If this realm of events is more intimately related than any other to our intuitive experience, it has also the characteristic of remaining closed to any research by external means. Much of what lies beyond the scope of external observation, however, reveals itself all the more clearly in the realms where nature is active on the widest scale. Certainly, we must school ourselves to read aright the phenomena which come to light in those realms. And once more we must look to the way of introspection, previously mentioned, for aid in investing our gaze with the necessary intuitive force. If we succeed in this, then the heavens will become for us a text wherein secrets of human nature, hidden from mere introspection, can be read; while at the same time the introspective way enables us to experience things which we cannot uncover simply by observing the outer universe. Apart from these methodological considerations, there is a further reason for our choice. Among the instances mentioned earlier in this chapter as symptoms of a greater 'youthfulness' prevailing in nature, and particularly in the element Fire, at a comparatively recent date, were the manifestations of the Divine-Spiritual World to man reported in the Bible as the event on Mount Sinai. There, thunder and lightning from above and volcanic action from below form the setting for the intercourse of Jehovah with Moses. To-day the function of these types of phenomena, though metamorphosed by the altered conditions of the earth, is not essentially different. Here, more than in any other sphere of her activities, nature manifests that side of her which we are seeking to penetrate with understanding. * Let us start with an observation known to the present writer from a visit to the Solfatara, a volcanic region near Naples. The Solfatara itself is a trough surrounded by hilly mounds; its smooth, saucepan-like bottom, covered with whitish pumice-sand, is pitted with craters containing violently boiling and fuming mud - the so-called fango, famous for its healing properties. All around sulphurous fumes issue from crevices in the rocks, and in one special place the Solfatara reveals its subterranean activity by the emergence of fine, many-coloured sand, which oozes up like boiling liquid from the depths below. The whole region gives the impression of being in a state of labile balance. How true this is becomes apparent if one drops pieces of burning paper here and there on the ground: immediately a cloud of smoke and steam rises. The effect is even more intense if a burning torch is moved about over one of the boiling fango holes. Then the deep answers instantly with an extraordinary intensification of the boiling process. The hot mud seems to be thrown into violent turmoil, emitting thick clouds of steam, which soon entirely envelop the spectator near the edge.