He finally succeeded in bracing himself in a curiously twisted attitude and driving the needle home under the proper auspices. To his delight it worked--when the needle went in the bars opened in the proper place, swinging back into position automatically as the pressure was withdrawn. With a new sense of freedom Sherman turned to the next step. This was obviously to find out more of the place in which he was confined and of the possibilities of escape. It seemed difficult. But even on this point he was not to be long without enlightenment. His unseen pupil in English was making most amazing progress. The white screen which was their means of communication now bore complicated messages about such subjects as what constituted philosophy. Sherman felt himself in contact with an exceptionally keen and active mind, though one to which the simplest earthly ideas were unfamiliar. There were queer misapprehensions--for instance, no process of explanation he could give seemed to make the unseen scholar understand the use and value of money, and they labored for a whole day over the words "president" and "political." In technical matters it was otherwise; Sherman had barely to express the idea before the screen made it evident that the auditor had grasped its whole purport. When he wrote the word "atom" for instance, and tried to give a faint picture of the current theory of the atom, it was hardly a second before the screen flashed up with a series of diagrams and mathematical formulae, picturing and explaining atoms of different types. After four weeks or more (as nearly as Sherman could estimate it in that nightless, sleepless place where time was an expression rather than a reality) the car that came for him one day discharged him into a room entirely different from the school-room. Like the school-room it was small, and some twenty feet across. Against the wall opposite the door stood a huge machine, the connections of which seemed to go back through the wall. Its vast complex of pulleys, valves and rods, conveyed no hint of its purpose, even to his mechanically-trained mind. Across the front of it was a long, black board, four feet or more across and somewhat like the instrument board of an airplane in general character. At the top of this board was a band of ground glass, set off in divisions. Beneath this band a series of holes, each just large enough to admit a finger, and each marked off by a character of some kind though in no language Sherman had ever seen.