the groove when the valve is shut, makes up the circle of the pipe, and prevents the air from passing the piston; one edge of this valve is securely held down by iron bars, fastened by screw bolts to a longitudinal rib cast on the pipe, and allows the leather between the plates and the bar to act as a hinge, similar to a common pump valve; the other edge of the valve falls into a groove which contains a composition of beeswax and tallow: this composition is solid at the temperature of the atmosphere, and becomes fluid when heated a few degrees above it. Over this valve is a protecting cover, which serves to preserve it from snow or rain, formed of thin plates of iron about five feet long hinged with leather, and the end of each plate underlaps the next in the direction of the piston's motion, thus ensuring the lifting of each in succession. The piston carriage would open and then close the valve: To the underside of the first carriage in each train is attached the piston and its appurtenances; a rod passing horizontally from the piston is attached to a connecting arm, about six feet behind the piston. This connecting arm passes through the continuous groove in the pipe, and being fixed to the carriage, imparts motion to the train as the tube becomes exhausted; to the piston rod are also attached four steel wheels, (two in advance and two behind the connecting arm,) which serve to lift the valve, and form a space for the passage of the connecting arm, and also for the admission of air to the back of the piston; another steel wheel is attached to the carriage, regulated by a spring, which serves to ensure the perfect closing of the valve, by running over the top plates immediately after the arm has passed. A copper tube or heater, about ten feet long, constantly kept hot by a small stove, also fixed to the underside of the carriage, passes over and melts the surface of the composition (which has been broken by lifting the valve,) which upon cooling becomes solid, and hermetically seals the valve. Thus each train in passing leaves the pipe in a fit state to receive the next train. Entering and leaving the pipe was described: The continuous pipe is divided into suitable sections (according to the