All these things having been put in order, Cobb, with the assistance of Hathaway, carefully lifted from a large box a heavy glass case, two feet nine inches high by three feet square. This case was set in the further corner of the chamber. Through a door in the top, which Cobb opened, both Craft and Hathaway saw a number of wheel and pinion works, while at the bottom of the case was a circular piece of bright aluminum divided into equal divisions. The center of the ring was sunk into the glass bottom half an inch, and on one side of the ring was a number of small wheels and rods; the whole presenting the aspect of very fine and delicate mechanism. Cobb now took out of the last box a large and very elegant compass, two feet in diameter and with a heavy needle; this he placed in the sunken center of the glass case. Craft noticed that there was no iron or steel in the works in this box; nothing but aluminum, save the needle itself. Through the sides of the case, Cobb adjusted an aluminum rod connecting with the pulley and weight attached to the beam over the batteries. By this time the needle in the compass had settled and the positive pole pointed to 283 on the aluminum scale. Both Craft and Hathaway had asked but few questions during all this work, curbing their curiosity until such time as their companion would enlighten them as to the meaning of all this apparatus. They had been on the point, a number of times, of asking for some information, but the other had, by a look, quickly given them to understand that he was not yet ready to explain things. But it was impossible for Craft to hold in any longer; he had to ask the use of this last glass case, with its many wheels and delicate machinery. "Wait! You will understand it all soon," answered Cobb. "There is little more to do to-night." Then, taking a paper from his pocket, he scanned it for fully five minutes, making a few notes upon it with his pencil during the time. At last, seeming satisfied, he bent over the compass in the box, and by a small screw in its side turned the whole delicately adjusted works around until a fine pointer, from which projected a tiny hook, became flush with the figures 260 from the zero of the scale, or to a reading of 4 degrees 20 minutes; then turning the whole compass-box around, he carefully adjusted it so that the needle should point exactly to the figures 993, equivalent to a reading of 16 degrees 33 minutes, the magnetic variation east, of San Francisco, California, in December, 1887. It was easy to see that the little hook which hung down from the overlapping works would become engaged with the needle of the compass if the latter were to retrograde in arc 12 degrees 13 minutes.