IN WHICH FRANK MANSFIELD MAKES AN IMPORTANT DISCOVERY. Had it occurred to Officer Schneider to remain quietly in the precise spot at which his prisoner had disappeared until the Trinity Church clock struck the hour of four, his patience would have been rewarded by seeing the iron door in the grave-yard wall cautiously open, and the head and shoulders of a boy thrust out into the silent street. But as neither that exceedingly astute member of the New York police force--the finest in America, we believe it has been said--nor any one else was about at the time, the head and shoulders were followed by a well-developed pair of arms and legs, and a boy stepped out upon the snow. Instantly this boy was followed by another, after which the iron door was softly closed from within. Turning their faces toward the north, both boys started upon the dead run up New Church street, and whipping around the corner of Cedar street like a flash, suddenly slackened their steps, and began slowly to ascend the hill in the direction of Broadway. In the stillness of the Sabbath morning not a sound is to be heard. The great city sleeps, its ceaseless roar is hushed. Even as the virtue of charity covereth a multitude of sins, so has covered the pure snow everything in and about these silent streets with an unbroken mantle of white. Let us glance at these two solitary travelers as they move along, and seek to learn who and what they may be. As to the larger of the pair there can be no doubt. Frank Mansfield disguised or Frank Mansfield in his usual dress must to the reader, who has free admission to all our secrets, be Frank Mansfield still. And we find him now clad in a rough, well-worn suit of clothes, with a blue woolen shirt and a low, slouch, felt hat, not unlike the garments which a few hours since we saw adorning the person of Barney, the bootblack, one of the "bats" in the vault of the church-yard wall. But his hands are free--there is no doubt of that, for he has one inserted in each side-pocket of his short monkey-coat as he hurries along by the side of his companion through the snow. And for this relief, one may as well say right here, Frank had to thank a sharp file, procured by one of his new-found friends and Master Barney's strength of arm. As to the second boy, he is likewise a "bat from the wall." The special "bat," in fact, mentioned by Barney in his graphic description of the robbery of the Webster Bank as having taken upon himself to track the burglars to their home. He was a well-built fellow of some eighteen or nineteen years, rough and uncouth in his dress and speech, but immeasurably superior, as could be seen at a glance, to either of his companions encountered by Frank in the vault. He rejoiced among his fellow "bats" in the short and easily-remembered appellation of "Jerry Buck." "Are you sure you'd know the place again, Jerry?" asked Frank, as they walked along.