<P> The character also appears briefly in Carroll's 1871 Through the Looking - Glass, the sequel to Alice's Adventures in Wonderland, under the name "Hatta" - alongside the March Hare under the name "Haigha", which is pronounced "hare ." Sir John Tenniel's illustration depicts Hatta as sipping from a teacup as he did in the original novel . Alice does not comment on whether Hatta is the Hatter of her earlier dream . </P> <P> Mercury was used in the manufacturing of felt hats during the 19th century, causing a high rate of mercury poisoning among those working in the hat industry . Mercury poisoning causes neurological damage, including slurred speech, memory loss, and tremors, which led to the phrase "mad as a hatter". In the Victorian age, many workers in the textile industry, including hatters, often suffered from starvation and overwork, and were particularly prone to develop illnesses affecting the nervous system, such as central nervous system (CNS) tuberculosis, which is portrayed in novels like Alton Locke by Charles Kingsley and North and South by Elizabeth Gaskell, which Lewis Carroll had read . Many such workers were sent to Pauper Lunatic Asylums, which were supervised by Lunacy Commissioners such as Samuel Gaskell and Robert Wilfred Skeffington Lutwidge, Carroll's uncle . Carroll was familiar with the conditions at asylums and visited at least one, the Surrey County Asylum, himself, which treated patients with so - called non-restraint methods and occupied them, amongst others, in gardening, farming and hat - making . Besides staging theatre plays, dances and other amusements, such asylums also held tea - parties . </P> <P> The Hatter introduced in Carroll's Alice's Adventures in Wonderland wears a large top hat with a hatband reading "In this style 10 / 6". This is the hat's price tag, indicative of The Hatter's trade, and giving the price in pre-decimal British money as ten shillings and six pence (or half a guinea). </P> <P> The Hatter and his tea party friend, the March Hare, are initially referred to as "both mad" by the distinctive Cheshire Cat . The first mention of both characters occurs in the sixth chapter of Carroll's Alice's Adventures in Wonderland, titled "Pig and Pepper", in a conversation between the child protagonist Alice and the Cheshire Cat, when she asks "what sort of people live about here?" to which the cat replies "in that direction lives a Hatter, and in that direction, lives a March Hare . Visit either you like: they're both mad!" Both then subsequently make their actual debuts in the seventh chapter of the same book, which is titled "A Mad Tea - Party". </P>

What is written on the mad hatter's hat