This is a short extract from a book by a Christian missionary which gives some historical observations on the Yezidi people of northern Iraq. For more information on the Yezidi, refer to Devil Worship: The Sacred Books and Traditions of the Yezidiz, which references this article heavily.
The Rev. Badger didn't get as close to the Yezidi as Isya Joseph did. His access was limited because he was a missionary, rather than an anthropologist. However, there aren't too many first-hand accounts of the Yezidi during the mid-nineteenth century, (actually this is the only one I've discovered so far). This document gives another perspective on this fascinating culture and their unique religious beliefs.