534 THE STEAM-ENGINE. 



doing so, must pass over exactly equal lengths of the road. If, therefore, the 

 circumference of the wheels be not accurately equal, that wheel which has 

 the lesser circumference must be dragged along so much of the road as that 

 by which it falls short of the circumference of the greater wheel ; or, on the 

 other hand, the greater wheel must be dragged in the opposite direction, to 

 compensate for the same difference. As no mechanism can accomplish a 

 perfect equality in four, much less in six wheels, it may be assumed that a 

 great portion of that dragging effect is a necessary consequence of the princi- 

 ple of this machine ; and even were the wheels, in the first instance accu- 

 rately constructed, it is not possible that their wear could be so exactly uniform 

 as to continue equal. 



The next stimulus which the progress of this invention received, proceeded 

 from the great national work undertaken at Liverpool, by which that town and 

 the extensive commercial mart of Manchester were connected bv a double line 

 of railway. When this project was undertaken, it was not decided what 

 moving power it might be most expedient to adopt as a means of transport on 

 the proposed road : the choice lay between horse-power, fixed steam-engines, 

 and locomotive engines ; but the first, for many obvious reasons, was at oace 

 rejected in favor of one or other of the last two. 



The steam-engine may be applied by two distinct methods to move wagons, 

 either on a turnpike road, or on a railway. By the one method, the steam- 

 engine is fixed, and draws the carriage, or train of carriages, toward it by a 

 chain extending the whole length of the road on which the engine works. By 

 this method, the line of road over which the transport is conducted, is divided 

 into a number of short intervals, at the extremity of each of which an engine 

 is placed. The wagons, or carriages, when drawn by any engine to its own 

 station,- are detached, and connected with the extremity of the chain worked 

 by the next stationary engine ; and thus the journey is performed, from station 

 to station, by separate engines. By the other method, the same engine draws 

 the load the whole journey, travelling with it. 



The directors of the Liverpool and Manchester railroad, when that work was 

 advanced toward its completion, employed, in the spring of the year 1829, 

 Messrs. Stephenson and Lock, and Messrs. Walker and Rastrick, experienced 

 engineers, to visit the different railways, where practical information respect- 

 ing the comparative effect of stationary and locomotive engines was likely to 

 be obtained ; and from these gentlemen they received reports on the relative 

 merits, according to their judgment, of the two methods. The particulars of 

 their calculations are given at large in the valuable work of Mr. Nicholas 

 Wood on railways ; to which we refer the reader, not only on this, but on 

 many other subjects connected with the locomotive steam-engine, into which it 

 would be foreign to our object to enter. The result of the comparison of the 

 two systems was, that the capital necessary to be advanced to establish a line 

 of stationary engines was considerably greater than that which was necessary 

 to establish an equivalent power in locomotive engines ; that the annual ex- 

 pense by the stationary engines was likewise greater ; and that, consequently, 

 the expense of transport by the latter was greater, in a like proportion. 



The decision of the directors was, therefore, in favor of locomotive engines ; 

 and their next measure was to devise some means by which the inventive ge- 

 nius of the country might be stimulated to supply them with the best possible 

 form of engines for this purpose. With this view, it was proposed and carried 

 into effect to offer a prize for the best locomotive engine which might be pro- 

 duced under certain proposed conditions, and to appoint a time for a public 

 trial of the claims of the candidates. A premium of five hundred pounds was 

 accordingly offered for the best locomotive engine to run on the Liverpool and 



