Gauge invariance at Loch Muick

The bizarre tracks heading into the loch must have been for launching boats. They are right next to the boat house. The width of railway lines has always been referred to as the GAUGE. I had always wondered why this word had come into particle physics. The idea seems to be that on railways, the change of scale doesn't affect the product - you get the same thing, a train down a track. In field theory, it seems to be that if you change certain things, you retain the same basics. There is a symmetry across different "gauges". Presumably a different gauge of track would still put a boat in the loch. I'm just developing my understanding of this area.