The world's smallest model railroad

Above is the World's smallest model train. It has a simple layout with the train passing through a tunnel as it runs on an oval track. The little train model was built to be a model inside of another model. The train was displayed in the window of a Z gauge hobby shop.
 

Pre-radar acoustic detection and tracking

In my earlier post The Besler Steam Plane I mentioned, "What impressed spectators the most was the silence of the airplane. That was an important selling point, because in those days before radar planes were located and tracked acoustically." 

The site Retronaut has an article, Listening Before Radar, that shows several examples of these old acoustic dection and tracking contraptions. I've included a few and there are more to see at the Retronaut article.

As an aside, while poking around the web for information about acoustic aircraft tracking I discovered that it is still being worked on. The EU is working on a system called SAFE-AIRPORT that uses phased arrays of microphones to track airplanes. The system is intended to be used in air traffic control around airports.