Fergusson is widely quoted (though often misspelt) as a source of accounts of the Battle of Copenhagen in 1801, where he was present (as Staff-Surgeon of the troops embarked) with Admiral Lord Nelson on the flagship Elephant, before being entrusted with the conveyance of the British wounded to Yarmouth [REF].
Having retired from military service in 1817, he settled in practice at Edinburgh, being elected a Fellow of the Royal Society of Edinburgh in 1818.