At first glance, I was sure the mirror was a computer monitor.

I worked on and repaired many of these interlocking machines when I was a signal maintainer in the NYCTA. Those and General Railway Signaling machines were scattered by the hundreds throughout the system. Great engineering for the day. Many still in use 80-90 years later.

It's a treasure trove. May the comments go on and on.

I would strongly suspect that the mirror allows the operator to see the "model board" of the interlocking behind him. The model board is not visible in this picture, but it would display the position of trains within and approaching the interlocking. The operator will throw switches and clear signals for train movements through "the plant", based on information from the dispatcher, employee timetables, and indications of approaching trains displayed on the model board.

Ah, the pants of my youth: Buttons, not Zippers.

he has hung his railroad grade pocket watch in full view -- 16 size, open-faced, bold arabic numerals on a white dial, heavy hands, and no doubt (as officially specified) accurate to within 30 seconds a week. Perhaps a Hamilton 992B or an Illinois Bunn Special, but many companies made them for the railroads to specifications.

Looking at the walls covered in all the dirt, grime, soot (coal dust) and what I'm guessing would have been stains from years of tobacco use in that office just makes me shudder.

Have to ask, what is the mirror for? Is it so he can see the switches behind him, or is it for making sure his hair is combed?

I have been licensed for more than fifty years, and I have never known the origin of the term "lid." This explanation clears things up. I did know that tobacco cans were used by news wire services and others to amplify the volume of the sounder. Now I know the other reason. Long ago, I picked up a tin can at a flea market and later found out it was one of the "preferred" tobacco cans to use.

73
Ken N2UK

The tobacco can was mounted to the telegraph sounder as a primitive yet effective means to amplify the clicks. These telegraph systems were a party line with many operators sending and receiving "traffic." The receiving operator would copy (listen for) a message header directed to them, otherwise it was just background noise.
When a poor "fist" (sending operator) came on line and the traffic wasn't for them. they would put the lid back on the can so they didn't have to listen to the novice operator. Hence the term "Put a lid on it!"

In the Ham Radio community, a poor operator today is referred to as a "Lid."

For a railroad environment, that's pretty much a white-collar job, and he's dressed for it, at least for the first half hour or so, until the grime and sludge start to slide off the walls and work surfaces. Turn me loose in there with a bottle of Windex and a roll of paper towels ...

Always the ubiquitous empty tobacco tin on the Morse code sounder, to amplify the sound.