The massive work was arranged according to a "tree of knowledge." The tree reflected the marked division between the arts and sciences, which was largely a result of the rise of empiricism. Both areas of knowledge were united by philosophy, or the trunk of the tree of knowledge. The Enlightenment's desacrilization of religion was pronounced in the tree's design, particularly where theology accounted for a peripheral branch, with black magic as a close neighbour. As the Encyclopédie gained popularity, it was published in quarto and octavo editions after 1777. The quarto and octavo editions were much less expensive than previous editions, making the Encyclopédie more accessible to the non-elite. Robert Darnton estimates that there were approximately 25 000 copies of the Encyclopédie in circulation throughout France and Europe before the French Revolution. The extensive, yet affordable encyclopedia came to represent the transmission of Enlightenment and scientific education to an expanding audience.