In addition to sorting letters, the clerk in charge has charge of the registered mail, which requires special care in its reception and delivery, booking and receipting therefor. Large pouches of registered mail are also placed in his charge, _en transit_ between large cities, and represent great value. The peculiar tooting of the whistle, or a peculiar movement of the train around a curve, warns the fourth clerk, who is on the alert, of a "catch" station; the letter mail for that post-office is quickly deposited by the local clerk in the pouch, the lock is snapped, and he is standing at the door not a minute too soon or too late; the pouch is thrown out at a designated spot and one deftly caught an instant after without a slackening of the speed of the train. The pouch thus caught is taken to the counter, opened and emptied by the fourth clerk, and the letters immediately placed in the hands of the second clerk, who assorts the local mail; the through letters, or those destined to go over distant lines beyond the terminus, are sorted by the clerk in charge; the local, or second, clerk distributes his mail as rapidly as possible, with a watchful eye for letters, etc., to be put into the pouch to be delivered at the next station; the pouch is locked and everything is ready for the next delivery and "catch." When the stations at which pouches are caught are within a mile or two of each other, the greatest activity is needed to assort the mail between stations, to avoid carrying mail by destination and subjecting it to considerable delay before its delivery by a railway post-office on the train to be met at a point perhaps many miles ahead. [Illustration: "CATCHING" AT FULL SPEED.] The manner of taking or "catching" the mail from the trackside by some invisible power on a railroad train plunging through space has seemed to many a feat of almost legerdemanic skill, when all that is required is a simple mechanical apparatus and a quick, firm movement of the arm in using it at the right moment. A crane similar in appearance to the oldtime gibbet is erected near the track, and may have served as a warning by its suggestive appearance to some would-be train-wrecker. Its base is a platform two feet and a half square, with two short steps on top to assist the person hanging the pouch; a post ten feet in height passes up through this platform near the edge; a stout joist about five feet in length is fixed across the top of the post and so balanced that when relieved of the weight of the pouch it flies up perpendicularly against the post. The pouch used for this purpose is made of canvas and is somewhat narrower than the ordinary leathern pouch. It is lightly suspended by a slender iron rod projecting from the horizontal joist, passed through a ring at the top and lightly held at the bottom in the same manner as at the top. [Illustration: POUCH HUNG ON "CRANE."]