Narrative of a Secret Mission to the Danish Islands in 1808 (1863) by James Robertson (1758–1820):
https://archive.org/details/narrativeasecre00robegoog
https://archive.org/details/narrativeasecre01robegoog
http://books.google.com/books?id=MD6SvyKnI6YC
http://catalog.hathitrust.org/Record/000606904
Author bio info:
http://en.wikipedia.org/wiki/James_Robertson_(monk)
http://en.wikisource.org/wiki/Robertson,_James_(d.1820)_(DNB00)