Heritage crochet

This is a wonderful book detailing the history of crochet in general and crochet during the late 1800s and early 1900s in particular. The author's focus is on the English and Irish crocheters. Do you know the reason for the sizing numbers of crochet thread? It's here! There are also several thread crochet patterns, all charted for ease. And the bibliography section is a gold mine of older crochet publications to investigate.