For years, I saw the signs pointing to the Joseph Priestley House in Northumberland, but I never deviated from Route 11 to investigate. I had the idea that it was a humble log structure, perhaps fancied-up with clapboard. So I was surprised to find this elegant Georgian mansion when I finally went to look. Joseph Priestley was the 18th-Century Unitarian minister who discovered oxygen and invented carbonated water. He was a friend and correspondent of two other dabblers in science, Ben Franklin and Tom Jefferson. Late in life, he came from England to Northumberland where he rounded out his career by discovering carbon monoxide. Continue.