E. G. Browne visited Yahya, Subh-i-Azal, in 1890 and 1896. He wrote about Azal with a positive tone in New History (1893) and a disillusioned tone in Materials (1918). This is a brief history of Browne's shifting perspective of the Azalis.
Browne's Mirza Yahya, Before and After His Second Visit: Tarikh-i-Jadid vs. Materials for the Study of the Babi Religion