Through the rest of the afternoon, Hamilton worked steadily over this set of cards, not only doing the work, but getting the principles of the whole thing thoroughly in his mind, and, as he had said to the sub-section chief, knowing just the manner in which the schedules had been made up helped him to an extraordinary degree.  He was well pleased, therefore, when he came down to work the following morning, to find at his machine a real schedule, not the test that he had been working on the afternoon before; the exact number of cards required for his schedule all ready in the hopper of the machine, and it was pointed out to him that error was not permissible and that he must account for every card.

“Why is that?” asked Hamilton, “what difference would a card or two make?”

“It isn’t the cards, it’s the numbering,” the other explained.  “Don’t you remember that each card was numbered, and so, if one card is wrong it would throw all the succeeding numbers out?  Besides, you never have a chance to see whether a card is right or not, because after you have touched the lever and the card is punched it slides into its own compartment.  You have all the chance you want to look over your arrangement of depressed keys before the card is punched, but none after.”

Before a week had passed by, Hamilton was so thoroughly at home with the machine that the work seemed to him to become more or less mechanical, and his interest in it began to wane.  As—­under government regulations—­he left work early, he sauntered over several times to the verification department to become familiar with the work of the machine used there.  There was a fascination to the boy in this machine, for it seemed almost to possess human intelligence in its results, and he was curious to know the principle on which it worked.  Generally every one quit at half-past four o’clock, just as he did, but sometimes a man would work a few minutes longer to finish a batch of cards, and the boy would go to watch him.

When he was over there one day, after hours, Hamilton saw Mr. Cullern on the floor.

“Still looking for information?” questioned the older man, with a smile.

“Yes, sir,” answered the boy, “I’ve been watching this machine and I’ve spoken to one or two of the operators about the principle of it, but they none of them seem to know.  They knew how to run it, and that was about all.”

“The principle is simple enough,” the chief replied, “but it would be a bit hard to understand the combination unless you had the clew.  Then it is all as clear as day, although the machine itself is a little complicated.  You noticed, of course, that the operator lays a card on this plate which is full of holes, and you probably noticed that these holes correspond with the points on the card, and that the way in which the card is fed into the machine insures that the holes shall coincide exactly.”

“That I saw,” Hamilton answered, “and I could see, of course, that this was one of the most important parts of the machine, and that upon it a good deal of the exactness of the work depended.”