"The man who made them must have had a pretty thorough knowledge of chemistry," Mary mused.

"Mighty near perfect," admitted Walters. "At least six exploded on time, and, from what I understand, they were loaded to the muzzle with a mixture that no one but an expert would dare handle."[51]

"And," continued Mary, with just a hint of excitement in her voice, "the bomb-maker would continue to investigate the subject. He would want to get the latest information, the most recent books, the—"

"What are you driving at?" Walters interrupted.

"Just this," and Mary leaned across the table so that there was no possibility of being overheard. "We girls have a good deal of time on our hands, so we get into the habit of making conjectures and forming theories about the 'regulars'—the people who come into the Library often enough for us to know them by sight.

"Up to a month ago there was a man who dropped into the reference room nearly every day to consult books from Shelf Forty-five. Naturally he came up to my desk, and, as he usually arrived during the slack periods, I had plenty of time to study him. Maybe it was because I had been reading Lombroso, or possibly it's because I am just naturally observant, but I noticed that, in addition to each of his ears being practically lobeless, one of them was quite pointed at the top—almost like a fox's.

"For a week he didn't show up, and then one day another man came in and asked for a book from Shelf Forty-five. Just as he turned away I had a shock. Apparently he wasn't in the least like the other man in anything save height—but neither of his ears had any lobes to speak of and the top of them was pointed! When he returned the book I looked him over pretty tho