Trenholm reached over and picked up his letter scales. "Try one," he suggested, and, as she did so, "Not quite one ounce. Try the next." Miriam laid each letter on the scales, first putting it back in its proper envelope; not one was above one ounce in weight! "They all come under the three-cent postage rate," she exclaimed. "Any one writing as many as thirteen letters to one correspondent would have found out that fact, especially a person living in Canada." Trenholm considered Miriam and then the letters in silence for a minute. Picking up the thirteenth letter, which Miriam had brought to him unopened that afternoon, he took out the sheet of paper and held the envelope up to the light and studied it intently. As he lowered it, Miriam caught sight of his face and sprang to her feet. "You have found something?" "Yes, thanks to your persistency!" And she colored warmly at the enthusiasm in his voice and manner. "See here!" and Trenholm again held the envelope up to the light and at an angle so that she could see it as well as he. "The edges of the stamps appear cut in a wedge shape in certain places, and there are several pinholes through two of the stamps. The cuts do not appear to result from the careless tearing off of the stamps from the sheet, and consequent damage to the perforations, but are apparently made with scissors." "You are right," agreed Miriam. "And when the letter has no light behind it, they do not show at all against the white ground of the envelope. Is it a code?" Trenholm twirled his mustache in perplexity. "The cuts appear at irregular intervals," he replied. "They seem to be hastily made and are not absolutely uniform. I wonder--" he broke off abruptly, stood in thought for several seconds, then going over to the book shelves which lined one of the walls, searched about until he located several books and carried them back to the table where Miriam stood examining the thirteenth envelope. "Strangely enough," he explained, "Paul's father gave me his stamp collection--a fine one--as Paul never had the craze for collecting stamps even as a boy, and being a human magpie I keep everything bestowed upon me," with a quick boyish smile which softened wonderfully his usually self-repressed expression. "I hope luck is with me and I still have tucked inside one of these albums a perforation gauge." "A what?" "Perforations, Miss Ward, have a definite position on each stamp with relation to one another, though they may be irregular on two separate stamps," went on Trenholm. "In other words, the distance between perforations is always the same, though they may vary a fractional part of a line in their position at the corners." "And the gauge," she prompted, as he paused.