We begin then the detailed evolution of form; it is like a great circle traced downwards and upwards. There is a great difference between the downward arc, the one-half of the circle, and the upward arc, the other half of the circle. In the one case, coming downwards, Íshvara imparts qualities and attributes; in the other half, going upwards, He builds the qualities and attributes into vehicles. These are the two great differences between the downward and upward arcs. In the downward, matter takes up qualities; in the upward, matter is formed into vehicles, or sheaths, or bodies, whatever may be the term we prefer. A process of specialisation goes on, up to a certain point. After a time the specialised materials are drawn together and combined into a vehicle, an organised unity, serving as a tabernacle for the Self. First comes differentiation, and the first step to that is to impart qualities to matter. Let me remind you, as the subject is so difficult a one, what is meant by tattvas, the fundamental forms of matter, and recall once more that passage in the _Vishnu Purâna_ where their evolution is described, and where it is stated that the tanmâtra of sound produces A'kâsha; that is, a modification of the consciousness of Íshvara produces the form of matter that we call the atom of A'kâsha; that atom has a mere film of subtlest matter for its envelope, and the vibrating life of Íshvara for the force within. Then we are told that A'kâsha generates another tanmâtra which is touch, and that, enveloped, permeated by A'kâsha, produces the film of denser matter which is called Vâyu, the two tanmâtras and the A'kâsha being the generating force.