Based on an extant example of a Welsh Wig in the collections of St Fagan's National History Museum dated 1854, the Welsh Wig was a popular nineteenth century choice with working men including soldiers and even polar explorers! The surviving example was a sample for a consignment of hats being sent to the Crimean.
The simple head hugging cap is adorned with a row of 'curls' at the nape of the neck which experiments have shown sit well under other hats and also prevent draughts or rain getting into your collar, very comforting in extreme weather.
Charles Dickens famously describes Mr Fezziwig as wearing a Welsh Wig in 'A Christmas Carol', making it an excellent choice for Dickensian events.
Sizing for this hat is somewhat dependent on your yarn choice, a fine '4ply'/fingering weight (the original hat is actually worked in singles, and in test knitting I found a 2/11.5 nm yarn worked well) in a pure wool or similar will give a very stretchy hat that fits up to a 23 inch head w