It could easily be seen by ships in the Firth of Forth and was a useful safeguard if prevailing winds carried the sound of the gunfire the wrong way.
Ships could never see it in the Firth of Forth.
mnli hypothesis: Ships could never see it in the Firth of Forth. premise: It could easily be seen by ships in the Firth of Forth and was a useful safeguard if prevailing winds carried the sound of the gunfire the wrong way.