In the Oriental theory this force is deemed to be always latent in the body, and is aroused, evoked, or stimulated in particular ways. The discussion of the relative values of these two main schools of thought--static and dynamic light--or their variants is beyond the scope of these notes. The lowest of the lotuses or centres is the nerve centre within the body in the region of the prostatic gland, the next is midway between this and the third which is the navel centre or solar plexus. The fourth is nominally the heart, the fifth, that at the base of the throat, the sixth, that between the eyebrows. In visualizing these lotuses with the “mental eye,” the depth back in the body of each centre is assumed to be close to the spine. Mind force is concentrated by the Yogi under the name Vogabala, and in Oriental black magic this is concentrated on the lowest centre, according to the ritual of the infamous Prayoga, with the result of inducing sexual hallucinations. In the so-called white or mediumistic magic, the centre of energy is apparently by the third centre (the navel), for materialization phenomena, and the fifth, or base of the throat centre for clairaudience. Those who can reach the sixth claim the power of astral voyaging in the spirit world and perception of things on the mortal plane at a distance. The physiology of the process is not yet understood, but following on the breathing processes or Pranayama, which relax the body and induce certain rhythms, a progressive excitation and rigor of the centres is induced by autohypnosis. The nerve centres control various limbs and functions, and as each is “put to sleep” so the Yogi becomes rigid and cataleptic. Yogis are able to hold out their arms for hours at a stretch without apparent fatigue--so in the same way can a hypnotized subject be placed in an attitude of rigidity by an operator. These progressive inhibitions of functions cannot be achieved by the Western occultist without the most careful study and painstaking preparations. The practices are both mentally and physically dangerous, but when mastered either in part or in whole, they can be evoked by systems entirely at variance with the accepted Indian methods. In fact, certain nonsense rhymes of the same rhythm and breathing values as some of the Tantric spells or mantras are equally efficacious. There was infinite wisdom in the old law of magic which said “Change not the _barbaric_ names of evocation,” but if they were changed, provided rhythm and breathing are preserved, the sense does not appear to matter. If one verse of Macaulay’s “Horatius”[52] was a powerful spell--almost any other verse in the same poem would produce the same effect--if delivered in the same way. This argument is sometimes used by a sceptic, but after all it only proves that the same result can be produced by analogous means. Salt disappears when dissolved in water, but so it does in half a dozen other liquids.