respective distance of the fixed steam engines) by separating valves, which are opened by the train as it goes along: these valves are so constructed that no stoppage or diminution of speed is necessary in passing from one section to another. The exit separating valve, or that at the end of the section nearest to its steam engine, is opened by the compression of air in front of the piston, which necessarily takes place after it has passed the branch which communicates with the air-pump; the entrance separating valve, (that near the commencement of the next section of pipe,) is an equilibrium or balance valve, and opens immediately the piston has entered the pipe. The main pipe is put together with deep socket joints, in each of which an annular space is left about the middle of the packing, and filled with a semi-fluid: thus any possible leakage of air into the pipe is prevented. At that time railway were developing rapidly, and solutions to the technical limitations of the day were eagerly sought, and not always rationally evaluated. Samuda's treatise put forward the advantages of his system: transmission of power to trains from static (atmospheric) power stations; the static machinery could be more fuel efficient; the train would be relieved of the necessity of carrying the power source, and fuel, with it; power available to the train would be greater so that steeper gradients could be negotiated; in building new lines this would hugely reduce construction costs by enabling reducing earthworks and tunnels; elimination of a heavy locomotive from the train would enable lighter and cheaper track materials to be used; passengers, and lineside residents, would be spared the nuisance of smoke emission from passing trains; this would be especially useful in tunnels; collisions between trains would be impossible, because only one train at a time could be handled on any section between two pumping stations; collisions were at the forefront of the mind of the general public in those days before modern signalling systems, when a train was permitted to follow a preceding train after a defined time interval, with no means of detecting whether that train had stalled somewhere ahead on the line; the piston travelling in the tube would hold the piston carriage down and, Samuda claimed, prevent derailments, enabling curves to be negotiated safely at high speed; persons on the railway would not be subjected