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, according 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 considerable degree than the pressure of steam in the boiler. If under such circumstances 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 not 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 throttlevalve, 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 be recollected that a reservoir of cold water is placed in the tender which follows the engine, and that the water is driven from this reservoir into the boiler by a forcing pump, which is worked by the engine itself. This pump is so constructed that it will supply as much cold water as is equal to the evaporation, so as to maintain constantly the same quantity of water in the boiler. But it is evident, on the other hand, that the supply of this water has a tendency to check the rate of evaporation, since in being raised to the temperature of the water with which it mixes it must absorb a considerable portion of the heat supplied by the fire. With a view to accelerate the production of steam, therefore, in ascending the inclines, the engine man may suspend the action of the forcing pump, and thereby stop the supply of cold water to the boiler; the evaporation will go on with increased rapidity, and the exhaustion of water produced by it will be repaid by the forcing pump on the next level, or still more effectually on the next descending incline. Indeed the feeding pump may be made to act in descending an incline, if necessary, when the action of the engine itself is suspended, and when the train descends by its own gravity, in which case it will perform the part of a brake upon the descending train.

5. The mechanical connexion between the piston of the cylinder and the points of contact of the working wheels with the road may be so altered, upon arriving at the incline, as to

give the piston a greater power over the working wheels. This may be done in an infinite variety of ways, but hitherto no method has been suggested sufficiently simple to be applicable in practice; and even were any means suggested which would accomplish this, unless the intensity of the impelling power were at the same time increased, it would necessarily follow that the speed of the motion would be diminished in exactly the same proportion as the power of the piston over the working wheels would be increased. Thus, on the inclined plane, which rises fifty-five feet per mile, upon the Liverpool line, the speed would be diminished to nearly one fourth of its amount upon the level.

RAILWAYS AND STONE ROADS COMPARED.-MR. GURNEY'S STEAM ENGINE. -CONVENIENCE AND SAFETY OF STEAM CARRIAGES.-HANCOCK'S STEAM ENGINE.-OGLE'S STEAM ENGINE.- TREVITHECK'S INVENTION. -DR. CHURCH'S STEAM ENGINE.

(203.) WE have hitherto confined our observations on steampower, as a means of transport by land, to its application on railways. But modern speculation has not stopped there; various attempts have been made, and attended with more or less. success, to work steam-carriages on common roads. The mere practicability of this project had long been regarded as very questionable; but enough has been done to show that the only doubt which can attend it, is as to whether it can be profitably resorted to, as a means of transport, and this question

has been materially affected by the recent extension of railways. In comparing the effect of a stone road with an iron railway, there are two circumstances which give great superiority and advantage to the latter: first, the resistance opposed by a railway to the moving power, no matter what that moving power may be, is considerably less in proportion to the load than on a stone road. The average resistance on a good level stone road, to the motion of carriages drawn at the speed usually attained by the application of horse-power, may be taken at about a thirty-sixth part of the load, while the resistance to a load drawn upon a railway at the same speed probably does not amount to a tenth part of this resistance. Thus the moving power, whatever it may be, would produce on a railway ten times the useful effect which it would produce on a stone road; secondly, the resistance which is opposed to the moving power on a level railway is much more uniform than on a stone road, and, consequently, the moving power is less subjected to jerks and inequalities. This renders the application of inanimate power more easy on the railway. Those inequalities of surface which increase the amount of resistance on stone roads as compared with railways also produce a jolting motion in the carriage, to counteract which, the use of springs become necessary. These springs render the motion of that part of the carriage which rests upon them different from that part of the carriage which supports them; and in the application of steam-machinery it becomes necessary so to connect the moving power with the wheels that the machinery may have one motion, and the wheels which are put in mechanical connexion with that machinery, and driven by it, shall have another motion. This, it is true, is the case with locomotive engines on railways; but owing to the greater smoothness and equality of the railway surface the difference between the motion of the carriage body suspended on springs and that of the wheels is much less than it would be on a stone road.

But besides the greater smoothness of railways compared with stone roads, the latter have another disadvantage, the effects of which have probably been exaggerated by those who are opposed to this application of steam-power. One of the