A similar need, though now in an amplified form, arises at the present stage of our studies. And here, out of the wealth of knowledge conveyed by Rudolf Steiner from the realm of supersensible Imagination, it is his characterization of the four modifications of levity which will now give the guidance necessary for our own observation. Adopting the terminology chosen by him for the description of this sphere, we shall in future speak of it as of the 'Ether' pervading the universe (thus using this word also in its true and original meaning). Accordingly, we shall refer to its fourfold differentiation as to the four kinds of ether: Warmth-Ether, Light-Ether, Chemical Ether and Life-Ether.