But there was a difficulty, and that was insurmountable. Had the carriages been within the tube they would have swung along readily enough. But they were without and yet connected with the piston within; and it was precisely over this connection that the system broke down. A complex and ingenious scheme was adopted for making the tubes air-tight in spite of the long slit through which slid the coulter that connected the carriages with the piston. The train carried with it a sort of hot flat-iron which it passed over the leather flap bedded in tallow that closed the slit. But the device was too intricate and too open to disturbance by accident to be successful. Trains ran spasmodically. The coulter, raising the flap, let the air rush into the artificially formed vacuum before it, and so act as a break on the propelling force of the air behind. The flap became displaced. The tallow under a hot sun melted away. The trains when they started were attended on their course by a fizzing noise as of a rocket about to explode, very trying to the nerves. They had a habit of sulking and stopping in the midst of tunnels, or of refusing to start from stations when expected to start. By no means infrequently they arrived at their destination propelled by panting passengers, and the only exhaustion of atmosphere of which anything could be spoken, was that of the lungs of those who had paid for their tickets to be carried along the line, not to shove along the carriages with their shoulders. At the time when our story opens, this unfortunate venture, so ruinous to many speculators, was in process of demonstrating how unworthy it was of the Italian churches and campaniles that had been erected for its use. After a while steam locomotives were brought to the stations and held in readiness to fly to the aid of broken-down atmospheric trains. A little later, and the atmospheric engines and tubes were broken up and sold for old iron, and the ecclesiastical edifices that had contained the pumps were let to whoever would rent them, as cider stores or depôts of guano and dissolved bone.