I recently realised that all of the basic technology needed to operate a micro-layout (direct current circuits, voltaic batteries, primitive motors) had been developed before the 1840s started. Reading a bit further, I discovered the US inventor Thomas Davenport - not the very first person to build an electric motor, but almost certainly the first one to use it to power a model tramcar in the mid-1830s. His design was elegant, but not ideally suited for today's smaller scales:

I also stumbled across Alfred P. Morgan's 1913 The Boy Electrician on Project Gutenberg, with its clever chapter on building a model electric tramway and this simple design (Fig 315) for a "A Pole-Changing Switch or Current Reverser":

Well, Tinories is supposed to be a portable layout that can be set up and operated anywhere, and I had always planned to build a very basic battery controller. This simply had to make the locos move backwards and forwards; for my own use I considered acceleration and braking to be unnecessary fripperies, and only the thought of soldering had deterred me from knocking something together earlier. Inspired by the pioneering vision of Davenport and the optimistic ingenuity of Mr Morgan, I finally set to work:

The base of the controller is just a plastic lottery card covered with Humbrol copper (MET 12) paint to disguise its origin. It only occurred to me afterwards to check that enamel copper paint isn't conductive; luckily it isn't!

A drawing pin is glued to one end of the card. This is the pivot around which the actual controller moves. Edit: I would now drill a hole through the card and push the drawing pin through it, gluing it to the underside of the card so that the pivot is a bit more robust:

A short length of PECO flexitrack was glued to a second strip of lottery card, using pre-soldered fishplates and a terminal block to make the rails live without any soldering:

A hole was drilled through the centre of the terminal block so that it could drop over the drawing pin that had been glued to the base of the controller:

Then the first terminal (taken from another electrical terminal block) was glued onto the base, at the opposite end of the  card to the drawing pin. To my surprise, it was actually very easy to stick the curved underside of the terminal to the plastic card with generic super glue::

The next step was the only one which required any care. I pressed one of the rails against the first terminal, and then glued the second terminal in place so that it touched the other rail and made a circuit. (A multimeter isn't necessary for this stage; a lamp or buzzer - or even a loco - would be just as effective in showing the right location to complete the circuit). Observant readers will note that I need to buy a new 9 volt battery:

The same for the third and last terminal:

... and finally a short wire between terminals 2 and 3 so that they become positive or negative depending on the rail that is making contact with them:

It's possible to customise the controller to taste, but I decided to leave it at that. I didn't even need to glue a knob onto the controller arm because a 9 volt battery fits snugly between the rails of 16.5 mm track and provides a convenient grip:

Update 22 May 2021: just an additional photo showing the 56 ohm dropper resistor I use to get the Bachmann Norris loco to crawl as slowly as possible. It varies by loco, so the deWitt Clinton needs a much smaller dropper to run.