In the 1950s, how is a message sent from a speeding train via “loop”?
November 27, 2022 2:07 PM   Subscribe

In the 1952 movie The Narrow Margin, the police officer hero sends a message from a speeding train, apparently by writing it on a piece of paper for a railway employee next to the track to physically swoop it down. What is this device/interaction/method of communication ?

This all happened very quickly, so it was hard for me to understand what was happening or know what I was looking at. This link briefly describes the shot:

“ At the next town, a railroad employee snags a loop off the speeding train with his arm and has Brown’s message for the Highway Patrol.”
posted by lewedswiver to Technology (9 answers total) 4 users marked this as a favorite
Mailbag loop.
posted by dobbs at 2:10 PM on November 27, 2022 [7 favorites]

I see this has already been answered, but adding two terms that may help if you want to read more about this: the mailbag is called a "catcher pouch" and the technique is called "mail on the fly".
posted by earth by april at 6:11 PM on November 27, 2022

Response by poster: Thank you both! I learned something from this… however, I just realized that my question hasn’t been fully answered. The mail bag indeed appears in the movie, and the hero on the train receives a message right after the train collects a mail bag. However, afterwards, he tells the train attendants to send a message (“to Highway Patrol”). You can see that at 59:23–

It seems like a different device is used than the mail bag/catcher pouch. Some sort of metal loop?
posted by lewedswiver at 6:36 PM on November 27, 2022

The person would usually drop the outgoing mail when picking up the bag. Not sure how fast the bag left behind would be picked up, though.
posted by praemunire at 7:02 PM on November 27, 2022

Best answer: It's the same principle. The loop was usually made out of bamboo that had been soaked so it could be bent into shape. Instead of an apparatus with a mailbag on it the loop would either be grabbed (looped on the arm) of an attendant or onto a stationary pole.

Exactly the same principle as the video I posted but would be for messages from/to the train staff / passengers, as opposed to mail that was being posted by non-train-related people.
posted by dobbs at 7:13 PM on November 27, 2022

Best answer: Here.
posted by dobbs at 7:15 PM on November 27, 2022

Best answer: This has some more detail & slow-mo showing how catcher pouches were picked up and dropped off. This scene from The Narrow Margin shows the mail pouch exchange (as you note above).

However, if a "loop" is involved, rather than a mail pouch exchange, then it is the general type of loop that dobbs links to above. Here is an example of such an exchange from the station staff's point of view - and here from the train crew's point of view (at what appears to be a MUCH higher speed!).

You'll notice in both cases, the person on the train tosses a loop down just before he catches a loop with his arm.

This system was commonly used - all over the world, apparently - for exchanging tokens, which controlled who could use a given single-track section. This video explains the system and shows examples of token exchange. Wikipedia has more info about the token system.

When using this system, you can slip a written note in, as well, and apparently this was often used to give written instructions to train crews, at least in the U.S.

This doesn't totally explain this sentence: "a railroad employee snags a loop off the speeding train with his arm". In all the cases I've seen, it's the crew on the train who snags the loop. The train crew member tosses his loop onto the ground, where the ground crew can just pick it up. In general, there is no reason for the crew on the ground to ALSO reach out and snag a loop, as it is easy to just toss it onto the ground instead. Although I suppose there might be some cases where that wouldn't work, and if so there is no reason a person on the ground couldn't reach out and snag a loop if necessary.

Just for example, this token exchange from Singapore shows an apparatus for catching the loop from the train, as well as a ground crew person passing a loop with token to the train. Presumably a ground crew person could do the same as the apparatus - just reaching out to catch the loop.

It's astonishing, with all this reaching and grabbing, that railroad workers managed to survive their careers with all limbs intact . . .
posted by flug at 7:53 PM on November 27, 2022 [1 favorite]

Response by poster: Ah thank you! So the purpose of the loop shape is to allow someone on the train to easily catch the message during a pick up, but when dropping off the message they could simply literally drop it off.

The scene in the movie with the loop doesn’t show the drop off itself, just the worker picking up the loop as the train speeds past. Of course, everyone in 1952 knew that the loop was just thrown out of an open door and didn’t need it explained like me!

That description in the online review is simply not quite exactly describing what is going on (or perhaps combining the mail bag pick up with the loop drop off).
posted by lewedswiver at 8:02 PM on November 27, 2022

Say, great train noir, thanks for the pointer! It was remade in 1990 with Gene Hackman, J. T. and M. Emmet Walsh, and the original is available at the Internet Archive. The snag occurs at 59:27.
posted by Rash at 8:30 PM on November 27, 2022 [2 favorites]

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