Whatever be the method adopted to surmount inclined planes upon a railway, inconvenience attends the descent upon them. The motion down the incline by the force of gravity is accelerated; and if the train be not retarded, a descent of any considerable length, even at a small elevation, would produce a velocity which would be attended with great danger. The shoe used to retard the descent down hills on turnpike roads cannot be used upon railroads, and the application of brakes to the faces of the wheels is likewise attended with some uncertainty. The friction produced by the rapid motion of the wheel sometimes sets fire to wood, and iron would be inadmissible. The action of the steam on the piston may be reversed, so as to oppose the motion of the wheels; but even this is attended with peculiar difficulty. From all that has been stated, it will be apparent that, with our present knowledge, considerable inclines are fatal to the profitable performance on a railway, and even small inclinations are attended with great inconvenience.[29] [Footnote 29: A contrivance might be applied in changes of level in railroads somewhat similar to locks in a canal. The train might be rolled upon a platform which might be raised by machinery; and thus at the change of level there would be as it were _steps_ from one level to another, up which the loads would be lifted by any power applied to work the machinery. The advantage in this case would be, that the trains might be adapted to work always upon a level.] (97.) To obtain from the locomotive steam engines now used on the railway the most powerful effects, it is necessary that the load placed on each engine should be very considerable. It is not possible, with our present knowledge, to construct and work three locomotive engines of this kind, each drawing a load of 30 tons, at the same expense and with the same effect as one locomotive engine drawing 90 tons. Hence arises what must appear an inconvenience and difficulty in applying these engines to one of the most profitable species of transport--the transport of passengers. It is impracticable, even between places of the most considerable intercourse to obtain loads of passengers sufficiently great at each trip to maintain such an engine working on a railway.[30] The difficulty of collecting so considerable a number of persons, at any stated hour, to perform the journey, is obvious; and therefore, the only method of removing the inconvenience is _to cause the same engine which transports passengers also to transport goods_, so that the goods may make up the requisite supplement to the load of passengers. In this way, provided the traffic in goods be sufficient, such engines may start with their full complement of load, whatever be the number of passengers.