The Agnostic Christmas by Robert Ingersoll (1892)
Becoming a Freethinker and a Scientist by Albert Einstein (Off Site)
The Bigotry Of Colleges by Robert Ingersoll
The Brooklyn Divines by Robert Ingersoll (1883)
Conversation on Religion and Antisemitism by Albert Einstein (Off Site)
Crumbling Creeds by Robert Ingersoll
The Development of Religion by Albert Einstein (Off Site)
The Foundations Of Faith by Robert Ingersoll
Effect Of The World's Fair On The Human Race by Robert Ingersoll
Note About Einstein's use of the word "God"; Albert Einstein (Off Site)
On Prayer, Purpose, and the Soul by Albert Einstein (Off Site)
Religion and Science: Irreconcilable? by Albert Einstein (Off Site)
This Full Text Digital Library includes a number of works that either challenged religion or discussed its relationship to science. Works discussed include: Charles Darwin's "Descent of Man;" Albert Einstein's "Science and Religion" and Andrew White's "The Warfare Between Science and Religion." A link to the full library provides links to articles by Richard Dawkins among other secularists.

