An Outline of Occult Science is Rudolf Steiner's thesis discussing the unknown, the nature of mankind, and his belief that science may be used to explain the unusual phenomena known as the occult. First published in 1910, this book strives to define, categorize and explain various manifestations of the occult. The author concedes at the opening of the book that many otherwise open-minded and receptive individuals immediately recoil from the concept of the the unknown, especially in relation to attempts to investigate it scientifically. After introducing the occult, Steiner delves into explaining the two worlds he thought comprised the reality we live in. The natural world, that which is visible and readily perceivable around us, and the spiritual world, where the unexplained phenomena arise. The nature of man as a bodily being, and how his physical self bridges the gap between these two worlds, is much detailed.