Mysticism

Evelyn Underhill (1875–1941) was an English writer and pacifist who became famous for her numerous works on religion and spiritual practice, in particular mysticism.
In the English-speaking world, she was one of the most widely read writers on these matters in the first half of the twentieth century, especially for this book "Mysticism" published in 1911. It sold so many copies that no other book of this type was able to meet with the same great success until Aldous Huxley came out with The Perennial Philosophy in 1946.