About: Black damp in a coal mine!
Old timers used to have caged canary's.They get quiet and quit chirping, better check on them to make sure they're still alive.
The lamp with 19th century technology told you the air was bad before the 20th century electronic doohickey. Globe installed upside down with the graduations wrong btw...
Where can I get one of those lamps?
is there more blacl damp in the summer?