THE STEAM-ENGINE. 567 



of a very steep character occur, as happens upon that line, then the engine 

 which is constructed to work upon the general gradients of the road is unfit to 

 draw the same load up those inclinations which form an exception to the 

 general character of the gradients. In such cases some extraordinary means 

 must generally be provided^ for surmounting those exceptionable inclinations. 

 Several expedients have been proposed for this purpose, among which the 

 following may be mentioned : 



1. Upon arriving at the foot of the plane the load is divided, and the engine 

 carries it up in several successive trips, descending the plane unloaded after 

 each trip. The objection to this method is the delay which it occasions a 

 circumstance which is incompatible with a large transport of passengers. 

 From what has been stated, it would be necessary, when the engine is fully 

 loaded on a level, to divide its load into two or more parts, to be successively 

 carried up when the incline rises 52 feet per mile. This method has been 

 practised in the transport of merchandise occasionally, when heavy loads 

 were carried on the Liverpool and Manchester line, upon the Rainhill incline. 



2. A subsidiary or assistant locomotive engine may be kept in constant 

 readiness at the foot of each incline, for the purpose of aiding the different 

 trains, as they arrive, in ascending. The objection to this method is the cost 

 of keeping such an engine with its boiler continually prepared, and its steam 

 up. It is necessary to keep its fire continually lighted, whether employed or 

 not ; otherwise, when the train would arrive at the foot of the incline, it should 

 wait until the subsidiary engine was prepared for work. In cases where 

 trains would start and arrive at stated times, this objection, however, would 

 have less force. This method is at present generally adopted on the Liverpool 

 and Manchester line. 



3. A fixed steam-engine may be erected on the crest of the incline, so as to 

 communicate by ropes with the train at the foot. Such an engine would be 

 capable of drawing up one or two trains together, with their locomotives, ac- 

 cording as they would arrive, and no delay need be occasioned. This method 

 requires that the fixed engine should be kept constantly prepared for work, and 

 the steam continually up in the boiler. 



4. In working on the level, the communication between the boiler and the 

 cylinder in the locomotives may be so restrained by partially closing the 

 throttle-valve, as to cause the pressure upon the piston to be less in a consider- 

 able degree than the pressure of steam in the boiler. If under such circum- 

 stances a sufficient pressure upon the piston can be obtained to draw the load 

 on the level, the throttle-valve may be opened on approaching the inclined 

 plane, so as to throw on the piston a pressure increased in the same proportion 

 as the previous pressure in the boiler was greater than that upon the piston. 

 If the fire be sufficiently active to keep up the supply of steam in this manner 

 during the ascent, and if the rise be riot greater in proportion than the power 

 thus obtained, the locomotive will draw the load up the incline without further 

 assistance. It is, however, to be observed, that in this case the load upon the 

 engine must be less than the amount which the adhesion of its working wheels 

 with the railroad is capable of drawing ; for this adhesion must be adequate 

 to the traction of the same load up the incline, otherwise, whatever increase 

 of power might be obtained by opening the throttle-valve, the drawing wheels 

 would revolve without causing the load to advance. This method has been 

 generally practised upon the Liverpool and Manchester line in the transport 

 of passengers ; and, indeed, it is the only method yet discovered which is 

 consistent with the expedition necessary for that species of traffic. 



In the practice of this method considerable aid may be derived also by 

 suspending the supply of feeding water to the boiler during the ascent. It will 



