"That is very probable, but I cannot enlighten you upon the point. In his conversations with me he never referred to it. It is not unlikely that the agents through whom he purchased the place may have known; or he may have found a clue to it after he came into possession. That, however, is mere speculation, and is not material to us. What is material _is_ the Will. Observe. Here before us is a sheet of steel, covered with numberless small knobs with shining round surfaces. There must be some peculiarity about the metal that it does not rust; or perhaps its lustre is due to the dryness of the air. When I say that the knobs are numberless I am inexact. They may be easily counted; they are in regular lines, and are alternately placed. From ceiling to floor there are twenty lines, and each line contains twenty knobs--four hundred in all. If you pressed every one of these four hundred knobs one after another with your thumb, you would find only one that would yield beneath the pressure. That knob is in the bottom line, at the extreme left hand corner. Kneel, and press with your thumb, and you will find that I am right." I followed his instructions. I knelt, and pressed the knob; it yielded, and upon my removing my thumb, it returned to its former position. "Still," I said, as I rose from my kneeling posture, "I see no hole in which a key can be inserted." "Wait," said the lawyer. "By pressing on that knob you have unlocked a second at the extreme end of the right corner in the same line. Press it as you did the other." I knelt and obeyed; it yielded as the other had done, and returned to its former position. But there was no apparent change in the steel door. "You have unlocked a third knob," said the lawyer. "You will now have to stand upon one of the chairs; place it here, on the right, and press again on the knob at the extreme right hand. It yields. One more, and the charm is nearly complete. Remove the chair to the left, and repeat the operation on the topmost knob at the extreme left hand. Now descend. Supposing this to be the door of a room, where would the keyhole be situated? Yes, you point to the exact spot. Press there, then, gently. What do we see? The keyhole revealed. The rest is easy." He inserted the key and turned the lock. Massive as was the door, there was no difficulty now in opening it. With very little exertion on our part it swung upon its hinges. I could not but admire the ingenuity of the device, and I wondered at the same time how my father could have found it out, supposing the secret not to have been imparted to him.