of the Dead_ of the Egyptians the souls journey painfully towards that light in the barque of Isis. Moses fully adopted this doctrine in Genesis: “Elohim said: Let there be light; and there was light.” Now the creation of this light precedes that of the sun and stars. This means that, in the order of principles and cosmogony, intelligible precedes material light. The Greeks, who moulded into human form and dramatized the most abstract ideas, expressed the same doctrine in the myth of Hyperborean Apollo. Consequently the human mind, by inner contemplation of the universe, from the point of view of the soul and the intelligence, came to conceive of an intelligible light, an imponderable element serving as an intermediary between matter and spirit. It would be easy to show that natural philosophers of modern times insensibly draw somewhere near the same conclusion along an opposite path, _i. e._ by searching for the constitution of matter and seeing the impossibility of explaining it by itself. Even in the sixteenth century, Paracelsus, whilst studying the chemical combinations and metamorphoses of bodies, went so far as to admit of a universal occult agent by means of which they are brought about. The natural philosophers of the sixteenth and seventeenth centuries, who conceived of the universe as being a dead machine, believed in the absolute void of celestial space. Yet when it was discovered that light is not the emission of a radiant matter, but rather the vibration of an imponderable element, one was obliged to admit that the whole of space is filled by an infinitely subtile fluid penetrating all bodies and through which waves of heat and light are transmitted. Thus a return was made to the Greek ideas of natural philosophy and theosophy. Newton, who had spent his whole life in studying the movements of the heavenly bodies, went even farther than this. He called this ether _sensorium Dei_, or the brain of God, _i. e._ the organ by which divine thought acts in the infinitely great as well as in the infinitely small. In emitting this idea, which he regarded as necessary to explain the simple rotation of the heavenly bodies, the great natural philosopher had embarked on the open sea of esoteric philosophy. The very ether Newton’s thought found in space Paracelsus had discovered at the bottom of his alembics, and had named it astral light. Now this imponderable fluid, which is everywhere present, penetrating all things, this subtile but indispensable agent, this light, invisible to our eyes, but which is at the bottom of all phosphorescence and scintillation, has been proved to exist by a German natural philosopher in a series of well-appointed experiments. Reichenbach had noticed that subjects of very sensitive nerve fibre, when placed in a perfectly dark room in front of a magnet, saw at its two ends strong rays of red, yellow, and blue light. Sometimes these rays vibrated with an undulatory movement. He continued his experiments