And yet, even in this dry as dust title of a scientific communication from a distinguished toxicologist there was some sinister significance. It was the letter of a great chemist, who demonstrated therein the fallibility of all tests in relation to a certain poison. It was one of those papers which, while they aid the cause of science, may also further the dark processes of the poisoner, by showing him the forces he has to encounter, and the weapons with which he may defend himself from their power. It is needless to dwell here upon the contents of this letter--one of a series on the same subject, or range of subjects. Valentine read it with eager interest. For him it had a terrible importance in its relation to the past and to the present. "I let the book fall open, and it opened at that letter," he thought to himself. "Will it open there a second time, I wonder?" He repeated the experiment, and the book opened in the same place. Again; and again the book opened as before. Again, many times, and the result was still the same. After this he examined the book, and found that it had been pressed open at this page, as by a reader leaning on the opened volume. He examined it still more closely, and found here and there on the page faint indications of a pencil, which had under-scored certain lines, and the marks of which had been as far as possible erased. The deduction to be drawn from these small facts seemed only too clear to Valentine Hawkehurst. By some one reader the pages had been deliberately and carefully studied. Could he doubt that reader to have been the man in whose possession he found the book, the man whom that very day he had heard plainly denounced as a poisoner? He drew out the previous volume, and in this a rapid search revealed to him a second fact, significant as the last. An old envelope marked the place where appeared an article on the coincidences common to the diagnostics of a certain type of low fever and the diagnostics of a certain class of poisons. Here the volume again opened of itself, and a blot of ink on the page seemed to indicate that the open book had been leant upon by a person engaged in making memoranda of its contents. Nor was this all. The forgotten envelope that marked the place had its own dismal significance. The postmark bore the date of the year and the month in which Charlotte's father had died. While this volume was still open in his hand the door opened suddenly, and Mrs. Woolper came into the room.