I did not need to have a very profound knowledge of secret springs and locks to know what it meant. The system is still used in safes, Fichet's and others. It meant that on the fire-back of the chimney-place in the Baron's Hall of the _Herrenhausen_ there were six lettered locks. You made the spring act by taking for each lock in turn one of the six letters forming the name of the inventor, Giroud. When you remember that this Giroud was the master-locksmith of the Grand Duke of Lautenburg you won't have much difficulty in realizing that my first thought was to use the fire-back in the armoury of the castle of Lautenburg as a test of the accuracy of my reasoning with regard to the fireplace of the Baron's Hall in the Castle of Hanover. So you may imagine how impatiently I watched Cyrus Beck's departure. When at last he had gone I waited a quarter of an hour. Then I turned out the lights, opened the right-hand door of the library and banged it to as if I had gone back to my room. Then, taking great care not to fall over anything and picking my way among the desks and show-cases I returned and cautiously opened the door on the left hand side which led into the armoury. Great pools of moonlight, shaped like the tall lancet windows, flecked the dark floor. I went straight to the chimney-place. I started at touching the heavy iron fire-back. It was only when my fingers found a kind of knob high up on the left that I switched on my electric torch. I had no difficulty in dealing with the knob. It pivoted on a hinge, revealing a kind of dial. The whole thing was not unlike one of our gas-metres. I started back in dismay. I was expecting letters, but this dial had numbers. It was divided into twenty-five sections. Turning off the lamp I sat down on a heavy oak stool close by. I didn't have to think long. 25! What a fool I was! I pulled out a pencil and a piece of paper, turned on the lamp again and, kneeling at the stool, I had soon written out the twenty-five letters of the alphabet and underneath a row of figures to correspond. Then I wrote Giroud's name and obtained the following combination: 7, 9, 18, 15, 21, 4. 791815214. It will be a long time before I forget that number. I examined the whole face of the metal rectangle with my lamp. A terrible disappointment was in store for me. Instead of the six knobs that I had _expected_ I could only find two. When a single factor throws out the kind of calculations I had just made it can only mean that one's theory is radically false. I might have known. That would have been much too simple.... Solely to prove myself wrong, I tried the first knob and turning the pointer on the dial I set it on the figure 7--g. I crossed to the other side and repeated the operation on the other knob, putting the pointer on the figure 9--i.