Such a conception by no means contradicts the findings of external research. For meteorology has come to know of a heat-mantle surrounding the earth's atmosphere for which various hypothetical explanations have been advanced. Naturally, none of them envisages the possibility of atmospheric substance changing into the heat-condition and back again. But if we learn to look on the chain of cloud-forms as a 'spiritual ladder', then we must expect the chain to conclude with a stage of pure heat, lying above the cirrus-sphere.⁹