I was watching “Secrets of the Shining Knights,” a Nova video on PBS Sunday night, when one of the commentators briefly explained the origins of the expression “mad as a hatter.” Apparently, Mercury gases emitted during the hat making process caused hat makers to go insane. I was surprised to hear that and I wanted to know a little more. I did an internet search and found a well-written, succinct article about hatters. The article contains what I found to be shocking information about the hatters. I don’t want to spoil it by adding an excerpt here, so I will just provide a link to the article.