There are other signals, too, which are of interest to passengers, particularly the whistle signals. There are sixteen of these, but the more important ones are: one short blast, stop; one long blast on approaching stations, junctions, or railroad-crossings at grade; two long blasts followed by two short ones on approaching public crossings at grade, which is the signal most frequently heard by the travelling public. A succession of short blasts means danger ahead--and is used, too, to scare cows and horses off the track. There is yet another class of signals, which are given with the signal-cord which runs overhead through every passenger-coach. Every one, of course, has seen this cord, and has also seen the conductor use it to signal to the engineer. It is connected with a little valve over the door of the car, and every time the conductor pulls it, there is a little hiss from the valve as of escaping steam. This is the compressed air escaping. The valve is connected with a compressed-air line which runs through the entire train, and every pull on the cord blows a little whistle in the cab of the engine. Two pulls at this cord, when the train is moving, means stop at once; when the train is standing, two pulls is the signal to start. Four pulls means reduce speed, and five, increase speed. Three pulls is the signal usually heard, and indicates that the train is to stop at the next station. It is always answered by two toots from the whistle to show that the engineer understands. This compressed-air line long ago replaced the old signal-cord which rang a bell in the cab. A call sounded on his instrument, and Allan laid down the book again to answer it. There was a short order to be taken, and just as he repeated it and snapped his key shut, he heard a step at the door behind him. He glanced around carelessly, then started suddenly upright, for on the threshold peering in at him stood Dan Nolan. CHAPTER X A PROFESSION OF FRIENDSHIP For a moment, neither of them spoke. Then Nolan drew back as though to go away, but thought better of it, entered the little room slowly, and without waiting for an invitation, sat down in the remaining chair. "Howdy," he said, and smiled at Allan in a manner intended to be amiable. "How are you?" Allan answered, striving vainly to guess what object Nolan could have had in coming here. Nolan coughed dismally. "You see I'm out," he said, grinning sheepishly. "Yes; I heard this evening that you had been parolled." Nolan coughed again. "It'd have been murder to keep me in any longer," he said. "One lung's gone as it is. Th' doctor told th' board I'd be dead inside o' six months if I wasn't let out."