So what do these dates have to do with the Mad Hatter? In the original Tenniel illustrations, the Mad Hatter has a price tag tucked into his hat band. It says "In this Style 10/6" which, for us ingnorant Yankees means ten schillings and sixpence, or half a guineau back in Alice's day! So Mad Hatter Day falls on 10/6, and you can decide which date system to follow.
Lenny's Alice in Wonderland site, there is more to it:
The actual amount was significant also. Professional people (doctors, lawyers, architects etc) all charged fees, not in pounds but in guinneas. One guinnea was one pound plus one shilling. And while pounds were the currency of trade, guinneas were the currency of the professions. We used to have a gold coin called, and valued at a guinnea, and a smaller gold coin, a half guinnea, valued at ten and six (10/6). The pound, however was merely a paper note, as was the half-pound or ten shillings.As for me, I say let's celebrate Mad Hatter Day twice a year! Hopefully we'll have enough readers by the next one to have some kind of blog event, a virtual Mad Hatter's tea party perhaps or a blog hop or challenge.
So the hat worn by the Mad Hatter was priced at half-a-guinnea, signifying its superior style.
Remember to celebrate your inner Mad Hatter!