The Fog Horn with compressed air cylinders at the Mull of Galloway, Lighthouse, the most southerly point of the Scottish Mainland,
The foghorn would be operated by lighthouse keepers should seaward visibility drop below 4 miles. It overlooks the North Channel which is the strait between north-eastern Ireland and south-western Scotland.

Link with excellent information including listening to the horn in action, mull-of-galloway.co.uk/albums/foghorn

HFF and a nice weekend,,,,, a large view recommended if possible.