The Boarded Window by Ambrose Bierce
http://sittingbee.com/the-boarded-window-ambrose-bierce/
Analysis of the short story "The Boarded Window"
Official Ambrose Bierce Site
Website with numerous articles and sources related to Ambrose Bierce
Supernatural Horror in Literature by HP Lovecraft
http://www.hplovecraft.com/writings/texts/essays/shil.aspx
Copy of an essay on supernatural horror by renowned author HP Lovecraft (who was heavily influenced by Bierce)