bearings 

 upon the carriage, or on springs, or on a suspending 

 chain, as the case may require. The weight usually 

 placed upon one car, varies from one to four tons, and 

 twenty or thirty, sometimes fifty of these cars are con- 

 nected together, and drawn along by a simple moving 

 power. The motion on a descending plane is regulated 

 by a brake or friction lever, also called a ' convoy.' 



MOVING POWER. 



Dugald Stewart has remarked of printing, that in the 

 fifteenth century, the wants of mankind were such that 

 if Faust and others had not invented the art, somebody 

 else would. So we may say of locomotion, in this cen- 

 tury, that as the horse cannot satisfy the wants, in veloci- 

 ty, something of greater epeed must be brought forward. 

 From 1802 to 180(5, appear the first effective experiments 

 with the locomotive steam engine. It was not, however, 

 supposed possible that the friction or adherence of the 

 plain wheels of such carriages upon the rail, could be suf- 

 ficient to allow any great weight to be drawn after them, 

 and, therefore, the cumbersome appendage of cog wheels, 

 and racket wheels, continuous and endless chains, pro- 

 pelling levers, &c, &c, continued to perplex the minda 

 of engineers until about 1814, when it was first found 



