human
It does, the other replied.
gpt
Now if you look into those holes in the plate you can see a little cup of bright metal under each hole. What do you suppose that is?
human
I'm not sure, of course, the boy responded,
gpt
That's exactly what it is, quicksilver, or mercury. Now mercury, you ought to know, can transmit an electric current, so that if an electrically charged pin comes down into the cup of mercury, the cup itself being attached to an electric current, a circuit is formed.
human
Now I'm beginning to see, the boy said,
gpt
It could, of course, but a piece of dust between would prevent contact, the pins would wear away quickly, and the plate would get worn, whereas, by the pin just dropping into the mercury there is no friction and no fear of a missed contact.
human
The pins are in that square box at the end of the long arm which comes down every time a card is put on the plate, aren't they, Mr. Cullern?
gpt
Yes, and if there is no card there and the pins in the square box are started down, they are automatically stopped before they reach the mercury so as not to make a contact on every point. Also if a card were there without any holes punched, none of the pins would reach the mercury and no contact would be made.
human
But with a punched census card, interrupted the boy, eager to show that he understood,
gpt
There is variety enough, answered the chief,
human
Couldn't it happen perhaps that two people of the same age should do the same work, be both married and so forth?
gpt
They would have to live in the same district, they would have to be employed the same way, they would have both to be married and have the same number of children and a whole lot more things, and even then--the cards would be different for they would represent different numbers on the schedule on which their names were registered. No, there are not two cards in the entire series punched alike.
human
Then I don't see how in the wide world this machine can tell which cards are right among millions so entirely different from each other.
gpt
They don't verify by finding the cards that are right, was the answer,
human
What's the difference?
gpt
There is a wide difference. You can see that it would be easy enough to arrange that machine so that if a wrong combination of contacts were made the bell would not ring. Such wiring might be highly complex, but you see the idea is simple. For a right group of contacts, all the wires are satisfied, as it were, and the bell rings; for an error, one wire, cut in on by a wrong wire, breaks the contact, and the bell does not ring.
human
But what do you mean by a wrong grouping?
gpt
You ought to be able to guess that, the chief said reproachfully.
human
For instance if a card is punched 'Wf' for Wife and also is punched 'Male' that card is sure to be wrong, and if 'Emp' for employer is punched on the same card as an age punch showing the person to be a three-year-old youngster, the card is wrong. There are twenty-three different possibilities of error which are checked by this verification machine, and for any one of these twenty-three reasons a card is thrown out.
gpt
For example if 'Na' for naturalized is punched on the same card as 'N' for native-born, and things of that sort, I suppose?
human
And many others of similar character,
gpt
But how about insufficiently punched cards? queried Hamilton.
human
I can see that it would be easy to arrange the wires so as to catch really bad inconsistencies, but supposing a figure were only left out, there would be no contact made to show the error.
gpt
Except in the age column, was the reply,
human
And what happens to the rejected cards?
gpt
A checker-up compares them with the original schedules, and if incorrectly punched, punches a new card, if only insufficiently punched, punches the missing place. But the number of cards found wrong does not reach a high percentage.
human
You know I've been thinking, Hamilton said thoughtfully,
gpt
To the eye, perhaps, the chief said,
human
Of course, the boy said,
gpt
We keep all those together from the time they are punched till after we are through with the verifying, so that all the cards of a certain enumeration district, and of every section in that district, are kept together in a separate box.
human
My word, Hamilton exclaimed,
gpt
You ought to go down and see it some time, the other said.
human
It's big enough, with every State and every county and every district in the country having its own place, and every little village in that district right where it belongs in a box of its own, under that State, county, and district. I'm telling you this just to show you that we don't have to sort the cards for location at all, and that in itself saves us a lot of labor and time.
gpt
And they were sorted into sexes on the punching machine, I remember,
human
Yes, and that prevents another handling of every card, you see, the chief went on,
gpt
Just how, Mr. Cullern?
human
Well, the other continued,
gpt
That is before sorting?
human
Or after. Cards may be tabulated along a lot of different lines. And the sorting device depends again upon another machine, operated by the same principle.
gpt
This sorter, he said,
human
It's hard to believe, said Hamilton wonderingly,
gpt
We're just building one in here, the supervisor replied, leading the way into a little partitioned-off section of the room,
human
he added,